GB2381328A

GB2381328A - Light Splitter with two layer systems and light tilted from emergent faces.

Info

Publication number: GB2381328A
Application number: GB0229992A
Authority: GB
Inventors: Johannes Edlinger; Claus Heine
Original assignee: Unaxis Balzers AG
Current assignee: OC Oerlikon Balzers AG
Priority date: 1999-02-04
Filing date: 2000-02-04
Publication date: 2003-04-30
Anticipated expiration: 2020-02-04
Also published as: GB2381328B; GB0229992D0

Abstract

A Spectrally selective light splitter divides white light into red, green and blue light or recombines white light from red, green and blue light. The light splitter comprises two separate layer systems 5, 7 each reflecting or transmitting colour-selectively. The layer systems are applied or embedded on or in at least one transparent base body such as X-cube 7. The base body determines emergent faces K R, G, and B each for the red, green and blue light and the light is reflected by light valves RLV B, G, and R. At least one emergent face is tilted with respect to the direction of the light emerging from it and reflected on at least one of the layer systems such that its face normal F RLV encloses with this direction an angle d which deviates from zero, specifically by more than is caused by the production tolerances of the light splitter, and for which d & 5{. The tilting may also be due to the cube being tilted with respect to the incoming light (see Fig 16), in which case the layer systems can be diagonal.

Description

Light splitter and optical transmitter configuration with a light splitter The present invention relates to light splitters according to the preamble of claim I and an optical transmitter configuration with a light splitter structured according to any of claims 1 to 10.

The present invention is based on problems found during the use of X-cubes and which are explained below. The findings can in principle be transferred to optical light splitters which, as will be explained, are used in connection with light of different polarisation. On this topic, reference can be made to A. Thelen,"Nonpolarizing interference films inside a glass cube", Appl. Optics, Vol 15, No 12, Dec. 1976.

For example, in DE 40 33 842 a cuboid optical structural component composed of single prisms with dichroic layers is referred to as a"dichroic prism".

In the present document the expression

is used for such a structural component. With regard to such X-cubes reference is made to US A 2 737 076, US A 2 754 718, DE A 40 33 842 and JP 7 109 443, further to US A 5 098 183, EP A 0 359 461. Furthermore, reference is made to W098/20383 by the same applicant as the present application.

Definitions The following definitions are used 'visible light : light with maximum energy in the spectral range 380 nm-720 nm red light: light with maximum energy in the spectral range 580 nm-720 nm, in particular in the spectral range 600 nm-680 nm . green light: light with maximum energy in the spectral range 490 nm-605 nm, in particular in the spectral range 500 nm-600 nm blue light: light with maximum energy in the spectral range 380 nm-510 nm, in particular in the spectral range 420 nm-500 nm yellow light: light with maximum energy in the spectral range of 475 nm-605 nm, in particular at 582 3 nm * white light: light with red, blue and green light components transparent : negligible absorption in the spectral range 380 nm-720 nm * cube: spatial shape formed by identical rectangles pairwise opposing each other in parallel.

With reference to fig. 1, first the fundamental effect of an X-cube will be explained. Optical light splitters of this type are mainly used in projectors in order to split white light into red, green and blue light or to recombine the latter into white light. According to fig. 1, an X-cube comprises four single prisms 2a-2d. Usually the prisms consist of BK7 glass. In cross section they form right-angled triangles with legs of equal length at a 900 angle. The length of the hypotenuse is for example between 5 mm and 50 mm, preferably 20-30 mm. Between the two prism pairs 2a and 2b on the one hand, and 2d and 2c on the other, a spectrally selectively reflecting and transmitting layer system 5 is embedded which largely reflects blue light but in contrast largely transmits green and red light.

Between the two prism pairs 2a and 2d on the one hand, and 2b and 2c on the other hand, a further spectrally selectively reflecting and transmitting layer system 7 is embedded which largely reflects red light but in contrast largely transmits green and blue light.

