Research On Phase-preserving Amplitude Regeneration Chips

The degradation of high-order modulated signals due to factors such as optical fiber dispersion,nonlinear effects,and amplified spontaneous emission noise is a significant concern in improving the transmission capacity and spectral efficiency of modern optical communication systems.All-optical regeneration technology can directly regenerate the amplitude or phase of degraded optical signals in the optical domain,thereby enhancing the optical signal-to-noise ratio and bypassing the need for complex optoelectronic devices.However,the high-order modulated signals are particularly susceptible to being influenced by the conversion from amplitude noise to phase disturbance in the all-optical amplitude regeneration process.To address this challenge,this thesis focuses on phase-preserving amplitude regeneration(PPAR)scheme through the application of an all-optical regenerator with a Mach-Zehnder interferometer(MZI)configuration.The primary research contents and innovations of this thesis are outlined below.1.A new all-optical regeneration scheme is proposed by cascading an optical phase conjugator(OPC)with two MZI units(OPC-MZI).The MZI regeneration unit is designed utilizing a highly nonlinear fiber(HNLF)for the regeneration of quadrature phase shift keying(QPSK)signals,with an average phase disturbance of 5.6°.In comparison,the proposed OPC-MZI regeneration scheme reduces the average phase disturbance of regenerated signals from 5.6° to 0.04° and achieves a noise reduction ratio(NRR)of 0.9d B,while the corresponding input signal-to-noise ratio is reduced by 3.5 d B.These results demonstrate the feasibility of the OPC-MZI regeneration scheme.2.An all-optical regenerator utilizing a MZI configuration integrated on silicon-oninsulator(SOI)substrate is designed and optimized to build an OPC-MZI regeneration system.The input and output couplers are constructed with ridge waveguides.Structural parameters,model simulation,and layout of this chip are subsequently optimized to achieve perfect transmission of guided waves.Specifically,the upper arm of MZI unit is designed with an arc-to-center angle of 60° and a bend radius of 30 μm.Simulation results demonstrate that the use of OPC-MZI regeneration scheme reduces the average phase disturbance of regenerated QPSK signals from 5.7° to 0.07°,and further improves the NRR by 1.0 d B.The corresponding input signal-to-noise ratio is reduced by 4.5 d B.Compared to the HNLF-based OPC-MZI regeneration scheme,the regenerative input power of OPC-MZI regeneration scheme is only about a half of the former,at 0.564 W.3.The effect of OPC suppression on phase disturbance in the OPC-MZI regeneration scheme is investigated,and the impact of OPC gain on the PPAR is also analyzed.Simulation results show that the optimized OPC gain enables the MZI unit to tolerate greater phase disturbances,up to a maximum of 9.1°,thereby relaxing requirements of the chip design.Moreover,the PPAR of OPC-MZI regeneration scheme remains superior to that of a single MZI unit when the OPC gain is not less than 69% of the optimal gain.