WO2015010214A1 - Projection screen for laser projection system - Google Patents

Projection screen for laser projection system Download PDF

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Publication number
WO2015010214A1
WO2015010214A1 PCT/CH2013/000136 CH2013000136W WO2015010214A1 WO 2015010214 A1 WO2015010214 A1 WO 2015010214A1 CH 2013000136 W CH2013000136 W CH 2013000136W WO 2015010214 A1 WO2015010214 A1 WO 2015010214A1
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microsurfaces
projection
projection screen
laser
s2
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PCT/CH2013/000136
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French (fr)
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Manuel Aschwanden
Marcel Suter
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Optotune Ag
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    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ELECTROGRAPHY; HOLOGRAPHY
    • G03BAPPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B21/00Projectors or projection-type viewers; Accessories therefor
    • G03B21/54Accessories
    • G03B21/56Projection screens
    • G03B21/60Projection screens characterised by the nature of the surface
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B27/00Other optical systems; Other optical apparatus
    • G02B27/48Laser speckle optics; Speckle reduction arrangements

Abstract

A projection screen (10) for a laser projection system (100) is dividable into at least 100000 projection pixels (pp) of identical area (app). Each of said projection pixels (pp) comprises a reference plane (r) with a surface normal (n) and a plurality of microsurfaces (sl...s2, s3...s4) in a first group (G1) and in a second group (G2), respectively. In the first group (G1), all microsurfaces (sl...s2) are arranged at a first orientation angle (al) to the surface normal (n) and in the second group (G2), all microsurfaces (s3...s4) are arranged at a second orientation angle (a2). Thus, an angular intensity distribution of the projection screen (10) does not vary to a very large degree over viewing angles smaller than 10°. Furthermore, in each group (G1, G2), all microsurfaces are arranged at different axial depths (dl...d2, d3...d4) from the reference plane (r) for inducing different phase shifts to reflected or transmitted light and thus for creating uncorrelated speckle patterns. By arranging the microsurfaces (sl...s2, s3...s4) such that a distribution of cumulated microsurface areas vs depth intervals is constant within a certain band for each group, subjective speckle contrast is reduced due to the superposition of a large enough number of the uncorrelated speckle patterns.

Description

PROJECTION SCREEN FOR LASER PROJECTION SYSTEM

Technical Field and Background Art

The invention relates to a projection screen for a laser projection system, to a laser projection system comprising such a projection screen, to a method for reducing subjective speckles in a laser projection system, and to a use of a projection screen.

Lasers have the unique characteristics to provide high power and low divergent light. Furthermore, laser light inherently exhibits a high degree of temporal and spatial coherence that enables, e.g., efficient interference processes. Although these characteristics of lasers are widely used in various scientific applications, they lead to significant drawbacks for applications such as laser projection systems, e.g., in movie theaters. When projecting a laser from a laser projector onto a projection screen, laser light is scattered by each corrugation point of the illuminated area of this projection screen. Each of these scattering corrugation points can be seen as a secondary coherent light source. If the corrugation depth of the projection screen is on the order of the laser wavelength, local interferences occur such that a random intensity pattern, also known as speckle pattern, is observed. This speckle pattern is considered disturbing by viewers and has to be eliminated or at least its perceivable contrast has to be reduced to enable a new generation of high-quality projection systems based on lasers .

Two classes of speckles can be distinguished, so called "objective speckles" and "subjective speckles".

Objective speckles are formed when coherent light from the laser is scattered by a projection optics and interferes on the projection screen. Thus, the inter- ference pattern on the projection screen is made up of contributions from all scatterings from the projection optics and the resulting speckle pattern on the projection screen stays the same regardless of how or from which direction the projection screen is viewed.

In contrast, in the case of subjective speckles, the scattered light from the projection screen is imaged by an imaging system (e.g., the human eye) onto an imaging surface (e.g., the retina). Here, the detailed structure of the speckle pattern on the imaging surface depends on imaging parameters such as, e.g., imaging direction, aperture, or resolving power of the imaging system.

US 2006/0126022 Al discloses a laser projection system including a custom-designed optically pumped, external cavity, surface-emitting semiconductor laser (OPS-laser) which emits a rather low-quality beam which thus has a reduced spatial coherence diameter. This reduced coherence diameter in combination with a custom projection screen contributes to reducing speckle contrast .

This solution has the drawback, however, that the necessity of custom OPS-lasers limits the applicability of the laser projection system.

Disclosure of the Invention

Therefore, it is an object of the present invention to provide a more universally applicable projection screen, a laser projection system comprising such a projection screen, a use of such a projection screen, as well as a method for reducing subjective laser speckles in a laser projection system.