On the X-cube there are thus three channels for red, green and blue light, KR, KG, KB and one channel KR+B+G for white light. On each of the layer systems 5,7 between the acting prism pairs, the correspondingly coloured incident light is reflected at 45 . The hypotenuse faces of the prisms 2 can be coated with an anti-reflection coating system.

Such X-cubes are mainly used today in projection apparatus in order to recombine in channel KR+B+G red (R), blue (B) and green (G) light, each of which is supplied via light valves, in particular LCD light valves, operating in transmission to the associated channels KR, KB, Ka.

This is indicated in fig. 1 in dashed lines. Light valves are therein image-forming elements comprising a multiplicity of individually controlled pixels. The number of pixels gives the resolution according to EVGA, SGA, EGA or XGA etc.

In such light valves operating in transmission, because of the conductor paths and control electronics, there is a lower limit to the pixel size and it is very difficult to go below this. As the pixel size decreases, the optical aperture per pixel also diminishes.

This restriction does not apply in light valves which do not work in transmission but rather in reflection, as shown in solid lines using light valves LCD in fig. 1, and rotate the polarisation of the reflected light by 90 .

The use of such light valves operating in reflection was previously hindered by the problems which will be explained below. Fig. 2 shows the conditions which prevail when conventional light valves working in transmission, LCD light valves in fig. 1, are replaced by light valves RLV working in reflection, or reflective light valves. If a light valve RLV working in reflection is connected to the arrangement according to fig. 1 in the manner according to fig.

2, for example on the layer system 5 of the X-cube according to fig. 1, S-polarised (direction of oscillation of electrical field) blue light B will be converted at light valve RLV into Ppolarised blue light and reflected, thrown back onto the layer system 5 and again reflected by the latter. On one and the same layer system 5 according to fig. 2 and similarly for red light on system 7, light of same spectrum but different polarisation is reflected.

Spectrally selectively reflecting and transmitting layer systems, such as are used in said Xcubes but also in other light splitters for colour-selective effects, are usually produced by means of dielectric multilayer systems. These comprise each at least one layer of a material with lower refractive index and one layer of a material with higher refractive index. Usually as the material with lower refractive index Si02 is used with a refractive index of 1.46, and as

the material with higher refractive index for example Ti02 is used today with a refractive index of 2. 4 or Ta205 with a refractive index of 2. 1.

Fig. 3 shows the reflection of S-polarised blue light on a colour-selective layer system of

Si02/Ti02 and that of P-polarised blue light on the same layer system. Both measurements were taken at an angle of light incidence of 45 as depicted in fig. 2.

Fig. 4 shows, on a layer system again composed of Si02/Ti02 layers and selectively reflecting red light R, the reflection behaviour of S-polarised and P-polarised red light. The measurements of figs. 3,4 were taken on an X-cube with BK7 glass as the base material in which the said colour-selective layer systems 5,7 of fig. 2 were embedded.

In figs. 3 and 4 it is evident that firstly, in both cases the reflection of P-polarised light is essentially less than that of S-polarised light, quite pronounced on the red-selective layer system, and that further a marked edge shift-polarisation shift-of the reflected spectra takes place, e. g. with selective reflection of blue light, the 50% reflection points for S-and Ppolarisation are spaced over 70 nm apart, corresponding to AB.

If we consider the path of rays shown in fig. 2, disregarding the second colour-selective layer system 7 on the X-cube, i. e. merely the reflection on one layer system, namely the layer system 5 for blue light, we have

where

1BoutP : intensity of P-polarised blue light reflected back by layer system 5 1m S : intensity of S-polarised blue light incident on layer system 5 RRBs : the reflection of blue-selective layer system 5 for S-polarised blue light RRB : the reflection of the blue-selective layer system 5 for P-polarised blue light.

Starting from the reflection behaviour shown in figs. 3 and 4 for blue light B on layer system 5 according to fig. 2, and similarly for red light R on layer system 7, taking into consideration the relevant transmitting layer systems, i. e. system 7 for blue light B and system 5 for red light R, we obtain the intensity spectra for 1Boul or for 1Rout as shown in fig. 5 or fig. 6.

