WO2014019399A1

WO2014019399A1 - Tunable optical filter of fixed frequency intervals and of single-mode output

Info

Publication number: WO2014019399A1
Application number: PCT/CN2013/076163
Authority: WO
Inventors: 高培良
Original assignee: 天津奇谱光电技术有限公司
Priority date: 2012-07-30
Filing date: 2013-05-23
Publication date: 2014-02-06
Also published as: CN102798987A; CN102798987B

Abstract

A tunable optical filter of fixed frequency intervals and of single-mode output, constituted by a Fabry-Pérot etalon (100) and a transmission frequency-tunable Fabry-Pérot filter (200) in a front/rear-opposite arrangement. The Fabry-Pérot etalon (100) and the transmission frequency-tunable Fabry-Pérot filter (200) are provided with a same spectral response range while the transmission frequency-tunable Fabry-Pérot filter (200) is only effective against a linear polarized light having a specific direction of polarization. The tunable optical filter has the characteristics of having no mechanical parts, a small size, and a large free spectral range.

Description

A tunable optical filter with fixed frequency spacing and single mode output

The invention belongs to the field of optoelectronics, in particular to a tunable optical filter with fixed frequency spacing and single mode output. Background technique

The traditional optical Fabry-Perot etalon is a filter element made by the principle of multi-beam interference. There are two main types: one is air-spaced and the other is optical glass-spaced. The multi-wavelength interference output of the Fabry-Perot cavity formed by the high reflectivity of the multilayer dielectric film on the two light-passing surfaces enables multi-wavelength narrow-band filtering output over a wide spectral range, with stable performance and clear light. It has wide aperture, high optical power destruction threshold, simple structure and low cost. Therefore, it is widely used in various types of lasers, optical measuring instruments and optical fiber communication devices. Tuning of the transmitted optical frequency can also be achieved using conventional optical Fabry-Perot etalon. For air-spaced Fabry-Perot etalons, tuning can be done by changing the angle of incidence of the light, but the tuning range of this method is small, or the Fabry-Perot is changed mechanically (such as a stepper motor) The cavity length of the etalon is realized. This method can realize a large tuning range, but the tuning precision is low, and the precision of the mechanical components is high and the stability is not good. With the development of PZT piezoelectric ceramics (lead zirconate titanate) technology, high-precision displacement can be achieved. Using this technique to change the cavity length of the Fabry-Perot etalon can improve the tuning accuracy and speed, but it is not easy to miniaturize and the drive source is complicated. Although a wide range of tuning can be achieved by changing the temperature of the etalon, the disadvantage of this method is that it is slow.

The output of a single Fabry-Perot etalon or a single Fabry-Perot filter is a multi-frequency or multi-mode output with an interval period of its free spectral range, for example, a free spectral range of 100 GHz at 1000 GHz Within the range, there are 10 narrowband multimode outputs with a spacing of 100 GHz. A single frequency output can only be achieved when the frequency range is less than the free spectral range. If you want to increase the free spectral range, reduce the thickness of the Fabry-Perot etalon. For example, for 1500 nm light waves, if ordinary fused silica glass is used, the 100 GHz and 1000 GHz free spectral ranges correspond to the thicknesses. It is about 1 mm and 0.1 mm, so even if you want to achieve a free spectral range of 1000 GHz, it is actually very difficult, let alone a larger free spectral range. In summary, in practical applications, it is almost impossible to use a single Fabry-Perot filter to achieve single-mode tuning output in a range of tens of nanometers wide.

Summary of the invention

The object of the present invention is to overcome the deficiencies of the prior art and to provide a tunable optical filter with fixed frequency spacing and single mode output, which passes the free spectral range of the Fabry-Perot etalon and the tunable method The intrinsic free spectral range of the Ley-Perot filter differs by a certain interval and is tunable using the tunable Fabry-Perot filter transmission frequency The tunable single-mode output function is achieved in the same spectral range as the Fabry-Perot etalon's free spectral range.

The present invention solves the prior art problem by adopting the following technical solutions:

A tunable optical filter with fixed frequency spacing and single mode output, consisting of a Fabry-Perot etalon set up front and rear and a tunable Fabry-Perot filter with a transmission frequency, the Fabry The Perot etalon has the same spectral response range as the transmission frequency tunable Fabry-Perot filter and the transmission frequency tunable Fabry-Perot filter is only effective for linearly polarized light having a particular polarization direction.

Moreover, the Fabry-Perot etalon has a certain free spectral range and sharpness coefficient; the transmission frequency tunable Fabry-Perot filter has an intrinsic free spectral range smaller than the method when no electric field is applied The free spectral range of the Brill-Perot etalon, and the difference is greater than the sharpness factor of the Fabry-Perot etalon or greater than the sharpness factor of the tunable Fabry-Perot filter of the transmission frequency.

Moreover, the transmissive frequency tunable Fabry-Perot filter includes a first mirror, a liquid crystal material, a second mirror, and a driving circuit, and the first mirror has a high reflectivity outside the light-passing surface a layer dielectric film, an optical antireflection film is disposed on a first layer inside the light-passing surface of the first mirror, a transparent electrode is disposed on the optical anti-reflection film; and a high-reflectivity multilayer dielectric film is disposed on an outer side of the second mirror, An optical antireflection film is disposed on the inner first layer of the second mirror, and a transparent electrode is disposed on the optical antireflection film, and a non-conductive material film having a thickness of several micrometers to ten micrometers is disposed on the transparent electrode to cover the light a portion other than the aperture and a channel extending to the edge of the mirror by a width of about one millimeter and forming a cavity having a thickness of several micrometers to ten micrometers from the inner side of the first mirror, the liquid crystal material being placed in the cavity; The driving circuit is connected to two transparent electrodes, and the outer side of the light passing surface of the first mirror and the outer side of the light passing surface of the second mirror are kept parallel and constitute a Fabry-Perot beam interference. Cavity.