These objects are achieved by the devices and methods of the independent claims. Accordingly, a projection screen for reducing subjective laser speckles in a laser projection system is dividable into at least 100000, particularly at least 2073600, in particular at least 12746752 projection pixels of identical area. Such a number of projection pixels can accommodate various commonly used projection resolutions .

Each of said projection pixels comprises a reference plane with a surface normal. The term "reference plane" refers to a main plane of the projection pixel which normally (at least in the case of an overall essentially planar projection screen) coincides with the reference planes of all other projection pixels as well as with a main plane of the projection screen itself. The exact position of the reference plane, e.g., if the backer the front-surface of the projection pixel is regarded as reference plane, is of secondary importance because only relative distances to the reference plane are relevant for characterizing the projection pixel (see below). The surface normal of the projection pixel is perpendicular to the reference plane of the projection pixel. Furthermore, each projection pixel comprises a plurality of microsurfaces which are distributed, in particular periodically or non-periodically distributed, over said projection pixel. Thus, the whole projection pixel can be more easily "covered" by the microsurfaces . The term "mi- crosurface" herein relates to an essentially (i.e., down to a radius of curvature of 1 μπι) section of a surface profile of the projection pixel. The microsurfaces can have essentially identical or - as another option - differing areas . Usually, not all microsurfaces will have identical areas .

The microsurfaces of the projection pixel comprise at least a first group of microsurfaces . In this first group, all microsurfaces are arranged at a plurality of axial distances (i.e., "depths") from said reference plane. This does not exclude the possibility, howev- er, that two or more disjointed microsurfaces of the first group are arranged at the same distance to the reference plane; usually, this will be the case. In other words, the microsurfaces are distributed at different (positive and/or negative) "depths" from the reference plane. This has the effect that the different microsur- faces in the first group induce different phase shifts to light that is reflected or transmitted by the different microsurfaces in the first group. In other words, different phase shifts are induced to different spatial parts of light that is reflected or transmitted by the projection pixel. This plurality of induced phase shifts facilitates the reduction of subjective speckle contrast.

The axial distances of the microsurfaces from the reference plane are advantageously on the order of λ/4, in particular λ/2, particularly λ (with λ being a wavelength of projection light within 350 nm to 800 nm) .

Furthermore, all microsurfaces in the first group are parallel to each other within an angle of 0.03°. Thus, plane wave projection light is reflected or transmitted from the different microsurfaces in the first group under practically the same angle.

Equivalently, all microsurfaces in the first group are within an angle of ±0.015° oriented at a first orientation angle to the surface normal of the reference plane. This first orientation angle corresponds to a first orientation angle of the first group of microsur- faces. Thus, the first group of microsurfaces is assigned a first orientation angle.

At least for one wavelength λ within 350 nm to 800 nm (the projection light wavelength) , the distances and the microsurfaces in the first group are such that for all i=0...m-l, ieNg

5Ί(/' · Δ, (/' + 1)· Δ) 0.25 _4

s\(o, X) m ' m Here, Sl(xl,x2) is the sum of areas of all microsurfaces in the first group having distances dj , j eM from said reference plane (r) with dj mod λ being between xl and x2. Square brackets denote a closed range in a mathematical notation.

In other words, the distances of all first- group-microsurfaces to the reference plane and the first- group-microsurfaces themselves (e.g., their areas) are distributed such that all proportionate cumulated areas for specific depth intervals (e.g., from 2·Δ to 3·Δ) are in the above stated range, i.e., between 1/4 and 4 times an average area contribution for a perfectly uniform area distribution over all depths. In particular, no single depth interval with an exceptionally high or low area contribution (single area-peak or single area-dip) is present in the distribution of cumulated microsurface- areas per depth interval.

As a consequence of this, a reflected or transmitted light intensity per depth interval does also not vary to a very large degree, i.e., it can vary only between 1/4 and 4 times an average value for a perfectly uniform area-distribution per depth interval. Because of the differing phase shifts induced by microsurfaces of different depths, this leads to a large enough number of different phases to be superimposed, which helps to efficiently average out subjective speckles.