Taking into consideration the said transmissions and in accordance with fig. 2 the reflection behaviour of any connected light valve RLV working in reflection, for blue light we get:

where: T RR s : the transmission of the red-selective layer system 7 for S-polarised light RRLVB : the reflection of the light valve TRR : the transmission of the red-selective layer system 7 for P-polarised light.

The expression for red light is obtained similarly.

The differing reflection properties of the selective red or blue layer systems with respect to Sand P-polarisation lead to serious consequences: The light from the spectral ranges AB or AR between the S-and P-reflection spectra according to figs. 3 and 4 is no longer output but passes the blue or red reflector correspondingly and remains as scattered light in the system, according to fig. 2 in the X-cube.

In fig. 7 the spectrum of the scattered light in the X-cube is shown in the said stated intermediate spectral ranges AB and AR according to figs. 3 and 4.

It is evident that a large quantity of scattered light remains in the system. Further, as evident in figs. 5 and 6, the total transmission in the red spectral range and also in the blue is insufficient, i. e. substantially less than it would be if, in view of fig. 2, on both colourselective layer systems 5 and 7 only S-polarised light were reflected.

The present invention provides a light splitter and an optical transmitter which solves the above problems.

On a light splitter of the said type i. e. in particular an X-cube and/or a transmitter device with a light splitter, an essentially higher total transmission of red and blue light is achieved if the light with different polarity passes through the light splitter in a divisive and recombining manner.

Further, the scattered light in the light splitter or in the transmitter configuration is to be minimised and where applicable the colour location optimised.

This can be achieved with a light splitter where the lower refractive index NLS :

As will be explained below, this means that the edge shift A-the polarisation shift-of the Pand S-reflection spectra, as explained in conjunction with figs. 3 or 4, is essentially reduced and also the reflection of P-polarised light is approximated to the value for S-polarised light.

The refractive index NLS is preferably selected as:

As the material with higher refractive index preferably is used a material comprising at least

mainly an oxide or oxynitride, preferably a material from the series Ti02, Ta20s, Nb20s, Hf02, Zr02, SiOxNy, especially preferred Ti02 and/or Ta20S. All these materials have indices of refraction of maximum 2.1.

The lower refractive index NLS is preferably set by the use as an associated material of a mixed material consisting of at least two materials mu and m2, for the refractive indices Nml, Nm2 of which:

The first material mi of the mixed material is preferably also a material used as the material with the higher refractive index, thus an oxide or oxynitride, preferably at least one of the above listed materials Ti02, Ta20s, Nb20s, Hf02, Zr02, SiOxNy, especially preferred Ti02 and/or Ta20S.

As the second material m2 of the mixed material is preferably used Si02 and/or A1203 and/or SiOxNy and/or Y203. By selecting the mixing ratio ml/m2 of the mixed material, the material with the lower refractive index, the desired refractive index NLS is achieved. As the material with the lower refractive index, a mixed material is preferably used comprising Si02 and Ti02, with an Si02 fraction Asio2 = (60 i 5) % and a Ti02 fraction ATio2 of (100%-Asio2).

Y203 with a refractive index of 1. 8 2% can also be used as the material with the lower refractive index.

The refractive index NK of the material of the at least one base body is preferably selected as follows :

The value 1. 52 corresponds to the refractive index of BK7 glass which is commonly used in particular for X-cubes. The said body can also be made of quartz glass with

Preferably, both layer systems are formed as the at least one described above. Furthermore, a light splitter formed as an X-cube of the type described above is proposed, in which the layer systems are embedded essentially along diagonal planes of a base body cube which is preferably square in a cutting plane perpendicular to the common lines of intersection of the layer systems.

To summarise, the proposed solution consists of a targeted selection of materials of the said layer systems.

