Design And Characterization Of Linear Optical Sampling Based Analog Front-end

Presently, electrical sampling is commonly used for optical signal performance monitoring in current optical fiber transmission systems. However, such technique is constrained by sampling clock accuracy, relaxation time of sample and hold circuit, and the speed of carrier mobility. In particular, it is mainly targeted for intensity parameter analysis. Due to the existence of electronic bottleneck, all-optical sampling technique becomes a hot research topic around the world. The signal under test is sampled in the optical domain, and complete optical-to-electronic conversion by low bandwidth photo-detector. All-optical sampling can be divided into linear and non-linear optical sampling. In this thesis, the development and debug of an analog front-end for linear optical sampling is comprehensively investigated. The analog front-end is composed of optics and circuit parts. Single channel 128 Gbps PDM-QPSK signals is successfully monitored by the self-developed prototype. The main contribution of thesis is summarized as follows.(1) After reviewing the development of all-optical sampling, we explain the operation principle of linear optical sampling and coherent detection. In particular, we theoretically the special requirements of optical sampling pulse source and corresponding digital signal processing techniques.(2) We design and develop the analog front-end for linear optical sampling application, which is composed of optics and circuit parts. We characterize the involved optoelectronic modules and carry out necessary optimization and compensation.(3) We design the bias board of passively mode-locking fiber laser, which acts as optical sampling source in the self-developed analog front-end. After experimental characterization, the average output power, central wavelength and repetition rate of pulse has substantially improved, whose variances are reduced to 1/21, 1/4 and 1/56 as a comparison with the results that before optimization.(4) We are able to characterize the constellation and eye-diagram of single-channel 128 Gbps PDM-QPSK signal successfully. After doing a comparison with the counterpart from Agilent modulation format analyzer N4391 A, the self-developed equipment is verified with almost the same performance for on-field measurement.