In general, by the superposition of a number of uncorrelated speckle patterns (i.e., speckle patterns with differing phases), the perceived overall subjective speckle pattern is smeared out, resulting in a decreased perceived subjective speckle contrast. With N uncorrelated speckle patterns being arranged inside a single resolvable area "app" (see below), a speckle contrast of 1/V(N) is achieved (Goodman, J.W., "Some fundamental properties of speckle", J. Opt. Soc. Am 66, 1145-1150, 1976) . In a projection screen according to the invention, uncorrelated speckle patterns are generated by the intro- duction of different phases to different parts of the illuminated projection pixel. Specifically, the spatially varying depth profile of the projection screen introduces a spatially varying optical path length which in turn introduces a spatially varying phase shift for different spatial parts of the originally coherent projection laser beam. Thus, due to the small structure size made up by the microsurfaces of each projection pixel, sufficient beam parts with differing phases are superimposed on the viewer's human eye at a viewing position and the resulting speckle pattern is smeared resulting in a reduced speckle contrast.

Specifically, according to the invention, m >= 49, in particular m >= 225, particularly m >= 625. A depth interval Δ thereby equals to λ / m. Thus, a sufficient number of microsurfaces with a sufficient number of distances from the reference plane (resulting in different phase shifts and therefore uncorrelated speckle patterns) is present in the first group of microsurfaces . Thus, the contrast of subjective speckles is more sufficiently reduced, even if no custom laser with reduced beam quality (and therefore reduced coherence diameter) is used but a standard laser with an in the range of 1.1 to 5. This enables the utilization of standard equipment which reduces manufacturing complexity and costs and enhances the applicability of the projection screen.

In an advantageous embodiment of the projection screen, in addition to the above-described first group of microsurfaces , the microsurfaces also comprise a second group of microsurfaces . In this second group, the microsurfaces are again - as in the first group - arranged at a plurality of axial distances ("depths") from the reference plane of the projection pixel. It should be noted here that these distances can be the same, but usually they are different from the distances of the micro- surfaces in the first group. Again, this has the effect that the different microsurfaces impose different phase shifts to light that is reflected or transmitted by these second-group-microsurfaces . This plurality of induced phase shifts again facilitates the reduction of subjective speckle contrast.

As discussed above with regard to the first group, also the microsurfaces in the second group are essentially parallel to each other, i.e., within an angle of 0.03°. In contrast to the first group, however, the microsurfaces in the second group are oriented within an angle of ±0.015° at a second orientation angle with regard to the surface normal of the reference plane, wherein this second orientation angle is different from the first orientation angle. Thus, light from the second group is reflected or transmitted into a different direction by the microsurfaces of the second group compared to the first group. As a consequence, an overall angular intensity distribution of the projection screen can be engineered to the desired characteristics.

Also for the second group of microsurfaces , for the at least one projection wavelength λ within 350 nm to 800 nm, the distances and the microsurfaces in the second group are such that for all i'=0...m'-l, i'eMg

S2(i'-A',(/'+l)-A') 0.25 4 "

i s m

S2(0,X) m m _

Here, S2 (xl ' , x2 ' ) is the sum of areas of all microsurfaces in the second group having distances dj ' , j ' e from said reference plane with dj ' mod λ being between xl' and x2 ' .

In other words, the distances to the reference plane of all microsurfaces (and the microsurfaces themselves, e.g., their areas) in the second group are distributed such that all proportionate cumulated areas for specific depth intervals (e.g., from 2 · Δ' to 3 · Δ' ) are in the above stated range, i.e., between 1/4 and 4 times an average area contribution for a perfectly uniform area distribution over all depths. In particular - just as in the first group - no single depth interval with an exceedingly high or low area-contribution (single area-peak or single area-dip) is present in the distribution of cumulated microsurface-areas per depth interval.

This - as described above with regard to the first group of microsurfaces - leads to the effect that the reflected or transmitted intensities per induced phase shift for the second group of microsurfaces do also not vary by more than 1/4 and 4 times an average value. Thus, subjective speckle contrast can be more efficiently reduced .

Again, with m' >= 49, in particular m' >= 225, particularly m' >= 625 and a depth interval Δ' = λ / m' , a sufficient number of microsurfaces with a sufficient number of distances from the reference plane (i.e., different induced phase shifts) is present in the second group of microsurfaces to more efficiently reduce perceived subjective speckle contrast.

To sum up, when looking at a single projection pixel at a larger scale, the projection pixel comprises a reference plane and a surface normal, which define the axial position and the orientation of the projection pixel. When looking at the projection pixel surface at a smaller scale, a plurality of essentially parallel microsurfaces of a first group are arranged

- at a first orientation angle to the surface normal of the projection pixel and

- at different depths to the reference plane of the projection pixel

in such a way that cumulated microsurface- areas in all depths intervals do not deviate to a large degree from each other.

