Homodyne Coherent Optical Communication System Based On Reflex Electro-optic Modulator

With the advancement and development of the Internet and its related industries,people's demand for bandwidth has also increased,which has promoted the revolution and progress of optical fiber communications.Compared with the conventional intensity modulation/direct demodulation optical fiber communication system,the advantages of coherent optical communication greatly increase the communication rate,and thus are widely applied to the current optical fiber communication systems.For its system performance,the best performance is 100 Gb / s double-polarization quadrature phase shift keying(DP-QPSK)homodyne coherent optical communication system,but the use of optical phase-locked loop will result in system performance degradation.In this paper,a homodyne coherent optical communication system based on the reflex LN electro-optic modulator is proposed,On the one hand,since the system transmitter and the local oscillator are the same laser,also solved the problem of optical phase lock loop realized the phase synchronization of carrier and local oscillator.On the other hand,since the input and output of the system are on the same optical fiber,the purpose of preventing the enemy from stealing the information from the optical fiber can be achieved so as to be applied to the secure communication system.This paper first briefly analyzes the basic principle of homodyne coherent optical communication system and proposes a reflective coherent optical communication system.As one of the important devices of the system,lithium niobate crystal and two kinds of electro-optic modulators,namely lithium niobate phase and intensity,were analyzed in detail.Based on this,reflective lithium niobate phase and intensity electro-optic modulators were proposed.The reflective modulator is analyzed in detail.Due to the mismatch of the speed of microwave and light waves,the forward modulation in the two modulations of the signal will form a noise,and the reverse modulation realizes the modulation of the signal.Finally,the law of the total phase shift change is given and the method of suppressing the noise produced by the forward modulation is proposed.After that,the structure and working principle of DP-QPSK homodyne optical communication system are introduced in detail.In the meantime,a reflective DP-QPSK homodyne coherent optical communication system is given in combination with the characteristics of the reflex electro-optical traveling wave modulator.The OptiSystem is used to simulate the reflective DP-QPSK system.However,due to dispersion and non-linear effects in the fiber,the result of the simulation is incorrect,which needs to be compensated for by the digital signal processing(DSP)in the electric domain.Finally,the electric field DSP compensation algorithm is introduced,including digital backward propagation compensation technology and constant modulus algorithm.Use these two algorithms to compensate for dispersion and nonlinear effects.Through the compensation of DSP,the constellation and bit error rate of the system are analyzed through simulation,which shows that the performance of the system is good and the corresponding phase modulation and demodulation can be completed within the allowable range of system error.At the same time,compared with the forward DP-QPSK system,the performances of the two systems are roughly the same when the cost of the two systems is roughly the same,which shows the feasibility of the system in practical engineering application.