Novel Time Lenses And Their Applications In Ultrafast Optical Signal Processing

Optical signal processing based on time lenses, with advantages of simple system configuration and powerful function, can provide ultrafast signal processing speed, which is not available by the present electrical signal processing systems. As a key component in optical signal processing system, time lenses play a key role in determining the system performance. Under the support of National Natural Science Foundation of China and excellent doctoral innovation fund of Beijing Jiaotong University, to address the present technical problems in time lens and their application for ultrafast optical signal processing such as optical pulse compression and temporal imaging, we focused on both theoretical and experimental research of time lenses and their applications in optical signal processing by improving the performance of conventional systems and proposing novel principles. The main achievements of this thesis are summarized as follows:1. Aberration elimination technology was applied in temporal imaging, time-to-frequency mapping and frequency-to-time mapping systems based on linear time lenses for the first time. We firstly built the theoretical model for aberration elimination, then derived the elimination condition for aberrations due to high-order terms, and finally proved the theory by numerical simulations. According to the numerical simulation, both high-order terms in time lenses and those in dispersion induce aberrations in the signal processing system. However, aberrations due to time lenses and those due to dispersion can compensate with each other and thus, aberration-free system can be realized, as long as the aberration elimination condition is satisfied. The system configuration can be simplified based on the aberration elimination technology, and can widely apply in improving the performance of the signal processing systems based on conventional time lenses.2. The theoretical implementation of the graded-index time lenses was firstly proposed by using cross phase modulation. The theoretical model was set up for modeling the transmission of optical pulses in the graded-index time lenses. Based on graded-index time lenses, three applications in optical signal processing, which are temporal Fourier transformation, temporal filtering and temporal imaging, were investigated in detail. Since the graded-index time lens integrates dispersion and time lens effectively, it will be helpful for simplying the optical signal processing system.3. The concept of temporal Gabor zone plate based on intensity modulation was firstly proposed. In addition, the theoretical model of temporal Gabor zone plate and linear optical pulse compression experimental system based on temporal Gabor zone plate were set up. According to the result, the modulation amplitude, temporal aperture and time-bandwidth product of the temporal Gabor zone plate are one half-wave switch voltage Vπ,1.88 ns and ≤39, respectively, whereas the corresponding parameters of time lenses based on electro-optic quadratic phase modulation are a dozen Vπ, tens of ps and ≤13. Thus, temporal zone plates have better performance than time lenses based on electro-optic quadratic phase modulation. Since the sinusoidal modulation profile of the temporal Gabor zone plate is easier to realize than the rectangular modulation profile of the temporal Fresnel zone plate, the bottle neck in the realization of the temporal zone plates is solved.4. The concept of temporal amplitude zone plates based on amplitude modulation was firstly proposed. The theoretical model of temporal amplitude zone plates was set up. Based on the theoretical model, the main performance parameters of the temporal amplitude zone plate was derived. By implementing the temporal amplitude zone plate into a linear optical pulse compression system, the energy efficiency is improved from 6.25% to 25%, and the background noise is decreased from 31.25% to 25%, although experimental devices used here are the same as temporal intensity zone plates. According to the result, the temporal amplitude zone plate has a higher energy efficiency and lower background noise than the temporal intensity zone plate.5. The concept of temporal phase zone plates based on phase modulation was firstly proposed. The theoretical model of temporal phase zone plates and linear optical pulse compression experiments based on temporal phase zone plates were set up. According to the result, the energy efficiency, temporal aperture, temporal resolution and time-bandwidth product are improved to 33.9%,5.77 ns,22 ps and 226, respectively. The technical problem in linear optical pulse compression based on time lenses is addressed by implementing temporal phase zone plates into linear optical pulse compression.6. The concept of incoherent-light temporal imaging based on a temporal pinhole was proposed. It is important to note that temporal imaging technique is implemented in the incoherent-light domain for the first time. The theoretical model and the experimental system of the incoherent-light temporal imaging based on a temporal pinhole were proposed. According to the result, the modulation amplitude, temporal aperture and time-bandwidth product are Vπ,8 ns and 162, respectively. The performance of the incoherent-light temporal imaging is much better than coherent temporal imaging based on electro-optic quadratic time lens.7. The concept of incoherent-light temporal imaging based on a temporal pinspeck was firstly proposed. The theoretical model and experimental system were set up. According to the result, the energy efficiency of the incoherent-light temporal imaging based on a temporal pinspeck is several tens of times that of the incoherent-light temporal imaging based on a temporal pinhole and thus, the key problem that the energy efficiency of the incoherent-light temporal imaging based on the temporal pinhole is low is addressed.