Thus, a distribution of reflected or transmitted light intensities per induced phase shift inter- vals does also not exhibit high peaks or low drops, but is uniform within a certain band. Due to a superposition of uncorrelated speckle patterns, this leads to a reduced speckle contrast in a first viewing direction.

A plurality of essentially parallel microsur- faces of a second group are also arranged

- at a second orientation angle to the surface normal of the projection pixel and

- at different depths to the reference plane of the projection pixel

in such a way that the cumulated microsur- face-areas in all depths intervals do not deviate to a large degree from each other.

Thus, a distribution of reflected or transmitted light intensities per induced phase shift interval does again not show high peaks or low drops. Due to a superposition of uncorrelated speckle patterns, this also leads to a reduced speckle contrast in a second viewing direction .

In a laser projection system with a non- negligible projection-NA (NA for numerical aperture) , i.e., with non plane-wave illumination, such as in a laser projection system with a DLP laser projector, also at least some of the microsurfaces in the second group can contribute to reducing subjective speckle contrast under the first viewing direction. This is because projection light is also reflected or transmitted into the first viewing direction by microsurfaces of the second group. Thus, subjective speckle contrast is further reduced because even more phases and thus uncorrelated speckle patterns are superimposed under the first viewing direction.

In another advantageous embodiment of the projection screen,

S\(0,X) - S2(0,X) <Q5 , in particular < 0.1

S\(0,X) In other words, the cumulated microsurface- areas for the first and for the second group (i.e., the areas for all depths in the respective groups) do not vary by more than 50% (or 10%, respectively) , at least in an angular range of the first orientation angle < 10° and the second orientation angle

Figure imgf000011_0001
< 10° . Thus, an angular reflection or transmission intensity distribution of the projection pixel and thus of the whole projection screen can be kept more uniform which leads to a better viewing experience, especially from more laterally located viewing positions.

According to another aspect of the invention, a laser projection system for reducing subjective laser speckles comprises a projection screen as described above. A laser projector of the laser projection system, in particular a DLP laser projector or another laser projector with a non-negligible proj ection-NA, is arranged at a projection distance to the projection screen. At least one viewing position, usually a plurality of viewing positions, is/are arranged at (a) viewing distance (s) to said projection screen, advantageously in a reflection mode configuration, i.e., with a first surface of the projection screen facing the laser projector and the viewing position(s) . By utilizing a projection screen as described above, subjective speckles as perceived from the viewing position (s) can be more efficiently reduced and the viewing experience is improved.

Advantageously, the area of the projection pixels is smaller than or equal to a smallest resolvable area on said projection screen as viewed from said viewing position without visual aids. To achieve this, the viewing distance (s) can be set accordingly. Thus, different projection pixels and projection pixel substructures (i.e., microsurfaces ) cannot be discerned from the viewing position. The smallest resolvable area on the projection screen as viewed from the viewing position can, e.g., be estimated by r2 = (2 * tan^/2) * IV) 2 with β being an angle resolution of the human eye (β ¾ 0.02°) and IV being the distance between the projection screen and the viewing position. Thus, a perceived image quality delivered by the projection system is improved.

As another aspect of the invention, a projection screen as described above is used in a laser projection system as described above. Thus, the perceivable contrast of subjective speckles in the laser projection system is reduced and a viewing experience is improved.

As yet another aspect of the invention, a method for reducing subjective laser speckles in a laser projection system as described above comprises steps of

- providing a projection screen as described above, and

- projecting at least partially coherent light, in particular from a laser projector, onto said projection screen. Thus, the perceivable contrast of subjective speckles in the laser projection system is reduced and a viewing experience is improved. This subjective speckle contrast reduction is even more pronounced for a DLP laser projector or another laser projector with a non-negligible proj ection-NA .

Remarks :

Throughout this description, the term "axial" relates to a direction which is substantially parallel to a projection direction and also viewing direction, i.e., perpendicular to a projection plane which is parallel to a plane or a tangent plane of the projection screen.

Equivalently, throughout this description, the term "lateral" relates to directions which are substantially perpendicular to the projection (and viewing) direction, i.e., "lateral" means "in-plane of" or "parallel to" the projected image from the laser projector on the projection screen.

Throughout this description, the term "to comprise" can be interpreted as "to contain" as well as "to consist of".

The described embodiments similarly pertain to the devices and methods. Synergetic effects may arise from different combinations of the embodiments although they might not be described in detail.

