# US 2017/0285267 A1 · Delay line interferometer with polarization compensation at selective frequency > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2017/0285267 A1 - Document ID: US20170285267A1 - Status: Published application - Kind: A1 - Application number: 15/088,862 - Filed: 2016-04-01 - Published: 2017-10-05 - Earliest claimed: 2016-04-01 - Assignees: Inphi Corporation - Applicants: Inphi Corporation - Inventors: Masaki KATO; Radhakrishnan L. NAGARAJAN - Web page: https://patentgrep.com/patent/US20170285267A1 ## CPC - G02B 6/274: {based on light guide birefringence, e.g. due to coupling between light guides (G02B6/105, G02B6/024 take precedence; mechanically induced birefringence G02F1/0134)} - G02B 6/125: Bends, branchings or intersections - G02B 6/29352: {in a light guide} - G02B 6/29395: {configurable, e.g. tunable or reconfigurable (switching G02B6/35)} - G02B 6/1228: {Tapered waveguides, e.g. integrated spot-size transformers (for coupling with fibres G02B6/305)} - G02B 6/126: using polarisation effects {(G02B6/1226 takes precedence)} - G02B 6/2793: {Controlling polarisation dependent loss, e.g. polarisation insensitivity, reducing the change in polarisation degree of the output light even if the input polarisation state fluctuates} - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract An apparatus of polarization self-compensated delay line interferometer. The apparatus includes a first waveguide arm of a first material of a first length disposed between an input coupler and an output coupler and a second waveguide arm of the first material of a second length different from the first length disposed between the same input coupler and the same output coupler. The apparatus produces an interference spectrum with multiple periodic passband peaks where certain TE (transverse electric) and TM (transverse magnetic) polarization mode passband peaks are lined up. The apparatus further includes a section of waveguide of a birefringence material of a third length added to the second waveguide arm to induce a phase shift of the lined-up TE/TM passband peaks to a designated grid as corresponding polarization compensated channels of a wide optical band. ## Claims ### Claim 1 (canceled) ### Claim 2 (depends on 3) The Demux apparatus of claim 3 wherein the first waveguide arm and the second waveguide arm comprises one or more planar waveguide sections having a same height formed in a same SOI substrate and isolated by silicon oxide. ### Claim 3 A Demux apparatus of polarization self-compensated delay line interferometer, the apparatus comprising: a first waveguide arm disposed between an input coupler and an output coupler; a second waveguide arm disposed between the input coupler and the output coupler, wherein the second waveguide arm is at least different from the first waveguide arm by a first length to induce an interference output spectrum having one or more passband peaks lined up for TE (transverse electric) polarization mode and TM (transverse magnetic) polarization mode at one or more channel frequencies of a designated optical band, wherein each of the one or more passband peaks having both TE/TM modes lined up is demultiplexed to a corresponding port of the output coupler; a birefringence waveguide section of a second length inserted in the second waveguide arm to induce a phase shift of the one or more passband peaks lined up for TE mode and TM mode at one or more alternative channel frequencies of the designated optical band, the second length being selected from a fixed set of values stepwisely increased from zero to a maximum value with a predetermined increment so that all channels with lined-up TE and TM mode in the designated optical band can be included, wherein the first waveguide arm comprises a material selected from silicon nitride and silicon nitride mixed with silicon oxide. ### Claim 4 (depends on 3) The Demux apparatus of claim 3 wherein the second waveguide arm comprises the same material or an alternative selection of silicon, silicon nitride, and silicon nitride mixed with silicon oxide. ### Claim 5 (depends on 3) The Demux apparatus of claim 3 wherein the birefringence waveguide section comprises a material selected from silicon and silicon nitride. ### Claim 6 (depends on 2) The Demux apparatus of claim 2 wherein the birefringence waveguide section comprises the same height as the planar waveguide section of the second waveguide arm but a wider waveguide width than the second waveguide arm for providing additional phase shift beyond length delay for TE mode and TM mode that is tuned in stepwise manner so that multiple Demux apparatuses of same kind but covering one or more alternative channels of a DWDM/CWDM band can be formed. ### Claim 7 (depends on 6) The Demux apparatus of claim 6 further comprising a width-adaptive taper for coupling the birefringence waveguide section to the