Polarization conversion systems for stereoscopic projection

Technical field [0002] The present disclosure relates to a projection system for displaying images to be viewed in three dimensions, and more specifically to a polarization conversion system that uses polarized light to encode stereoscopic images.

Background Art [0003] Three-dimensional (3D) images can be synthesized using polarization control behind the projector and polarization controlling eyeglasses (see, e.g., US Patent No. 4,792,850 to Lipton).

[0004] The conventional implementation of polarization control in the projector is shown in Figure 1. In this implementation, the lens 10 exits almost parallel rays that appear to come from the pupil 12 inside the lens 10 and converge to form points on the screen 14. Beams of rays A, B and C in Fig. 1 are beams forming points at the bottom, middle and top of the screen 14, respectively. The light 20 coming out of the projection lens is randomly polarized as shown in Fig. 1 as light with polarization s (perpendicular to the plane of incidence) and with polarization p (parallel to the plane of incidence) [light with polarization s is conventionally presented in the form of circles; p ~ polarized light in the form of an arrow with a tip at both ends]. The light 20 passes through the linear polarizer 22, obtaining one polarization state after the polarizer 22. The perpendicular polarization state is absorbed (or reflected) and the light beam behind the polarizer 22 is usually less than half the original stream, resulting in a darker final image. The polarization switch 30 is synchronized with the image frame, and the polarization state 24 coming out of the polarization switch is changed, giving the screen images with alternating perpendicular polarization. Selective polarization glasses let one polarized image pass through to the left eye, and perpendicular polarized images pass through to the right eye. By showing each eye a different image, you can synthesize 3D images.

[0005] This conventional system is used in cinemas. However, the conventional system requires that more than 50% of the light is absorbed by the polarizer and the resulting image is more than 50% darker than the image in a typical two-dimensional (2D) cinema. A darker image may limit the size of the cinema used for 3D projection and / or cause less desirable to the audience.

[0006] Document US 6,206,532 discloses a projector in which non-polarized light from a light source is separated by a beam splitter into two polarizations. The polarization of one of the beams is changed, the beams are combined and then delivered to a spatial light modulator to create an image.

[0007] Document US 4,792,850 discloses placing a push-pull modulator in the image path to encode the image for stereoscopic viewing.

Summary of the Invention [0008] According to a first aspect of the invention, a polarization conversion system according to claim 1 is provided.

[0009] According to a second aspect of the invention there is provided a method according to claim 12.

[0010] Various embodiments of polarization conversion systems receiving light from the projector are described below, which systems solve the problems mentioned earlier. Polarization conversion systems display a brighter image on the screen in cinema applications using polarized light for three-dimensional projection.

[0011] In one embodiment, the polarization conversion system comprises a polarization beam splitter (PBS), a polarization rotator, and a polarization switch. The PBS divider is adapted to receive beams of randomly polarized light from a projector lens and to direct the first beams of light in the first state of polarization (SP) along the first light path. The PBS divider is also adapted to direct the second light beams in the second SP along the second light path. The polarization rotator is placed on the second light path and is adapted to change the second SP into the first SP. The polarization switch is adapted to receive the first and second light beams from the first and second light paths respectively, and to selectively change the polarization states of the first and second light beams to one of the following: first output SP and second output SP. The first beams of light are transmitted towards the screen. A reflecting element may be arranged in the second light path to direct the second light beams towards the screen so that the first and second light beams substantially overlap, creating a brighter image on the screen.

[0012] Other aspects and embodiments are described in detail below.

Description of the figures [0013]

Fig. 1 is a schematic diagram of a conventional polarization switch for stereoscopic projection;

Fig. 2 is a schematic diagram of a polarization conversion system (PCS) for cinema projection according to the present disclosure;

Fig. 3 is a schematic diagram of another embodiment of PCS for cinema projection in accordance with the present disclosure;

Fig. 4 is a schematic diagram of another embodiment of PCS for cinema projection comprising a telephoto lens by optical path with field of view centered on the optical axis in accordance with the present disclosure;

Fig. 5 is a schematic diagram of another embodiment of PCS for cinema projection comprising a telephoto lens by optical path with a field of view not centered on the optical axis according to the present disclosure;

Fig. 6 is a schematic diagram of another embodiment of PCS for cinema projection having the purpose of providing a circularly polarized output signal comprising a telephoto lens by optical path with a field of view centered on the optical axis according to the present disclosure;

Fig. 7 is a schematic diagram of another embodiment of PCS for cinema projection having the purpose of providing a linearly polarized output signal comprising a telephoto lens by optical path with a field of view centered on the optical axis according to the present disclosure;

Fig. 8 is a schematic diagram of another embodiment of PCS for cinema projection in accordance with the present disclosure.