The present invention provides an alternative solution but one which can be combined with the targeted selection of materials of the said layer systems as described above. A solution is attained by a spectrally selective light splitter according to the wording of claim 1. In such a light splitter, which splits white light into red, green and blue light, or recombines white light from red, green and blue light, with two separate layer systems, each reflecting and transmitting colour-selectively, which are applied or embedded on or in at least one transparent base body and on which the body defines emergent faces for the red, green and blue light, at least one of the emergent faces with respect to the direction of light emerging from it and reflected on at least one of the layer systems is tilted such that the face normal of the emergent face forms with the said direction an acute angle (p which differs from 0 . Due to production tolerances on the light splitter, angles between the light emergent direction and the face normal which differ from 0 may occur, but firstly such tolerance-dependent angle deviations are not reproducible and secondly the tolerance-dependent angle deviations which must be taken into account due to production are known in advance. The zero deviation realised according to the invention is in any case greater than the said tolerance deviation

known in advance.

Preferably and as will be explained, the maximum angle deviations concerned are 5 .

It is now possible on such a light splitter to apply directly onto the emergent faces light valves working in reflection with which, with regard to the layer systems, for example according to fig. 2, S-polarised light to be spectrally divided and incident on a layer system concerned is reflected on the layer system at a different angle from the P-polarised light to be recombined of the same spectrum which is reflected by light valve RLV.

However, it is also possible to achieve the reflection angle shift on one and/or the other layer system without corresponding tilting of the emergent faces on the light splitter itself, i. e. without changing the light splitter itself, by mounting the light valves at a corresponding relative tilt.

A corresponding optical transmitter arrangement with a light splitter, with an incident and emergent face for white light and emergent faces each for red, blue and green light, comprises reflectors actively connected with the emergent faces of the said light splitter, and according to the wording of claim 11, which change the polarisation of light and on which the light emerging at the emergent faces is reflected at an angle deviating from 0 by more than is given by the production tolerances of the total arrangement. Such an optical transmitter arrangement can now be achieved by the direct application of light valves working in reflection onto the tilted emergent faces of a light splitter as specified in claim 1, or the reflector tilt can be achieved by mechanical mounting measures separate from the light splitter structure itself.

The light splitter according to the invention considered by itself may comprise a combination of both the measures with regard to layer material and also the measures for realising on the layer systems differing reflection angles specific to the direction of the incidence of rays.

The principle according to the invention, namely the reflection specific to direction of incidence on at least one, preferably on both layer systems, now permits working with reflecting light valves in particular also for projector configurations.

An optical transmitter arrangement in which according to claim 11 the said tilt is achieved and/or which comprises a light splitter with the material selection according to the invention of the layer systems, preferably also comprises a polarisation beam splitter on the input side and/or an HMI lamp as an illumination source.

Here the said HMI lamp has low energy values at the point in its light spectrum where the spectral shift range in the reflection behaviour relating to S-and P-polarised light also lies, i. e. corresponding to the spectral ranges AR and AB according to figs. 3 to 7.

The invention will now be explained further by example with reference to the figures.

These show: Fig. 8 the reflection of blue light on a light splitter according to the first solution with a layer material selection according to the first solution for S-and P-polarisations,

Fig. 9 in a view similar to fig. 8, with the layer material selection according to the first solution, the resulting reflection of red light in S-and P-polarisation, Fig. 10the total transmission of blue light in an X-cube with the layer materials selected according to the first solution, i. e. with layer systems which each lead to the results according to figs. 8 and 9, and the spectrum of an HMI lamp, Fig. 11 in a view similar to fig. 10, registered on the same X-cube, the spectrum of the total transmission of red light and of the said HMI lamp, Fig. 12 the spectrum of the scattered light resulting on said X-cube according to the first solution and of the said HMI lamp, Fig. 13 diagrammatically a first optical transmitter configuration according to the first solution in the form of a projection arrangement with a light splitter according to the first solution with the materials of the layer systems selected according to the first solution, Fig. 14 diagrammatically and with only one of the layer systems shown, an X-cube and light valve configuration to explain the invention under the aspect of its tilt with regard to red light, Fig. 15 in a view similar to fig. 14, the conditions for blue light, Fig. 16 a simple realisation possibility of the invention under the aspect of its tilt using a conventionally formed X-cube, and

