Research On Photonic Time-stretch ADCS And Their Parallel Multichannel Characteristics

Nowadays, DSP technology has been largely improved, in the contrast, ADC technology has not enjoyed the same improvement, as a consequent, ADCs cannot match DSPs gradually. For traditional electronic ADCs are difficult to overcome their bottlenecks such as time jitter and comparator ambiguity to progress more, new developing photonic ADCs attract more and more attention.Photonic time-stretch ADCs take advantage of the unique property of analog electronic signal in the optical domain, to utilize slow electronic ADCs to deal with high-speed analog signals. Specifically, a time-stretch ADC makes use of the group-velocity dispersion of optical pulses to stretch them to a certain width in a length of fiber, so that the analog electronic signal to be dealt with can be intensively modulated on them, after that another fiber is added to widen the pulses once more, so the signal modulated on them is stretched at the same time. After converting them back into the electronic domain using a photoelectric converter, a “slowed-down” replica of the input RF signal can be obtained, so it can fold increase the sampling rate of existing electronic ADCs.This article gives the mathematical derivation to describe time-stretch ADCs’ problems such as envelope removing and power penalty, and the methods to overcome them accordingly; numerical simulation experiments are done in this article to simulate time-stretch analog-to-digital converter systems. For the first time, these experiments are used to study the impacts of nonlinear effects to this system, and the efficacy of adaptive online calibration, and all these results are used to guide the design of a realistic system.In order to overcome the problem of power penalty, this article newly raises a phase correction method based on single-sideband modulation. Both utilizing single-sideband modulation and this phase correction method in a time-stretch analog-to-digital converter results in output without power penalty and phase distortion. Simulation results also test and verify this method’s effectiveness.Because of the overlap of photonic pulses, one-channel time stretch ADCs can only deal with discrete time signals, as for continuous time signals, parallel multichannel processing should be introduced. So from the view of its components, a parallel multichannel time-stretch ADC system makes use of several slow electronic ADCs to form an ADC system which has a high sampling rate.In this article, through designing a system, we experimentally realized the function of this kind of ADC. A single channel time-stretch ADC is established whose stretch factor is 10 and its output without envelope is also got. Moreover, a parallel multichannel time-stretch ADC is designed and realized, whose stretch factor is 4, it is able to form an optical carrier which is able to deal with signals that are continuous in time; and every channel’s time-stretched output signal is also got and analyzed.