# US 2017/0285453 A1 · Dmd projector with tir prism > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2017/0285453 A1 - Document ID: US20170285453A1 - Status: Published application - Kind: A1 - Application number: 15/507,349 - Filed: 2015-09-01 - Published: 2017-10-05 - Earliest claimed: 2014-09-04 - Assignees: BAE SYSTEMS plc - Applicants: BAE SYSTEMS plc - Inventors: PAUL STEWART MORANT; GRAHAM LAURENCE HOGG - Web page: https://patentgrep.com/patent/US20170285453A1 ## CPC - G03B 21/28: Reflectors in projection beam {(in illumination beam G03B21/2066)} - G02B 5/04: Prisms - G02B 27/0101: {characterised by optical features (G02B27/0172 takes precedence)} - G03B 21/008: {using micromirror devices} - G03B 21/2066: {Reflectors in illumination beam (in projection beam G03B21/28)} - H04N 9/3102: {using two-dimensional electronic spatial light modulators (micromechanical modulators as such G02B26/0833; liquid crystal modulators as such G02F1/13)} - G03B: APPARATUS 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 (optical parts of such apparatus G02B; photosensitive materials or processes for photographic purposes G03C; apparatus for processing exposed photographic materials G03D) - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION ## Abstract A projection apparatus comprising a prism assembly 7 including an input sub-prism 1 possessing a first interface surface and an output sub-prism 2 adjacent to the input sub-prism possessing a second interface surface. The second interface surface is spaced from the first interface surface immediately proximate to it and extends over it to receive display light 12 transmitted through the first interface surface. A panel 8 comprising a plurality of selectively adjustable reflecting elements is arranged to receive from the input sub-prism an illumination light totally internally reflected from the first interface surface and selectively to reflect received illumination light back through the input sub-prism for transmission through the first interface surface for receipt as display light 13 by the output prism at said second interface surface. ## Claims ### Claim 1 A projection apparatus comprising: a prism assembly including an input sub-prism possessing a first interface surface and an output sub-prism adjacent to the input sub-prism possessing a second interface surface spaced apart from the first interface surface in immediate proximity thereto so as to extend thereover to receive display light transmitted through the first interface surface; and a panel comprising a plurality of selectively adjustable reflecting elements arranged to receive from the input sub-prism an illumination light totally internally reflected from the first interface surface and selectively to reflect received illumination light back through the input sub-prism for transmission through the first interface surface for receipt as display light by the output sub-prism at said second interface surface; wherein the input sub-prism possesses a base surface that is substantially congruent to a matching base surface of the output sub-prism. ### Claim 2 (depends on 1) The projection apparatus according to claim 1 in which the input sub-prism has a substantially plane panel-facing surface relative to which the first surface is inclined and which faces in a direction towards the panel for receiving said reflected illumination light therefrom, and the output sub-prism has a substantially plane output surface for outputting said display light from the prism assembly wherein the output surface is inclined relative to second surface and is substantially parallel to the panel-facing surface thereby substantially to equalize the optical paths of light passing from the panel-facing surface to the output surface through different respective parts of the first and second interface surfaces. ### Claim 3 (depends on 1) The projection apparatus according to claim 1 in which a non-base surface of the input sub-prism defines an input surface for receiving said illumination light into the input sub-prism from an illumination light source, wherein the input surface is inclined relative to the first interface surface such that illumination light incident at the input surface at an incidence angle within a range of incidence angles consistent with an acceptance cone angle of the panel is subsequently incident at the first interface surface at an incidence angle within a range of incidence angles suitable to cause total internal reflection thereat towards the panel. ### Claim 4 (depends on 1) The projection apparatus according to claim 1 in which the panel is arranged selectively to reflect received illumination light back through the input sub-prism in a direction relative to the prism assembly which substantially minimises the angular deviation of light along its optical path through the prism assembly. ### Claim 5 (depends on 1) The projection apparatus according to claim 1 in which the panel is arranged to reflect received illumination light in any selected one of two different input directions relative to the prism assembly such that display light is consequently output from the prism assembly in a respective one of two different output directions relative to the prism assembly thereby selectively to spatially separate light to permit light associated with a selected use to be assigned to a selected said output direction. ### Claim 6 (depends on 5) The projection apparatus according to claim 5 including an optical monitor arranged for receiving light assigned to one of said two different output directions and to generate a monitoring signal according to said received light, for use in monitoring the operation of the panel. ### Claim 7 (depends on 1) The projection apparatus according to claim 1 in which the first interface surface is the largest non-base surface of the input sub-prism. ### Claim 8 (depends on 1) The projection apparatus according to claim 1 in which the output surface is the largest non-base surface of the output sub-prism. ### Claim 9 The projection apparatus according to claim in which the substantially congruent base surfaces of at