WO2000045202A1

WO2000045202A1 - A tunable electrooptic interference filter and method of manufacturing same

Info

Publication number: WO2000045202A1
Application number: PCT/US2000/002468
Authority: WO
Inventors: Mark A. Ray; Brian H. Augustine
Original assignee: Mcnc
Priority date: 1999-02-01
Filing date: 2000-01-31
Publication date: 2000-08-03
Also published as: AU3477600A

Abstract

The present invention provides an optic filter having first (12) and second (14) sets of alternating layers of material, where each set of alternating layers of material has a first dielectric material and a second dielectric material stacked upon each other. Further, the first and second dielectric materials have different indices of refraction. The optic filter of the present invention also includes an intermediate material (20) disposed between the first and second sets of alternating layers. The intermediate material has an index of refraction that varies as a function of the intensity of an electric field applied thereto. Additionally, the first set of alternating layers is connected to a transparent substrate (24). In operation, to filter an optic signal of interest, the composition, thickness, and number of first and second dielectric layers are chosen to filter or reflect the desired wavelengths of the optic signal. The optic signal is then directed incident to the optic filter and an electrical field is applied to the intermediate layer of the optic filter. The introduction of the electrical field causes a change in the index of refraction of the intermediate material of the optic filter, thereby causing the optic filter to either transmit or reflect the wavelengths of interests in the optic signal.

Description

A TUNABLE ELECTROOPTIC INTERFERENCE FILTER AND METHOD OF MANUFACTURING SAME

RELATED APPLICATIONS The present application claims priority from U.S. Provisional Application

Serial No. 60/118,152 entitled Electrooptic Interference Filters filed February 1, 1999, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION The present invention relates to optic filters, and more particularly relates to optic filters containing a layer of material having a variable index of refraction, where the index of refraction is varied to alter the transparency and reflectivity of the optic filter.

BACKGROUND OF THE INVENTION

Optic filters play an important part in many optic applications. For instance optic filters are widely used in windows, sunglasses, and other viewing items to filter certain light waves such as ultra-violet light. Optic filters are also widely used in fiber optic applications. For instance, some fiber optic applications use gradient-index (GRIN) lenses to demodulate or split fiber optic signals into discrete signals. These GRIN lenses use fine angular displacements of the optic filter structures or lens and mirror structures to filter the optic signals. Further, optic filters are used as optic logic gates in optic electronic applications.

Optic filters are not only used to filter optic signals; they are also used to reflect optic signals of interest. For example, optic filters may be configured to reflect certain wavelengths of light such as visible light to form mirrors, or other colors of light that may be of interest. Additionally, the optic filters may be configured to reflect optic signals such as for use in heads-up and head mounted displays, where the read out information is projected onto the optic filter and reflected into the viewing area of the vehicle operator. Further, optic filters may be used in video displays as pixels.

A typical optic filter is an interference optic filter. Interference optic filters are formed by depositing a series of thin layers of transparent material having various refractive indices on a transparent substrate. These layers are known as interference layers, and controlling the thickness of these layers can alter the transmission or filtering characteristics of the filter. For example, interference filters are sometimes used in window applications. Alternating layers of transparent material having different refractive properties are deposited on the surface of the window. The thickness and material used to form the layers is controlled such that the filter filters out unwanted light such as ultra-violet light or reflects certain wavelengths of light such as in a mirror.

Although these types of conventional optic filters generally are efficient filters, they do have some drawbacks. Specifically, because the filtering characteristics of these filters is generally determined by the composition and thickness of the alternating layers, the filtering characteristics of the interference filters cannot be subsequently modified after manufacture. As such, these conventional interference filters are not conducive to use in applications requiring variations in the filtration of light.

Another conventional interference filter is a tunable Fabry-Perot etalon filter. These filters are similar to conventional interference filters. Specifically, they include two sets of alternating layers of material having different indices of refraction. Each set of alternating layers has a low index of refraction layer and high index of refraction layer. For at least some conventional Fabry-Perot etalon filters, to tune the optic filters, the two sets of layers are spaced apart, such that the two high index layers face each other. The separation between the two layers is maintained by a spacer ring, typically of quartz, and two plates. The spacer and the assembly of two plates is referred to as an etalon. The space between the two sets of layers defines a region having a low index of refraction. To tune the optic filter, the tunable Fabry- Perot etalon filter further includes a motor-driven moving mechanism for moving the two sets of alternating layers relative to each other. By increasing and decreasing the distance between the two sets of alternating layers, the tunable Fabry-Perot etalon filter can adjust the filtration of a light transmitted through the filter. Although conventional tunable Fabry-Perot etalon filters are widely used, especially in fiber optic electronics, these filters also experience some drawbacks. Specifically, as discussed, at least some of these conventional filters typically use motors to alter air gap between the two alternating layers. The ability to accurately control these motors and the driving mechanism for desired filtration may be difficult. Further, these motors typically have slow response times, (i.e., 50 to 100 Hz). Moreover, the motors are typically large, (i.e., 2 to 4 inches), when compared to remaining electrical components in which the filter is used.

Another type of tunable optic filter is disclosed in U.S. Patent No. 5,434,943 to Dentai, et al. This tunable optic filter contains a wave guide layer sandwiched between a first contact layer and a substrate and a second contact layer. To tune the optic filter, a current is applied to the optic filter, which, in turn, injects carriers in the wave guide region. The carriers change the index of refraction of the waveguide. While this tunable optic filter remedies some of the problems associated with the use of motor-driven mechanisms for tuning, it does have some drawbacks.

Specifically, this tunable optic filter requires a relatively high current density in order to force the carriers to move in the wave guide region. This requirement of high current density limits the size and shape in which these filters may be constructed. The larger the filter is made the more current it will consume to maintain the high current density. In light of this, it would be desirable to provide an optic filter that is more accurately tunable, has increased reaction time, and does not require components, such as a motor-driven mechanism, that can be relatively large and slow in response to tune the optic filter. Further, it would be desirable to provide an optic filter that is adaptable to many different shapes and sizes, without significant increase in the energy required to operate the filter.

SUMMARY OF THE INVENTION

As set forth below, the optic filter of the present invention overcomes many of the deficiencies identified with conventional optic filters. In particular, the optic filter of the present invention provides an intermediate material that has a variable index of refraction based on the intensity of an electric field applied to the intermediate material. By varying the intensity of the electric field, the optic filter of the present invention can be controlled to provide either a desired filtering or reflection of incident light. Because the index of refraction of the intermediate material can be controlled by the introduction of an electric field, the reflective characteristics can be controlled without requiring the alteration of the thickness of the alternating layers. Further, because the reflectivity of the intermediate material is dependent on the input of an electric field and not upon a mechanical movement of the two alternating layers, the reflective characteristics of the optic filter can be more easily controlled with increased reaction time. Additionally, because the index of refraction can be altered by changing the electric field across the intermediate layer, the optic filter is adaptable to many different shapes as an implemented design requires and can be made either relatively small or large. These and other advantages are provided, according to the present invention, by an optic filter having a first and second set of alternating layers of material, where each set of material has a first dielectric material and a second dielectric material stacked upon each other. Further, the first and second dielectric materials have different indices of refraction. The optic filter of the present invention also includes an intermediate material disposed between the first and second set of alternating layers. Importantly, the intermediate material has an index of refraction that varies as a function of the intensity of an electric field applied thereto. Additionally, the first set of alternating layers is disposed upon a transparent substrate.

According to one advantageous embodiment of the present invention, the intermediate material is an electrooptic material having optic properties that are altered by external electrical field stimulus. In a further embodiment, the intermediate material is a ferroelectric ceramic material comprising electrooptic properties. Further, in another advantageous embodiment, the intermediate material comprises an electrostrictive material having a slim loop hysteresis of polarization versus energy bias and a quadratic dependence of the index of refraction as a function of the polarization of the electrostrictive material.

In addition to providing an optic filter containing an intermediate material having an index of refraction that can be altered with an electric field, in one embodiment, the optic filter further includes electrically conductive layers of material to provide an electric field across the intermediate material. Specifically, the conductive layers are positioned on opposite sides of the intermediate material depending on the desired direction of polarization of the intermediate material. In embodiments where polarization of the intermediate material is desired in a horizontal direction, the conductive layers are positioned on the opposed vertical sides of the intermediate material. However, in embodiments where it is desired to polarize the intermediate material in a vertical direction, the conductive layers are positioned on the opposed horizontal sides of the intermediate material. Further, in some embodiments, the conductive layers may be transparent to allow the transmission of light. Specifically, in one advantageous embodiment of the present invention, the electrical conductive layers of material comprise indium tin oxide ITO. Other suitable, conductive, transparent materials for the electrically conductive layer include tin oxide SnO₂, indium oxide In O₃, zinc oxide ZnO, and ruthenium oxide RuO₂. Further, the electrically conductive layers may be either in contact with the intermediate layer or spaced apart from the intermediate layer by the alternating layers.