Brief Description of the Drawings

Embodiments of the invention are described in the following detailed description. Such description makes reference to the annexed drawings, wherein

fig. 1 shows a laser projection system 100 according to the invention, which laser projection system 100 comprises a DLP laser projector 101 with an integrated moving diffuser 103, a projection screen 10, and a viewing position 102,

fig. 2 shows a zoomed-in view of a part of a projection pixel pp of a projection screen 10 according to a first embodiment of the invention, e.g., that of fig. 1, in which zoomed-in view a plurality of microsur- faces sl...s4 of the projection pixel pp of the projection screen 10 at different distances dl...d4 to a reference plane r and at different orientation angles al, a2 to a surface normal n of the reference plane r of the projection pixel pp can be discerned,

fig. 3 shows a cumulated-microsurface-area- vs-depth-interval-diagram for a first group Gl of micro- surfaces of the projection pixel pp of figure 2,

fig. 4 shows a three dimensional representation of a measured surface profile of a projection pixel pp of a projection screen 10 according to the invention, fig. 5 shows a three dimensional plot of a measured surface profile of a projection pixel of a prior art projection screen, and

fig. 6 shows a projection screen 10 according to a second embodiment of the invention with an anti- reflective coating lib on the microsurfaces sl...s4 and a reflective coating 12a on a second surface 12 of the projection screen 10.

Detailed Description of the Drawings

Fig. 1 shows a laser projection system 100 according to the invention. The laser projection system 100 comprises a projection screen 10, which is arranged in a reflection configuration. This means, that a first surface 11 of the projection screen 10 faces a laser projector 101 of the laser projection system 100 as well as a viewing position 102 in the laser projection system 100. However, a transmission configuration would be possible as well (not shown) .

The viewing position 102 is located at a viewing distance IV from the projection screen 10, whereas the laser projector 101 (a DLP laser projector) is arranged at a projection distance IP from the projection screen 10. This results in a projection pixel size "app" of a single projection pixel "pp" (as schematically shown by the area labeled "pp, app" on the backside of the projection screen 10 in figure 1) on the projection screen 10, which projection pixel size "app" is essentially equal to a smallest resolvable area ("eye resolution pixel") on the projection screen 10 as viewed from the viewing position 102 without visual aids. Thus, single projection pixels and their substructures (i.e., microsur- faces, see line pattern inside "pp" in fig. 1, see below) cannot be discerned by a viewer at the viewing position 102 without visual aids.

The smallest resolvable area on the projection screen 10 as viewed from the viewing position 102 without visual aids can be estimated by app2 * r2 = (2 * tan^/2) * IV) 2 * 12.2 mm2 with β ~ 0.02° being the angle resolution of the human eye and IV = 10 m.

The projection screen 10 can be divided into 12746752 projection pixels of identical area 12.2 mm2 and it can thus accommodate future Full Aperture 4K projections. Only a single projection pixel pp is shown in figure 1 for clarity.

Each projection pixel pp comprises a reference plane r at the far side of the laser projector 101 and it comprises a surface normal n along the +z direction (axial direction) . These quantities are essentially identical for all projection pixels pp because the projection screen 10 is arranged in a planar configuration in the x-y-plane . The surface normal n and the reference plane r are furthermore indicative of a projection pixel orientation and enable a quantification of distances and orientations of microsurfaces sl...s4 on the laser- projector-facing-side of the projection pixel pp, i.e. an "elevation" or "surface profile" of the projection pixel on the first surface 11 of the projection screen 10. See figure 2 for details.

A moving diffuser 103 (as, e.g., described in WO 2010/078666 which is hereby included by reference in its entirety, or, alternatively, a spinning wheel diffuser, or other active speckle reducing elements as known to the skilled person) is arranged in the laser projector 101 for reducing objective laser speckles. The laser projector 101 projects light with a projection wavelength λ between 400 and 750 nm onto the projection screen 10. For this, high quality red, green, and blue lasers with an = 1.1 are used in the laser projector 101.

The projection screen 10 is made of PVC, i.e., a solid material in contrast to more complicated prior-art projection screens comprising light scattering liquids and/or emulsions and/or suspensions. The micro- surfaces sl...s4 on the first surface 11 are formed by recesses in the solid material. Any known production technique such as hot embossing can be used to produce such a projection screen 10. This makes production of the projection screen 10 easier and cheaper.

Furthermore, the first surface 11 of the projection screen 10 (and thereby the microsurfaces sl...s4 on said first surface 11) is covered by a reflective coating 11a which reflects at least 80% of the projected light (see first embodiment of the projection screen 10 in fig. 2) . This helps to improve the "gain" of the projection screen 10.