Description of Embodiments [0014] Various embodiments of polarization conversion systems receiving light from the projector are described below. Polarization conversion systems display a brighter image on the screen in cinema applications using polarized light for three-dimensional projection.

[0015] Fig. 2 is a schematic diagram of a polarization conversion system (PCS) 100 for cinema projection. An embodiment of a polarization conversion system 100 includes a polarizing beam splitter (PBS) 112, a polarization rotator 114 (e.g., a half-plate), a reflecting element 116 (e.g., a refractive mirror) and a polarization switch 120, configured as shown. The polarization conversion system 100 can accept images from a conventional projector with a projection lens 122. In operation, the beams of rays A, B and C exit randomly polarized from the lens 122 and are projected towards the screen 130 to form an image. In this embodiment, the PBS 112 divider is placed in place of the polarizer 22 shown in Figure 1. The PBS 112 divider transmits light with polarization p 124 and reflects light with polarization s 126. The polarized light p 124 passes through the polarization switch (beams A, B and C) and is rotated by the polarization switch in alternating cages, just like the beams A, B and C in Fig. 1.

[0017] The light with polarization s 126, reflected by PBS 112, passes through a polarization rotator 114 (e.g. a semi-phono plate preferably achromatic in some embodiments) and is rotated to the form of light with polarization p 128. The new light with polarization p 128 passes to refractive mirror 116. Refractive mirror 116 reflects new light with polarization p 128 and sends it to polarization switch 120. Polarization switch 120, operating on beam of polarization p A¹, B 'and C', rotates the polarization of ray beams in alternating cages synchronously with the rotation of the beams A, B and C. Beam positions¹, B¹ and C 'on the screen can be adjusted (e.g., by adjusting the tilt of the refractive mirror 116) so that they closely or exactly coincide with the positions on the screen of the beams A, B and C. Almost all randomly polarized light 106 from the projection lens 122 is displayed on screen 130 in one polarization state, so the resulting image of the system shown in Fig. 2 is approximately twice as bright as the image on the screen of the system shown in Fig. 1.

[0018] In this embodiment, the PBS divider 112 is shown in Figure 2 as a plate. However, different types of PBS dividers can be used. For example, PBS can be built using glass wire mesh (e.g. Moxtek Proflux polarizer from Orem, Utah), polarization recycling film (e.g. Double Brightness Enhancing Film from 3M from St Paui (Minnesota), film polarization recycling on glass (for flatness) or multi-layer dielectric on glass. Divider PBS 112, shown in fig. 2, can be implemented alternatively in the form of a glass cube (with wire mesh foil "polarization recycling" or dielectric layers along the diagonal) to reduce astigmatism in the final image, associated with the passage of light through the inclined plate. Alternatively, the inclined PBS 112 plate shown in Fig. 2, can be made in various embodiments using spherical, aspherical, cylindrical or toroidal surfaces to reduce astigmatism in the final image on screen 130. To reduce astigmatism in the final image, non-centered spherical, aspherical, cylindrical surfaces can be used or toroidal on the plate and / or additional non-centered spherical, aspherical, cylindrical or toroidal elements on the optical path behind the plate. See, e.g., "Simple method of correcting the aberrations of a beamsplitter in converging iight", V. Doherty and D. Shafer, Proc. SPIE, vol. 0237, pp. 195-200, 1980. It should also be noted that it is possible to insert into the system a second flat plate behind the inclined PBS 112 plate and adjust its slope to reduce or correct astigmatism in the final image.

