DE10327963A1 - Polarization beam splitter for microscopy or projection system or UV lithography using grid array with parallel grid lines formed by multi-layer system with alternating non-metallic dielectric layers with differing optical characteristics - Google Patents

Abstract

The polarization beam splitter has an optically transparent carrier substrate (1) provided with an array of parallel grid lines (2,3) formed by a multi-layer system, for splitting an unpolarized light beam (UP) received at a given incidence angle into reflected and transmitted polarized beams (TE,TM). The individual layers (H,L) of the multi-layer system are provided by non-metallic dielectric materials with differing optical characteristics in alternation with one another.

Description

The The invention relates to a polarization beam splitter, preferably to Application in microscopy or in projection systems via a broadband spectral range from 400 to 700 nm and for applications in UV lithography in the wavelength range from 150 to 400 nm, comprising one of an optically transparent one Material existing carrier substrate, on its surface applied an array of mutually parallel grid bars is, wherein the grid webs consist of multilayer systems and that at an angle of incidence θ on the grid bars and the carrier substrate impinging unpolarized light in a reflective and a transmissive polarization beam path is shared.

Known dielectric polarization beam splitters are based on the use of unstructured thin-film systems, as used, for example, in US Pat US 6462873 B1 to be discribed. Such solutions often do not meet the stated optical requirements, since only a relatively low extinction is achievable.

More solutions are out US 6462873 B1 and US 6351296 B1 known. On the one hand, these solutions have the disadvantage that due to the embedding of the polarization-optical means in prisms, a sufficient compact form of the arrangement is not possible or that, on the other hand, birefringent materials are used for polarization beam splitting.

Known diffractive arrangements, as described for example by the company MOXTEK ( US 6288840 B1 . US 6243199 B1 ) are based on the use of simply coated metallic diffraction gratings or combinations of metallic with dielectric layers in the form of a structured metallo-dielectric multilayer system are used ( US 02/122236 A1 . EP 1239308 A2 ). At the solution after US 02/122236 A1 The design of alternating metallo-dielectric double layers and the effect of resonance-enhanced tunneling through individual metal layers is exploited to meet the optical requirements for efficient beam splitting.

One major disadvantage of a diffractive design of metallic Materials is the presence of absorption of light energy in this optical component and adversely affects the optical properties of the diffractive polarization beam splitter (DPBS). For applications where very high light intensities are required, as in digital cinema projectors, this can even be to destruction lead of the component.

In addition, a large number of narrow-band solutions for the visible and infrared spectral range are known (US Pat. US 5748368 . US 5914811 ), which are not suitable for applications with a broadband white light source.

One narrow-band design of a DPBS for the infrared spectral range, which is the structuring of a dielectric full-layer system by the effect of the anisotropic spectral reflectance (ASR) for polarization splitting, for example, in Rong-Chung Tyan, et al., "Design, fabrication, and characterization of form-birefringent multilayer polarizing beam splitter ", Journal of the Optical Society of America A, Vol.14, No.7 / July 1997, p. 1627-1636 described. Here is a design of alternating dielectric λ / 4 bilayers used at which the effect of the anisotropic spectral reflectivity occurs and for exactly one wavelength λ to the required optical Properties leads. For the Use in the broadband, visible spectral range is the described Design inappropriate.

outgoing from the described disadvantages of the prior art is the Invention the task of a diffractive polarization beam splitter to further develop that using unpolarized White light (UP) a beam split over the entire Wellängenbereich with an efficiency of nearly 100% and an angular separation of more than 90 degrees with simultaneous reduction of light losses by absorption in the material itself as well as by unwanted radiation possible in other diffraction orders is.

These Task is by a polarization beam splitter the above described type according to the invention thereby solved, that the individual layers of the grid bars are made of non-metallic, in their optical behavior differently composed, consist dielectric substances, expediently each grid web has at least three (in H-L-H or four in H-L-H-L) layers, the same or have different layer thicknesses between 0.1 nm and 300 nm and the overall height the structure of the grid webs in a range of 0.3 nm to 30 microns is.

The layers of the lattice webs consist of a combination of different high-index substances (H) and various low-index substances (L), the order alternating (H1-L1-H1-L1 ...) or not al terning (H1-L1-H2-L2 ... or H1-H2-L1-L2 ...).

conditioned through the use of pure dielectric layers, both in their sequence of reflective behavior as well as their height can be varied Structure profiles depending on from the purpose of use. The avoidance of metallic Substances enable the Use even at higher light intensities without destroying the DPBS becomes. Absorption losses, especially when using metallic Substances occurring are largely avoided, which in turn leads to an improvement in efficiency over the solutions of the prior art.