Fig. 17 spectra of red and blue light to explain the effect of the tilt according to the invention, and Fig. 18 in the same way as fig. 12, the residual light spectrum resulting from an X-cube with combined solutions according to the invention in accordance with the spectra of fig. 17, with the spectrum of the HMI lamp Philips UHP 120 W.

The results presented below in conjunction with figs. 8 to 12 were measured using a configuration as shown in principle in fig. 2. An X-cube was provided with colour-selective layer systems 5 and 7. The material with the higher refractive index in the layer systems 5,7 was Ti02, the material with the lower refractive index was a mixed material comprising Si02 and Ti02 in a mixing ratio of ASi02/ATi02 = 60/40. The body of the X-cube comprised quartz glass.

The effects of the transmission resulting during reflection measurements on the layer system not concerned-i. e. for blue light, the red-selective system 7 and for red light, the blueselective system 5-in particular the transmission differences for S-and P-polarised red and blue light respectively, were negligible.

In the arrangement in fig. 2, in the same way as fig. 3 in an X-cube with Ti02 as the material with the higher refractive index and Si02 as the material with the lower refractive index on the light splitter according to the first solution, were measured spectra for reflected blue light in S-and P-polarisation as shown in fig. 8, and similarly for red light R in fig. 9. The refractive index NLS within the range

was selected as 1.8 2%.

By selecting the said mixing ratio of the mixed material with lower refractive index, and thus setting the lower refractive index, a substantial reduction of the polarisation shifts AB and AR was achieved and thus an essential approximation of the reflection spectra edges of S-and Ppolarised light. If on previously known optical structural components according to fig. 3, at 50% reflection a polarisation shift of 70 nm results between the reflection spectrum for S-and P-polarised light, in the case of the structural component according to the first solution a polarisation shift of only 30 nm is obtained for this light. Similarly, for red light at 30% reflection on the structural component according to the first solution a polarisation shift of only 25 nm results while on previously known structural elements this is 50 nm according to fig. 4.

Furthermore the maximum reflection of P-polarised blue light according to the first solution and according to fig. 8 is approximately 92% of that of S-polarised blue light, whereas in previously known structural components according to fig. 3 this value is only 75%. As is readily apparent, with respect to red light, the maximum reflection attained according to the first solution with P-polarisation is 97% of that with S-polarisation, whereas in the case of previously known structural components according to fig. 4, this figure is only 40%.

Fig. lO shows, on the system according to fig. 2 as defined above and structured according to the first solution, the total transmission of blue light and similarly fig. 11 shows the total transmission of red light, thus via the light division on the X-cube, reflection on RLV and

light recombination on the X-cube. 0 An HMI lamp, for example a lamp UHP 120 W by Philips, gives the lamp spectrum A also shown in figs. 10 and 11. It is clear that the lamp spectrum has low energy or a low intensity at the point where the blue light, due to the remaining polarisation shift A'a according to fig. 8 has a low transmission. Also and extremely advantageously, the lamp spectral line lies at 580 nm, corresponding to the yellow lines faded out through the layer system provided according to the first solution (fig. 10), which prevents a green coloration of the blue component or orange coloration of the red component. Based on the comparison of the scattered light spectrum of fig. 12 with that resulting on a conventional X-cube according to fig. 7, it is clear that the total scattered light losses on the light splitter produced according to the first solution with layer system materials selected according to the first solution, are substantially less than with a conventional light splitter of the said type, in particular also if the light splitter according to the first solution is combined with an HMI light source.

Fig. 13 shows the realisation of a projector according to the first solution in which, thanks to the implementation according to the first solution of the optical light splitter structured as an X-cube, namely with layer system materials selected according to the first solution, light valves RLV working in reflection are used.

