Fundamental Research On All-optical ADC Employing Soliton Self-frequency Shift

ADC is widely used in high-speed broadband communication systems,high accuracy radar over a long distance,medical imaging,image processing and so on.All-optical ADC avoids bottleneck problem of electronic ADC primarily,and reduces the noise induced by the conversion between the optical signal and electrical signal.Compared with the electronic ADC,all-optical ADC has the advantage of high sampling rate and wide bandwidth.Therefore,the research of high performance all-optical ADC is of great significance and value.In this thesis,the all-optical ADC based on soliton self-frequency shift effect is discussed and studied in detail.The main contents are as follows:(1)The theory of soliton self-frequency shift(SSFS)is studied,which is applied to all-optical quantitation.The physical model of all-optical quantitation based on soliton self-frequency shift is established,which is adopted to simulate the SSFS-based quantization.Also,the soliton self-frequency shift effect of high nonlinear optical fiber with different nonlinear coefficient are compared.To improve the accuracy of quantitation,spectral compression employing the “SMF-HNLF” optical fiber structure.is utilized after self-frequency shift.Both the simulation and the experimental results show that the best compression effect can be achieved when the pulse chirp is full compensated.Therefore,the spectral compression method effectively improves the quantitative accuracy.(2)A multistage bi-directional SMF-HNLF structure is studied for spectral compression.Experiments have been done to verify the results of compression.In the experiments,this structure achieves a total compression ratio of 11.58 as well as quantitative accuracy of 5.99 bits which is increased by 2.25 bits.The results show that this structure has effectively improve the accuracy of quantization while the complexity of the system has been simplified.The structure of multistage spectral compression is also being studied.The results show that compression saturation exists,so it is infeasible to increase the quantitative accuracy by increasing the stages of the compression structure infinitely.(3)A novel optical coding scheme employing Sagnac-loops is proposed for all-optical ADC based on soliton self-frequency shift effect.The proposed optical coding scheme has a simple architecture and a broad wavelength range,and easy to achieve a larger coding bit.The scheme is numerically demonstrated in a 5-bit SSFS-based all-optical ADC with a wavelength range of 1601 nm to 1707 nm,and is experimentally demonstrated in 3 bits SSFS-based all-optical ADC with 50 nm wavelength range.Compared with the coding method based on Waveshaper,the range of operating wavelength is increased by 5 times.