Research On Key Technologies Of High-Speed All-Optical Polarization Control

With the rapid development of “quantum control” and “precise measurement physics”,there is an urgent need for a technology capable of contring the state of polarization of picosecond or even femtosecond optical pulses at high-speed.However,the response time of the fastest electric polarization controller only can achieve nanosecond timescale to date,and it also requires complex electric control system,which makes it difficult to achieve high-speed control of the polarization state of picosecond or even femtosecond optical pulse.To solve this problem,in this thesis,a novel technology about all-optical proportional-integral-derivative(OPID)polarization control based on all-optical signal processing is proposed to realize high-speed all-optical polarization control for optical pulses.Supported by National Natural Science Foundation of China(NSFC),this thesis focuses on the key technologies of all-optical polarization control: all-optical proportional amplification,all-optical differentiation,all-optical integration,as well as other important issues of high-speed scrambling,control algorithms and density of polarization states statistics method.The main innovative achievements are listed as below:1.A novel method to analyze polarization control based on density of polarization states statistics is proposed,which not only can give the uniformity distribution index of polarization states and identify defective devices with polarization blind areas,but also locate accurately blind areas on the Poincaré sphere.Furthermore,a set of polarization scrambling demonstration experimental system based on piezoelectric ceramics(PZT)is developed independently,whose algorithm can be flexibly selected to optimize the polarization scrambling performance by LABVIEW.Analyzing the polarization scrambling system with the density of polarization states statistics method,it is found that the polarization scrambler with only two control units cannot achieve polarization states cover the whole sphere with existed blind areas,so that a polarization scrambler with good performance needs at least three control units.In order to highlight the advantage of the density of polarization states statistics method,we have selected commercial perfect and defective scramblers for analysis.The results show that the Stokes component method cannot distinguish their scrambling performance,while the density of states statistics method can achieve and point out the location and size of the polarization blind areas on the Poincaré sphere of device.It can be seen that the density of polarization states statistics method has unique advantages in the research on polarization control and analyzing the performance of polarization devices.2.Based on programmable differential group delay(DGD),a multi-functional alloptical femtosecond signal processing method is proposed,which can realize all-optical differentiation and all-optical integration of femtosecond pulses,and flexibly switch between the two functionalities by simply tuning the orientation of a polarizer.By programming DGD,the appropriate differential time delay and integral window can be generated,and the required differential and integral pulse waveforms also can be obtained,which can realize ultrashort optical pulses shaping.An experimental testing platform for all-optical signal processing of femtosecond pulses is designed and built,and experiments of all-optical differentiation and all-optical integration of 400 fs Gaussian optical pulses are completed,whose results are in good agreement with the theoretical calculations with relative error less than 10%.The measurement of femtosecond pulse differential waveforms is difficult,because femtosecond pulses become shorter and more complex after differentiation,which cannot be directly observed with an oscilloscope.To deal with it,we propose a method to measure the autocorrelation of femtosecond pulse differential waveform and its deconvolution,and observe the differential waveform vary process of femtosecond pulse under different DGD in detail.The realization of all-optical differentiation and all-optical integration of femtosecond pulses has taken the most critical step to realize all-optical polarization control.3.In order to build a complete OPID system,we propose an all-optical proportional amplification technology based on a quantum well semiconductor optical amplifier(QWSOA).The experimental results show that the linear proportional amplification has a dynamic range of up to 23 d B at mall signal input,which meets the system requirements.Furthermore,a femtosecond all-optical integrator and an all-optical differentiator are integrated to complete the OPID control system and test platform,and carry out a highspeed control and stabilization of femtosecond pulses polarization states experiment successfully.We use the fastest polarization scrambler made by General Photonics(PCD-104)to randomly perturb femtosecond pulses polarization state and then is stabilized by the OPID control system,the polarization state is almost fixed at a point on the Poincarésphere.By the test of a high-speed oscilloscope combined with an analyzer,the eye diagram of femtosecond pulse changes significantly in the process of polarization stabilization,which further verifies that femtosecond pulses polarization states can be controlled at high speed and effectively.The above research achievements,especially the completion of the OPID polarization control system,have important reference value for the research of ultrashort optical pulse control technology,and contribute to the further development of “quantum control” and “precision measurement physics”.