Acquisition And Processing Of High-speed Signal By Linear Optical Sampling Technique

The multi-dimensional division multiplexing technique, advanced modulation formats and digital coherent detection technique promote the progress of fiber-optic transmission systems. Advanced signal performance monitoring technique of high speed signal is a key technique for next-generation ultra-high capacity, ultra-high speed and ultra-long haul(3U) fiber-optic transmission systems. Traditional electronic sampling technique is challenging to characterize high speed optical signal due to the existence of electronic bottleneck. Howerer, optical sampling technique is one of the most promising methods to circumvent electronic bottleneck, because the electronic sampling process is converted to the optical domain. The high speed optical signals are sampled by optical sampling pulse, together with cost-effective low bandwidth photodetector to realize optical-to-electronic conversion. Thus, the system cost reduces greatly and the narrow pulse-width of optical sampling pulse significantly improves the system analysis bandwidth. In this thesis, I first explain the operation principle of linear optical sampling and the digial signal processing. Then, we develop a high-bandwidth and high-speed optial signal analyzer and perform on-field characterization trial. The main contributions in this thesis can be summarized as follows.(1) This thesis theoretically investigates the acquisition of linear optical sampling, when the high-speed signal under test is either periodic or random. Especially, when the pulse profile is asymmetrical, the repetition frequency of sampling pulse need fine adjustment in order to obtain correct waveform.(2) This thesis proposes a peak extraction algorithm for software-sychronization sampling technique. The ratio of sampling rate of ADCs and repeating rate of optical sampling pulse is the interval between two incident peak points. A recursive search algorithm is used to extract peak value of individual sampling points.(3) We develop a high-bandwidth and high-speed optial signal analyzer based on linear optical sampling technique and Lab VIEW. Then, we demonstrate on-field characterization trial of simultaneous four commercial 128 Gbps PDM-QPSK signals with truly random characteristics, by self-developed linear optical sampling equipment. Finally, we carry out performance comparison with conventional optical modulation analyzer(OMA), and verify that the self-developed analyzer is capble of simultaneously characterizing four-channel 128 Gbps PDM-QPSK signals, without any adjustment of LO wavelength. Compared with Agilent OMA, the EVM difference is less than 2% and Q factor difference is no more than 2dB.