Research Of Photonic Crystal Fiber In Time Stretched Analog To Digital Conversion System

Analog to digital conversion (ADC) as bond between analog and digital signals, contacts the analog sensor and digital signal processing system. With the popularity of computer, improvement of automation and digital signal processors, ADC has become more and more important. The paper extends the scope of application of photonic crystal fiber (PCF), researches and provides high performance ADC methods, it has a good prospect in broadband radar, electronic surveillance and other signal processing. The main contects and innovative achievements of the paper are as follows:(1) Linear chirp and flat supercontinuum spectrum (SC) has been researched through theory and simulation. Discussing relationship between SC and fiber parameters and using highly nonlinear PCF combined with conventional fibers to produce SC, the spectrum has491nm and the flat bandwidth has100nm with+/-0.5dB. The SC is suitable as broadband light source in time stretched analog to digital (TS-ADC) system. In the scheme length of PCF is only0.45m, reducing the cost.(2) The TS-ADC based on large dispersion PCF has been research. In the system, analog signal is modulated on linear chirp and flat SC optical pulse and stretched in large dispersion PCF.3.3TSa/s effective sampling rate and660GHz effective bandwidth have been achieved. Because of large dispersion PCF, the length of fiber, complexity of the device and transmission power have been reduced, meanwhile distrotion from amplifier and optical bandpass filter has been avoided.(3) Research on improved TS-ADC based on PCF. Using coherent detection instead of traditional direct detection, so many advantages have been gained as high detection ability, convension efficiency, signal to noise ratio, stability and reliability. Using phase modulation instead of amplitude modulation to overcome random jitter from amplifier and bandpass filter.(4) The all optical ADC scheme has been proposed combining time stretched module with four-wave mixing (FWM) module. It has been stimulated using two40Gb/s pseudo-random sequence with40stretched factor. In order to avoid frequency attenuation using single-sideband modulation, the effective sampling rate is1.6TSa/s.(5) Based on the study of TS-ADC, PCF nonlinearity has been researched by theory and simulation, comparing with single-mode fiber (SMF) and dispersion compensation fiber (DCF). The curves of three fibers will overlap with no nonlinear curves by different input power or pulse bandwidth. Comparatively, PCF is not sensititve with changing input pulse width. In TS-ADC system, PCF is most suitable for broadening medium.