Furthermore is the contrast, especially in the blue spectral range, in the stronger metallic substances absorb, significantly improved.

in the Unlike the previously known designs, one is for both Polarization states highly reflective Multilayer system (HR) is assumed (up to about 40 layers), the first is unstructured. It is predesigned so that the spectral Properties, such as broadband and wavelength range, are sufficiently fulfilled. Subsequently the layer system is structured accordingly.

By structuring becomes the well-known effect of shape birefringence exploited for TE polarization (s-polarization) a highly reflective structure and the TM polarization (p-polarization) an anti-reflective To create structure.

advantageously, the high-index substances (H) consist of TiO2 and / or Ta2O5 and / or HfO2 and / or Al2O3 and / or Nb2O5 and / or ZnS and / or LaF3 or other lathanoid fluorides and the low-breaking substances (L) from SiO 2 and / or MgF 2 and / or chiolite and / or cryolite and / or Al2O3.

to Achieving a very high bandwidth proves it Cheap, when the layer thicknesses of the various layers of the grid bars do not form an integer relationship to each other.

Usually the polarization beam splitter has a rectangular cross-section (Lamellar profile, where the angle of incidence θ of the unpolarized light perpendicular to the carrier standing level between 30 and 60 degrees should be variable.

It but are also trapezoidal Cross-sectional shapes of the grid bars conceivable.

When Advantageously, it has been shown, an angle of incidence θ of 45 Degree to choose just for a lamellar profile a separation of the two polarizers to realize in transmission and reflection.

In dependence from the application case, it can also prove to be advantageous if the carrier substrate, which is unstructured, in addition an antireflecting layer (AR).

hereby This is reflected by Fresnel reflection on the substrate surface Proportion of TM polarization is reduced and thus the contrast in reflection elevated.

Around to optimize beam splitting at different angles of incidence or a separation of the two polarizers either only in transmission or to obtain only in reflection, there is an embodiment of the invention Furthermore, it is to arrange the grid bars so that their cross-section has the shape of a parallelogram (skewed profile), wherein the layers are parallel to the surface of the carrier substrate and the faces perpendicular to the surface of the carrier substrate standing plane an angle α, which is up to 45 degrees. The undercut may be slightly with the left foot the grid bars overlap. But this is not mandatory.

From It is also advantageous if the grating period is in a range of 50 to 200 nm and the fill factor chosen from 0.1 to 0.9 becomes.

following the invention will be explained in more detail by way of example. Show it:

1 : a schematic representation of the polarization beam splitter (lamellar) with two grid bars,

2 : a schematic representation of the polarization beam splitter (oblique angle) with two grid bars,

3 : a representation of the efficiencies of the transmitted (tTE) and reflected (rTE) light wave for the TE polarization (s-polarization),

4 : A representation of the efficiencies of the transmitted (tTM) and reflected (rTM) lightwave for the TM polarization (p-polarization) and

5 : a contrast representation in transmission (T) and in reflection (R)

1 shows the polarization beam splitter according to the invention with a carrier substrate 1 on which an array of grid bars (lamellae) with a grating period GP = 140 nm and a fill factor of 0.5 is applied and of which two grid bars 2 and 3 are shown. The grid bars 2 and 3 consist of a combination of high refractive index layers H and low refractive index layers L, where H is TiO2 for the high refractive index layers and L SiO2 for the low refractive index layers. The respective layer thicknesses are different, with the smallest layer thickness being 51 nm and the largest layer thickness being 183 nm. They are not in an integer relationship to each other. In the present embodiment, the total height of the dielectric layers is 3.679 μm. The carrier substrate 1 is for the purpose of applying the polarization beam splitter in the spectral range of 300 to 400 nm additionally provided with an antireflecting layer AR.

The unpolarized light UP emanating from a light source not shown in detail strikes the support substrate at an angle θ of 45 degrees 1 lying level 4 on the grid bars 2 and 3 as well as on the carrier substrate 1 and is doing in a through the carrier substrate 1 transmitted p-polarized component TM and split into a reflected s-polarized component TE.

By structuring the grid bars 2 and 3 the effect of shape birefringence is exploited to produce a highly reflective structure for s-polarization (TE) and an antireflective structure for p-polarization (TM).

2 shows a skewed polarization beam splitter, in which the grid bars 2 and 3 with the plane 4 an angle α of 20 degrees. This arrangement allows beam splitting of the unpolarized light UP at different angles of incidence. Furthermore, the skew angle makes it possible to separate the polarizations in either only transmission TM or in only reflection TE. A possible undercut may be slightly the base point 5 but it does not have to overlap. The overlap will be in 2 under the reference number 6 shown.

