Abstract: This invention provides a compact delay-line interferometer that can be used in Differential Phase Shift Keying (DPSK) and Differential Quardratic Phase Shift Keying (DQPSK) demodulators. The delay-line interferometer is based on polarization components including beam shifter, beam splitter and wave plates. The realized demodulators can be used as either discrete components or integrated with balanced detectors. Time delay generated in the interferometer can be controlled with a phase shifter, using either thermal, piezoelectric, mechanical of electrical means. This application claims priority to US Provisional Patent Application Ser. No. 61/238,687, filed Sep. 1, 2009, titled “Polarization Based Interferometer.” This application also claims priority to US Provisional Patent Application Ser. No. 61/295,766, filed Jan. 18, 2010, titled “Delay-Line-Interferometer for Integration with Balanced Receivers.

Abstract: This invention provides a DPSK demodulator and a DQPSK demodulator. Both of the demodulators are based on polarization delay-line interferometers. They can be integrated with photodetectors in fiber-optic communication systems. The demodulators consist of polarization beam shifter, polarization beam splitter and wave plates. Coupling of the demodulators with photodetectors can be through free space or fibers. Time delay generated in the interferometer can be controlled with a phase shifter, using either thermal, piezoelectric, mechanical or electrical means. Examples of phase shifter using a piezo bender and an actuator respectively are also disclosed.