In many optic filter applications, it is advantageous to configure the filter such that it will either filter, reflect and/or shift an optic signal of interest. For instance, if the optic filter is used to filter or transmit certain wavelengths of light, the alternating layer of materials must be deposited in thickness that will allow the desired wavelengths to be either transmitted or reflected when the intermediate material is excited by an electric field. As such, in one embodiment of the present invention, the two sets of alternating materials are configured with chosen thickness such that the optic filter will allow efficient transmission, reflection and/or shifting of chosen optic wavelengths.

In this embodiment of the present invention, each set of alternating materials has a first dielectric material and a second dielectric material stacked upon each other, where the first and second dielectric material have different indices of refraction. Further, the thickness of each of layer of the first and second dielectric material is configured such that the optic thickness of the materials is one quarter of the operating wavelength of the filter. For instance, in one advantageous embodiment, the thickness of each layer of the first and second dielectric material is defined by the following equation:

_ mλ 4n where L is the film thickness, λ is the chosen wavelength, n is the index of refraction, and m is an odd integer order. By utilizing this equation and knowing the wavelength that the filter is designed to transmit, the thickness of the layered materials can be determined to provide the performance characteristics desired. Importantly, however, in some embodiments, it may be advantageous to alter the thickness of some of the layers (i.e., bias the layers) depending on the desired properties of the filter.

In addition to configuring the thickness of the alternating layer of materials to reflect or transmit desired wavelengths, it may also be advantageous to select the materials comprising each layer. For example in alternative embodiments, the first layer and second dielectric layers may comprise one of the following dielectrics: silicon dioxide SiO , silicon nitride Si₃N₄, magnesium fluoride MgF₂, titanium oxide TiO₂, aluminum oxide Al₂O₃, chrome oxide Cr₂O₃, barium fluoride BaF₂, cerium fluoride CeF₃, cerium oxide CeO₂, hafnium oxide HfO₂ or any other suitable material. The selection of the material for the first and second layers and their thickness is dependent on the desired wavelength transmission or reflection.

Further, in addition to configuring the thickness and composition of the alternating layer of materials, in some embodiments, it may be desired to configure the optic thickness of the intermediate layer of material. For instance, in one embodiment, it is advantageous to configure the intermediate layer to an optic thickness that is one half the operating wavelength of the filter. This provides a strong band-pass filter with a narrow transmission region at the designed wavelength surrounded by reflection near the designed wavelength. The thickness of this layer can be even multiples of the half wavelengths and still achieve the designed filter attributes. Thicker layers at the center can provide increased tuning range for the filter.

For instance, in one advantageous embodiment, the thickness of the intermediate layer is defined by the following equation:

_ ^mλ 2n where L is the film thickness, λ is the chosen wavelength, n is the index of refraction, and m is an integer. By utilizing this equation and knowing the wavelength that the filter is designed to transmit, the thickness of the intermediate material can be determined to provide the performance characteristics desired.

In some embodiments of the present invention, it may be advantageous to provide an optic filter, which can be operated alternatively to either transmit, or reflect a desired wavelength of light (i.e., in an "on" and "off logic state), or shift a desired wavelength of the optic signal. In these embodiments, the optic filter includes an intermediate material that has an index of refraction that varies as a function of the intensity of an electric field applied thereto. Additionally, the optic filter includes first and second sets of alternating layers of material, where each set of material has a first dielectric material and a second dielectric material stacked upon each other. The first and second dielectric materials have different indices of refraction and thickness depending upon the wavelength of interest to be switched. Additionally, the first set of alternating layers is connected to a transparent substrate.

In one embodiment of the present invention, the optic switch comprises an optic filter for filtering an optic signal and transmitting a desired wavelength optic signal. The optic filter of this embodiment includes an intermediate material and first and second sets of alternating layers comprising first and second dielectric materials of determined thickness to properly filter the incident light. Specifically, the first and second dielectric materials are deposited in desired thickness such that when an electric field is applied to the intermediate material the desired optic wavelength will be transmitted through the optic switch while all other wavelengths of light are either reflected or absorbed by the optic filter.

For example, one advantageous embodiment comprises an optic filter for filtering light having a wavelength of 600 nanometers. In this embodiment, the intermediate material comprises a ferroelectric/electrooptic material having a thickness of approximately 115 nanometers. Further, the optic filter of this embodiment comprises first and second sets of alternating layers of material having two alternating layers of a first dielectric material of silicon oxide SiO and a second dielectric material of silicon nitride Si₃N₄. The layers of SiO₂ have a thickness of 102 nanometers and the Si₃N₄ layers have thickness of 75 nanometers. Further, the optic switch of this embodiment comprises electrically conductive layers of indium tin oxide ITO connected between the intermediate material and the first and second sets of alternating material. These conductive layers have thickness of 83 nanometers.

In operation, a voltage is applied across the electrically conductive layers thereby producing an electric field in the intermediate material. In response to the electric field, the intermediate layer is polarized thereby changing the index of refraction of the intermediate material. Specifically, the index of refraction is altered such that optic signals at 600 nanometers in wavelength are transmitted through the filter, while the remaining wavelengths of light are either absorbed or reflected by the optic filter. For other intensities of the electric field, the index of refraction of the intermediate material is altered such that it may shift the wavelength of the optic signal.

As known in the art, optic switches have many applications including use in filtering optic signals transmitted in optic fibers. Specifically, conventional fiber optic networks use GRIN lenses to demodulate and split modulated optic signals. One embodiment of the present invention provides an alternative to GRIN lenses by employing an optic filter according to the present invention to operate as an optic switch that either alternatively transmits or reflects (i.e., "on" and "off logic states) a fiber optic signal or varies the index of refraction to shift or redirect the optic signal. Specifically, one embodiment of the present invention comprises an optic switch for alternately reflecting, filtering, and/or shifting 1.55 μm wavelength signal, which is a typical wavelength used for transmission of optic data information in fiber optics.

In this embodiment, the intermediate material comprises a ferroelectric/electrooptic material having a thickness of approximately 316 nanometers. Further, the optic filter of this embodiment comprises first and second sets of alternating layers of material having two alternating layers of a first dielectric material of silicon oxide SiO and a second dielectric material of silicon nitride TiO₂. The layers of SiO have a thickness of approximately 270 nanometers and the TiO₂ layers have thickness of approximately 168 nanometers. Further, the optic switch of this embodiment comprises electrically conductive layers of SnO connected between the intermediate material and the first and second sets of alternating material. These conductive layers have thickness of approximately 194 nanometers. The thickness and composition of the optic switch are provided below in Table 1 :

TABLE 1

Layer (Unpolarized) Thickness (Unpolarized)

TIO₂ 168.55 nanometers

SIO₂ 270.22

TIO₂ 168.55

SIO₂ 270.22

TIO2 168.55

SIO₂ 270.22

TIO₂ 168.55

SIO₂ 270.22

TIO₂ 168.55

SIO2 270.22

TIO2 168.55

SIO₂ 270.22 Layer (Unpolarized) Thickness (Unpolarized)

TIO₂ 168.55

SIO₂ 270.22

TIO₂ 168.55

SIO₂ 270.22

TIO2 168.55

SIO2 270.22

SNO₂ 193.75

PLZT 316.33

SNO₂ 193.75

TIO₂ 168.55

SIO₂ 270.22

TIO₂ 168.55

SIO₂ 270.22

TIO₂ 168.55

SIO₂ 270.22

TIO₂ 168.55

SIO₂ 270.22

TIO₂ 168.55

SIO₂ 270.22

TIO₂ 168.55

SIO2 270.22

TIO2 168.55

SIO₂ 270.22

TIO2 168.55

SIO2 270.22

TIO₂ 168.55

SIO₂ 270.22

In operation, an incident light such as the light from a fiber optic cable is directed at the optic switch. The optic switch is initially set with no electric field across the intermediate material providing an "on" state that allows the 1.55 μm wavelength signal to transmit through optic switch. Specifically, due to the configuration of the optic switch, optic signals having a wavelengths of 1.55 μm are transmitted through the optic filter, while other wavelengths are either absorbed or reflected by the optic switch. To turn the optic switch to the "off position (i.e.. to stop transmitting the 1.55 μm wavelength signal), a voltage is applied to the electrically conductive layers thereby forming an electrical field across the intermediate material. As the electric field increases, the refractive index of the intermediate material is shifted or shifted such that the optic filter no longer transmits the 1.55 μm wavelength signal. Instead, the optic filter shifts or shifts the wavelength of the optic signal. Further, in some embodiments, the optic signal may be shifted or shifted by varying the intensity of the electric field across the intermediate material. In addition to providing optic switches, the optic filter of the present invention may also be used to transmit desired optic wavelengths for displaying specified colors. As such, one embodiment of the present invention provides an optic filter pixel. In this embodiment of the present invention, the optic filter pixel may include one or several optic filters stacked upon each other, where each optic filter has a first set of alternating material. Deposited on the first set of alternating materials are a first electrically conductive material, a layer of intermediate material, and a second layer of electrically conductive material. Deposited on the second layer of electrically conductive material is a second set of alternating materials. As discussed previously, the number of layers and the composition and thickness of the first and second dielectric materials are chosen based on the equation:

_ mλ 4n such that the desired wavelengths are either reflected or transmitted by the optic filter pixel. Further, the intermediate layer is defined by the following equation:

_ mλ In where L is the film thickness, λ is the chosen wavelength, n is the index of refraction, and m is an integer.

For example, in one embodiment of the present invention, an optic pixel is formed having three optic filters stacked upon each other. The composition and thickness of the first and second dielectric materials of each optic filter are selected such that at a zero electric field on the intermediate material the optic fiber pixel transmits an optic wavelength representing a yellow color. As an electric field is applied across the intermediate material of each optic filter of the optic filter pixel, the index of refraction of the intermediate material is altered. As such, the optic filter pixel transmits different wavelengths of color, until at a maximum chosen electric field strength, the optic filter pixel transmits a wavelength representing a purple color. In additional embodiments, the intermediate layer of each optic filter may be operated independently, (i.e., driven by different electrical fields to provide different colors). For example, the optic filters of the optic pixel could be controlled independently to provide an optic filter pixel that provides three separate colors, such as red, blue, and green.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a graphical illustration of the molecule of a ferroelectric material illustrating the polarization effects of applying an electrical field across the material. Figures 2A and 2B graphically illustrate the memory and refractive properties, respectively of a typical ferroelectric ceramic material.

Figures 3A and 3B graphically illustrate the memory and refractive properties, respectively of a typical electrostrictive material.

Figure 4 is a cross-sectional view of an optic filter according to one embodiment of the present invention.

Figure 5 is an operational block diagram of a method for filtering optic signals according to one embodiment of the present invention.

Figures 6A and 6B are side and top view, respectively, illustrating graphically the manufacture of an optic filter according to one embodiment of the present invention.

Figure 7 is an operational block diagram of a method for manufacturing of an optic filter according to one embodiment of the present invention.

Figure 8 is a cross-sectional view of an optic filter for filtering a 600 nanometer wavelength optic signal according to one embodiment of the present invention.

Figure 9 is graphic representation of the reflective properties of an optic filter for filtering a 600 nanometer wavelength optic signal according to one embodiment of the present invention. Figure 10 is a cross-sectional view of an optic switch in an optic network according to one embodiment of the present invention implemented in optic fiber network.

Figure 11 is a cross-sectional view of an optic switch according to one embodiment of the present invention implemented in optic fiber network.

Figure 12 is a graphical representation of the switching properties of an optic switch for switching "on" and "off or shifting the transmission of an optic signal according to one embodiment of the present invention.

Figure 13 is also a graphical representation of the switching properties of an optic switch for switching "on" and "off or shifting the transmission of an optic signal according to one embodiment of the present invention.

Figure 14 is a graphic representation of the color transition of an optic filter pixel according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

As discussed previously, the present invention provides an optic filter having an intermediate material that has a variable index of refraction based on the intensity of an electric field applied to the intermediate material. By varying the intensity of the electric field, the optic filter of the present invention can be controlled to provide either a desired filtering or reflection of incident light. Because the index of refraction of the intermediate material can be controlled by the introduction of an electric field, the reflective characteristics can be controlled without requiring the alteration of the thickness of the first and second dielectric layers. Further, because the reflectivity of the intermediate material is dependent on the input of an electric field, as opposed to a mechanical movement by motor of two sets of alternating dielectric layers, the optic filter of present invention may be more easily and precisely controlled, demonstrate increased response time, and miniaturized. Further, because the index of refraction can be altered by changing the electric field across the intermediate layer, the optic filter is adaptable to many different shapes as an implemented design requires and can be made either relatively small or large.

In one advantageous embodiment of the present invention, the optic filter includes a ferroelectric ceramic material. The use of ferroelectric materials are advantageous because of the index of refraction of these materials may be altered by applying an electric field across the material. Specifically, ferroelectric ceramic materials are a class of piezoelectric material that exhibits spontaneous reversible polarization in the presence of a sufficiently high electric field. Electric polarization is produced by the cooperative reordering of domains within the crystal. With reference to Figure 1. the physical change in the crystalline structure of a typical ferroelectric ceramic material as a result of polarization is represented. The ferroelectric ceramic material 2 includes lead atoms 4, oxygen atoms 6. and atoms 8 of either zirconium Zr or titanium Ti. Polarization results in displacement of oxygen O atoms upward with a concomitant displacement of the zirconium Zr or titanium Ti atoms downward in the PLZT material. This polarization characteristic of ferroelectric materials allows the refractive index of the material to be altered (and hence the optic transmission and reflection characteristics) by applying an electrical field across the ferroelectric material. With reference to Figure 2A, the memory properties of ferroelectric materials are shown. Specifically, Figure 2A provides a hysteresis plot of ferroelectric materials illustrating their desirable atom memory properties such that the material quickly reorders itself into a steady state orientation after the electric field has been removed from the material. These memory properties allow the ferroelectric material to be quickly transitioned from one refraction index to another without much delay time for the material to reorient itself. Specifically, a sample under a sufficiently high positive electric field will polarize positively when the field is applied and a remnant polarization P_r will remain when the field is removed. The field strength must be greater than the critical field, E_c, to switch the material. The inverse process will occur when a similar negative field is applied giving rise to the complete hysteresis loop.

In addition to the change in polarization of the material, the lattice distortion, evidenced by the hysteresis loops, also gives rise to changes in the optic parameters of the materials, such as the index of refraction. For example with reference to Figure 2B, the polarization of ferroelectric materials yields polarization induced birefringence. Here the hysteresis effect in the ferroelectric material gives rise to a similar hysteresis in the index of refraction.

As known in the art, ferroelectric ceramic materials produce a variety of hysteresis loops that depend on the composition of the materials, as well as the crystal structure and grain size. As such, the performance of the optic filter of the present invention may be altered by changing the composition and crystal structure of the intermediate material. For example, one advantageous embodiment of the present invention includes an intermediate material comprising an electrostrictive material. Electrostrictive materials exhibit induced polarization with the application of an electric field and have little remnant polarization when a zero electric field is present on the material. The electrostrictive material has desired memory properties that allow the optic filter of the present invention to be quickly transitioned between refraction indices. Further, due to its slim-loop hysteresis, the material is generally less stressed when connected to an electric potential, thereby making the material more durable. With reference to Figure 3A, when an electrical field is removed from the electrostrictive material, the electrostrictive material has a small remnant polarization P_r and therefore, requires a low level field strength to switch the material. Further, with reference to Figure 3B, the "slim loop" hysteresis results in a quadratic birefringence dependence of the index of refraction as a function of the polarization. As discussed above, the present invention provides many advantages for optic filters, optic switches, optic pixels, and other devices that use filtering of optic signals. The optic filter of the present invention includes an intermediate material that has an index of refraction that is variable based on the electric field applied to the intermediate material. Specifically, in advantageous embodiments, the intermediate material is a ferroelectric material, and in more advantageous embodiments, the intermediate material comprises an electrostrictive material.

