Performance Analysis Of Heterodyne Coherent Optical Receiver For Under-Water Acoustic Signal Detection

Coherent heterodyne detection technology is an important technology that has been rapidly developed in high-speed fiber-optic communications in recent years.With the development of fiber-optic hydrophone array technology and the underwater acoustic signal detection system is now developing in the direction of high sensitivity,high signal-to-noise ratio and large spurious-free dynamic range,it is a feasible solution to apply coherent heterodyne detection technology to underwater acoustic signal detection.In the paper,we investigate the coherent heterodyne detection technology,we provide a general analytical approach for all the potential noise and look for methods to achieve the suppression of noise.Further with the theoretical basic knowledge of coherent heterodyne detection technology,we present a noise model with simulation software matlab applicable to evaluate,characterize and optimize the performance of the remote link.At the same time,we build a complete direct detection system as a comparison.To verify the advantages of the heterodyne coherent optical receiver in the long-distance transmission of narrowband low-power signals.The paper mainly studies the performance optimization of heterodyne coherent detection receivers.The main works of this dissertation are presented as follows:1.Based on the theoretical basic principle of heterodyne coherent detection and direct detection system,we systematically analyzed the noise model of ASE noise in EDFA.In this paper,we provide a general analytical approach for all the potential noise.The influence of the phase noise of the laser,the relative intensity noise of the laser,thermal noise,shot noise,and ASE noise in EDFA on the total noise of the detection system are analyzed theoretically.Compare and analyze the link gain and signal-to-noise ratio of the two detection systems.2.Develop a complete simulation model with simulation software matlab.In order to optimize the noise performance of detection system,with the actual device parameters for reference,the impact of the laser linewidth,optical filter,local oscillator optical power for the two systems overall noise performance are analyzed by using the method of control variables.Finally,the simulation results show that the optical amplification without signal-to-noise ratio loss can be realized by increasing the local oscillator optical power.When the signal transmission distance reaches 370km,the signal-to-noise ratio of the heterodyne coherent detection system is optimized by 23dB compared with the IM/DD system.3.Based on the theoretical analysis results and simulation results,a complete experimental verification system is built.The experimental results of the two receiving and demodulating systems are measured and compared.It is concluded that the heterodyne coherent detection system is better than the direct detection system.The signal-to-noise ratio can be greatly improved during long-distance transmission.In the experiment,when the input signal power is-47dBm before the receiver,the signal-to-noise ratio improvement of 1 OdB is achieved.