Moreover, the transmissive frequency tunable Fabry-Perot filter includes a first mirror, a liquid crystal material, a second mirror, and a driving circuit, and an optical antireflection film is disposed outside the light passing surface of the first mirror a first layer on the inner side of the light-passing surface of the first mirror is provided with a high-reflectivity multilayer dielectric film, and a transparent electrode is disposed on the high-reflectivity multilayer dielectric film; and a high-reflectivity multilayer is disposed on the outer side of the second mirror a dielectric film, an inner first layer of the second mirror is provided with an optical antireflection film, a transparent electrode is disposed on the optical antireflection film, and a non-conductive material film having a thickness of several micrometers to ten micrometers is disposed on the transparent electrode, covering a portion other than the clear aperture and a channel extending to the edge of the mirror by a width of about one millimeter and forming a cavity having a thickness of several micrometers to ten micrometers from the inner side of the first mirror, the liquid crystal material being placed in the space The driving circuit is connected to the two transparent electrodes, and the inner side of the light passing surface of the first mirror and the outer side of the light passing surface of the second mirror are kept parallel and constitute Fabry-Perotdo Beam interference cavity.

Moreover, the transmissive frequency tunable Fabry-Perot filter includes a first mirror, a liquid crystal material, a second mirror, and a driving circuit, and an optical antireflection film is disposed outside the light passing surface of the first mirror , in the light-passing surface of the first mirror a high-reflectivity multilayer dielectric film is disposed on the first layer, a transparent electrode is disposed on the high-reflectivity multilayer dielectric film; an optical antireflection film is disposed on an outer side of the second mirror, and an inner first layer of the second mirror is disposed Providing a high-reflectivity multilayer dielectric film, wherein a transparent electrode is disposed on the high-reflectivity multilayer dielectric film, and a non-conductive material film having a thickness of several micrometers to ten micrometers is disposed on the transparent electrode, covering a pass-through aperture a portion and a channel extending to the edge of the mirror by a width of about one millimeter and forming a cavity having a thickness of several micrometers to ten micrometers from the inner side of the first mirror, wherein the liquid crystal material is placed in the cavity; The driving circuit is connected to the two transparent electrodes, and the inner side of the light passing surface of the first mirror and the inner side of the light passing surface of the second mirror are kept parallel and constitute a Fabry-Perot multi-beam interference cavity.

Moreover, the transmissive frequency tunable Fabry-Perot filter includes a first mirror, a first optically transparent glass sheet, a liquid crystal material, a second optically transparent glass sheet, and a second mirror; A high-reflectivity multilayer dielectric film is disposed outside the light-passing surface of the mirror, and an inner side of the light-passing surface of the first mirror is an optically polished surface; the first optically transparent glass sheet is disposed inside the first mirror, and the first optically transparent glass sheet is An outer side of the light-transmitting surface is an optically polished surface, and an inner surface of the light-transmitting surface of the first optically transparent glass sheet is provided with an optical anti-reflection film, and a transparent electrode is disposed on the optical anti-reflection film; a light-passing surface of the second mirror A high-reflectivity multilayer dielectric film is disposed on the outer side, and an inner side of the light-passing surface of the second mirror is an optically polished surface; a second optically transparent glass sheet is disposed inside the second mirror, and an outer side of the light-transmitting surface of the second optically transparent glass sheet is An optically polished surface, an inner first layer of the second optically transparent glass sheet is provided with an optical antireflection film, and a transparent electrode is disposed on the optical antireflection film, and a thickness of a few micrometers is set on the transparent electrode a film of non-conductive material of a few micrometers covering a portion other than the clear aperture and a channel extending to the edge of the mirror by a width of about one millimeter and forming an empty space of several micrometers to ten micrometers from the inner side of the first optical glass sheet a cavity, the liquid crystal material is placed in the cavity; a driving circuit is connected to the transparent electrodes of the first optically transparent glass piece and the second optically transparent glass piece, the outer side of the light-passing surface of the first mirror and the second mirror The outside of the light-passing surface remains parallel and constitutes a Fabry-Perot beam interference cavity.

Moreover, the transmissive frequency tunable Fabry-Perot filter includes a first mirror, a first optically transparent glass sheet, a liquid crystal material, a second optically transparent glass sheet, and a second mirror; An optical antireflection film is disposed outside the light passing surface of the mirror, and a high reflectivity multilayer dielectric film is disposed inside the light passing surface of the first mirror; the first optical transparent glass sheet is disposed inside the first mirror, and the first optical transparent glass sheet The outer side of the light-transmitting surface is an optical polishing surface or an optical anti-reflection film is disposed. The first layer of the light-transmitting surface of the first optically transparent glass sheet is provided with an optical anti-reflection film, and a transparent electrode is disposed on the optical anti-reflection film; A high-reflectivity multilayer dielectric film is disposed outside the light-passing surface of the second mirror, and an inner side of the light-passing surface of the second mirror is an optically polished surface; a second optically transparent glass sheet is disposed inside the second mirror, and the second optically transparent glass The outer side of the light-passing surface of the sheet is an optically polished surface, and the first inner layer of the second optically transparent glass sheet is provided with an optical anti-reflection film, and a transparent electrode is disposed on the optical anti-reflection film, and the transparent electrode is disposed on the transparent electrode a film of non-conductive material having a degree of a few micrometers to a dozen micrometers, covering a portion other than the light-passing aperture and a channel having a width of about one millimeter to the edge of the mirror and forming a thickness of a few micrometers with the inner side of the first optical glass sheet To a cavity of a dozen micrometers, a liquid crystal material is placed in the cavity; On the transparent electrode connected to the first optically transparent glass piece and the second optically transparent glass piece, the inner side of the light-passing surface of the first mirror and the outer side of the light-transmitting surface of the second mirror are kept parallel and constitute Fabry-Perotdo The beam interferes with the cavity.