With reference to Figure 4, one embodiment of an optic filter according to the present invention is illustrated. The optic filter 10 of this embodiment includes a first 12 and second set 14 of alternating layer of materials, where each set of alternating materials has a first dielectric material 16 and a second dielectric material 18 stacked upon each other. Further, the first and second dielectric materials have different indices of refraction. Additionally, the first set of alternating layers is connected to a transparent substrate 24. The optic filter of the present invention also includes an intermediate material 20 disposed between the first 12 and second set 14 of alternating layers. Importantly, the intermediate material has an index of refraction that varies as a function of the intensity of an electric field applied thereto. To apply an electric field to the intermediate material, the optic filter 10 further includes two electrically conductive layers 22. These electrically conductive layers 22 are connected to an electrical power source, not shown, to supply an electric field across the intermediate material to thereby alter the index of refraction of the intermediate material. While the electrically conductive layers 22 are illustrated in contact with the intermediate layer in this embodiment, it must be understood that the electrically conductive layers may be located in other positions in the optic filter, such as to create an electric field across the intermediate layer of material. For instance, in one embodiment, one of the electrically conductive layers may be placed below the first set 12 of alternating layers, while the other electrically conductive layer is placed on top of the second set 14 of alternating layers. Further, the electrically conductive layers may be spaced at distances from the optic filter at positions that create and electric field across the intermediate layer of material in a desired direction.

With reference to Figure 5, the operation of the optic filter of this embodiment is illustrated. Specifically, an optic light source containing wavelengths of interest are directed such that it is incident on the optic filter. (See step 100). The first and second dielectric layers are configured as described in detail below to either reflect or filter the optic wavelength of interest of the signal. To filter the optic signal, an electric potential is applied to the electrically conductive layers 22, which in turn, creates an electrical field across the intermediate material 20. (See step 110). The electric field alters the refractive index of the intermediate material such that the intermediate material either transmits or reflects the wavelength of interest based on the configuration of the optic filter. (See step 120).

As discussed above, ferroelectric ceramic materials provide advantageous characteristics for use in optic filters. Ferroelectric ceramic materials demonstrate advantageous memory properties that allow the materials to be transitioned from a polarized state to a non-polarized state in a short time frame. Specifically, in embodiments in which the intermediate material is a ferroelectric ceramic material, the polarization time for the optic filter ranges from 10-100 nanoseconds. In a further embodiment, the intermediate material is a electrostrictive material having a slim loop hysteresis of polarization versus energy bias and a quadratic dependence of the index of refraction as a function of the polarization of the electrostrictive material. Suitable optic materials for the intermediate layer, to name a few, are lead lanthanum zirconium titanate PLZT, lead zirconium titanate PZT, barium titanate BaTiO₃, ferroelectric polymers, electrooptic polymers, potassium niobate KNbO₃, lithium niobate LiNbO₃, and lead magnesium niobate Pb(Mg_xNbι_ _xO₃). It must be understood that this is only an example of some of the electrostrictive materials, and that the present invention should not be limited to the use of the above materials for the intermediate layer.

As shown in the present embodiment in Figure 4, the present invention includes electrically conductive layers 22 for supplying an electrical potential to the intermediate material 20. Specifically, the conductive layers are positioned on opposite sides of the intermediate material depending on the desired direction of polarization of the intermediate material. Specifically, in embodiments where polarization of the intermediate material is desired in a horizontal direction, the conductive layers are connected to the opposed vertical sides of the intermediate material. However, in embodiments where it is desired to polarize the intermediate material in a vertical direction, the conductive layers are positioned on the opposed horizontal sides of the intermediate material between the intermediate material and the set of alternating layers of material. Further, in some embodiments, the conductive layers may be transparent to allow the transmission of light. Specifically, in one advantageous embodiment of the present invention, the electrical conductive layers of material comprise indium tin oxide ITO. Other suitable, conductive, transparent materials for the electrically conductive layer include tin oxide Snθ₂, indium oxide In₂O₃, zinc oxide ZnO, ruthenium oxide RuO₂.

Also, the electrically conductive layers may be in contact with the intermediate layer of material, or they may be spaced apart from the intermediate layer of material. For instance, in one embodiment, one of the electrically conductive layers may be placed below the first set of alternating layers, while the other electrically conductive layer is placed on top of the second set of alternating layers. Further, the electrically conductive layers may be spaced at distances from the optic filter at positions that create an electric field across the intermediate layer of material in a desired direction. In many optic filter applications, it is advantageous to configure the filter such that it will either filter or reflect an optic signal of interest. For instance, if the optic filter is used to filter or transmit certain wavelengths of light, the alternating layer of materials must be deposited in thickness that will allow the desired wavelengths to be either transmitted or reflected when the intermediate material is excited by an electric field. As such, in one embodiment of the present invention, the two sets of alternating materials are configured with chosen thickness such that the optic filter will allow efficient transmission or reflection of chosen optic wavelengths.

In this embodiment of the present invention, each set of alternating materials has a first dielectric material and a second dielectric material stacked upon each other, where the first and second dielectric material have different indices of refraction. Further, the thickness of each of layer of the first and second dielectric material is configured such that each of the layers optic thickness is one quarter of the operating wavelength of the filter. For instance, in one advantageous embodiment, the thickness of each layer of the first and second dielectric material is defined by the following equation: mλ

4n where L is the film thickness, λ is the chosen wavelength, n is the index of refraction, and m is an odd integer order. By utilizing this equation and knowing the wavelength that the filter is designed to transmit, the thickness of the layered materials can be determined to provide the performance characteristics desired. Additionally, it must be understood that increasing the difference in the indices of refraction between the two first and second dielectrics increases the sharpness of the filter response. A greater difference in index also means that fewer layers have to be used to obtain a given sharpness criteria. Further, in some embodiments, it may be advantageous to alter the thickness of some of the layers (i.e., bias the layers) depending on the desired properties of the filter.

In addition to configuring the thickness of the alternating layer of materials to reflect or transmit desired wavelengths, it may also be advantageous to select the materials comprising each layer having desired indices of refraction. For example in alternative embodiments, the first layer and second dielectric layers may comprise one of the following dielectrics: silicon dioxide Siθ2, silicon nitride Si₃N₄, magnesium fluoride MgF₂, titanium oxide Tiθ2, aluminum oxide Al₂O₃, chrome oxide Cr₂O₃, barium fluoride BaF2, cerium fluoride CeF₃, cerium oxide CeU2, hafnium oxide HfO₂ or any other suitable material. The selection of the material for the first and second layers and their thickness is dependent on the desired wavelength transmission or reflection. Further, in many advantageous embodiments, the dielectric materials will be transparent.

In addition to configuring the thickness and composition of the alternating layer of materials, in some embodiments, it may be desired to configure the optic thickness of the intermediate layer of material. For instance, in one embodiment, it is advantageous to configure the intermediate layer to an optic thickness that is one half the operating wavelength of the filter. This provides a strong band-pass filter with a narrow transmission region at the designed wavelength surrounded by reflection near the designed wavelength. The thickness of this layer can be even multiples of the half wavelengths and still achieve the designed filter attributes. Thicker layers can provide increased tuning range for the filter. For instance, in one advantageous embodiment, the thickness of the intermediate layer is defined by the following equation:

where L is the film thickness, λ is the chosen wavelength, n is the index of refraction, and m is an integer. By utilizing this equation and knowing the wavelength that the filter is designed to transmit, the thickness of the intermediate material can be determined to provide the performance characteristics desired.

With reference to Figures 6A , 6B and 7, the formation of an optic filter according to one embodiment of the present invention is illustrated. Important to the manufacture of the optic filter of the present invention is the formation of the electrodes or contacts on the electrically conductive layers, 22 A and 22B.

Specifically, the electrodes should be formed on the electrically conductive material such that they do not impede the expansion and contraction of the intermediate material 20 during operation. In particular, when an electric field is applied to the intermediate material, the intermediate material, being piezoelectric in nature, will expand in the range of 5 to 50 angstroms, in the preferred embodiment, depending on film thickness of the layer. If the electrodes are placed such that they restrict this expansion and contraction, it may disrupt the operation of the optic filter. In light of this, the various layers of material that form the optic filter, (i.e., alternating layers of dielectric material, intermediate layer of material, and electrically conductive layers of material), are first deposited by any conventional procedure on the a transparent substrate 24. (See step 200). For instance, the various layers may be formed by evaporative coating, ion assisted deposition, ion plating, sputtering, spin coating, or any other deposition procedure having controllable parameters such that the layer has be deposited with specified thickness.

