# US 8,787,710 B2 · Wideband interferometer type polarization light beam combiner and splitter > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,787,710 B2 - Document ID: US8787710B2 - Status: Granted - Kind: B2 - Application number: 13/321,780 - Filed: 2010-06-02 - Published: 2012-03-15 - Granted: 2014-07-22 - Earliest claimed: 2009-06-02 - Assignees: Nippon Telegraph and Telephone Corporation - Applicants: Takayuki Mizuno; Takashi Goh; Hiroshi Yamazaki; Shin Kamei; Tsutomu Kitoh - Inventors: Takayuki Mizuno; Takashi Goh; Hiroshi Yamazaki; Shin Kamei; Tsutomu Kitoh - Web page: https://patentgrep.com/patent/US8787710B2 ## CPC - G02B 6/12007: {forming wavelength selective elements, e.g. multiplexer, demultiplexer} - G02B 6/12023: {characterised by means for reducing the polarisation dependence, e.g. reduced birefringence} - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract A interferometer type polarization beam combiner and splitter, which can combine or split polarized light over a wide band, is provided. The interferometer type polarization beam combiner and splitter includes: an optical splitter; an optical coupler; an optical path length difference imparting unit, which includes a plurality of optical waveguides arranged between the optical splitting unit and the optical coupling unit; one or two input/output ports connected to the optical splitter; and two input/output ports connected to the optical coupler. A half-integer of a wavelength of λc is set as a normalized phase difference, for the optical path length difference imparting unit, between two polarization states, and means for generating a difference in refractive index dispersion is provided between the optical waveguides of the optical path length difference imparting unit, so that the change rate of the transmittance with respect to wavelength is suppressed for the two polarization states. ## Claims ### Claim 1 A wideband interferometer type polarization beam combiner and splitter, comprising: an optical splitting unit; an optical coupling unit; an optical path length difference imparting unit comprising a plurality of optical waveguides arranged between the optical splitting unit and the optical coupling unit; one or two first input/output ports connected to the optical splitting unit; and two second input/output ports connected to the optical coupling unit; wherein: the optical path length difference imparting unit includes, along the optical waveguides, means for generating differential birefringence and means for generating a difference in refractive index dispersion; and wherein: polarization combining is performed by inputting light in a first polarization state and light entering in a second polarization state at the two second input/output ports connected to the optical coupling unit, and by outputting the light through the one or two first input/output ports connected to the optical splitting unit, or polarization splitting is performed by inputting light at the one or two first input/output ports connected to the optical splitting unit, and by outputting light in the first polarization state and light in the second polarization state, respectively, through the two second input/output ports connected to the optical coupling unit, and wherein: a half-integer of a wavelength of λc is set as a normalized phase difference, for the optical path length difference imparting unit, between the first polarization state and the second polarization state; and wavelength fluctuation of the normalized phase difference is suppressed by a difference in refractive index dispersion that is provided by the means for generating a difference in refractive index dispersion, the wavelength fluctuation having opposite plus and minus signs for the first polarization state and the second polarization state. ### Claim 2 (depends on 1) The wideband interferometer type polarization beam combiner and splitter according to claim 1, wherein a sum total of the products of birefringence and path lengths of an optical waveguide with respect to another optical waveguide at the optical path length difference imparting unit can be approximated by γ(λ−λc)+(m′+(1/2))λc where: γ is a parameter describing wavelength dependency of birefringence, λ is a wavelength, and λc is a center wavelength, and m′ is an integer. ### Claim 3 (depends on 2) The wideband interferometer type polarization beam combiner and splitter according to claim 2, wherein when ψ1(λ) is the sum total of the normalized phases of the optical splitting unit, the optical coupling unit, and the optical path length difference imparting unit of the first polarization state, and when ψ2(λ) is the sum total of the normalized phases of the optical splitting unit, the optical coupling unit, and the optical path length difference imparting unit of the second polarization state, the absolute values of the change rate of ψ1(λ) and ψ2(λ) with respect to wavelength are the same and has opposite plus and minus signs. ### Claim 4 (depends on 3) The wideband interferometer type polarization beam combiner and splitter according to claim 3, wherein: the optical splitting unit and the optical coupling unit are wavelength insensitive couplers, each of which includes two directional couplers and an optical path length difference imparting unit formed of two optical waveguides arranged between the two directional couplers; and the wavelength insensitive couplers employed as the optical splitting unit and the optical coupling unit are arranged point symmetrical with the center of a circuit. ### Claim 5 (depends on 3) The wideband interferometer type polarization beam combiner and splitter according to claim 3, wherein the optical splitting unit is a Y-branch splitter, the optical coupling unit is an optical coupler, and a splitting