White light, S-polarised or both S-and P-polarised, is incident on a polarisation beam splitter 13. The layer system 10 of the beam splitter has in known manner the property of deflecting S-polarised light by 90 and allowing P-polarised light to pass. The P-polarised light can also be reflected back to the light source by means of a mirror (not shown). The S-polarised white light enters the X-cube 12, structured as explained in conjunction with fig. 2, but with the

layer system materials according to the first solution. At the three emergent faces corresponding to the three colour channels of the X-cube 12 are provided light valves RLVR, RLVG, and RLVB working in reflection. With a change in the polarisation, the light of the associated spectra is there reflected back P-polarised onto the associated colour-selective reflection layer systems structured according to the first solution, and output after recombination by the polarisation beam splitter 13. Thus the light is split in the X-cube into S-polarisation into RGB and in the same X-cube recombined from RGB in P-polarisation.

The P-polarised light can pass unhindered through the polarising beam splitter and is projected via a projection lens onto a screen (not shown).

With reference to fig. 14, the solution according to the invention of the task posed above will be explained in principle, the solution of which, as already mentioned, can be optimally combined with the first solution just described, namely the special layer system material selection.

Again, the problem to be solved is that, as has been explained in connection with figs. 3 and 4, on the particular layer systems of a light splitter a decisive polarisation shift occurs of the reflected spectra corresponding to AB and AR.

In principle, and in view of said figures, the aim is to attain: * a shift of the spectral edge of the reflected red light in S-polarisation (see fig. 4) toward longer wavelengths; a shift of the spectral edge of the reflected red light in P-polarisation toward shorter

wavelengths; w a shift of the spectral edge of the reflected blue light in S-polarisation toward shorter wavelengths; and * a shift of the spectral edge of the reflected blue light in P-polarisation toward longer wavelengths.

It is highly surprising that all of these conditions can in principle be fulfilled if the angles of incidence for P-and S-polarised light on the associated layer systems are selected to be different. This process will be explained in principle with reference to fig. 14. Apart from conditions yet to be explained, this shows diagrammatically an X-cube 20 with the one layer system 5a-the red reflector-and light valve RLV working in reflection which is shown only for one channel for the sake of clarity.

It is essential in the solution according to the invention that the light incident on RLV arrives at RLV at an angle (p deviating from 0 with respect to the face normal FRLV and no longer, as for example according to figs. 2 or 13, at an angle < p = 00. The requirements for the spectrum of the red light for a decrease of the polarisation shift according to fig. 4 are now fulfilled in that the angle of reflection aR for the S-polarised red light is selected to be smaller than the angle ssR for the P-polarised red light.

Conversely, the conditions with regard to the polarisation shift of the spectra of the blue light are fulfilled in that, as shown in fig. 15, the reflection angle an of the blue light in S-

polarisation on the layer system 7a is greater than the angle of reflection ssB of the blue light reflected by the associated light valve RLV. According to figs. 14,15, on the red reflector or blue reflector layer system Sa, 7a :

The angle a is set by the geometric relative position of the layer system 5a according to fig. 14 to the direction of the light incident on channel KR+B+G, angle ss as a function of this said angle of incidence a and the angular orientation of the reflector on RLV with respect to the light emerging at channel KR or KB.

With regard to both red light and blue light, in a preferred embodiment the angles a and P are selected symmetrical at 450. If the deviation of angles a, ss from 450 is denoted by 8, then

where the upper sign applies in each case for blue light at reflector 7a according to fig. 15, the lower sign for the conditions at the red channel with reflector 5a according to fig. 14. Hence

In a further preferred embodiment, 5 is selected as

It follows that at the light valve RL V R associated with the red channel KR, and/or at light valve RLVB associated with the blue channel KB, preferably on both, the incident light is to be reflected at an angle (p greater than 0 and preferably maximum 50. Since even small angles of incidence (p which deviate from 00 can be caused by production, this angle (pof0 can be selected to deviate to an extent more than that caused by production tolerances.