After depositing the various layers, a mask is placed on the optic filter, which masks a center portion of the optic filter. The optic filter is etched using reactive ion etching down to the second electrically conductive layer 22A. (See step 210). A second mask is then placed on the optic filter protecting the center portion and a portion of the second electrically conductive layer 22A. The unmasked portions of the second electrically conductive layer 22A and the intermediate layer 20 are then etched thereby, exposing the first electrically conductive layer 22B. (See step 220). Finally, the optic filter is patterned and contacts 26 are deposited on the first and second electrically conductive layers. (See step 230). By depositing the contacts on the top portions of the electrically conductive layers, as opposed to the side of the layers where they may overlap on to the intermediate layer, the electrodes are less likely to interfere with the expansion and contraction of the intermediate material. It must be understood that, while the electrically conductive layers 22 are illustrated in contact with the intermediate layer, that the electrically conductive layers may be located in other positions in the optic filter, such as to create an electric field across the intermediate layer of material. For instance, in one embodiment, one of the electrically conductive layers may be placed below the first set of alternating layers 12, while the other electrically conductive layer is placed on top of the second set 14 of alternating layers. Further, the electrically conductive layers may be spaced at distances from the optic filter at positions that create an electric field across the intermediate layer of material in a desired direction.

Further, it must be understood that while Figures 6A, 6B, and 7 illustrate etching the optic filter from the top to make connections with the electrically conductive layers, the optic filter could be etched from the bottom, as opposed to the top. In embodiments in which the optic filter is etched from the top as depicted in Figures 6A, 6B, and 7, the mask could be placed on the transparent substrate 24, which masks a center portion of the optic filter. The optic filter is etched using reactive ion etching down to the first electrically conductive layer 22B. (See step 220). A second mask is then placed on the optic filter protecting the center portion and a portion of the first electrically conductive layer 22B. The unmasked portions of the first electrically conductive layer 22B and the intermediate layer 20 are then etched thereby, exposing the second electrically conductive layer 22A. (See step 210). Finally, the optic filter is patterned and contacts 26 are deposited on the first and second electrically conductive layers. (See step 230).

Having now described the basic structure and function of the optic filter of the present invention, provided below are specific embodiments illustrating the use of the optic filter for specific applications. These embodiments are provided for illustrative purposes and should not limit the scope of use of the present invention.

With reference to Figure 8, an illustrative embodiment of the optic filter of the present invention is shown. In this embodiment, the optic filter is configured to transmit an optic signal having a wavelength of 600 nanometers and filter some of the remaining components of an incident optic signal. With reference to Figure 8, the optic filter 10 of this embodiment includes a first 12 and second set 14 of alternating layers of material, where each set of material has two layers of a first dielectric material 16 and two layers of a second dielectric material 18 stacked upon each other. The first dielectric material is silicon dioxide Siθ2 and the second dielectric material is silicon nitride Si₃N₄. Additionally, the first set of alternating layers is connected to a transparent substrate 24, such as either quartz or glass.

The optic filter of the present invention also includes an intermediate material 20 disposed between the first 12 and second set 14 of alternating layers. The intermediate material comprises an electrostrictive PLZT material and has an index of refraction that varies as a function of the intensity of an electric field applied thereto. To apply an electric field to the intermediate material, the optic filter 10 further includes two electrically conductive layers 22 in contact with the intermediate material. These conductive layers 22 are connected to an electrical power source, not shown, to supply an electric field across the intermediate material to thereby alter the index of refraction of the intermediate material. The conductive materials comprise indium tin oxide ITO material.

Additionally, the thickness of the first and second dielectric material layers are defined by the following equation: _ mλ 4n where L is the film thickness, λ is the chosen wavelength, n is the index of refraction, and m is an odd integer order. The intermediate layer of material may have a thickness that is one half the wavelength of the wavelength of interest, (i.e., L = mλ/2n). However, in this embodiment, it has a thickness of 115 nanometers. With reference to Table 2, the thicknesses of the various layers are shown.

Table 2

Layer (Unpolarized) Thickness > (Unpolarized)

Si₃N₄ 75 nanometers

SiO₂ 102

Si₃N₄ 75

SiO₂ 102

ITO 83

EO 115

ITO 83

SiO₂ 102

Si₃N₄ 75

SiO 102

Si₃N₄ 75

With reference to Figure 5, the operation of the optic filter of this embodiment is illustrated. Specifically, an optic light source containing a 600 nanometer wavelength optic signal is directed such that it is incident on the optic filter 10. (See step 100). To filter the optic signal and transmit the 600 nanometer optic signal through the optic filter, an electric potential is applied to the electrically conductive layers 22, which in turn, creates an electrical field across the intermediate material 20. (See step 110). The electric field alters the refractive index of the intermediate material such that the intermediate material filters the optic signal and transmits the 600 nanometer wavelength. (See step 120).

With reference to Figure 9, the performance of the optic filter of this embodiment is illustrated. Specifically, Figure 9 is a graph of the reflectiveness of the optic filter versus the optic wavelength of an optic signal incident on the filter, as seen by a detector. The optic filter is designed to filter 600 nanometer wavelength light with a 50 nanometer half- width. As shown, the peak 28 prior to the 600 nanometer wavelength 30 is labeled with a reflection efficiency of 91% meaning that 91% of the optic signal having a wavelength close to the 600 nanometer wavelength of interest is reflected. Further, the reflectivity point 30 at the 600 nanometer wavelength shows ~ 1-10% reflection. Therefore the total contrast ratio, from the top of the reflected wavelength 28 to the 600 nanometer wavelength 30. is ~ 25 : 1. This high contrast ratio is achieved with high light transmission. Further, the intermediate and electrically conductive layers absorb most of the optic signal.

As discussed previously, conventional fiber optic networks use GRIN lenses to demodulate and split modulated optic signals. One embodiment of the present invention provides an alternative to GRIN lenses by employing an optic switch according to the present invention to operate as a switch by alternatively transmitting or reflecting or absorbing a fiber optic signal. Specifically, with reference to Figure 10, one advantageous embodiment of the optic switch of the present invention is illustrated. In this embodiment, the optic switch 10 is an in-line type optic filter that is placed such that the optic signal, propagating through the optic fiber 32, is incident to the optic filter 10. In this configuration, the index of refraction of the optic switch can be changed to alternately filter and reflect or absorb an optic signal, such that the optic signal propagating through the optic fiber can be ether transmitted in an "on" state of the optic switch or filtered or reflected in the "off state of the switch.

Further, by varying the electric field in the intermediate material, the optic signal may be shifted or redirected.

In an advantageous embodiment, the optic switch of the present invention is configured to alternately transmit or reflect or absorb an optic signal having a wavelength of 1.55 μm, which is the typical wavelength of data transmitted in fiber optic networks. With reference to Figure 11, an illustrative embodiment of the optic filter 10 of the present invention is shown. In this embodiment, the optic filter is configured to transmit an optic signal having a wavelength of 1.55 μm and filter the remaining components of an incident optic signal. With reference to Figure 11, the optic filter 10 of this embodiment includes a first 12 and second set 14 of alternating layers of material, where each set of material has seven layers of a first dielectric material 16 and seven layers of a second dielectric material 18 stacked upon each other. The first dielectric material is silicon dioxide SiO₂ and the second dielectric material is titanium oxide ΗO2. Additionally, the first set of alternating layers is connected to a transparent substrate 24, such as either quartz or glass.

The optic filter of the present invention also includes an intermediate material 20 disposed between the first 12 and second set 14 of alternating layers. The intermediate material comprises an electrostrictive PLZT material and has an index of refraction that varies as a function of the intensity of an electric field applied thereto. To apply an electric field to the intermediate material, the optic filter 10 further includes two electrically conductive layers 22. These conductive layers 22 are connected to an electrical power source, not shown, to supply an electric field across the intermediate material to thereby alter the index of refraction of the intermediate material. The conductive layers 22 comprise a tin oxide Snθ₂ material. The alternating layers are chosen based on the equation:

_ — — ^m —λ —

In where L is the film thickness, λ is the chosen wavelength, n is the index of refraction, and m is an integer. With reference to Table 1 , reprinted below, the thickness and number of layers is shown. Table 1

Layer (Unpolarized) Thickness (Unpolarized)

TIO₂ 168.55 nanometers

SIO₂ 270.22

TIO₂ 168.55

SIO₂ 270.22

TIO2 168.55

SIO2 270.22

TIO₂ 168.55

SIO₂ 270.22

TIO₂ 168.55

SIO₂ 270.22 Layer (Unpolarized) Thickness (Unpolarized)

