Research And Implementation Of Time Lens Based On Linear Frequency Sweeping Signal Modulation

The development of big data,AI and ultra-high definition video will accelerate the speed of communication transmission.The traditional electrical processing speed is far less than the speed of communication transmission.Applying optical signal processing instead of electrical signal processing has become a trend to break through the bottleneck of communication system.In spatial optics,complex functions such as spatial Fourier transformation and holographic image can be realized by optical lenses.As the principle of space-time duality develops,signal processing technology in spatial optics is gradually applied to time-domain,namely,time lens.Like the spatial lens,time lens also has the characteristics of less system components and powerful functions,which has great potential in optical signal processing.Based on the principle of space-time duality and analogy with the concept of Airy disk in spatial lens,this thesis deduces the calculation formula of time-domain resolution and the figure of merit,and then analyses the common ways to realize time lens.The performance of traditional linear time lens based on electro-optical phase modulation is limited,and the method based on nonlinear process is too complicated and also has instable problem.Therefore,this thesis proposes a method that directly generates quadratic phase and then realizes the time lens through modulation.Two orthogonal linear sweep signals are directly generated by high-speed arbitrary waveform generator and modulated by I/Q modulator.Compared with the traditional electro-optical phase modulation time lens,the time aperture and figure of merit can be increased by orders of magnitude.On this basis,the modulation principles of phase modulator,Mach-Zehnder modulator and I/Q modulator are studied.For the sake of accuracy,experiments of high linearity sweep signal modulation are carried out.The time aperture reaches 4.4ns and the FOM exceeds hundreds,which are much larger than the traditional electro-optical phase modulation time lens.In addition,two methods for extending the linear frequency sweeping time-lens bandwidth are also studied.Aiming at the application of time lens in optical signal processing,an optical pulse shaping simulation system based on linear sweep time lens is constructed.In the aspect of temporal imaging,we investigate the scaling factor range of the time lens for a 1 ps Gauss pulse.And then combining the modulation process of I/Q modulator,the influence of various factors in temporal imaging is studied.The simulation results show that highorder phase terms and misfocus are the main causes of temporal aberration.In the aspect of time-domain Fourier transformation,the Fourier transformation process of time lens is simulated and analyzed.Based on the invariance of pulse spectrum transmission in dispersion system and the correspondence between the time domain waveform and the spectrum envelope of the Gauss pulse,a distortion-free transmission system of the Gauss pulse based on the conversion from frequency domain to time domain through Fourier transformation is realized.