The arrangement according to the invention of the layers H and L can be used for a wavelength range of 400 to 700 nm, that is to say broadband, diffraction efficiencies rTE and tTM of> 95 for the useful light (FIG. 3 and 4 upper curve) and a high contrast of useful light to stray light as efficiencies rTM and tTE ( 3 and 4 lower curve) can be achieved.

The contrast in reflection is defined as VR = efficiency / efficiency while the contrast in transmission through the relationship VT = EfficiencyTM / EfficiencyTE

5 shows the representation of contrasts in transmission T and in reflection R. It can be seen that the contrast in the visible spectral range and in reflection and transmission is very broadband and, especially in the blue spectral range, almost the same size, which is for the application, for example in the digital projection is of considerable benefit to imaging.

1

carrier substrate

2, 3

grid bar

4

level

5

nadir

6

overlap

GP

grating period

UP

unpolarized light

H

high refractive index layer

L

low refractive layer

AR

antireflective layer

TM

p-polarized component

TE

s-polarized component

RTE, tTE, rTM, tTM

efficiencies

θ, α

angle

Claims (15)

Polarization beam splitter, preferably for use in microscopy or in projection systems over a broadband spectral range of 400 to 700 nm and for applications in UV lithography in the wavelength range of 150 to 400 nm, comprising a carrier substrate consisting of an optically transparent material ( 1 ), on whose surface an array of mutually parallel grid bars ( 2 . 3 ) is applied, wherein the grid webs ( 2 . 3 ) consist of multilayer systems and that at an angle of incidence θ on the grid bars ( 2 . 3 ) and the carrier substrate ( 1 ) incident unpolarized light (UP) into a reflective (rTE or rTM) and a transmissive (tTM or tTE) polarization beam path , characterized in that the individual layers (H, L) of the grid bars ( 2 . 3 ) consist of non-metallic, in their optical behavior differently composed dielectric substances. Polarization beam splitter according to claim 1, characterized in that each grid web ( 2 . 3 ) has at least three layers (H, L), the same or have different layer thicknesses between 0.1 nm and 400 nm. Polarization beam splitter according to claims 1 to 2, characterized in that the total height of the structure of the grid bars ( 2 . 3 ) Is 0.3 nm to 30 μm. Polarization beam splitter according to claims 1 to 3, characterized in that the layer systems (H, L) in the grid bars ( 2 . 3 ) are constructed of a combination of different high-index substances (H) and various low-refractive substances (L), the order being alternating (H1-L1-H1-L1 ...) or not alternating (H1-L1-H2-L2 .. or H1-H2-L1-L2 ...). Polarization beam splitter according to claim 4, characterized characterized in that the high-index substances (H) of TiO2 and / or Ta2O5 and / or HfO2 and / or AL2O3 and / or Nb2O5 and / or ZnS and / or LaF3 or other Lathanoidfluoride and the low refractive substances (L) of SiO2 and / or MgF2 and / or chiolite and / or cryolite and / or Al2O3. Polarization beam splitter according to claims 1 to 5, characterized in that the layer thicknesses of the different layers (H, L) of the grid webs ( 2 . 3 ) in a grid web ( 2 . 3 ) do not form an integer ratio to each other. Polarization beam splitter according to claims 1 to 6, characterized in that the cross section of the grid bars ( 2 . 3 ) is rectangular. Polarization beam splitter according to claims 1 to 6, characterized in that the cross section of the grid bars ( 2 . 3 ) is a parallelogram, wherein the layers (H, L) parallel to the surface of the carrier substrate ( 1 ) and the side surfaces perpendicular to the surface of the carrier substate ( 1 ) level ( 4 ) include an angle α. Polarization beam splitter according to claim 8, characterized characterized in that the angle α between 0 and 45 degrees. Polarization beam splitter according to claims 1 to 6, characterized in that the grid bars ( 2 . 3 ) are trapezoidal in cross-section, wherein the layers (H, L) parallel to the surface of the carrier substrate ( 1 ) lie. Polarization beam splitter according to one of the preceding claims, characterized in that the angle of incidence θ of the unpolarized light perpendicular to the carrier substrate ( 1 ) level ( 4 ) is variable between 30 and 60 degrees. Polarization beam splitter according to claim 11, characterized characterized in that the angle of incidence θ = 45 degrees. Polarization beam splitter according to one of the aforementioned Claims, characterized in that the grating period (GP) is in a range from 50 to 300 nm at a fill factor from 0.1 to 0.9. Polarization beam splitter according to one of the preceding claims, characterized in that the carrier substrate ( 1 ) is unstructured and has an antireflecting layer (AR). Polarization beam splitter according to claims 8 and 9, characterized in that the grid bars ( 2 . 3 ) are undercut, wherein the upper edge of a grid web ( 1 ) slightly ( 6 ) the base ( 5 ) of the adjacent grid web ( 2 ) overlaps.