Patent ID: 8433204

Claim:
A phase shift keyed signal demodulator comprising: a first small incident angle beam splitter configured to split an input signal into first and second output signals; a second small incident angle beam splitter positioned to receive the first and second output signals and configured to simultaneously split each of the first and second output signals into a transmitted signal and a reflected signal; a first optical path defined by an optical path of each transmitted signal from a 50:50 beam splitting surface of the second small incident angle beam splitter to a reflector and back to the 50:50 beam splitting surface; a second optical path defined by an optical path of each reflected signal from the 50:50 beam splitting surface to a mirror surface of the second small incident angle beam splitter and back to the 50:50 beam splitting surface; an optical path difference compensator positioned in the first optical path and configured to substantially maintain a predetermined difference between a length of the first optical path and a length of the second optical path under varying temperature conditions, the predetermined difference configured to introduce a delay between the transmitted signal and the reflected signal, each transmitted signal and corresponding reflected signal interfering with each other to generate a constructive interference signal and a destructive interference signal; and a wavelength tuner positioned in the first optical path, the wavelength tuner configured to tune the demodulator to a predetermined central wavelength and to introduce a phase shift between a first transmitted signal generated from the first output signal and a second transmitted signal generated from the second output signal.