Linear Optical Sampling Technique Based On Simplified Coherent Detection

Rapidly increasing bandwidth request of global Internet has stimulated the development of next-generation photonic interconnection with high-speed and large capacity.In view of4-level pulse amplitude modulation(PAM-4)signal with simple generation structure and easy detection,it plays a vital role in next generation photonic interconnection.Therefore,real-time monitoring of high-speed optical PAM-4 signals is important for ensuring the quality of optoelectrical components,which relies on the advanced signal characterization instrument.However,traditional electrical solution is challenging to be implemented,because of the bandwidth constraint of photodetectors(PDs)and the limited precision of analog-to-digital converter(ADC).Alternatively,linear optical sampling technique can circumvent the electronic measurement bottleneck with low-cost and high-sensitivity for the high-speed PAM-4 signal.In particular,linear optical sampling technique is able to obtain the full-field information of signals including amplitude,phase and polarization information.My thesis is focused on the sampling and acquisition of high-speed PAM-4 signals,the main research outcomes include(1)We propose the simplified coherent detection based linear optical sampling for the intensity modulation signal.The traditional linear optical sampling system can be simplified by the use of a 3×3 optical couplers and three single-ended PDs with narrow bandwidth.We develop the software of broadband high-speed optical signal eye diagram analyzer with the capabilities of digital equalization and software synchronization.Our numerical simulation results indicate that,the accurate sampling and the eye-diagram acquisition of high-speed PAM-4 signals over a wide operation wavelength range can be realized.(2)We successfully develop the broadband high-speed optical signal eye diagram analyzer based on the simplified coherent detection enabled linear optical sampling technique,by using a tunable pulsed laser with a repetition frequency of 100 MHz.The experimental characterization results of 10 GBaud non-return-to-zero(NRZ)signals agrees with the traditional electronic counterpart,leading to the verification of the proposed linear optical sampling equipment with the simplified coherent detection.Meanwhile,the impact of the imperfection of the sampling pulse has been investigated in details.