As an alternative, it is also possible to cover the first surface 11 and thus the microsurfaces sl...s4 with an anti-reflective coating lib and to cover a second surface 12 of the projection screen 10 which opposes the first surface 11 and - in a reflection configuration - faces away from the viewing position 102 and the laser projector 101 with a reflective coating 12a (see second embodiment of the projection screen 10 in fig. 6). This allows a double passing of the projection light through the first surface 11 with the microsurfaces sl...s4 and could thus enhance the speckle reduction effect even further .

It should be noted here that it would also be possible to arrange the recesses and thus the microsur- faces sl...s4 solely on the second surface 12 of the projection screen 10 or - alternatively - on the first and the second surfaces 11, 12 of the projection screen 10 (both not shown) . Then, if the projection screen 10 is still arranged in a reflection configuration with its first surface 11 facing the laser projector 101 and the viewing position 102, an anti-reflection coating lib of the first surface 11 and a high-reflection coating 12a of the second surface is advantageous. It would also be possible to arrange the microsurfaces inside the projection screen material, i.e., sandwiched between the first and the second surface (not shown) .

Fig. 2 shows a zoomed-in view of a part of a projection pixel pp of a projection screen 10 according to a first embodiment of the invention. In fig. 2, the ellipsoid region of fig. 1 is shown. Here, a plurality of microsurfaces sl...s4 of the projection pixel pp of the projection screen 10 at different distances dl...d4 to the reference plane r and at different orientation angles al, a2 to the surface normal n can be discerned.

The microsurfaces sl...s4 comprise a first group Gl (comprising microsurfaces sl...s2) and a second group G2 (comprising microsurfaces s3...s4). It should be noted here, that in reality, each projection pixel pp comprises a lot more groups and each of these groups comprises a lot more microsurfaces . However, for reasons of clarity, only two groups each comprising two microsurfaces are referenced in figures 1 and 2.

In the first group Gl, microsurface si is arranged at a distance dl from the reference plane r and microsurface s2 is arranged at a distance d2 from the reference plane r. Thus, different phase shifts are induced onto light which is reflected by these two micro- surfaces si and s2. The microsurfaces sl...s2 in the first group Gl are parallel to each other within an angle of 0.03° and thus reflect light into essentially the same direction. Furthermore all microsurfaces sl...s2 in the first group Gl are oriented at a first orientation angle l=0° to the surface normal n of the projection pixel pp. The angle l is measured between the microsurfaces ' surface normals (small arrows) and the surface normal n of the projection pixel pp.

Furthermore, in the first group Gl, the distances dl...d2 and the areas of the microsurfaces sl...s2 are such that for all projection wavelengths λ and for all i=0...624, ieM0,

Sl(. - A,(. + l)- A) 0.25 4

is m

s\(o, X) 624 624

Here, Sl(xl,x2) is the sum of areas of all microsurfaces sl...s2 in the first group Gl having distances dj , j <≡M from said reference plane r with

dj mod λ being between xl and x2. A depth interval Δ = λ / 624.

In the second group G2, microsurface s3 is arranged at a distance d3 from the reference plane r and microsurface s4 is arranged at a distance d4 from the reference plane r. Distances d3...d4 are measured at a center of gravity of the respective microsurfaces s3...s4. Thus, different phase shifts are induced onto light which is reflected by these two microsurfaces s3 and s4. The microsurfaces s3...s4 in the second group G2 are parallel to each other within an angle of 0.03° and thus reflect light into essentially the same direction. Furthermore all microsurfaces s3...s4 in the second group G2 are oriented at a second orientation angle x2=10 ° to the surface normal n of the projection pixel pp (figure not drawn to scale) . The angle 2 is measured between the microsurfac- es' surface normals and the surface normal n of the projection pixel pp.

Furthermore, in the second group G2, the distances d3...d4 and the areas of the microsurfaces s3...s4 are such that for all projection wavelengths λ and for all i'=0...624, i'efJo

■72(/'·Δ',('+!)-A') 0.25 4

is m

S2{0,X) 624 624

Here, S2(xl',x2') is the sum of areas of all microsurfaces s3...s4 in the second group G2 having distances dj ' , j ' eM from said reference plane r with dj mod λ being between xl' and x2' . A depth interval Δ' λ / 624.

The area and depth distributions of the mi- crosurfaces sl...s2 in the first group Gl of the projection pixel pp lead to a distribution of cumulated microsurface areas vs depth intervals which is shown in fig. 3. It should be noted here, that for the purposes of the example in figure 3, not only microsurfaces si and s2 with distances dl and d2 were considered, but many more micro- surfaces s and depths d that are not referenced in figure 2 for clarity. As it can be seen from figure 3, the cumulated microsurface areas (i.e., the summed areas of all microsurfaces in one group in a specific depth interval Δ) are - within a band of 1/(4 · 624) and 4 / 624 - uniformly distributed over all depths. This leads to an improved reduction of subjective speckle contrast because a distribution "reflected intensity vs. induced phase shift" is similarly uniformly distributed. Thus, the viewing experience is improved.