Moreover, the transmissive frequency tunable Fabry-Perot filter includes a first mirror, a first optically transparent glass sheet, a liquid crystal material, a second optically transparent glass sheet, and a second mirror; An optical antireflection film is disposed outside the light passing surface of the mirror, and a high reflectivity multilayer dielectric film is disposed inside the light passing surface of the first mirror; the first optical transparent glass sheet is disposed inside the first mirror, and the first optical transparent glass sheet The outer side of the light-transmitting surface is an optical polishing surface or an optical anti-reflection film is disposed. The first layer of the light-transmitting surface of the first optically transparent glass sheet is provided with an optical anti-reflection film, and a transparent electrode is disposed on the optical anti-reflection film; An optical antireflection film is disposed outside the light passing surface of the two mirrors, and a first layer of the second reflecting mirror is provided with a high reflectivity multilayer dielectric film; the second optical transparent glass sheet is disposed inside the second mirror, The outer surface of the light-transmitting surface of the optically transparent glass sheet is an optical polishing surface or an optical anti-reflection film, and the first inner layer of the second optical transparent glass sheet is provided with an optical anti-reflection film, and the optical anti-reflection film is disposed on the optical anti-reflection film. a bright electrode on which a thin film of a non-conductive material having a thickness of several micrometers to ten micrometers is provided, covering a portion other than the light-passing aperture and a channel having a width of about one millimeter to the edge of the mirror and the first optical The inside of the glass sheet forms a cavity having a thickness of several micrometers to ten micrometers, and the liquid crystal material is placed in the cavity; the driving circuit is connected to the transparent electrode of the first optically transparent glass sheet and the second optically transparent glass sheet Above, the inner side of the light-passing surface of the first mirror and the inner side of the light-passing surface of the second mirror are kept parallel and constitute a Fabry-Perot multi-beam interference cavity.

Moreover, the liquid crystal material is a nematic liquid crystal having a thickness of several micrometers to ten micrometers. Moreover, the first mirror and the second mirror are both optically transparent materials and have the same refractive index of light. Moreover, the driving circuit is a square wave pulse circuit having a frequency of 1 kHz to 10 kHz, and the pulse voltage amplitude is adjustable from 0 volts to 5 volts.

Moreover, the inner side of the first mirror is bonded to the outer side of the first optically transparent glass sheet by an optically transparent index matching glue or the assembly method of the glue on the light path of the industry is generally used: The joints other than the optical path are bonded by glue; the inner side of the second mirror is bonded to the outer side of the second optically transparent glass sheet by an optically transparent index matching glue or the glue is not used in the industrially used light path. Assembly method: that is, bonding at a joint other than the light path; the first mirror, the second mirror, the first optical transparent glass sheet and the second optical transparent glass sheet are all optically transparent materials and Having the same or substantially the same refractive index of light; the refractive index of the optically transparent index matching glue is substantially the same as the refractive index of the optically transparent material.

Moreover, incident light enters the transmission frequency tunable Fabry-Perot filter from the light-passing surface of the Fabry-Perot etalon.

Moreover, incident light enters the Fabry-Perot etalon from the light-transmitting surface of the transmission frequency tunable Fabry-Perot filter. The advantages and positive effects of the present invention are:

The invention is reasonably designed to effectively combine a Fabry-Perot etalon with a transmission frequency tunable Fabry-Perot filter to place the liquid crystal in Fabry-Perot. The cavity of the etalon uses the electronically controlled birefringence effect of the liquid crystal and optical phase modulation of the linearly polarized light incident on a particular polarization direction to achieve linearly polarized light transmitted through the Fabry-Perot filter. Continuous, fast and precise tuning of frequency. Since the thickness of the liquid crystal layer is very thin, a wide-bandwidth tunable Fabry-Perot filter having a small size and a large free spectral range can be fabricated, and at the same time, fast and precise tuning of the optical frequency over a wide spectral range can be realized. The invention has the characteristics of no mechanical moving parts, stable and reliable performance, simple structure, low cost, small size, easy installation and production, and can meet the requirements of small size and extremely reliable operation under extreme working conditions, in laser, optical test, optical fiber. Wide range of applications in communications, biology, medical devices and fiber optic sensor networks.

DRAWINGS

Figure 1 is a schematic view of a conventional Fabry-Perot etalon;

2 is a schematic structural view of a tunable Fabry-Perot filter including a nematic liquid crystal material layer; FIG. 3 is a schematic diagram showing a phase of light transmission through a liquid crystal material according to an applied electric field;

4 is a schematic view of another structure of a tunable Fabry-Perot filter including a nematic liquid crystal material layer; FIG. 5 is a schematic diagram of a transmission spectrum of a Fabry-Perot etalon;

Figure 6 is a schematic diagram of the transmission spectrum of a tunable Fabry-Perot filter;

Figure 7 is a schematic structural view of the present invention;

Figure 8 is a schematic diagram of the intrinsic transmission spectrum of the present invention;

Figure 9 is a schematic illustration of the tunable transmission spectra of the fixed interval and single mode output of the present invention.