[0019] In some embodiments, the polarization rotator 114 shown in Figure 2 may be an achromatic half-wafer plate. The half-wave plate can be made of polymeric membranes (e.g., the Achromatic Retardation Plate from ColorLink, Inc., Boulder, Colorado), quartz plates or a static liquid crystal device, optionally coated with a pattern to account for geometric change in polarization. The half-wave plate 114 can be positioned as shown in Fig. 2 or, in other embodiments, it may be placed between the refractive mirror 116 and the polarization switch 120 so that it intersects the beams A ', B' and C '. This implementation may be desirable because the beams A ', B¹ and C 'bounce off the refractive mirror 116 in the polarized state s, and the mirrors more often give greater reflection in the case of polarized light s. However, in this embodiment half-wave plate 114 should be placed in such a way that the beams A' and C do not overlap on the plate. Although in most embodiments described herein, the polarization rotator 114 is located in the second light path, alternatively it can be placed in the first light path and the polarization conversion system will operate in a similar manner in accordance with the principles of the present disclosure.

[0020] In some embodiments, the refractive mirror 116 can be replaced with a PBS element (e.g., wire mesh plate). In this case, a cleaner polarization can be maintained with the PBS element.

[0021] Polarity switch 120 may be the switch indicated in US Patent No. 4,792,850; any switch indicated in US Patent Application Publication No. 11 / 424,087 titled "Achromatic Polarization Switches", filed June 14, 2006; or any other polarization switch known in the art that selectively changes the input polarization state. In some embodiments, the polarity switch 120 may be split (to increase device yield). If the polarity switch 120 is separated, it is desirable for both devices to be positioned so that the A beams¹ and C in Fig. 2 did not overlap. Separation of the polarization switch 120 allows one of the parts to be transferred between the half-wave plate 114 and refractive mirror 116 in the optical path A ', B', C '. Placing polarization switch 120 here may require better polarization properties by refraction mirror 116 (e.g., Oerlikon Silflex coatings from Golden, Colorado), as this may be the last element in the optical path A ', B', C 'in front of the screen . [0022] In the polarization conversion system 100 of Fig. 2, the optical path of the A 'ray beam is longer than the A' ray beam (similar for B'-B and C'-C), which leads to a difference in the degree of magnification between the image produced by A ', B', C¹ and the image produced by A, B, C. This magnification difference may be unacceptable for audiences, especially for wide and near projection systems. Some techniques for correcting this magnification difference may include (1) providing a reflexive curved surface 116 on the refractive mirror 116 to compensate for the difference in magnification; this solution is achromatic, which is beneficial; (2) adding to the refractive mirror 116 Fresneia or diffraction surfaces with focusing ability to compensate for the difference in magnification (which may be achromatic or not); (3) adding a refraction element (lens) between refraction mirror 116 and polarization switch 120 or between divider PBS 112 and refraction mirror 116; a single lens will most likely not be achromatic, but the lens doublet may be achromatic; (4) adding a telephoto lens as shown in Figures 3 and 4; or (5) a combination of at least two of the above four techniques.

[0023] Although, as described, light with polarization p is transmitted towards polarization switch 120, while light with polarization s is directed towards wafer 114, it should be obvious to those skilled in the art that an alternative configuration in which light with polarization s can be used transmitted in the direction of polarization switch 120, while the light with polarization p is directed towards half-board 114.

[0024] Fig. 3 is a schematic diagram of another embodiment of PCS for cinema projection 200. The elements of PCS 200 may be of a similar type and may function similarly to those shown in relation to PCS 100 of Fig. 2. For example, elements 2xx are similar to elements 1xx, where xx is the last two digits of the numbers of the corresponding elements. In this embodiment, the beams of rays A, B and C can be directed through an additional set of refractive mirrors 232, 234 adapted to equalize the length of the optical paths of the beams A and A¹, B and B ', C and C' as shown in Fig. 3. [Note: the beams A 'and C' are present, only not shown. They follow a similar path as the beams A ', B', C 'shown in Fig. 2], Naieży noted that although PBS and refractive mirrors are shown here oriented at an angle of 45 degrees relative to the optical axis, PBS 212 and refractive mirrors 216, 232 , 236 may have different orientations as per these instructions. In addition, glass can be placed in the optical path A ', B' and C '(e.g. by replacing the refractive mirror 216 with a rectangular prism and / or using PBS in the form of a glass cube instead of a PBS plate) to reduce or eliminate the difference in optical paths between the beams A, B, C and A ', B', C '.

[0025] With reference to Figs. 2 and 3, for viewing comfort the image from the beam A¹, B 'and C' should generally overlap the image of the A, B and C bundles (although perfect overlap is not absolutely necessary). Techniques for adjusting the position of one image relative to another include: (1) the use of thumbscrews or similar mechanical techniques to tilt the refractive mirror, PBS plates or PBS cubes; (2) mechanical detachment from the centering state of the lens or focusing element (e.g. curved mirror); (3) using a feedback system to automatically adjust the image position using one of the image adjustment techniques mentioned above; or (4) a combination of at least two of the above three techniques.

[0026] Optical transmission and scattered light control on optically permeable elements can be optimized by providing them with an anti-reflection coating to maintain high transmission and low reflection. Reflections from the permeable elements can be a source of scattered light in the system that worsens the contrast and / or causes disturbing artifacts in the final image. In some embodiments, additional absorption polarizers may be placed behind the half-wave plate 114 on the A ', B', 0 'path and / or after the PBS 112 divider to control polarization leaks and improve the contrast of the final image.

[0027] Fig. 4 is a schematic diagram of another PCS embodiment for cinema projection 300. The PCS elements 300 may be of a similar type and may function similarly to those shown in relation to PCS 100 in Fig. 2. For example, elements 3xx are similar to elements 1xx, where xx is the last two digits of the numbers of the corresponding elements.

[0028] In this embodiment, a telephoto lens 340 can be placed in the optical path in which the light passes through PBS 312. A telephoto lens 340 is placed here along the optical path, with the field of view centered on the optical axis. Typically, a 340 telephoto lens allows you to control the properties of zoom, distortion and imaging using two elements so that the two images overlap relatively close, i.e. within 1-4 pixels apart, maintaining pixel fraction row sizes and pixel row side color. Alternatively, an inverted telephoto lens (not shown) can be placed in the optical path in which the light is reflected from the PBS 312 divider (positioned between polarization switch 320 and refractive mirror 316 or after refractive mirror 316). When using a telephoto or inverted telephoto lens to control zoom on one optical path, the radial and trapezoidal distortion of the final image can be adjusted by transverse displacement of individual elements or pairs of elements relative to the optical axis.

[0029] Fig. 5 is a schematic diagram of another embodiment of PCS for cinema projection 400. The components of PCS 400 may be of a similar type and may function similarly to those shown in relation to PCS 100 of Fig. 2. For example, elements 4xx are similar to elements 1xx, where xx is the last two digits of the numbers of the corresponding elements. In this embodiment, a telephoto lens 440 can be placed in the optical path in which the light passes through the PBS 412 divider. The telephoto lens 440 is placed here on the optical path with the field of view detached from the centering position relative to the optical axis. As described above, the radial and trapezoidal distortion of the final image can be adjusted by transverse displacement of individual elements or pairs of elements 440 relative to the optical axis.

[0030] Figure 6 is a schematic diagram of another PCS embodiment for cinema projection 500 that provides a circularly polarized output signal. The PCS 500 includes a 540 telephoto lens on the optical path with a field of view centered on the optical axis. In this case, each polarization switch 520 is a circular polarization (or Z-Screen) switch, e.g., as described in US Patent Application No. 4,792,850. Cleaning polarizers 542, 544 on each road are optional, depending on the level of contrast required for the system. The inclusion of one or both cleaning polarizers can, for example, increase the contrast in the system.

[0031] Fig. 7 is a schematic diagram of another PCS embodiment for cinema projection 600 that provides a linearly polarized output signal. Each polarization switch 620 here is an achromatic linear polarization switch as described in the United States patent application

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No. 11 / 424,087 under the title "Achromatic Połarization Switches", filed June 14, 2006; also produced by ColorLink, Inc. from Boulder, Colorado. As in the example of Fig. 6, cleaning polarizers 642, 644 on each path are optional, depending on the level of contrast required for the system. The inclusion of one or both cleaning polarizers can, for example, increase the contrast in the system. In addition, a 648 achromatic rotator is also optional, depending on the achromatic properties of the 620 polarity switch.

