# US 4,392,722 A · Prism polarizer > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,392,722 A - Document ID: US4392722A - Status: Granted - Kind: A - Application number: 06/261,877 - Filed: 1981-05-08 - Granted: 1983-07-12 - Earliest claimed: 1980-05-09 - Assignees: Fujitsu Limited - Inventors: Masataka Shirasaki - Web page: https://patentgrep.com/patent/US4392722A ## CPC - G02B 5/04: Prisms - G02B 5/3058: {comprising electrically conductive elements, e.g. wire grids, conductive particles} - G02B 5/3066: {involving the reflection of light at a particular angle of incidence, e.g. Brewster's angle} - G02B 27/283: {used for beam splitting or combining} - G02F 1/093: {used as non-reciprocal devices, e.g. optical isolators, circulators (G02F1/0955 takes precedence)} - G02F 2203/06: Polarisation independent - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS - G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS ## Abstract A prism polarizer comprising a pair of anisotropic crystal prisms faced to each other. Each of the crystal prisms comprises a crystal which has an optical characteristic such that the difference between the square of the refractive index for extraordinary rays and the square of the refractive index for ordinary rays is larger than 1. The angle of incidence of a beam upon the facing plane of the pair of prisms is equal to the Brewster angle for the refractive index for P-polarization rays. P-polarization rays are transmitted through the facing plane. S-polarization rays are totally reflected at the facing plane. Thereby, the incident beam is separated into two polarized beams. Each of the pair of prisms is formed so that each polarized beam is totally reflected within each prism and that the separated outlet beams from the pair of prisms are parallel with each other. ## Claims ### Claim 1 A prism polarizer for separating an incident light beam having P-polarization and S-polarization light rays, comprising: a pair of anisotropic crystal prisms, wherein each prism has a boundary surface, the boundary surface of a first prism of said pair faced to the boundary surface of the second prism, thus defining a facing plane; wherein each comprises a crystal which has an optical axis and an optical characteristic such that the difference between the square of the refractive index for light rays having a polarization plane parallel to the optical axis, and the square of the refractive index for light rays having a polarization plane perpendicular to the optical axis, is larger than 1; the angle of incidence of a beam, exiting one of said prisms, upon the boundary surface of said beam-exiting prism being equal to the Brewster angle for the refractive index for the P-polarization rays, so that the P-polarization rays are transmitted through said boundary surface of said beam-exiting prism, while the S-polarization rays are totally reflected at said boundary surface of said beam-exiting prism, thereby said incident beam being separated into two polarized beams, and wherein each prism is formed so that each of said two separated polarized beams is totally reflected within each respective prism and the separated polarized beams exit said respective prisms parallel with each other. ### Claim 2 (depends on 1) A prism polarizer according to claim 1, wherein each prism has an inlet end surface inclined with respect to the plane perpendicular to an inlet beam and each prism has an outlet end surface inclined with respect to the plane perpendicular to an outlet beam. ### Claim 3 (depends on 1) A prism polarizer according to claim 1, wherein each prism is made of titanium dioxide. ### Claim 4 (depends on 1) A prism polarizer according to claim 1, wherein a layer of air is formed between said boundary surfaces defining said facing plane of said pair of prisms. ### Claim 5 (depends on 1) A prism polarizer according to claim 1, wherein the S-polarized beam reflected at said boundary surface is again totally reflected within the prism so that this S-polarized beam leaves the prism parallel with said facing plane. ### Claim 6 (depends on 5) A prism polarizer according to claim 5, wherein at least one prism of said pair of prisms is of quadrilateral sectional shape, and formed so that an inlet beam entering said at least one prism is directly transmitted to said boundary surface and is incident on said boundary surface at the Brewster angle, without being reflected within the prism. ### Claim 7 (depends on 5) A prism polarizer according to claim 5, wherein at least one prism of said pair of prisms is of quadrilateral sectional shape, and formed so that an inlet beam entering said at least one prism is totally reflected once within the prism before said inlet beam is incident upon said boundary surface at the Brewster angle. ### Claim 8 (depends on 5) A prism polarizer according to claim 5, wherein at least one prism of said pair of prisms is of quadrilateral sectional shape, and formed so that an inlet beam entering said at least one prism is totally reflected two or more times within the prism before said inlet beam is incident upon said boundary surface at the Brewster angle. ### Claim 9 An optical circulator comprising: two prism polarizers for separating incident light beams having P-polarization and S-polarization light rays, each prism polarizer including a pair of anisotropic crystal prisms, wherein each prism has a boundary surface, the boundary surface of a first prism of said pair faced to the boundary surface of the second prism, thus defining a facing plane; wherein each prism comprises a crystal which has an optical axis such that the difference between the square of the refractive index for light rays having a polarization plane parallel to the optical axis, and the square of the refractive index for light rays having a polarization plane perpendicular to the optical axis, is larger than 1; the angle of incidence of a beam, exiting one of said prisms, upon the boundary surface of said beam-exiting prism being equal to the Brewster angle for the refractive index for the P-polarization rays, so that the P-polarization rays are transmitted through said boundary surface of said beam-exiting prism, while the S-polarization rays are totally reflected at said boundary surface of said beam-exiting prism, thereby said incident beam being separated into two polarized beams, and wherein each prism of said pair of prisms has an inlet end surface and an outlet end surface, and each of said two separated polarized beams is totally reflected within each respective prism and the separated polarized beams exit said respective prisms parallel with each other; the outlet end surfaces of said two polarizers are faced to each other; a rotatory polarization device disposed between the two polarizers and arranged so that said device rotates the polarization plane of a polarized beam from one direction by 90.degree., while said device does not rotate the polarization plane of a polarized beam from the reverse direction; and wherein said inlet end surfaces of said prisms are used as an inlet and an outlet of said optical circulator. ### Claim 10 (depends on 9) An optical circulator according to claim 9, wherein each prism has an inlet end surface inclined with respect to the plane perpendicular to an inlet beam entering said at least one prism and each prism has an outlet end surface inclined with respect to the plane perpendicular to an outlet beam entering said at least one prism. ### Claim 11 (depends on 9) An optical circulator according to claim 9, wherein each prism of said pair of prisms is made of titanium dioxide. ### Claim 12 (depends on 9) An optical circulator according to claim 9, wherein a layer of air is formed between said boundary surfaces defining said facing plane of said pair of prisms. ### Claim 13 (depends on 9) An optical circulator according to claim 9, wherein the S-polarized beam reflected at said boundary surface is again totally reflected within the prism so that this S-polarized beam leaves the prism parallel with said facing plane. ### Claim 14 (depends on 13) An optical circulator according to claim 13, wherein at least one prism of said pair of prisms is of quadrilateral sectional shape, and formed so that an inlet beam entering said at least one prism is directly transmitted to said boundary surface and is incident on said boundary surface at the Brewster angle, without being reflected within the prism. ### Claim 15 (depends on 13) An optical circulator according to claim 13, wherein at least one prism of said pair of prisms is of quadrilateral sectional shape, and formed so that an inlet beam entering said at least one prism is totally reflected once within the prism before said inlet beam is incident upon said boundary surface at the Brewster angle. ### Claim 16 (depends on 13) An optical circulator according to claim 13, wherein at least one prism of said pair of prisms is of quadrilateral sectional shape, and formed so that an inlet beam entering said at least one prism is totally reflected two or more times within the prism before said inlet beam is incident upon said boundary surface at the Brewster angle.