Measurements Of DPSK High-Speed Optical Signal

The real-time monitoring of high-speed optical signal quality is essential to ensure the stability and reliability of optical fiber communication systems. With increasing fiber transmission rate, the traditional electronic measuring instruments cannot meet the bandwidth requirements. Measurement method based on optical sampling is an effective way to break through the electronic bottleneck. And the new phase modulation format as DPSK will be more widespread in optical fiber communication, but non-linear optical sampling technique can only be sampling intensity modulated signal and the phase modulation signal cannot be directly sampled.There are two ways of sampling the DPSK optical signal, First, building the eyediagram by applying the nonlinear optical sampling technique after demodulating the DPSK optical signal to monitor the RZ-DPSK; Second,reconstructing the constellation diagram by using linear optical sampling technique. This paper chose the first way and measurements of high-speed DPSK optical signal based on nonlinear optical sampling technique was made a depth theoretical study and numerical simulation.the paper includes the following aspects:1. Overviewed the structure and basic principles of Mach-Zehnder modulator (MZM), described the implementations of producing a variety of high speed DPSK optical signal using MZM and its cascade form, and based on the above implementations, simulated waveform of NRZ-DPSK, RZ-DPSK, CSRZ-DPSK, analyzed and compared the performance of DPSK optical signal.2. On the basis of extensive reading of literature, the basic principles and the realization of all-optical sampling was introduced. The principle of frequency-shift sampling was described in this paper.Besides, the advantages and disadvantages of linear optical sampling and nonlinear optical sampling was analyzed and compared, the synchronous sampling,asynchronous sampling and software synchronous sampling was introduced and several key technologies of optical sampling as sampling gate, sampling pulse source, clock recovery and clock processing, optical detection and data acquisition was tell.3.The classical theory model and ultra-fast dynamic model of semiconductor optical amplifier (SOA) was descried, establishing a sub-model of semiconductor optical amplifiers.Additionally,the structure and working principle of semiconductor laser amplifier loop mirror (SLALOM) optical sampling gate basing on SOA was introduced and the features of SLALOM switching windows was simulated by Matlab to analyze the impact of switching window from different SOA injection current and internal parameters, different controlling power, different controlling optical pulse width, provided theoretical basis for optimal of switching windows.4. RZ-DPSK optical signal was demodulated to RZ(ASK) signal by using Mach-Zehnder delay interferometer(MZDI) and all-optical sampling simulation of40Gb/s high-speed RZ optical signal based on SLALOM optical sampling gate was made, recovering synchronous optical sampling eye diagram of Pseudo-random RZ optical signal.Finally, the effects caused by the pulse width on the sampling results are discussed in theory.