Apparatus and method for using orthogonally polarized light in projection cockpit displays

[0002] This application relates to co-pending application entitled “APPARATUS AND METHOD FOR INTEGRATING LIGHT FROM MULTIPLE LIGHT SOURCES IN PROJECTION COCKPIT DISPLAYS” filed on even date herewith by the same inventor and assigned to a common assignee.

[0003] The present invention generally relates to projection cockpit displays, and even more particularly relates to such displays having multiple tiled display surfaces.

[0004] In the past, designers of avionics displays have endeavored to provide projection displays with ever-increasing image quality, reliability, and economic efficiency. Projection displays based on liquid crystal display (LCD) technology generally use a single, linear polarization state for light incident upon the display element. Typically, this is accomplished by the use of a linearly polarizing filter, prism, or reflector disposed in front of the LCD device. Linearly polarizing filters, prisms, and reflectors are all well known in the art. These polarizing devices typically transmit one linear polarization state, while a second orthogonal polarization state is either reflected into a different path, or absorbed within the polarizing element. In either case, the state which is not transmitted becomes unusable by the display. This results in a significant (typically greater than 50 percent) attenuation of the light flux which is usable by the display.

[0005] In the past, display designers have proposed methods and devices to capture and reuse the otherwise discarded orthogonally polarized light and direct it into the display device, along with the polarized light originally produced from the incident light. These devices have been called “polarization recovery devices”, which are typically an array of prisms and half-wave retarders which divide the light into two polarization states, rotate one polarization state by 90 degrees, then recombine the now parallel polarization states. These “polarization recovery devices” have found limited acceptance in the LCD projector industry because they are quite expensive to fabricate, and they can also result in significant other performance deficiencies.

[0006] Consequently, there exists a need for improvement in illumination of tiled projection displays.

[0007] It is an object of the present invention to provide tiled projection displays having a superior image luminance characteristic.

[0008] It is a feature of the present invention to utilize multiple tiled viewing surfaces which receive illumination through the same front-end polarizer.

[0009] It is another feature of the present invention to utilize a polarizing prism or reflector as the front-end polarizer.

[0010] It is an advantage of the present invention to optically divide light from a single light source and use the divided light through multiple LCDs.

[0011] It is another feature of the present invention to include a half wave retarder to rotate the polarization state of light directed to an adjacent LCD.

[0012] It is another advantage of the present invention to increase commonality of component parts by having the same polarization state for all light incident on the LCDs in both optical channels in pairs of tiled projection displays.

[0013] The present invention is an apparatus and method for illuminating tiled projection displays designed to satisfy the aforementioned needs, provide the previously stated objects, include the above-listed features, and achieve the already articulated advantages. The present invention is carried out in an efficient manner that wastes less light flux than is typically done when an absorbing polarization filter is used to provide linearly polarized light.

[0014] Accordingly, the present invention is a tiled projection display system which utilizes a tiled multi-viewing surface display where multiple viewing segments are illuminated by light, which has been conditioned by the same polarizing device prior to its passing through separate liquid crystal display (LCD) devices.

[0015] The invention may be more fully understood by reading the following description of the preferred embodiments of the invention, in conjunction with the appended drawing wherein:

[0016] FIG. 1 is a simplified block diagram of a tiled projection display system of prior art which uses two polarization recovery devices.

[0017] FIG. 2 is a simplified block diagram of a system of the present invention, including a single input polarization beam splitter and two LCDs.

[0018] FIG. 3 is a simplified block diagram of a system of the present invention which includes two input polarization beam splitters where output from each is shared with two LCDs.

[0019] Now referring to the drawings wherein like numerals refer to like matter throughout, there is shown a system of the prior art, generally designated 100, having a tiled projection display system 100 having a first light source 110 and a second light source 120, which are well known in the art for illuminating projection LCDs.

[0020] The light from first light source 110 and second light source 120 is incident upon first polarization recovery device 112 and second polarization recovery device 122, respectively. These devices are arrays of miniature prism and half wave retarder combinations which separate the incident light into two linear polarization states, allow the first state to pass through and further process the second state so as to be converted by the half wave retarder into the light having the first polarization state and then be redirected so as to be combined with the light of the first polarization state which was originally passed. As stated above, these polarization recovery devices are expensive and often exhibit other undesirable performance qualities.

[0021] First liquid crystal cell 114 and second liquid crystal cell 124 are well known in the art, as are first exit polarizer 116, second exit polarizer 126, first projection optics 118, and second projection optics 128. These well-known components are used to provide a two-channel tiled display where the first channel 101 provides a display on the first viewing surface segment 119 of unified tiled displays viewing surface 130, and the second channel 102 provides a display on second viewing surface segment 129 of unified tiled displays viewing surface 130. The two channels are essentially identical except that the drive signals applied to first liquid crystal cell 114 and second liquid crystal cell 124 are different so as to produce different images.