As is readily evident in figs. 14 and 15, the angle a is determined by the relative orientation of the particular layer system 7a or 5a and the direction of light incidence of the light entering through channel KR+B+G for white light.

The geometric conditions according to the invention on light splitters and valves RLV, in particular X-cubes and light valves RLV as shown qualitatively in figs. 14 and 15, can be achieved by specific formation of the X-cube or the light splitter itself, namely by tilting their emergent faces corresponding to KR and KB and their layer systems 5a and 7a and direct application of the valves on the tilted faces (in figs. 14,15 in dashed lines at Kpq, KB. ?). Alternatively-and more simply-the"tilting"is achieved by the corresponding positioning of the RLVs and the structure of illumination or recombination lenses, with geometrically unchanged X-cube or light splitter.

A simple embodiment is achieved, according to fig. 16 and as can be seen from the combined consideration of figs. 14 and 15, by tilting an X-cube such as shown for example in

conjunction with fig. 2 in relation to light valves RLV arranged for example in parallel.

Fig. 17 shows several spectra for red and blue light as measured on an X-cube on which both the first solution and the solution according to the invention were combined, namely firstly material selection of the layer systems and secondly design of the incidence angles according to the invention. These spectra were measured on X-cubes which had already led to the spectra described above according to figs. 8 and 9.

In the red spectra of fig. 17: Spectrum (a) is the spectrum of the reflected S-polarised red light at an angle of incidence aR according to fig. 14 on the red reflector 5 of 450 according to the first solution. This spectrum corresponds to the first spectrum of fig. 9.

Spectrum (b) is the spectrum of the reflected P-polarised red light reflected on the red

reflector 5 according to the first solution at PR = 450.

These spectra again show clearly the reduction of the polarisation shift according to fig. 9 attained according to the first solution by the selection of the material layer systems.

Spectrum (c) is the spectrum of S-polarised red light on the same red reflector 5 according to the first solution reflected at aR = 420.

Spectrum (d) is the spectrum of P-polarised red light reflected on the same red reflector 5 at ssR = 48 .

Comparison of the spectra (c) and (d) shows clearly that the remaining polarisation shift A"R is again reduced by almost 50% by the specific polarisation-dependent design of the angles of

incidence aR, PR- In the blue spectra B of fig. 17: Spectrum (e) is the spectrum of reflected S-polarised blue light on the blue reflector 7 designed according to the first solution with regard to layer materials, at an angle of incidence aB = 450.

This spectrum corresponds to the first in fig. 8.

Spectrum (f) is the spectrum of the reflected P-polarised blue light on the blue reflector 7 according to the first solution, with ssB = 450.

This spectrum corresponds to the second in fig. 8.

Between spectra (e) and (f) the polarisation shift AB according to fig. 8 can be seen.

Spectrum (g) is the spectrum of the S-polarised blue light reflected on the blue reflector 7 structured according to the first solution, with aB = 48 .

Spectrum (h) is the spectrum of the P-polarised blue light reflected on the blue reflector 7 structured according to the first solution, with ssB = 420.

Again, spectra (g) and (h) show the further reduction of the polarisation shift with respect to that already attained merely by the layer material selection according to the first solution according to fig. 8.

Fig. 18, in the same way as the view in fig. 12, firstly shows the spectrum of an HMI lamp,

0 namely the UHP 120 W by Philips, and secondly the spectrum of scattered light attained with an X-cube with the layer systems designed according to the first solution and with the polarisation-specific design of the angles of incidence a, P according to the spectra of fig. 17.

On the light splitter according to the invention, in particular an X-cube, it is quite possible to form for example only the layer system 5 forming the red reflector with the materials according to the first solution and to achieve the layout of the angles of incidence according to the invention, for example according to fig. 16, by tilting the X-cube.

