Research On Homodyne Receiver Phase Noise Cancellation And IQ Imbalance Compensation

This paper first reviews the research and development history of coherent optical communication,and describes the basic principles and key technologies of coherent detection,including phase noise elimination and compensation for imbalance between in-phase(I)and quadrature(Q).These two key technologies are also the focus of this paper.For the elimination of phase noise,the forward phase noise elimination technique,the optical phase-locked loop and the phase diversity method used in the differential phase-shift keying are described by this paper.Compared with the optical phase-locked loop,phase diversity can not only eliminate the random phase difference between the signal light and the local oscillator,but also eliminate the phase noise caused by the optical path mismatch,and it is also easy to realize in structure.Based on the phase diversity method of,this paper proposes a phase diversity method which can be used in multi-phase differential phase shift keying,and uses optisystem and Matlab software to simulate quadrature differential phase-shift keying and 8 differential phase shift keying.The results show phase diversity method can eliminate all kinds of phase noise well.However,when the IQ imbalance exists,the effect of phase diversity is very bad,because the premise of this method is the phase of the IQ component is orthogonal and the amplitude is equal,so when the IQ imbalance exists,it must be compensated and then the asynchronous demodulation.Aiming at IQ imbalance compensation,this paper introduces digital compensation algorithm,finite-impulse-response filter compensation method and the adaptive phase diversity method proposed in this paper.Digital compensation algorithms,which are complex and generally not suitable for high-order quadrature amplitude modulation,need analog-to-digital converters and high speed DSP;The 16 structure of finite-impulse-response filter is suitable for quadrature amplitude modulation,but the structure is too complex.In this paper,the causes of IQ imbalance are analyzed and the proposed adaptive phase diversity method can theoretically compensate multi-phase differential phase shift keying and quadrature amplitude modulation for IQ imbalance.The adaptive phase diversity system replaces the 90° phase shifter in the traditional 2×2 90° mixer into an electro-optic modulator.The electro-optic modulator has an inherent phase shift of ?2,and then generates an additional phase shift according to the phase error signal to complete the phase imbalance compensation.The phase error signal is obtained from the IQ components input the multiplier and the low-pass filter.The amplitude imbalance compensation is performed by an automatic gain amplifier according to the amplitude error signal,which is obtained from the IQ components input the peak detector,the differential amplifier.The simulation results show that the imbalance between the IQ channels can be fully compensated over a wide imbalance range for quadrature differential phase-shift keying and 8 differential phase shift keying,and the system is simple and has a large tolerance to the environment.It is expected to provide a feasible scheme in the field of coherent communication or coherent detection.