In addition, a projection screen according to the invention can also comprise birefringent structures, in particular at least some of the microsurfaces (si, s2, s3, s4, ...) can be birefringent (not shown) . This helps to further reduce subjective speckles by - in addition to the induced phase shifts - introducing multiple polarization angles into reflected or transmitted light.

Fig. 4 shows a three dimensional plot of a measured surface profile of a projection pixel pp of a projection screen 10 according to the invention. Dimensions of the plot are 477 μηα by 637 μηα. This surface profile has been measured by an optical 3D Profilometer .

In contrast, fig. 5 shows a three dimensional plot of a measured surface profile of a projection pixel of a prior art projection screen (sandblasted screen) . Dimensions and measurement technique are the same as in figure .

From figures 4 and 5 it can be concluded, that a screen with finer and "steeper" microsurface arrangements, i.e., more microsurfaces per projection pixel, can lead to a reduced subjective speckle contrast and thus to an improved viewing experience, if the micro- structures and their distance-distributions from the reference plane exhibit the features as stated in the independent claims .

While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

Claims
1. A projection screen (10) for reducing subjective laser speckles in a laser projection system (100) ,
wherein the projection screen (10) is divida- ble into at least 100000 projection pixels (pp) of identical area (app) ,
wherein each of said projection pixels (pp) comprises a reference plane (r) with a surface normal (n) perpendicular on said reference plane (r) and a plurality of microsurfaces (si, s2, s3, s4, ...) distributed over said projection pixel (pp) ,
wherein said microsurfaces (si, s2, s3, s4, ...) comprise at least a first group (Gl) of microsurfaces (si, s2,...) in which first group (Gl)
* said microsurfaces (si, s2,...) are arranged at a plurality of distances (dl, d2,...) from said reference plane (r),
* said microsurfaces (si, s2,...) are parallel to each other within an angle of 0.03°, and
* said microsurfaces (si, s2,...) are within an angle of ±0.015° oriented at a first orientation angle ( l) to said surface normal (n) of said reference plane ( r) ,
wherein at least for one wavelength λ within 350 nm to 800 nm, said distances (dl, d2,...) are such that for all i=0...m-l, ieMn
£1(/ · Δ, (/ + 1)- Δ) 0.25 4
is m
S\(O, A) m m
with Sl(xl,x2) being the sum of areas of all microsurfaces (si, s2 , ...) in said first group (Gl) having distances dj , jeM from said reference plane (r) with dj mod λ being between xl and x2,
with m >= 49, and
with Δ = λ / m.
2. The projection screen (10) of claim 1 wherein said microsurfaces (si, s2, s3, s4, ...) comprise a second group (G2) of microsurfaces (s3, s4,...) in which second group (G2)
* said microsurfaces (s3, s4,...) are ar¬ ranged at a plurality of distances (d3, d4,...) from said reference plane (r) ,
* said microsurfaces (s3, s4,...) are parallel to each other within an angle of 0.03°, and
* said microsurfaces (s3, s4,...) are within an angle of ±0.015° oriented at a second orientation angle (a2) to said surface normal (n) of said reference plane (r), wherein said second orientation angle (a2) is different from said first orientation angle ( l) , wherein at least for said one wavelength λ within 350 nm to 800 nm, said distances (d3, d4,...) are such that for all i' =0...m' -1, i'eln
Figure imgf000022_0001
with S2(xl',x2') being the sum of areas of all microsurfaces (s3, s4,...) in said second group (G2) having distances dj ' , j ' eF from said reference plane (: with dj ' mod λ being between xl' and χ2' ,
with m' >= 49, and
with Δ' = λ / m' .
3. The projection screen (10) of claim
S O, ) - S2(O, X)\
wherein < 0.5 , in particular <0.1 ,
S] {0, )
at least for said first orientation angle <10° and for said second orientation angle Ia2j<10° .
4. The projection screen (10) of any of the preceding claims wherein m >= 225 and in particular wherein m >= 225 and m' >= 225.
5. The projection screen (10) of claim 4 wherein m >= 625 and in particular wherein m >= 625 and m' >= 625.
6. The projection screen (10) of any of the preceding claims wherein said projection screen (10) is made of at least one solid material, in particular only of said solid material or solid materials .
7. The projection screen (10) of any of the preceding claims wherein said microsurfaces (si, s2, s3, s4, ...) are formed by recesses, in particular by recesses in a or said solid material.
8. The projection screen (10) of any of the preceding claims wherein said microsurfaces (si, s2, s3, s4, ...) are adapted to reflect at least 50 %, in particular at least 80 %, of said wavelength λ, and in particular wherein said projection screen (10) comprises a reflective coating, in particular on said microsurfaces (si, s2 , s3, s4, ...) .
9. The projection screen (10) of any of the preceding claims wherein said microsurfaces (si, s2, s3, s4, ...) are arranged on a first surface (11) of said projection screen (10) .
10. A laser projection system (100) for reducing subjective laser speckles, the laser projection system (100) comprising
- a projection screen (10) of any of the preceding claims, - a laser projector (101), in particular a DLP laser projector, at a projection distance (IP) to said projection screen (10), and
- at least one viewing position (102) at a viewing distance (IV) to said projection screen (100) .
11. The laser projection system (100) of claim 10 further comprising a moving diffuser (103) for reducing objective laser speckles, said moving diffuser (103) being arranged in said laser projector (101) or between said laser projector (101) and said projection screen ( 10 ) .
12. The laser projection system (100) of any of the claims 10 or 11, wherein a or said first surface (11) of said projection screen (10) faces said laser projector (101) and said viewing position (102).
13. The laser projection system (100) of any of the claims 10 to 12 wherein said area (app) of said projection pixels (app) is smaller than or equal to a smallest resolvable area on said projection screen (10) when viewed from said viewing position (102) without visual aids.
14. A use of a projection screen (10) of any of the claims 1 to 9 for reducing subjective laser speckles in a laser projection system (100) of any of the claims 10 to 13.
15. A method for reducing subjective laser speckles in a laser projection system (100) of any of the claims 10 to 13, the method comprising steps of
- providing a projection screen (10) of any of the claims 1 to 9, and
- projecting at least partially coherent light, in particular from a laser projector (101), par- ticularly from a DLP laser projector, onto said projection screen ( 10 ) .
PCT/CH2013/000136 2013-07-25 2013-07-25 Projection screen for laser projection system WO2015010214A1 (en)