TIO₂ 168.55

SIO2 270.22

TIO2 168.55

SIO2 270.22

TIO2 168.55

SIO2 270.22

SNO₂ 193.75

PLZT 316.33

SNO₂ 193.75

TIO₂ 168.55

SIO2 270.22

TIO₂ 168.55

SIO₂ 270.22

TIO₂ 168.55

SIO₂ 270.22

TIO₂ 168.55

SIO₂ 270.22

TIO₂ 168.55

SIO₂ 270.22

TIO₂ 168.55

TIO2 168.55

SIO₂ 270.22

TIO₂ 168.55

In operation, with reference to Figure 5, an incident light, such as the light from a fiber optic cable, is directed at the optic switch 10. (See step 100). The optic switch is initially set with no electric field across the intermediate material providing an "on" state that allows the 1.55 μm wavelength signal to transmit through the optic switch. Specifically, due to the configuration of the optic switch (i.e.. the types and thickness of the first and second dielectric materials), optic signals having a wavelengths of 1.55 μm are transmitted through the optic filter, while other wavelengths are either absorbed or reflected by the optic switch. To turn the optic switch to the "off position (i.e.. to stop transmitting the 1.55 μm wavelength signal), a voltage is applied to the electrically conductive layers 22, thereby forming an electrical field across the intermediate material 20. (See step 110). As the electric field increases, the refractive index of the intermediate material is shifted such that the optic filter no longer transmits the 1.55 μm wavelength signal, because the wavelength of the light is shifted. (See step 120). As such, the optic signal may be switched from "on" to "off by applying an electrical field to the optic filter. The optic filter in this configuration can also be used to shift or redirect the optic signal by varying the intensity of electric field in the intermediate layer. With reference to Figure 12, the performance of the optic filter of this embodiment is illustrated. Specifically, Figure 12 is a graph of the transmission of the optic filter versus the optic wavelength of an optic signal incident on the filter. The optic filter is designed to filter 1.55 μm wavelength light with a 0.4 nanometer half- width. As shown, the region 34 prior to and following the 1.55 μm wavelength 36 is reflecting with an efficiency approaching 100%, meaning that almost all of the optic signal having a wavelength close to the 1.55 μm wavelength of interest is reflected. Further, point 38 at the 1.55 μm wavelength shows ~ 91%) transmission. Therefore a conservative estimate of the total contrast ratio, from the wavelength with the least transmission as represented by the point 34 to the 1.55 μm wavelength with the greatest transmission at point 38, is ~ 91 : 1. This high contrast ratio is achieved with high light transmission.

In addition to Figure 12, Figure 13 illustrates the alteration of the index of refraction of the intermediate material due to changes in the electrical field. Figure 13 also illustrates the shifting or shifting of the light signal. As illustrated in Figure 13, in the "on" position the output of the optic filter has a strong transmission peak at 1.55 μm wavelength representing the optic signal. (See plot 1). However, when an electric field is applied to the intermediate layer, transmission of the narrow bandpass filter begins to decrease. (See plots 2-4). Finally, in the "off position, the amplitude of the transmission at 1.55 μm for a polarized sample using 5-10V potential across the intermediate material is close to zero. (See plot 5). This is because the index of refraction of the intermediate layer has been altered or shifted by the electric field. This, in turn, shifts the peak of the wavelength by approximately 16 angstroms. Recent designs of an optic switch according this embodiment has shown shifts in the peak as high as 75 angstroms.

The configuration of the present embodiment, results in a narrow bandpass filter with a full-width at half maximum wavelength in the nanometer range. Additionally, a small change in the index of refraction of the intermediate layer 20 creates an optic transition from transparent to reflecting (or vice versa). As such, an Electrooptic Interference Filter switch as designed above can be designed to work at 1.55 μm wavelengths, which is typically used for optic fiber transmission. The optic switch can pass 1.55 μm at no applied potential with 90%> transmission and <1% transmission at 5-10 V potential. The optic switch of this embodiment is generally a robust, integrated structure that has very high optic transmission and very high contrast ratios. Further, operation voltages are typically in the volt range with the highest allowed operating voltages in the tens of volts. The optic switch of this embodiment can operate in nanosecond range with very little temperature sensitivity. Since it switches so fast, the same optic switch structure can be operated in a small subset of allowed states (i.e., digital mode) or continually varying (i.e., AC mode). However, this optic switch could also be used for amplitude modulation in the nanosecond range if desired.

As illustrated in Figure 13, the optic filter of the present invention provides a narrow high pass filter. Further, as illustrated, the optic filter can effectively filter or pass an optic signal with a wavelength of 1.55 μm. It must be understood that at higher wavelengths the transparent, electrically conductive material may begin to lose transparency. Specifically, at higher frequencies the electrically conductive material may reach the plasma frequency, which causes the electrically conductive material to screen or reflect light. The optic filter of the present invention counteracts this problem by using indium tin oxide ITO or ZnO as the electrically conductive material. ITO and ZnO may transmit higher wavelengths before reaching the plasma frequency. For example, in one embodiment, the ITO can transmit wavelengths up to about 1.8 μm to 2.0 μm. It must be understood that the present embodiment is not limited to an "inline" type optic filter. Instead, the optic filter may comprise a block of material that is connected to the optic fiber to split the optic signal into many optic signals.

In addition to providing an optic switch that will effectively filter optic signals, there are several additional advantages to this design. First it can be operated at very high frequencies since the typical polarization time for a thin film is on the order of 100 nanoseconds. The filter produces a smooth and progressive change in intensity as a function of polarization so that it can be used for a modulator or a switch. It maintains a high contrast ratio at a high optic transmission. The device is a capacitance load so the total power used in the device is generally low. The devices can be fabricated on glass substrates and are relatively cheap and simple to fabricate. The size of the packages can be extremely small leading to, for example, fabrication of in-line optic filters of only 2 mm in the case of the 1.55 μm switch. Further, the optic signal may be shifted or redirected by varying the intensity of the electric field in the intermediate layer, as shown in Figure 13.

In addition to providing an optic filter for filtering certain wavelengths and an optic switch, the optic filter of the present invention can also be used in an optic filter pixel. Specifically, optic filters according to the present invention can be designed such that when there is zero electrical field across the intermediate layer of each optic filter, the optic filter pixel transmits or reflects a desired wavelength of light representing a color of interest, and as various levels of electrical field strengths are applied to the intermediate materials, the index of refraction of the optic filter is shifted such that the optic filter pixel either transmits or reflects different wavelengths of light representing the different colors. For example, in one embodiment of the present invention, an optic filter pixel is formed having three optic filters stacked upon each other. The composition and thickness of the first and second dielectric materials of each optic filter are selected such that at a zero electric field on the intermediate material the optic fiber pixel transmits an optic wavelength representing a yellow color. As an electric field is applied across the intermediate material of each optic filter, the index of refraction of the intermediate material is altered, such that the optic filter pixel transmits different wavelengths of color until at a maximum chosen electric field strength, the optic filter pixel transmits a wavelength representing a purple color. Each optic filter of this embodiment of the present invention is similar to previous embodiments and includes a first set 12 of alternating material deposited on a transparent substrate 24. Deposited on the first set of alternating material is a first electrically conductive material 22, a layer of intermediate material 20, and a second layer of electrically conductive material 22. Deposited on the second layer of electrically conductive material is a second set 14 of alternating materials. As discussed previously, the number of layers and the composition and thickness of the first and second dielectric materials are chosen based on the equation:

_ ^mΛ 4n such that the desired wavelengths are either reflected or transmitted by the optic filter pixel. Further, the intermediate layer is defined by the following equation:

_ ^mλ ^~ ^2n^~ where L is the film thickness, λ is the chosen wavelength, n is the index of refraction, and m is an integer. The various layers of the optic filter pixel of this embodiment are shown in

Table 3. Specifically, Table 3 illustrates three optic filters stacked upon each other.

