Coherent Lightwave Receivers with a Laser Diode Local Oscillator for Inter-orbit Optical Communication

摘要

Coherent lightwave receivers are experimentally demonstrated with a laser diode as local light source. The laser diode local oscillator is available for not only reducing weight and power consumption of a coherent receiver, but expanding the wavelength tuning range of receiver. In our study, a narrow line-width (<50 kHz) DFB laser diode is introduced into coherent receivers as a local oscillator light source. And two kinds of heterodyne coherent lightwave receiver (ASK-envelope detection and PSK-synchronous detection) have been designed and evaluated. In the experiment, the signal light was generated in a system consist of a DFB laser diode operated at the wavelength of 1.55 μm, an electro-optic extra-cavity wideband modulator and an Erbium doped fiber amplifier (EDFA). After attenuating power, the signal light was introduced into the receiver. An optical attenuator was inserted between the EDFA and the receiver instead of space loss in actual communication link. Coherent lightwave detection using a laser-diode local light source was successfully performed at data rate of 2.5 Gbps. Sensitivity under 174 photons/bit at Bit Error Rate (BER) of 10~(-9) is experimentally achieved in the PSK coherent system. The PSK coherent receiver also shows good wavelength tracking characteristics for the variation of signal beam wavelength. It is demonstrated that the combination of tunable local optical sources and an intermediate frequency-phase lock loop (PLL) is effective to compensate Doppler effect, which is indispensable in inter-orbit communication link.