[0032] Fig. 8 is a schematic diagram of another embodiment of PCS for cinema projection 700, showing an alternative configuration in which polarizers 746, achromatic rotator 714, and polarization switch 720 are placed behind other optical elements. PCS 700 components may be of a similar type and may function similarly to those illustrated in relation to PCS 100 in Fig. 2. For example, elements 7xx are similar to elements 1xx, where xx is the last two digits of the corresponding element numbers.

[0033] During operation, the light comes out of the projection lens 722 towards the PBS 712 divider. The light with polarization p passes through PBS 712 towards the telephoto lens 740, then towards the polarization switch 720. An optional cleaning polarizer between the telephoto lens 740 and the 720 switch can be located 746 to further improve contrast. Light with polarization s, reflected by the PBS 712 divider, is directed to the refractive mirror 716, where it is reflected in the direction of the achromatic rotator 714, which converts light with polarization sw, light with polarization p, which then passes through the optional cleaning polarizer 746. polarization p from the achromatic rotator 714 passes through the polarization switch 720. In this configuration, the polarized light, reflected by PBS 712, is efficiently reflected with polarization maintained by the refractive mirror 716. This satisfies all requirements for maintaining polarization by the refraction path and maximizes brightness. An achromatic 90 ° 714 rotator (probably based on a retarder stack) can be used to convert light from the refractive mirror into a perpendicular state. In order to eliminate p-polar reflection from the PBS 712 divider, a cleaning polarizer 746 will probably be desirable. It will preferably be located behind the achromatic rotator 714, thereby reducing polarization conversion efficiency as a factor affecting the level of contrast in the system.

[0034] PCS 700 provides a highly contrasting screen image. In this embodiment, the final screen image has a center located on the optical axis of the projection lens. In some other embodiments, the final screen image may be eccentric with respect to the optical axis - for example, half of the screen height may be below the optical axis of the projection lens. In such embodiments, the polarizing beam splitter 712 can be displaced to capture full illumination from the projection lens 722, and the refractive mirror 716 can be tilted to correctly superimpose two screen images. The polarity switch 720 in this embodiment has been split into two elements (one for each route) to increase production yield; however, as described earlier, it may alternatively be a single module.

[0035] The term "cinema projection" as used herein refers to the projection of images using front and / or rear projection techniques, and includes, but is not limited to, use in cinemas, home theaters, simulators, instrumentation, head-up displays, and other environments. projection screens in which stereoscopic images are displayed.

[0036] Although several embodiments and variations of polarization conversion systems for stereoscopic projection have been described above, it should be understood that they are provided only as examples and not as limitations. Therefore, the scope and scope of the invention (s) should not be limited by any of the above embodiments, but should be defined only by the claims and their equivalents arising from the present disclosure. Furthermore, the above advantages and features are provided in the described embodiments, but they do not limit the application of such resulting claims to processes and structures realizing any or all of the above advantages.

[0037] Furthermore, the section headings provided herein are provided for reasons of consistency. These headers will not limit or characterize the invention (s) set forth in the claims, which may result from the present disclosure. In particular and for example, although the heading refers to "Technical field", such reservations should not be limited to the language selected for the description under that heading of the so-called technical field. Furthermore, the description of the technology in the "Prior Art" section cannot be considered an admission that this technology is prior art for any invention or any inventions of this disclosure. Also, the "Essence of the Invention" cannot be considered as a characteristic of the invention (s) indicated or indicated in the resulting claims. Furthermore, no reference to "invention" made in the present disclosure in the singular may be used as an argument that there is only one novelty element in this disclosure. In accordance with the restrictions imposed by the many claims of the present disclosure, many inventions can be made, and such claims define accordingly the inventions and their equivalents that are hereby protected. In all cases, the scope of such claims should be determined on the basis of their merits in the light of this disclosure, with the section headings in this document not introducing any restrictions.