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1667144A2 (en) * 2001-07-09 2006-06-07 Matsushita Electric Industrial Co., Ltd. Model change device
US20060126022A1 (en) 2004-12-14 2006-06-15 Govorkov Sergei V Laser illuminated projection displays
US20090002818A1 (en) * 2005-03-08 2009-01-01 Kuraray Co., Ltd Rear Surface Projection Type Screen and Rear Surface Projection Type Display Device
WO2010078666A1 (en) 2009-01-09 2010-07-15 Optotune Ag Electroactive optical device
US7782800B2 (en) * 2006-12-22 2010-08-24 Texas Instruments Incorporated Discovery, detection, and management of daisy-chain system topology
US20100259818A1 (en) * 2009-04-10 2010-10-14 Seiko Epson Corporation Reflective screen, projection system, front projection television, and reflective screen manufacturing method

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7418202B2 (en) * 2005-08-04 2008-08-26 3M Innovative Properties Company Article having a birefringent surface and microstructured features having a variable pitch or angles for use as a blur filter
JP2008009119A (en) * 2006-06-29 2008-01-17 Toppan Printing Co Ltd Fresnel lens sheet and transmission type screen
JP2008033097A (en) * 2006-07-31 2008-02-14 Toppan Printing Co Ltd Fresnel lens sheet and transmission type screen

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1667144A2 (en) * 2001-07-09 2006-06-07 Matsushita Electric Industrial Co., Ltd. Model change device
US20060126022A1 (en) 2004-12-14 2006-06-15 Govorkov Sergei V Laser illuminated projection displays
US20090002818A1 (en) * 2005-03-08 2009-01-01 Kuraray Co., Ltd Rear Surface Projection Type Screen and Rear Surface Projection Type Display Device
US7782800B2 (en) * 2006-12-22 2010-08-24 Texas Instruments Incorporated Discovery, detection, and management of daisy-chain system topology
WO2010078666A1 (en) 2009-01-09 2010-07-15 Optotune Ag Electroactive optical device
US20100259818A1 (en) * 2009-04-10 2010-10-14 Seiko Epson Corporation Reflective screen, projection system, front projection television, and reflective screen manufacturing method

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
GOODMAN, J.W.: "Some fundamental properties of speckle", J. OPT. SOC. AM, vol. 66, 1976, pages 1145 - 1150

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