Concrete

The embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

1 is a schematic illustration of a conventional Fabry-Perot etalon 100. The material of the Fabry-Perot etalon 100 is generally optical glass such as fused silica or BK7 in the near-infrared and visible-light bands, assuming that the material has a refractive index n and both light-passing surfaces 2 and 4 are plated high. Reflective film, assuming that the reflectivity is R, the thickness is h, and the light is incident at an incident angle close to zero, the free spectral range FSR of the optical etalon 100 can be expressed as: Δ λ = λ 2 / (2nh), or expressed by frequency : Δ ν =c/(2nh), where c is the speed of light. The peak frequency of transmitted light can be expressed as: v = mc / (2nh), where m is the interference order, and the frequency broadband of the transmitted light can be expressed as: Δ ν 1/2 ( FWHM ) = c(lR) / (2nhRl / 2), where c is the speed of light.

As can be seen from the above two equations, the free spectral range FSR of the optical etalon 100 is inversely proportional to the thickness h. Assuming that the material has a refractive index of n = 1.5, FSRl = 100 GHz and a thickness of mm are to be achieved. The larger the FSR is required, the thicker The smaller the degree. After the material and thickness of the etalon are determined, the frequency broadband of the transmitted light is mainly related to the reflectance R. The higher the reflectance, the smaller the frequency broadband or the finesse. The Fabry-Perot etalon's transmission spectrum is characterized by a very narrow bandwidth per transmission spectrum, a uniform frequency spacing of the transmission spectrum and a very wide optical band width, typically covering more than 100 nm. Light spectrum band. Figure 5 shows a schematic of the Fabry-Perot optical etalon 100 output spectrum.

Figure 2 shows a tunable Fabry-Perot filter designed to change the refractive index of linearly polarized light by a nematic liquid crystal under the action of an electric field. Liquid crystal materials generally used as photovoltaic devices have high resistivity. Therefore, it can be considered as an ideal dielectric material. The liquid crystal has anisotropic dielectric properties and uniaxial symmetry due to the ordered orientation of the constituent molecules and the stretched morphology. Like a uniaxial crystal, the direction of the optical axis coincides with the alignment of the molecules. When the liquid crystal molecules act under the external electric field, an electric dipole is formed. Under the action of the moment formed by the electric dipole, the orientation of the liquid crystal molecules is turned to the direction of the electric field, and the direction of the optical axis of the liquid crystal can be changed by changing the strength of the electric field. Therefore, this characteristic of the liquid crystal can be utilized to fabricate an optical phase modulator, a tunable filter, or other optoelectronic devices such as an optical switch and a light emphasizer. The thickness of the liquid crystal film layer generally used as a photovoltaic device is from several micrometers to ten micrometers.

As shown in FIG. 2, a tunable Fabry-Perot filter 200 includes a first mirror 10, a liquid crystal material 18, a second mirror 20, and a driving circuit 14, a first mirror 10 and a second mirror. 20 are optically transparent materials.

The tunable Fabry-Perot filter 200 has three different configurations, which are described below:

The first structure of the tunable Fabry-Perot filter 200 is: a high-reflectivity multilayer dielectric film is plated on the outer surfaces 8 and 22 of the light-passing surfaces of the first mirror 10 and the second mirror 20, respectively. Forming a Fabry-Perot cavity between two high-reflectivity multilayer dielectric films; an optical anti-reflection film 12 is disposed in order from the inside to the outside of the light-passing surface of the first mirror 10; a transparent electrode film layer 16; an optical anti-reflection film 24, a transparent electrode 26, and a non-conductive material film 19, an optical anti-reflection film 12 and an optical anti-reflection film are sequentially disposed from the inside to the outside on the inner side of the light-passing surface of the second mirror 20. 24 is plated on the inner surface of the light-passing surface of the first mirror 10 and the inner surface of the light-passing surface of the second mirror 20, respectively. The non-conductive material film 19 has a thickness of several micrometers to ten micrometers, covers other portions except the light-passing aperture, and a channel extending to the edge of the mirror by a width of about one millimeter, in order to provide a liquid crystal for injecting excess liquid in the cavity. Export channel. The non-conductive material film 19 and the inner side of the first mirror 10 form a cavity having a thickness of several micrometers and a few micrometers for arranging the liquid crystal material 18, and the liquid crystal material 18 is a nematic liquid crystal. The thickness of the liquid crystal material is from about several micrometers to ten micrometers. Since the thickness of the liquid crystal is small (several micrometers to ten micrometers), tunable Fabry-Perot can be made in the intrinsic free spectral range (ie, the free spectral range of the tunable filter without an applied electric field) filter. Two transparent electrodes are connected to the driving circuit 14, and a driving signal generated by the driving circuit forms a driving electric field between the two transparent electrode film layers; the Fabri is adjusted by changing the effective refractive index n of the liquid crystal in the Fabry-Perot cavity by the electric field. -Perot filter for transmitted light Optical frequency v and free spectral range (FSR). A typical driving electric field is a square wave signal having a voltage of several volts and a frequency of 1 kHz to several kilohertz.

In FIG. 2, the light beam 6 incident on the filter 200 is a beam traveling in the z direction, and the polarization axis is linearly polarized light in the X direction, assuming that the refractive index of the optically transparent material is n, the two light passing surfaces 8 and 22 Both are highly reflective films. Assuming a reflectivity of R and a thickness of D, the free spectral range FSR1 and transmitted light of the filter 200 are: Δ λ = λ 2 / (2nD + "), or expressed by frequency: Δ V =c/(2nD+"), where c is the speed of light, "represents the optical path produced by the liquid crystal under the applied electric field by the refraction to change the incident light. The peak frequency of the transmitted light can be expressed as: _V = m _C / (2nD+ "), where m is the interference level, and the broadband of the transmitted light (also called the sharpness coefficient) can be expressed as: Δ ν 1/2 ( FWHM ) = c(lR) / ((2nD + ") Rl / 2), Where c is the speed of light.

