Direct detection of OC-192 DPSK signal using polarization-controlled differential-phase-to-intensity conversion (DPIC)

The differential-phase-to-intensity conversion (DPIC) can be used to detect an optical phase-shift of laser light. The system is based on injection locking of a semiconductor laser. We have now found the waveform of a DPIC signal can be adjusted by controlling and selecting the polarization of the lightwaves before and after the slave laser. We experimentally investigated the phenomenon, and concluded that it originated in TM-mode excitation and interference between the TE and TM modes within and after the slave laser. Such adjustment of the waveform according to the condition of polarization is useful because it can achieve direct demodulation of an optical DPSK signal without using an electrical circuit. The adoption of the DPSK signal format enables a higher bit rate than the original DPIC scheme. We demonstrated direct detection of an OC-192 (9.95328 Gb/s) DPSK signal by using polarization-controlled DPIC.