Delay line interferometer with polarization compensation at selective frequency

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.

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.