Opto-electronic Joint Optimization Design Of High-speed Coherent Optical Communication System

With the development of emerging technologies such as artificial intelligence,the Internet of Things and big data,the volume of data is growing exponentially.In order to meet the needs of users,large data centers have been developed around the world,represented by cloud data centers.The Data Center Interconnect(DCI)market presents new challenges and requirements for network transmission capacity,panel density,cost and power consumption.Compared with the traditional Intensity Modulation-Direct Detection(IM-DD)system,the coherent optical communication system adopts the phase dimension and Digital Signal Processing(DSP),which can achieve higher sensitivity and spectral efficiency,provides an effective solution for high speed and large capacity transmission.Compared with traditional coherent optical communication systems,self-homodyne coherent optical communication systems can effectively reduce the performance requirements of laser and simplify the complexity of DSP,significantly reduce the power consumption of the system,and can be more suitable for high-speed and large-capacity transmission in shortdistance scenarios.The higher order of modulation format reduces the requirement of cost per bit and has higher frequency spectrum utilization.At the same time,the Euclidean distance between adjacent constellation points is reduced,which bring more stringent requirements of Optical Signal to Noise Ratio(OSNR).Large-bandwidth signal transmission mainly faces two problems:on the one hand,the device bandwidth is limited,which can not meet the requirements of signal transmission bandwidth,resulting in distortion;On the other hand,the sampling rate of Digital to Analog Converter(DAC)and Analog to Digital Converter(ADC)cannot meet the requirements of the sampling theorem,and can only be undersampled,which will cause significant damage.It mainly includes causing signal spectrum aliasing and sensitive to sampling phase.In the high-speed coherent optical communication system,the damage received by optical signals during transmission accumulates continuously,leading to the deterioration of the Quality of Transmission(QoT).In order to ensure the safe transmission quality required by services,we need to estimate QoT before deploying an optical path.In view of the above situation,the main research work of this paper is as follows:(1)The self-homodyne coherent optical communication system is optimized by electronic domain compensation.In this paper,we firstly design the structure of self-homodyne coherent optical communication system and analyze the advantages of its application in short-distance scenarios.It can realize the simplification of DSP and the reduction of laser linewidth requirements.Then we improves the DAC model of self-homodyne coherent optical communication system.We use Effective Number of Bits(ENoB)to characterize the DAC effective resolution and analyzes the effect of ENoB of DAC on the system performance.For the scenario where device bandwidth is limited,Digital Pre-emphasis(DPE)is used to compensate the high frequency component that the signal is to decayed,and the DPE compensation effect is shown.When the modulator bandwidth is 25 GHz,the system bit error rate can be lower than that when the modulator bandwidth is 55 GHz under the same OSNR after DPE.The method of anti-aliasing filter and sampling phase optimization is selected to compensate the influence of under-sampling.At 1.3 baud rate sampling,the anti-aliasing filter reduces the OSNR requirement by 2 dB at the BER of 0.0125 compared with that without using it.At baud rate sampling,the sampling phase optimization reduces the OSNR requirement by 2 dB compared with that without using it.(2)Achieve QoT estimation of coherent links based on photon-assisted artificial neural network.In this paper,modulation format(number of constellation points),bit rate,incoming fiber optical power and fiber span number are used as input feature vectors of artificial neural network to estimate transmission quality of coherent link.The overall recognition accuracy of the data set can reach 90.7%.We use semiconductor optical amplifiers to achieve the weighting operation of artificial neural network in the optical domain.Taking advantage of the high bandwidth and low energy consumption of photonics,we can realize the classification of QoT of high-speed and low-power coherent optical communication links.