Claims

Claims 1. Spectrally selective light splitter which divides white light into red, green and blue light or recombines white light from red, green and blue light, with two separate layer systems, each reflecting or transmitting colour-selectively and applied or embedded on or in at least one transparent base body where the said at least one base body determines emergent faces each for the red, green and blue light, characterized in that at least one emergent face is tilted with respect to the direction of the light emerging from it and reflected on at least one of the layer systems such that its face normal encloses with this direction an angle (p which deviates from zero, specifically by more than is caused by the production tolerances of the light splitter, for which:

0 < ps5O.
2. Light splitter according to claim 1, where at least one of the layer systems comprises at least one layer of a material with lower refractive index and at least one layer of a material with higher refractive index, such that for the lower refractive index NLS : 1. 7 S NLs S 2. 1
3. Light splitter according to claim 2, such that NLS = 1. 8 2%
4. Light splitter according to one of claims 2 or 3, such that the material with the lower refractive index is a mixed material comprising at least two materials mI, m2, for

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which materials N 1. 05 NLs Nm2 : : ; 0. 95 NLS
5. Light splitter according to any of claims 2 to 4, such that the material with the higher refractive index at least largely comprises at least one oxide or oxynitride, preferably at least one of the following materials:

Ti02, Taos, MOs, Hf02, Zr02, SiOxNy.
6. Light splitter according to any of claims 2 to 5, such that the material with the lower refractive index comprises at least one of the following materials : Ti02, Ta205, Nb20s, Hf02, Zr02, SiOxNy, preferably Ti02 and/or Ta205 and at least one of the following materials: Y203, Sitz, A1203, SiOxNy, preferably that the material with the lower refractive index comprises at least mainly

Si02 and Ti02, preferably with a ratio of fraction Asio2 = (60 5) % and ATi02 = (100%-asia2).
7. Light splitter according to any of claims 2 to 6, such that the material with the lower refractive index comprises Y203.

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8. Light splitter according to any preceding claim, such that for the refractive index Nk of the material of at least one base body:

preferably
9. Light splitter according to any preceding claim, such that both layer systems are formed as the said at least one layer system.
10. Light splitter according to any preceding claim structured as an X-cube, in which the layer systems are essentially embedded along diagonal planes of a base body cube which is preferably at least approximately square viewed in a cutting plane perpendicular to the common lines of intersection of the layer systems.
11. Optical transmitter arrangement with a light splitter structured according to any of claims 1 to 10, with an incident/emergent face for white light and emergent faces each for red, blue and green light, characterised in that operationally connected with the emergent faces are reflectors which change the light polarisation and at which the light emerging from the emergent face is reflected at an angle which deviates from 0 by more than is caused by the production tolerances of the arrangement.

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12. Transmitter arrangement according to claim 11, characterized in that each reflector is formed by arrangements of reflecting light valves, preferably each by LCD arrangements.
13. Transmitter arrangement according to one of claims 11 or 12, characterized in that the light is reflected on the reflectors at an angle (p for which:

which deviates from zero by more than is caused by production tolerances.
14. Transmitter arrangement according to any of claims 11 to 13, characterized in that the light reflection takes place at the specified angle on more than one of the reflectors.
15. Optical transmitter arrangement according to any of claims 11 to 14, characterized in that an incident face of the light splitter for light to be divided has a polarisation beam splitter and/or also an HMI lamp as illumination source for the incident face.
16. A method of manufacturing a spectrally selective light splitter which divides white light into red, green and blue light or recombines white light from red, green and blue light, the method comprising the steps of : providing two separate layer systems, each reflecting or transmitting colour- selectively, applying or embedding the layer systems on or in at least one transparent base body,

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determining by the at least one transparent base body an emergent face each for the red, green and blue light, and tilting at least one emergent face with respect to the direction of the light emerging from it and reflected on at least one of the layer systems such that it its face normal encloses with this direction an angle (p which deviates from zero, specifically by more than is caused by the production tolerances of the light splitter, for which: