Research On Carrier Phase Recovery Algorithm For High-Speed Coherent Optical Communication Systems

With the advent of the information age,the rapid development of new technologies and applications has placed higher demands on the speed and capacity of communication systems.Coherent wavelength division multiplexing(WDM)systems are key to achieving high throughput and spectral efficiency transmission.Currently,WDM systems typically use laser arrays as light sources,which face problems such as complex structure,high algorithm complexity,and difficulty expanding channels.Optical frequency combs have advantages such as phase coherence and stable spectral line spacing.Using them as the light source for WDM systems can further reduce the guard interval between channels,improve spectral efficiency,and simplify the receiving end algorithm complexity using a master-slave phase recovery framework.Applying coherent optical WDM systems based on optical frequency combs to power-sensitive data center interconnects is a research direction worthy of attention,and further research on low-complexity algorithms is of great significance.Based on the simplified scheme of the existing carrier phase recovery(CPR)algorithm,this paper applies it to coherent optical WDM systems based on optical frequency combs,and compares it with traditional WDM systems using laser arrays as light sources.The main contents of this work are as follows:1.This paper investigates two carrier phase recovery(CPR)algorithms for coherent optical communication,namely pilot-symbols-aided CPR(PACPR)and blind phase search(BPS).In optical communication,pilot symbols usually have the same phase distribution as quadrature phase shift keying(QPSK)but different amplitudes(known as QPSK-like symbols).For polarization multiplexed 64QAM format,this paper proposes an improved PACPR algorithm that uses QPSK-like symbols in the second outermost ring as pilot symbols.Simulation results show that at the bit error rate(BER)threshold of 1e-2,the proposed algorithm reduces the optical signal-to-noise ratio(OSNR)requirement by approximately 0.1 dB compared to the PACPR algorithm that uses QPSK-like pilot symbols in the outermost ring.In addition,this paper proposes to use a polarized joint compensation scheme to reduce the overhead of pilot symbols,which can reduce the pilot symbol overhead by half while maintaining the same performance.2.Aiming at the high complexity of the traditional BPS algorithm,this paper proposes a threshold blind phase search(T-BPS)scheme based on threshold simplification and conducts feasibility verification through experiments.Simulation results show that T-BPS can achieve the same performance as the traditional BPS algorithm using only half of the test phase numbers,with a computational complexity that is 50%of that of the traditional BPS algorithm.3.Based on the single-carrier phase recovery algorithms,this paper applies the improved T-BPS algorithm to a.coherent optical WDM system based on an optical frequency comb,and analyzes the complexity of different carrier phase recovery algorithms and recovery schemes.First,different transmission scenarios are investigated through simulation,and the BER is analyzed.Simulation results show that,within an 80 km transmission distance,the proposed T-BPS algorithm performs comparably to the traditional BPS algorithm with a complexity of only 50%of the latter.However,the performance of the optical frequency comb system is affected by amplified spontaneous emission(ASE)noise after passing through an erbium doped fiber amplifier(EDFA),which leads to performance degradation.This paper optimizes the performance of the optical frequency comb using a micro ring resonator(MRR)to improve the communication link performance.Simulation results show that at the BER threshold of 1e-2,MRR optimization on both the transmitting and receiving ends of the optical frequency comb system reduces the OSNR requirements for different channels by 1 dB to 1.7 dB.When only one end of the system is optimized,the OSNR requirements for different channels are reduced by 0.3 dB to 0.9 dB.Theoretical analysis and simulations both demonstrate the significant advantages of the optical comb system in achieving high-capacity transmission.