Table 3

Layer Material Thickness (nanometers)

1 TIO₂ 57.65

2 SIO₂ 94.50

J TIO₂ 57.65

4 SIO₂ 94.50

5 TIO₂ 57.65

6 SIO₂ 94.50

7 TIO₂ 57.65

8 SIO₂ 94.50

9 TIO₂ 57.65

10 SIO₂ 94.50

12 SIO2 94.50

13 TIO₂ 57.65

14 SIO₂ 94.50

15 ITO 57.29

16 PLZT 56.12

17 ITO 57.29

18 TIO2 57.65

19 SIO₂ 94.50

20 TIO2 57.65

21 SIO2 94.50 Layer Material Thickness (nanometers)

22 TIO₂ 57.65

23 SIO₂ 94.50

24 TIO₂ 57.65

25 SIO2 94.50

26 TIO₂ 57.65

27 SIO₂ 94.50

28 TIO₂ 57.65

29 SIO₂ 94.50

31 SIO₂ 94.50

32 TIO₂ 42.66

SIO₂ 72.77

34 TIO₂ 42.66

35 SIO₂ 72.77

36 TIO₂ 42.66

37 SIO₂ 72.77

38 TIO₂ 42.66

39 SIO₂ 72.77

41 SIO₂ 72.77

42 TIO₂ 42.66

43 SIO₂ 72.77

44 TIO₂ 42.66

45 SIO₂ 72.77

46 ITO 44.11

47 PLZT 43.21

48 ITO 44.11

49 TIO₂ 42.66

50 SIO₂ 72.77

51 TIO₂ 42.66

52 SIO₂ 72.77

53 TIO₂ 42.66

54 SIO₂ 72.77

55 TIO₂ 42.66

56 SIO₂ 72.77

57 TIO₂ 42.66

58 SIO₂ 72.77

59 TIO₂ 42.66

60 SIO₂ 72.77

61 TIO₂ 42.66

62 SIO₂ 72.77

63 TIO₂ 72.64

66 SIO2 116.24

61 TIO₂ 72.64

69 TIO₂ 72.64

70 SIO₂ 116.24 Layer Material Thickness (nanometers)

71 TIO₂ 72.64

72 SIO₂ 1 16.24

73 TIO₂ 72.64

74 SIO₂ 116.24

75 TIO₂ 72.64

76 SIO2 1 16.24

77 ITO 70.47

78 PLZT 69.03

79 ITO 70.47

80 TIO₂ 72.64

81 SIO₂ 116.24

82 TIO₂ 72.64

83 SIO₂ 116.24

84 TIO2 72.64

85 SIO₂ 116.24

86 TIO₂ 72.64

87 SIO₂ 116.24

88 TIO₂ 72.64

89 SIO2 116.24

90 TIO₂ 72.64

91 SIO2 116.24

92 TIO₂ 72.64

93 SIO₂ 116.24

With reference to Figure 14, the performance of the an optic filter pixel having the above configuration is illustrated. In this embodiment, the interference filter stacks built atop each other (a total of -100 layers) the sample can be designed for optic yellow (a lime green color) and then be switched to a deep purple. Specifically, the unpolarized sample starts at optic yellow and follows a "candy-cane^" path 40 toward deep purple with increasing applied voltages to the intermediate material. The path 40 represents the estimated path the transmitted light would take. This is a graphic illustration of the use of one pixel for more than one color. Although the present embodiment illustrates an optic filter pixel for transitioning from a yellow color to a purple color, it must be understood that any wavelengths of the color spectrum may be filtered by changing the thickness, composition, number of alternating layers of dielectric material, and number of optic filters. Further, due to the fast transition times of the optic filter of the present invention, the colors could be changed in continuous fashion or very rapidly from one shade to the next by applying either analog or digital voltages to the intermediate material. As mentioned above, the optic filter pixel of this embodiment includes three optic filters stacked atop each other. In additional embodiments, the intermediate layer of each optic filter of the optic filter pixel may be operated independently, (i.e.. provided with different electrical fields to provide different colors). For example, the optic filters of the optic pixel could be controlled independently to provide an optic pixel that provides three separate colors, such as red, blue, and green, as the different optic filters are varied.

Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings.

Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

THAT WHICH IS CLAIMED:

1. A tunable optic filter comprising: first and second sets of alternating layers of material, wherein each set has first and second alternating layers of dielectric material stacked upon each other, and wherein the first and second layers of dielectric material have different indices of refraction; and an intermediate layer of material disposed between said first and second set of alternating layers of dielectric material, wherein said intermediate layer of material has an index of refraction that varies as a function of the intensity of an electric field applied thereto.

2. A tunable optic filter according to Claim 1 further comprising a transparent substrate layer, wherein said first set of alternating layers is disposed on said transparent substrate, such that said transparent substrate and said intermediate layer are on opposed sides of said first set of alternating layers.

3. A tunable optic filter according to Claim 1 further comprising first and second layers of electrically conductive material, wherein said first and second layers of electrically conductive material are positioned relative to said intermediate layer of material to provide an electric field across said intermediate layer of material.

4. A tunable optic filter according to Claim 1 further comprising at least one layer of electrically conductive material disposed between said intermediate material and at least one of said first and second sets of alternating layers, wherein said layer of electrically conductive material is positioned to provide an electric field across said intermediate layer of material.

5. A tunable optic filter according to Claim 1 further comprising first and second layers of electrically conductive material, wherein said first layer of electrically conductive material is disposed between said intermediate material and said first set of alternating layers, wherein said second layer of electrically conductive material is disposed between said intermediate material and said second set of alternating layers, and wherein said first and second layers of electrically conductive material are positioned to provide an electric field across said intermediate layer of material.

6. A tunable optic filter according to Claim 5, wherein said second layer of electrically conductive material extends beyond at least one side of said intermediate layer of material, such that an electrical connection can be made with said second layer of electrically conductive material without substantially hindering contraction and expansion of said intermediate layer.

7. A tunable optic filter according to Claim 5, wherein said first layer of electrically conductive material extends beyond at least one side of said intermediate layer of material, such that an electrical connection can be made with said first layer of electrically conductive material without substantially hindering contraction and expansion of said intermediate layer.

8. A tunable optic filter according to Claim 1, wherein the first and second alternating layers of each set of alternating layers have respective optic thicknesses that correspond to a predetermined operating wavelength of said tunable optic filter.

9. A tunable optic filter according to Claim 8, wherein the first and second alternating layers of each set of alternating layers have respective optic thicknesses that correspond to one quarter of a predetermined operating wavelength of said tunable optic filter.

10. A tunable optic filter according to Claim 9, wherein the first and second alternating layers of each set of alternating layers have respective optic thicknesses defined by the following equation:

_ mλ 4n

wherein L is the optic thickness of the alternating layer, λ is the predetermined operating wavelength, n is an index of refraction of the alternating layer, and m is an odd integer order.

11. A tunable optic filter according to Claim 1 , wherein said intermediate layer of material has an optic thickness that correspond to one-half of a predetermined operating wavelength of said tunable optic filter.

12. A tunable optic filter according to Claim 11, wherein said intermediate layer of material has an optic thickness defined by the following equation: _ m

In

wherein L is the optic thickness of said intermediate layer of material, λ is the predetermined operating wavelength, n is an index of refraction of said intermediate layer of material, and m is an integer.

13. A tunable optic filter according to Claim 1 , wherein said intermediate material is ferroelectric material.

14. A tunable optic filter according to Claim 1, wherein said intermediate material is an electrostrictive material.

15. A tunable optic filter according to Claim 14, wherein said intermediate material is a material selected from the group consisting essentially of lead lanthanum zirconium titanate PLZT, lead zirconium titanate PZT, barium titanate BaTiO₃, ferroelectric polymers, electrooptic polymers, potassium niobate KNbO₃, lithium niobate LiNbO₃, and lead magnesium niobate Pb(Mg_xNbι_-xO₃).

16. A tunable optic filter according to Claim 3, wherein said layer of electrically conductive material is indium tin oxide ITO.

17. A tunable optic filter according to Claim 3, wherein said layer of electrically conductive material is a material selected from the group consisting essentially of indium tin oxide ITO, tin oxide SnO₂, indium oxide In₂O₃, zinc oxide ZnO, and ruthenium oxide RuO .

18. A method of manufacturing a tunable optic filter, wherein said method comprises the steps of: depositing a first set of alternating layers of dielectric material on a transparent substrate, wherein said depositing a first set of alternating layers step deposits first and second alternating layers of dielectric material stacked upon each other, and wherein the first and second layers of dielectric material have different indices of refraction; depositing an intermediate layer of material on the first set of alternating layers of dielectric material, wherein the intermediate layer of material has an index of refraction that varies as a function of the intensity of an electric field applied thereto: and depositing a second set of alternating layers of dielectric material on the intermediate layer of material, wherein said depositing a second set of alternating layers step deposits first and second alternating layers of dielectric material stacked upon each other, and wherein the first and second layers of dielectric material have different indices of refraction.

19. A method according to Claim 18 further comprising, prior to said depositing a first set of alternating layers step, the step of depositing a first layer of electrically conductive material on a transparent substrate.

20. A method according to Claim 19 further comprising, after said depositing a second set of alternating layers step, the step of depositing a second layer of electrically conductive material on the second set of alternating layers.

21. A method according to Claim 18 further comprising, prior to said depositing an intermediate layer step, the step of depositing a first layer of electrically conductive material on the first set of alternating layers of dielectric material.

22. A method according to Claim 21 further comprising, prior to said depositing a second set of alternating layers step, the step of depositing a second layer of electrically conductive material on the intermediate material.