Figure 3 shows the phase change of a light phase with a wavelength of 1550 nm for a nematic liquid crystal with a thickness of 10 μm driven by a 2 kHz square wave voltage. A maximum optical phase delay of about 2π can be achieved. According to the above formula, the tunable Fabry-Perot filter 200 can obtain a tuning range of the transmitted optical frequency of about 100 GHz for linearly polarized light incident at near zero degrees. In comparison, according to the above formula, the change in the band width Δ ν 1/2 of the free spectral range Δ ν and the transmitted light is much smaller. Figure 6 is a schematic diagram of the transmission spectrum of the tunable Fabry-Perot filter 200.

It can be seen that the tunable Fabry-Perot filter 200 can achieve a wide range of transmission optical frequency tuning under the action of an applied electric field without substantially changing the frequency broadband and free spectral range of the transmitted light. This feature is important for many applications of the tunable Fabry-Perot filter 200, such as lasers and spectrum instruments.

The second structure of the tunable Fabry-Perot filter 200 is: plating an optical antireflection film on the outer surface 8 of the light-passing surface of the first mirror 10; from the inside to the inner side of the light-passing surface of the first mirror 10 The high-reflectivity multilayer dielectric film 12 and the transparent electrode film layer 16 are sequentially disposed outside, and the other structure is the same as that of the tunable Fabry-Perot filter 200. The second structure of the tunable Fabry-Perot filter 200 is characterized by a greater free spectral range than the first.

The third structure of the tunable Fabry-Perot filter 200 is: plating an optical antireflection film on the outside of the light-passing surface of the second mirror 20; from the inside to the inside of the light-passing surface of the second mirror 20 A high-reflectivity multilayer dielectric film 24, a transparent electrode 26, and a non-conductive material film 19 are sequentially disposed. The other structure is the same as the second structure of the tunable Fabry-Perot filter 200. The third structure of the tunable Fabry-Perot filter 200 is characterized by the ability to achieve a larger free spectral range than the second structure.

Since the tunable Fabry-Perot filter 200 is fabricated, the surface of the light-passing surface of the two mirror-coated high-reflectivity multilayer dielectric film is required to be strictly parallel, which is for tuning the Fabry-Perot filter 200. The assembly brings certain difficulties. To this end, we have designed another tunable Fabry-Perot filter 300, as shown in Figure 4. The tunable Fabry-Perot filter 300 includes a first mirror 32, a first optical glass sheet 36, a liquid crystal material 41, and a second optical glass sheet. 50. Second mirror 46 and drive circuit 56. The difference between the filter 300 and the filter 200 is that, in the filter 300, the liquid crystal material 41 is first placed between two optically transparent glass sheets 36 and 50, and the light passing through the two optically transparent glass sheets 36 and 50 The inner side of the face is respectively coated with optical anti-reflection layers 38 and 52, transparent electrodes 40 and 54, and a film layer 41 of non-conductive material is disposed on the optically transparent glass piece 50 and the inner side of the first optically transparent glass piece 36 is formed. A cavity having a thickness of a few micrometers and a few micrometers is used to place the liquid crystal material. The other light-passing surfaces of the above two optically transparent glass sheets 36 and 50 are not coated or coated with an optical antireflection film, and the optically transparent glass sheets 36 and 50 and the liquid crystal material 42 constitute a liquid crystal cell. When the above liquid crystal cell is assembled, it is not necessary to keep the light-transmitting surfaces of the optically transparent glass sheets 36 and 50 strictly parallel, which makes it easier to handle at the time of assembly.

The tunable Fabry-Perot filter 300 also has three different configurations, which are described below:

The first configuration of the tunable Fabry-Perot filter 300 is such that the outer light-passing surface 30 of the first mirror 32 is plated with a high-reflectance film, and the inner light-passing surface is a polished surface having no coating. First, the inner side of the first reflecting mirror 32 is bonded to the outer side of the optically transparent glass piece 36 on the above liquid crystal cell by the index matching adhesive 34. The outer light-passing surface 44 of the second mirror 46 is plated with a high-reflectance film, and the inner light-passing surface is a polished surface having no plating film. Then, the inner light-passing surface of the second mirror 46 is bonded to the outer side of the optically transparent glass sheet 50 on the liquid crystal cell by the index matching glue 48, in the process, the two mirrors 32 and The faces 30 and 44 of the two plated high reflectivity films of 46 are closely aligned to achieve the multi-beam interference effect of the Fabry-Perot etalon. Typically, since the optically transparent materials used in 32, 36, 50 and 46 have the same or nearly the same optical index of refraction, the index matching glue 48 and the index matching glue 34 are identical or nearly identical. The disadvantage of the structure of the filter 300 is that it is thicker than the filter 200 because of the use of four optically transparent materials. According to the previous calculations, for 1550 nm light and ordinary optical glass materials (refractive index is about 1.5), when the free spectral range is 100 GHz and the thickness H is about 1 mm, it is more difficult to achieve if a larger free spectral range is required. .

The second structure of the tunable Fabry-Perot filter 300 is such that the outer light-passing surface 30 of the first mirror 32 is plated with an optical antireflection film, and the inner light-passing surface is plated with a high reflectivity film. The outer side of the optically transparent glass piece 36 on the above liquid crystal cell may be coated with an optical antireflection film or a non-coated polishing surface. The inner side of the first reflecting mirror 32 and the outer side of the optical transparent glass sheet 36 on the liquid crystal cell are bonded together by the index matching adhesive 34, and the assembly method of the optical path without glue in the industry can be used, that is, only two The optical parts are bonded with glue outside the light path. The other structure is the same as the first structure of the filter 300. Since the Fabry-Perot cavity is composed of the inner light-passing surface of the first mirror 32 and the high-reflectivity film on the outer light-passing surface of the second mirror 46, the characteristic of the structure is that the ratio can be achieved. The first structure of filter 300 has a larger free spectral range.

The third structure of the tunable Fabry-Perot filter 300 is such that the structure differs from the second structure of the filter 300 in that the outer light-passing surface 44 of the second mirror 46 is optically plated. Through-film, high-reflectivity on the inner side of the light-passing surface Membrane. The outer light-passing surface of the optically transparent glass sheet 50 on the liquid crystal cell may be coated with an optical antireflection film or a non-coated polishing surface. The inner side of the second reflection 46 is bonded to the outer side of the optically transparent glass sheet 50 on the liquid crystal cell by an index matching glue, and an assembly method of the optical path without glue in the industry is generally used, that is, only two opticals are used. The parts outside the light path are glued together. The other structure is the same as the second structure of the filter 300. Since the Fabry-Perot cavity is composed of the inner light-passing surface of the first mirror 32 and the high-reflectivity film on the inner light-passing surface of the second mirror 46, the structure is characterized in that the ratio can be achieved. The second structure of filter 300 has a larger free spectral range.

The invention will now be described with reference to Figure 7.

A tunable optical filter 400 with fixed frequency spacing and single mode output is comprised of a Fabry-Perot etalon 100 and a tunable Fabry-Perot filter 200 or 300. The Fabry-Perot etalon 100 has a free spectral range of FSR1, the tunable Fabry-Perot filter 200 or 300 has a free spectral range of FSR2, and FSR2 has a smaller Δf than FSR1, as shown in Figures 5 and 6. Show. If Δ ί = 0.25 FSR1 , then in the spectral range of ν 1 to ν 4 , there are 4 modes through the Fabry-Perot etalon 100, and through the tunable Fabry-Perot filter 200 or 300 There are 5 modules. Therefore, only the two modes V 1 and V 4 through the tunable filter 400, or the tunable filter 400, are 4 times FSR2 or 3 times FSR1 as shown in FIG. As can be seen from Figure 8, the free spectral range FSR3 of the tunable filter 400 can be greatly increased by adjusting the value of Δf.

In practical applications, the difference between FSR2 and FSR1 can be adjusted as needed. FSR3 can be adjusted, but the minimum difference should be equal to or greater than twice the Δ ν 1/2 to ensure the single-mode output characteristics of the tunable filter 400.

The tuning process of the present invention is described below: Referring to Figures 5 and 6, when the transmission spectrum V 2a of the tunable Fabry-Perot filter 200 or 300 is tuned to V 2 with the Fabry-Perot etalon 100 When coincident, only V 2 can pass through the tunable filter 400 in the spectral FSR3 range. Similarly, when the transmission spectrum V 3a of the tunable Fabry-Perot filter 200 or 300 is tuned to coincide with V 3 of the Fabry-Perot etalon 100, only V 3 can be in the spectral FSR3 range. Through the tunable filter 400, as shown in FIG. However, in the process of tuning V 3a , since v 2a will pass V 2 , one way to eliminate this phenomenon through the tunable filter 400 is to add one at the output of the filter 400 during the tuning process. Fast optical switch. During tuning from one mode to another, the optical switch is turned off, and after V 3a and V 3 coincide, the optical switch is turned on. The tuning of other modes can be analogized by analogy. Since the maximum difference between the two adjacent transmission spectra of the Fabry-Perot etalon 100 and the tunable Fabry-Perot filter 200 or 300 is less than FSR1, therefore, as long as the tunable Fabry-Perp is guaranteed The tunable range of the transmission spectrum of the filter 200 or 300 is equal to or close to FSR1, and the tunable filter 400 enables an equally spaced single mode tunable output with a frequency interval of FSR1 in the spectral FSR3 range, the tunable transmission spectrum As shown in Figure 9. It is worth noting that when incident light enters the tunable optical filter 400 from the light-passing surface of the tunable Fabry-Perot filter 200 or 300, The same single-mode and fixed-frequency-interval output is achieved, but the output spectral width may vary in different applications. It is to be understood that the foregoing description is not intended to be a Many modifications and variations of the present invention are possible in the light of the above description. The specific implementations chosen are merely illustrative of the principles and practical applications of the invention. This description enables those skilled in the art to make better use of the present invention, designing different implementations and making corresponding changes according to actual needs.

Claims

claims

1. A tunable optical filter with fixed frequency spacing and single-mode output, characterized by: a Fabry-Perot etalon and a transmission frequency tunable Fabry-Perot filter arranged oppositely in front and back Composed, the Fabry-Perot etalon has the same spectral response range as the transmission frequency tunable Fabry-Perot filter, and the transmission frequency tunable Fabry-Perot filter only responds to signals with a specific polarization direction. Effective for linearly polarized light.

2. A tunable optical filter with fixed frequency interval and single-mode output according to claim 1, characterized in that: the Fabry-Perot etalon has a certain free spectral range and sharpness coefficient; The intrinsic free spectral range of the transmission frequency tunable Fabry-Perot filter when no electric field is applied is smaller than the free spectral range of the Fabry-Perot etalon, and the difference is larger than the Fabry-Perot etalon. The sharpness coefficient of the etalon may be greater than the sharpness coefficient of the transmission frequency tunable Fabry-Perot filter.

3. A tunable optical filter with fixed frequency interval and single-mode output according to claim 1, characterized in that: the transmission frequency tunable Fabry-Perot filter includes a first reflector, Liquid crystal material, second reflector and drive circuit, a high reflectivity multi-layer dielectric film is set outside the light-passing surface of the first reflector, and an optical anti-reflection film is set on the first layer inside the light-passing surface of the first reflector, A transparent electrode is provided on the optical anti-reflection film; a high reflectivity multi-layer dielectric film is provided on the outside of the second reflector; an optical anti-reflection film is provided on the first layer inside the second reflector; an optical anti-reflection film is provided on the optical anti-reflection film. A transparent electrode, on which a non-conductive material film with a thickness of several microns to more than ten microns is set, covering the part except the clear aperture and a channel about one millimeter wide leading to the edge of the mirror and connected with the first reflection The inner side of the mirror forms a cavity with a thickness of several microns to more than ten microns, and the liquid crystal material is placed in the cavity; the drive circuit is connected to two transparent electrodes, and the outside of the light-passing surface of the first reflector and The outside of the light-passing surface of the second reflector remains parallel and forms a Fabry-Perot multi-beam interference cavity.

4. A tunable optical filter with fixed frequency interval and single-mode output according to claim 1, characterized in that: the transmission frequency tunable Fabry-Perot filter includes a first reflector, liquid crystal material, a second reflector and a drive circuit, an optical anti-reflection film is set outside the light-passing surface of the first reflector, and a high-reflectivity multi-layer dielectric film is set on the first layer inside the light-passing surface of the first reflector, A transparent electrode is provided on the high-reflectivity multi-layer dielectric film; a high-reflectivity multi-layer dielectric film is provided on the outside of the second reflector, and an optical anti-reflection film is provided on the first layer inside the second reflector. A transparent electrode is set on the film, and a non-conductive material film with a thickness of several microns to more than ten microns is set on the transparent electrode, covering the part except the clear aperture and a channel about one millimeter wide leading to the edge of the reflector and connected with the third The inside of a reflector forms a cavity with a thickness of several microns to more than ten microns, and the liquid crystal material is placed in the cavity; the drive circuit is connected to two transparent electrodes, and the light of the first reflector The inner side of the surface and the outer side of the light-passing surface of the second reflector remain parallel and form a Fabry-Perot multi-beam interference cavity.

5. A tunable optical filter with fixed frequency interval and single-mode output according to claim 1, characterized in that: the transmission frequency tunable Fabry-Perot filter includes a first reflector, Liquid crystal material, second reflection Mirror and drive circuit, an optical anti-reflection film is provided outside the light-passing surface of the first reflector, and a high-reflectivity multi-layer dielectric film is provided on the first layer inside the light-passing surface of the first reflector. A transparent electrode is provided on the dielectric film; an optical anti-reflection film is provided on the outside of the second reflector; a high-reflectivity multi-layer dielectric film is provided on the first layer inside the second reflector; and a high-reflectivity multi-layer dielectric film is provided on the first layer of the second reflector. A transparent electrode, on which a non-conductive material film with a thickness of several microns to more than ten microns is set, covering the part except the clear aperture and a channel about one millimeter wide leading to the edge of the mirror and connected with the first reflection The inner side of the mirror forms a cavity with a thickness of several microns to more than ten microns, and the liquid crystal material is placed in the cavity; the driving circuit is connected to two transparent electrodes, and the inner side of the light-passing surface of the first reflector and The inner side of the light-passing surface of the second reflector remains parallel and forms a Fabry-Perot multi-beam interference cavity.

6. A tunable optical filter with fixed frequency interval and single-mode output according to claim 1, characterized in that: the transmission frequency tunable Fabry-Perot filter includes a first reflector, A first optically transparent glass sheet, a liquid crystal material, a second optically transparent glass sheet and a second reflective mirror; a high reflectivity multi-layer dielectric film is provided outside the light-passing surface of the first reflector, and the light-passing surface of the first reflector The inner side is an optically polished surface; the first optically transparent glass piece is arranged inside the first reflector, the outer side of the light-passing surface of the first optically transparent glass piece is an optically polished surface, and the first layer inside the light-passing surface of the first optically transparent glass piece An optical antireflection film is provided, and a transparent electrode is provided on the optical antireflection film; a high reflectivity multilayer dielectric film is provided outside the light-passing surface of the second reflector, and an optically polished surface is provided inside the light-passing surface of the second reflector. ; The second optically transparent glass piece is arranged inside the second reflector. The outside of the light-passing surface of the second optically transparent glass piece is an optically polished surface. The first layer inside the second optically transparent glass piece is provided with an optical anti-reflection film. A transparent electrode is set on the optical anti-reflection coating, and a non-conductive material film with a thickness of several microns to more than ten microns is set on the transparent electrode, covering the part except the clear aperture and a channel about one millimeter wide leading to the edge of the reflector. And the inside of the first optical glass sheet forms a cavity with a thickness of several microns to more than ten microns, and the liquid crystal material is placed in the cavity; the driving circuit is connected to the first optically transparent glass sheet and the second optically transparent glass On the transparent electrode of the sheet, the outside of the light-passing surface of the first reflector and the outside of the light-passing surface of the second reflector remain parallel and form a Fabry-Perot multi-beam interference cavity.

7. A tunable optical filter with fixed frequency interval and single-mode output according to claim 1, characterized in that: the transmission frequency tunable Fabry-Perot filter includes a first reflector, A first optically transparent glass sheet, a liquid crystal material, a second optically transparent glass sheet and a second reflecting mirror; an optical anti-reflection film is provided on the outside of the light-passing surface of the first reflecting mirror, and a high-reflection film is provided on the inner side of the light-passing surface of the first reflecting mirror. Reflectivity multilayer dielectric film; the first optically transparent glass piece is arranged inside the first reflector, the outside of the light-passing surface of the first optically transparent glass piece is an optically polished surface or an optical anti-reflection film is provided, and the first optically transparent glass piece is provided with an optically polished surface or an optical anti-reflection film. An optical anti-reflection film is provided on the first layer inside the light-passing surface, and a transparent electrode is provided on the optical anti-reflection film; a high-reflectivity multi-layer dielectric film is provided on the outside of the light-passing surface of the second reflector, The inside of the smooth surface is an optically polished surface; the second optically transparent glass piece is arranged inside the second reflector, the outside of the light-passing surface of the second optically transparent glass piece is an optically polished surface, and the first layer is arranged inside the second optically transparent glass piece. Optical anti-reflection film, a transparent electrode is set on the optical anti-reflection film, a non-conductive material film with a thickness of several microns to more than ten microns is set on the transparent electrode, covering the pass The part outside the optical aperture and a channel about one millimeter wide leading to the edge of the reflector and the inside of the first optical glass sheet form a cavity with a thickness of several microns to more than ten microns, and the liquid crystal material is placed in the cavity; The driving circuit is connected to the transparent electrodes of the first optically transparent glass sheet and the second optically transparent glass sheet, and the inner side of the light-passing surface of the first reflector and the outer side of the light-passing surface of the second reflector remain parallel and form a Fabry-Persian Rodo beam interference cavity.

8. A tunable optical filter with fixed frequency interval and single-mode output according to claim 1, characterized in that: the transmission frequency tunable Fabry-Perot filter includes a first reflector, A first optically transparent glass sheet, a liquid crystal material, a second optically transparent glass sheet and a second reflecting mirror; an optical anti-reflection film is provided on the outside of the light-passing surface of the first reflecting mirror, and a high-reflection film is provided on the inner side of the light-passing surface of the first reflecting mirror. Reflectivity multilayer dielectric film; the first optically transparent glass piece is arranged inside the first reflector, the outside of the light-passing surface of the first optically transparent glass piece is an optically polished surface or an optical anti-reflection film is provided, and the first optically transparent glass piece is provided with an optically polished surface or an optical anti-reflection film. An optical anti-reflection film is provided on the first layer inside the light-passing surface, and a transparent electrode is provided on the optical anti-reflection film; an optical anti-reflection film is provided on the outside of the light-passing surface of the second reflector, and an optical anti-reflection film is provided on the inner side of the light-passing surface of the second reflector. The first layer is provided with a high reflectivity multi-layer dielectric film; the second optically transparent glass sheet is provided inside the second reflector; the outside of the light-passing surface of the second optically transparent glass sheet is an optically polished surface or is provided with an optical anti-reflection film; the second The first layer inside the optically transparent glass sheet is provided with an optical anti-reflection film, a transparent electrode is provided on the optical anti-reflection film, and a non-conductive material film with a thickness of several micrometers to more than ten micrometers is provided on the transparent electrode to cover the surface except for light transmission. The part outside the aperture and a channel about one millimeter wide leading to the edge of the reflector and the inside of the first optical glass sheet form a cavity with a thickness of several microns to more than ten microns, and the liquid crystal material is placed in the cavity. ; The driving circuit is connected to the transparent electrodes of the first optically transparent glass sheet and the second optically transparent glass sheet, and the inside of the light-passing surface of the first reflector and the inside of the light-passing surface of the second reflector remain parallel and form a Fabric Ri-Perot multi-beam interference cavity.

9. The transmission frequency tunable Fabry-Perot filter according to any one of claims 3 to 8, characterized in that: the liquid crystal material adopts nematic liquid crystal, and the liquid crystal The thickness of the layer ranges from a few microns to a dozen microns.

10. The transmission frequency tunable Fabry-Perot filter according to any one of claims 3 to 8, characterized in that: the first reflector and the second reflector are both optically transparent materials and have Same light refractive index.

11. The transmission frequency tunable Fabry-Perot filter according to any one of claims 3 to 8, characterized in that: the driving circuit is a method with a frequency of 1 kilohertz to 10 kilohertz. Wave pulse circuit, the pulse voltage amplitude is adjustable from 0 volts to 5 volts.

12. The transmission frequency tunable Fabry-Perot filter according to claim 6, 7 or 8, characterized in that: the inner side of the first reflector and the outer side of the first optically transparent glass sheet are optically transparent. The refractive index matching glue is bonded together or the glue-free assembly method commonly used in the industry is used on the clear light path: that is, the connections outside the clear light path are bonded with glue; the inner side of the second reflector and the second optical The outer sides of the transparent glass sheets are bonded together with optically transparent refractive index matching glue or the glue-free assembly method commonly used in industry on the light path: that is, the joints outside the light path are bonded with glue; A reflecting mirror, a second reflecting mirror, a first optically transparent glass piece and a second optically transparent glass piece are all light The optically transparent material has the same or substantially the same optical refractive index; the refractive index of the optically transparent refractive index matching glue is substantially the same as the optically transparent material.

13. A tunable optical filter with fixed frequency interval and single-mode output according to claim 1, characterized in that: incident light enters the transmission from the light-passing surface of the Fabry-Perot etalon. Frequency tunable Fabry-Perot filter.

14. A tunable optical filter with a fixed frequency interval and single-mode output according to claim 1, characterized in that: the incident light passes through the light-passing surface of the tunable Fabry-Perot filter with a transmission frequency Enter the Fabry-Perot etalon.