planar waveguide section of the second waveguide arm. ### Claim 8 (depends on 3) The Demux apparatus of claim 3 wherein the third length is selected to be the maximum value corresponding to 2π phase shift of a determined by difference between a TE polarization mode group index and a TM polarization mode group index of the birefringence waveguide section. ### Claim 9 (depends on 3) The Demux apparatus of claim 3 wherein the fixed set of values stepwisely increased define a stepper reticle field for determining the second length to allow each channel frequency of the designated optical band to be reached by at least one phase shift of the one or more passband peaks lined-up for TE mode and TM mode. ### Claim 10 (depends on 3) The Demux apparatus of claim 3 further comprising a heater over at least a partial section of either the first waveguide arm or the second waveguide arm to change temperature locally to introduce an additional phase delay to ensure that the one or more passband peaks lined-up for TE mode and TM mode are accurately aligned to one or more corresponding channel frequencies of the designated optical band. ### Claim 11 (canceled) ### Claim 12 (depends on 13) The method of claim 13 wherein providing a first delay line interferometer comprises forming the first waveguide arm and the second waveguide arm in a common SOI substrate and isolating each other by an insulator cladding material made by silicon oxide. ### Claim 13 A method for forming a set of polarization-independent demultiplexers based on polarization self-compensated delay line interferometers, the method comprising: providing a first delay line interferometer comprising: a first waveguide arm of a first length disposed between an input coupler and an output coupler; a second waveguide arm of a second length disposed between the input coupler and the output coupler, wherein the second length is at least different from the first length to induce an interference output spectrum having one or more passband peaks lined up for TE (transverse electric) polarization mode and TM (transverse magnetic) polarization mode at one or more channel frequencies of a designated optical band, wherein each of the one or more passband peaks having both TE/TM modes lined up is demultiplexed to a corresponding port of the output coupler; selecting a birefringence phase shifter of a third length, the third length being assigned a value from a fixed set of values stepwise increased from a first non-zero value up to a maximum value with a predetermined increment forming a set of delay line interferometers by respectively adding a set of the birefringence phase shifters of various assigned values in the third length to the second waveguide arm of the first delay line interferometer so that all channels with lined-up TE and TM mode in the designated optical band can be included, wherein the first waveguide arm comprises a material selected from silicon nitride and silicon nitride mixed with silicon oxide. ### Claim 14 (depends on 13) The method of claim 13 wherein the second waveguide arm comprises the same material or an alternative selection of silicon, silicon nitride, and silicon nitride mixed with silicon oxide. ### Claim 15 (depends on 13) The method of claim 13 wherein the birefringence phase shifter comprises a waveguide section of the third length made by silicon or silicon nitride. ### Claim 16 (depends on 15) The method of claim 15 wherein the waveguide section of the third length is a planar waveguide having a same height as the second waveguide arm but a wider waveguide width than the second waveguide arm for providing additional phase shift beyond length delay for TE mode and TM mode. ### Claim 17 (depends on 16) The method of claim 16 further comprising using a width-adaptive taper to couple the waveguide section of the third length to the second waveguide arm. ### Claim 18 (depends on 13) The method of claim 13 wherein the maximum value corresponds to a phase shift up to 2π determined by difference between a TE polarization mode group index and a TM polarization mode group index of the birefringence phase shifter. ### Claim 19 (depends on 13) The method of claim 13 wherein the first non-zero value equals to the predetermined increment corresponding to a minimum phase shift to cause at least one passband peak lined-up for TE and TM modes to shift from one channel frequency to a nearest channel frequency of the designated optical band. ### Claim 20 (depends on 13) The method of claim 13 further comprising disposing a heater over at least a partial section of the either the first waveguide arm or the second waveguide arm to change temperature locally to introduce an additional phase delay to ensure that the one or more passband peaks lined-up for TE mode and TM mode are accurately aligned to corresponding one or more channel frequencies of the designated optical band.