23. A method according to Claim 22 further comprising the steps of: selectively etching at least a portion of the second set of alternating layers to thereby expose the second layer of electrically conductive material; and depositing a layer of electrically conductive material on an exposed portion of the second layer of electrically conductive material in the form of a contact, such that an electrical connection can be made with the second layer of electrically conductive material without substantially hindering contraction and expansion of the intermediate layer of material.

24. A method according to Claim 22 further comprising the steps of: selectively etching at least a portion of the second set of alternating layers, second electrically conducting layer of material, and the intermediate layer of material to thereby expose the first layer of electrically conductive material; and depositing a layer of electrically conductive material on an exposed portion of the first layer of electrically conductive material in the form of a contact, such that an electrical connection can be made with the first layer of electrically conductive material without substantially hindering contraction and expansion of the intermediate layer of material.

25. A method according to Claim 22 further comprising the steps of: selectively etching at least a portion of the transparent substrate and the first set of alternating layers to thereby expose the first layer of electrically conductive material; and depositing a layer of electrically conductive material on an exposed portion of the first layer of electrically conductive material in the form of a contact, such that an electrical connection can be made with the first layer of electrically conductive material without substantially hindering contraction and expansion of the intermediate layer of material.

26. A method according to Claim 22 further comprising the steps of: selectively etching at least a portion of the transparent substrate, first set of alternating layers, first electrically conducting layer of material, and the intermediate layer of material to thereby expose the second layer of electrically conductive material; and depositing a layer of electrically conductive material on an exposed portion of the second layer of electrically conductive material in the form of a contact, such that an electrical connection can be made with the second layer of electrically conductive material without substantially hindering contraction and expansion of the intermediate layer of material.

27. A method according to 18, wherein at least one of said depositing a first set of alternating layers and depositing a second set of alternating layers steps comprises depositing the first and second alternating layers such that the first and second layers have respective optic thicknesses that correspond to a predetermined operating wavelength of the tunable optic filter.

28. A method according to Claim 18, wherein at least one of said depositing a first set of alternating layers and depositing a second set of alternating layers steps comprises depositing the first and second alternating layers such that the first and second layers have respective optic thicknesses that correspond to one quarter of a predetermined operating wavelength of the tunable optic filter.

29. A method according to Claim 18, wherein at least one of said depositing a first set of alternating layers and depositing a second set of alternating layers steps comprises depositing the first and second alternating layers such that the first and second layers have respective optic thicknesses defined by the following equation:

L = ^

4n

30. A method according to 18, wherein said depositing an intermediate layer of material step comprises depositing the intermediate layer of material such that the intermediate layer of material has an optic thickness that corresponds to a predetermined operating wavelength of the tunable optic filter.

31. A method according to Claim 18, wherein said depositing an intermediate layer of material step comprises depositing the intermediate layer of material such that the intermediate layer of material has an optic thickness that corresponds to one half of a predetermined operating wavelength of the tunable optic filter.

32. A method according to Claim 18, wherein said depositing an intermediate layer of material step comprises depositing the intermediate layer of material such that the intermediate layer of material has an optic thickness defined by the following equation:

wherein L is the optic thickness of the intermediate layer of material, λ is the predetermined operating wavelength, n is an index of refraction of the intermediate layer of material, and m is an integer.

33. A method according to Claim 18, wherein said depositing an intermediate layer of material step comprise depositing a ferroelectric material on the first set of alternating layers of dielectric material.

34. A method according to Claim 33, wherein said depositing an intermediate layer of material step comprise depositing a material selected from the group consisting of lead lanthanum zirconium titanate PLZT, lead zirconium titanate PZT. barium titanate BaTiO₃, ferroelectric polymers, electrooptic polymers, potassium niobate KNbO₃, lithium niobate LiNbO₃, and lead magnesium niobate Pb(Mg_xNb). _xO₃) on the first set of alternating layers of dielectric material.

35. A method according to Claim 20, wherein at least one of said depositing a first and second layer of electrically conductive materials steps comprises depositing a layer of indium tin oxide ITO.

36. A method according to Claim 20, wherein at least one of said depositing a first and second layer of electrically conductive materials steps comprises depositing a layer of material selected from the group consisting of indium tin oxide ITO, tin oxide SnO₂, indium oxide In₂θ₃, zinc oxide ZnO, and ruthenium oxide RuO₂.

37. A method of tuning an optic filter to selectively filter different wavelengths of an optic signal, wherein said method comprises the steps of: providing an optic filter having first and second sets of alternating layers stacked upon each other and having different indices of refraction and an intermediate layer of material disposed between the first and second sets of alternating layers of dielectric material having an index of refraction that varies as a function of the intensity of an electric field applied thereto; directing an optic signal at the optic filter having at least one wavelength of light; and applying an electric field to the intermediate material of the optic filter to selectively filter and reflect different wavelengths of the optic signal.

58-

38. A method according to Claim 37 wherein said providing step provides an optic switch for selectively filtering and reflecting a wavelength of interest, and wherein said applying step comprises applying no more than a nominal electric field to the intermediate material to place the optic switch in an on state, such that the optic switch filters the optic signal thereby allowing the wavelength of interest to be transmitted through the optic switch.

39. A method according to Claim 37 wherein said providing step provides an optic switch for selectively filtering and reflecting a wavelength of interest, and wherein said applying step comprises applying an electric field to the intermediate material to place the optic switch in an off state such that the optic switch reflects the wavelength of interest of the optic signal.

40. A method according to Claim 37, wherein said providing step provides an optic pixel for selectively filtering and reflecting different wavelengths of the optic signal, and wherein said applying step comprises applying an electric field to the intermediate layer at varying intensities to selectively filter and reflect differing wavelengths of the optic signal.

41. A tunable optic pixel for selectively filtering and reflecting different wavelengths of an optic signal comprising: first and second sets of alternating layers of material, wherein each set has first and second alternating layers of dielectric material stacked upon each other, and wherein the first and second layers of dielectric material have different indices of refraction; and an intermediate layer of material disposed between said first and second sets of alternating layers of dielectric material, wherein said intermediate layer of material has an index of refraction that varies as a function of the intensity of an electric field applied thereto, such that as the index of refraction of said intermediate material varies, said optic pixel filters and reflects different wavelengths of the optic signal.

42. A tunable optic pixel according to Claim 41 further comprising a transparent substrate layer, wherein said first set of alternating layers is disposed on said transparent substrate, such that said transparent substrate and said intermediate layer are on opposed sides of said first set of alternating layers.

43. A tunable optic pixel according to Claim 41 further comprising first and second layers of electrically conductive material, wherein said first and second layers of electrically conductive material are positioned relative to said intermediate layer of material to provide an electric field across said intermediate layer of material.

44. A tunable optic pixel according to Claim 41 further comprising at least one layer of electrically conductive material disposed between said intermediate material and at least one of said first and second sets of alternating layers, wherein said layer of electrically conductive material provides an electrical connection with said intermediate layer of material.

45. A tunable optic pixel according to Claim 41 further comprising first and second layers of electrically conductive material, wherein said first layer of electrically conductive material is disposed between said intermediate material and said first set of alternating layers, wherein said second layer of electrically conductive material is disposed between said intermediate material and said second set of alternating layers, and wherein said first and second layers of electrically conductive material provide an electrical connection with opposed sides of said intermediate layer of material.

46. A tunable optic pixel according to Claim 41, wherein the first and second alternating layers of each set of alternating layers have respective optic thicknesses that correspond to one quarter of a predetermined operating wavelength of said tunable optic pixel.

47. A tunable optic pixel according to Claim 46, wherein the first and second alternating layers of each set of alternating layers have respective optic thicknesses defined by the following equation:

48. A tunable optic pixel according to Claim 41, wherein said intermediate layer of material has an optic thickness that corresponds to one half of a predetermined operating wavelength of said tunable optic pixel.

49. A tunable optic pixel according to Claim 48, wherein said intermediate layer of material has an optic thickness defined by the following equation:

_ mλ l~ι —

2n

50. A tunable optic pixel according to Claim 41, wherein said intermediate material is a ferroelectric material.

51. A tunable optic pixel according to Claim 41 , wherein said intermediate material is an electrostrictive material.

52. A tunable optic pixel according to Claim 43, wherein said layer of electrically conductive material is indium tin oxide ITO.

53. A tunable optic pixel according to Claim 41 comprising a plurality of first and second sets of alternating layers of material, wherein each set has first and second alternating layers of dielectric material stacked upon each other and an intermediate layer of material disposed between each of the plurality of first and second sets of alternating layers of dielectric material, such that as the index of refraction of each intermediate material is varied, said optic pixel filters and reflects different wavelengths of the optic signal.