PSK HOMODYNE EXPERIMENT USING A 1300NM DFB LASER

Abstract

An experimental phase-shift keying (PSK) self-homodyne system using the Mach-Zehnder interferometer configuration is set up in the laboratory. A distributed feedback (DFB) semiconductor laser operating at a wavelength of 1300nm is used as the source and phase shift keying of the carrier is accomplished by means of a titanium optical guided wave (OGW) phase modulator. Two APO optical receivers are used to reduce the local oscillator excess noise and to improve the detection sensitivity. The bit error rates (BER) are measured and the results indicate an error rate floor which can be attributed to the phase noise of the laser diode. In order to make comparison with the measured results, the theoretical BER performance of a PSK homodyne optical communication system in the presence of shot noise and phase noise is evaluated. A new upper bound of this BER performance is obtained. This bound is simple and convenient to use. It is also the tightest bound known so far, and which predicts correctly the high SNR behaviour of the error probability. Finally, the alternative use of phase diversity receivers (which employs the 90° optical hybrid), as opposed to optical phase-locked loops, is investigated.