least one of the input sub-prism and the output sub-prism are substantially parallel. ### Claim 10 (depends on 1) The projection apparatus according to claim 1 in which the plane of each non-base surface of each of the input sub-prism and the output sub-prism is substantially perpendicular to the plane of each substantially congruent surface thereof. ### Claim 11 (depends on 1) The projection apparatus according to claim 1 in which each of the input sub-prism and the output sub-prism is a triangular prism having two triangular substantially congruent base surfaces separated by three contiguous sides defining the non-base surfaces of the respective sub-prism. ### Claim 12 (depends on 1) The projection apparatus according to claim 1 in which the input sub-prism is substantially identical in shape and size to the output sub-prism. ### Claim 13 (depends on 1) A head-up display comprising the projection apparatus according to claim 1. ### Claim 14 A method of projection comprising: providing a prism assembly including an input sub-prism possessing a first interface surface and an output sub-prism adjacent to the input sub-prism possessing a second interface surface spaced apart from the first interface surface in immediate proximity thereto so as to extend thereover to receive display light transmitted through the first interface surface; providing a panel comprising a plurality of selectively adjustable reflecting elements; receiving at the panel an illumination light from the input sub-prism by total internal reflection from the first interface surface and selectively reflecting the received illumination light back through the input sub-prism and through the first interface surface to the second interface surface; and outputting the reflected illumination received light from the second sub-prism as display light; wherein the input sub-prism possesses a base surface that is substantially congruent to a matching base surface of the output sub-prism. ### Claim 15 (depends on 14) The method according to claim 14, further comprising controlling said panel to selectively reflect said received illumination light back through the input sub-prism in a direction relative to the prism assembly which substantially minimises the angular deviation of light along its optical path through the prism assembly. ### Claim 16 (depends on 14) The method according to claim 14, further comprising reflecting received illumination light at said panel in any selected one of two different input directions relative to the prism assembly such that display light is consequently output from the prism assembly in a respective one of two different output directions relative to the prism assembly thereby selectively to spatially separate light to permit light associated with a selected use to be assigned to a selected said output direction. ### Claim 17 (canceled) ### Claim 18 (canceled) ### Claim 19 A projection apparatus comprising: a prism assembly including an input sub-prism possessing a first interface surface and an output sub-prism adjacent to the input sub-prism possessing a second interface surface spaced apart from the first interface surface in immediate proximity thereto so as to extend thereover to receive display light transmitted through the first interface surface; and a panel comprising a plurality of selectively adjustable reflecting elements arranged to receive from the input sub-prism an illumination light totally internally reflected from the first interface surface and selectively to reflect received illumination light back through the input sub-prism for transmission through the first interface surface for receipt as display light by the output sub-prism at said second interface surface; wherein the input sub-prism possesses a base surface that is substantially congruent to a matching base surface of the output sub-prism, and the first interface surface is the largest non-base surface of the input sub-prism, and the output surface is the largest non-base surface of the output sub-prism; wherein the substantially congruent base surfaces of at least one of the input sub-prism and the output sub-prism are substantially parallel, and the plane of each non-base surface of each of the input sub-prism and the output sub-prism is substantially perpendicular to the plane of each substantially congruent surface thereof; and wherein each of the input sub-prism and the output sub-prism is a triangular prism having two triangular substantially congruent base surfaces separated by three contiguous sides defining the non-base surfaces of the respective sub-prism. ### Claim 20 (depends on 19) The projection apparatus according to claim 19 in which the input sub-prism has a substantially plane panel-facing surface relative to which the first surface is inclined and which faces in a direction towards the panel for receiving said reflected illumination light therefrom, and the output sub-prism has a substantially plane output surface for outputting said display light from the prism assembly wherein the output surface is inclined relative to second surface and is substantially parallel to the panel-facing surface thereby substantially to equalize the optical paths of light passing from the panel-facing surface to the output surface through different respective parts of the first and second interface surfaces. ### Claim 21 (depends on 19) The projection apparatus according to claim 19 in which a non-base surface of the input sub-prism defines an input surface for receiving said illumination light into the input sub-prism from an illumination light source, wherein the input surface is inclined relative to the first interface surface such that illumination light incident at the input surface at an incidence angle within a range of incidence angles consistent with an acceptance cone angle of the panel is subsequently incident at the first interface surface at an incidence angle within a range of incidence angles suitable to cause total internal reflection thereat towards the panel. ### Claim 22 (depends on 19) A head-up display comprising the projection apparatus according to claim 19.