[0022] The term “tiled display” is used herein to refer to a display system where two or more distinct display surfaces are located immediately adjacent to each other, and each display surface is controlled by its own display modulation device (e.g. LCD, etc.). However, each display surface is caused to display a segment of a larger image, such that a viewer sees one continuous image across the two rearwardly distinct display surfaces.

[0023] Now referring to FIG. 2, there is shown a display system of the present invention generally designated 200. The system 200 includes a first light source 110 which illuminates a first polarizing beam splitting prism 202. First polarizing beam splitting prism 202 is well known in the art as a MacNeille-type prism.

[0024] First polarizing beam splitting prism 202 performs the function of producing P polarized light 204 directed toward the first liquid crystal cell 114 and polarized light 206, which is directed away from first liquid crystal cell 114 and toward a mirror 208, which reflects this light into a half wave retarder 210. Half wave retarder 210 is well known in the art. The output of half wave retarder 210 is a P polarized light 212, which is converted from S polarized light.

[0025] The P polarized light converted from S polarized light 212 may be thought of as recaptured or recovered light in the sense that often the light which is orthogonal to light passed by a front-end polarizer, is lost and unusable. After the S polarized light 206 is passed through half wave retarder 210, then all light incident upon either the first liquid crystal cell 114 or second liquid crystal cell 124 is P polarized light. This allows for the remainder of each channel 220 and 230 to utilize identical components. Also shown is an avionics sensor/display driver 240, which could be any combination of known avionics equipment which provides signals which are representative of operational characteristics of an aircraft while in flight, such as attitude displays, navigation equipment, weather radar etc. Either avionics sensor/display driver 240 or another intermediate device provides manipulation of the aviation related signals to signals which are ready for use by an LCD device.

[0026] Another embodiment of the present invention is shown in FIG. 3, which is generally designated 300, which includes a dual lamp, dual channel, and dual light cross-over approach. First channel 320 is similar to that shown in FIG. 2 except that the first polarizing beam splitting prism 202 is adapted and configured so that the S polarized light 206A is directed to mirror 308, and subsequently into half wave retarder 312. The output of half wave retarder 312 is a P polarized light 206B, which is converted from S polarized light. The remainder of first channel 320 is similar to first channel 101 of FIG. 1 and first channel 220 of FIG. 2. Second channel 330 is similar to that shown in FIG. 2 except that the second polarizing beam splitting prism 302 is adapted and configured so that the S polarized light 304A is directed to mirror 308, and subsequently into half wave retarder 312. The output of half wave retarder 312 is a P polarized light 304B, which is converted from S polarized light. P polarized light 306 from prism 302 is directed by mirrors 308 toward the first liquid crystal cell 114.

[0027] In operation, the apparatus and method of the present invention could function as follows:

[0028] For the single lamp configuration of FIG. 2, light is emitted by first light source 110. It is conditioned by first polarizing beam splitting prism 202 so that P polarized light 204 is directed to first liquid crystal cell 114, and the S polarized light 206 is directed to the adjacent section of the tiled display where it is reflected by mirror 208 into half wave retarder 210, which converts the S polarized light into P polarized light converted from S polarized light 212. In this design, only one lamp is needed to illuminate two adjacent tiled display sections.

[0029] With respect to the dual lamp configuration of FIG. 3, light is provided by first light source 110 and second light source 120. This light is incident upon first polarizing beam splitting prism 202 and second polarizing beam splitting prism 302, respectively. The first channel 320 passes P polarized light and reflects the S polarization state over to the second channel 330. Second channel 330 passes the S polarization state and reflects the P polarized light across to the first channel 320. With the use of appropriately positioned mirrors 308 in each channel, polarized light which is not used by one adjacent channel is crosscoupled and used to increase the luminance of the other adjacent channel. If either source 110 or 120 fails, both channels remain active, but at a reduced luminance.

[0030] While the above description refers to avionics projection displays and to LCDs, this is done because it is believed that the benefits of the present invention will be readily apparent in such cases. It is not the intention of the present invention to be limited to avionics projection displays and LCDs, but it should extend to any type of display where the advantage of the present invention can be utilized.

[0031] It is thought that the method and apparatus of the present invention will be understood from the foregoing description and that it will be apparent that various changes may be made in the form, construct steps, and arrangement of the parts and steps thereof, without departing from the spirit and scope of the invention or sacrificing all of their material advantages. The form herein described is merely a preferred exemplary embodiment thereof.