Studies On Tunable Multi-wavelength Optical Fiber Source For True Time Delay System Of Phased Array Radar

Phased array radar is widely used in missile target positioning system,ship radar sign system,meteorological precipitation monitoring system and so on.Optically controlled phased array radar has become a hot research topic because of the requirement of modern military development and civil monitoring.Various schemes of true time delay system for optically controlled phased array radar at home and abroad are analyzed.On this basis,a true time delay scheme based on a novel tunable multi-wavelength optical fiber source and linearly chirped fiber grating is proposed.Tunable multi-wavelength optical fiber source for true time delay system in optically controlled phased array radar is designed in the paper.A single frequency carrier generated by DFB laser is modulated to optical carrier side frequency by double quadrature phase shift keying(DQPSK)modulator.Multi-wavelength optical signal output with same frequency spacing is generated owing to cascaded four wave mixing effect in highly nonlinear optical fiber(HNLF).The frequency spacing(wavelength spacing)of multi-wavelength optical signal is precisely and flexibly adjustable controlled by RF signal driven DQPSK modulator.The true time delay system consists of tunable multi-wavelength optical fiber source and linearly chirped fiber grating.Results of true time delay with large delay range and high delay precision are obtained.The main work is as follows:1.Studies on generation of optical carrier side frequency by DQPSK modulatorThe principle of generating the side frequency signal in the DQPSK modulator is analyzed in theory.The process of generating the side frequency signal in the DQPSK modulator is experimentally studied.The influence of the power of distributed feedback laser and the power and frequency of RF signal generator on the generation of side frequency signal is analyzed.2.Studies on generation of multi-wavelength optical signals owing to cascaded four wave mixing effect in high nonlinear fiberThe principle of four wave mixing and cascaded four wave mixing effect occurred in the highly nonlinear optical fiber is analyzed in theory.The process of the formation of multi-wavelength in high nonlinear fiber is experimentally studied.The influence of the power of erbium doped fiber amplifier,the frequency of RF signal generator,the power difference in main frequency and side frequency and the length and dispersion slope of high nonlinear fiber on the formation of multi-wavelength is analyzed.Finally,a stable broadband multi-wavelength fiber source is formed,and the radio frequency of the RF signal generator controls the wavelength interval of the multi-wavelength fiber source precisely.Tunable multi-wavelength output of 1550 nm is obtained experimentally.When the wavelength spacing is 0.16 nm,20 multi-wavelength signals are output in the 3dB bandwidth of 3.233 nm.When the wavelength spacing is 0.064 nm,32 multi-wavelength signals are output in the 3dB bandwidth of 2.083 nm.By adjusting the RF driving signal,the multi wavelength spacing can be adjusted in the range of 0.08pm~0.16 nm,and the tuning accuracy is 0.024 pm.3.Studies on the true time delay system composed of tunable multi-wavelength optical signal and linearly chirped fiber gratingThe principle of time delay characteristics of linearly chirped fiber grating is analyzed in theory.The process of the generation of the true time delay in the linear chirped fiber grating is numerically simulated.The influence of the frequency variation in linear function and sine function on the generation of the true time delay and radar beam's emission angle is analyzed.Finally,the linearly control of radar beam's emission angle is realized.Numerical simulation and analysis,the delay difference between adjacent channels is adjustable in the range of 0.08ps~133ps,the precision is 0.024 ps.The output range of the delay difference is 0.08ps~133ps and the delay precision is 0.08 ps.The range of radar beam transmitting angle is 0.34 degree ~90 degree and the precision is 0.01 degree.The linear output of beam transmitting angle can be realized by programming and controlling the radio frequency driving signal.