ratio for the optical splitting unit and a coupling ratio for the optical coupling unit are 50%, regardless of the wavelength. ### Claim 6 (depends on 2) The wideband interferometer type polarization beam combiner and splitter according to claim 2, wherein: the optical splitting unit and the optical coupling unit are wavelength insensitive couplers, each of which includes two directional couplers and an optical path length difference imparting unit formed of two optical waveguides arranged between the two directional couplers; and the wavelength insensitive couplers employed as the optical splitting unit and the optical coupling unit are arranged point symmetrical with the center of a circuit. ### Claim 7 (depends on 2) The wideband interferometer type polarization beam combiner and splitter according to claim 2, wherein the optical splitting unit is a Y-branch splitter, the optical coupling unit is an optical coupler, and a splitting ratio for the optical splitting unit and a coupling ratio for the optical coupling unit are 50%, regardless of the wavelength. ### Claim 8 (depends on 2) The wideband interferometer type polarization beam combiner and splitter according to claim 2, wherein the optical splitting unit is a Y-branch splitter, the optical coupling unit is an optical coupler, the absolute values of the change rate of a normalized phase with respect to wavelength of a first polarization state and a second polarization state of the path length difference imparting unit are the same and has opposite plus and minus signs. ### Claim 9 (depends on 8) The wideband interferometer type polarization beam combiner and splitter according to claim 8, wherein the means for generating differential birefringence is provided by employing different structures for the optical waveguides of the optical path length difference imparting unit. ### Claim 10 (depends on 8) The wideband interferometer type polarization beam combiner and splitter according to claim 8, wherein the means for generating differential birefringence is provided by an adjustment of a stress to be applied to the optical waveguides of the optical path length difference imparting unit. ### Claim 11 (depends on 8) The wideband interferometer type polarization beam combiner and splitter according to claim 8, wherein the means for generating a difference in refractive index dispersion is provided by employing different structures for the optical waveguides of the optical path length difference imparting unit. ### Claim 12 (depends on 11) The wideband interferometer type polarization beam combiner and splitter according to claim 11, wherein the wideband interferometer type polarization beam combiner and splitter is formed on a planar substrate, and the optical waveguides are silica-based optical waveguides that include core and cladding layers. ### Claim 13 (depends on 1) The wideband interferometer type polarization beam combiner and splitter according to claim 1, wherein: when ψ1(π) is the sum total of the normalized phases of the optical splitting unit, the optical coupling unit, and the optical path length difference imparting unit of the first polarization state, and when ψ2(λ) is the sum total of the normalized phases of the optical splitting unit, the optical coupling unit, and the optical path length difference imparting unit of the second polarization state, the absolute values of the change rate of ψ1(λ) and ψ2(λ) with respect to wavelength are the same and has opposite plus and minus signs; the optical splitting unit and the optical coupling unit are wavelength insensitive couplers, each of which includes two directional couplers and an optical path length difference imparting unit formed of two optical waveguides arranged between the two directional couplers; and the wavelength insensitive couplers employed as the optical splitting unit and the optical coupling unit are arranged point symmetrical with the center of a circuit. ### Claim 14 (depends on 1) The wideband interferometer type polarization beam combiner and splitter according to claim 1, wherein: when ψ1(λ) is the sum total of the normalized phases of the optical splitting unit, the optical coupling unit, and the optical path length difference imparting unit of the first polarization state, and when ψ2(λ) is the sum total of the normalized phases of the optical splitting unit, the optical coupling unit, and the optical path length difference imparting unit of the second polarization state, the absolute values of the change rate of ψ1(ψ) and ψ2(λ) with respect to wavelength are the same and has opposite plus and minus signs; the optical splitting unit is a Y-branch splitter, the optical coupling unit is an optical coupler, and a splitting ratio for the optical splitting unit and a coupling ratio for the optical coupling unit are 50%, regardless of the wavelength. ### Claim 15 (depends on 1) The wideband interferometer type polarization beam combiner and splitter according to claim 1, wherein: the optical splitting unit and the optical coupling unit are wavelength insensitive couplers, each of which includes two directional couplers and an optical path length difference imparting unit formed of two optical waveguides arranged between the two directional couplers; and the wavelength insensitive couplers employed as the optical splitting unit and the optical coupling unit are arranged point symmetrical with the center of a circuit. ### Claim 16 (depends on 1) The wideband interferometer type polarization beam combiner and splitter according to claim 1, wherein the optical splitting unit is a Y-branch splitter, the optical coupling unit is an optical coupler, and a splitting ratio for the optical splitting unit and a coupling ratio for the optical coupling unit are 50%, regardless of the wavelength.