The Studies And Applications Of Continuous Wave Quadratic Phase Modulation

This paper is based on the linear frequency swept module of broadband linear frequency swept source, which is the key component of high-resolution laser radar imaging system(No.61471256) and high-resolution real-time spectrum analyzer. When a continuous wave is modulated by a quadratic profile phase, a series of optical frequency combs(OFC) and linear frequency swept signal are generated. This OFC can be used as multi-wavelength source, which can be used in multi-wavelength parallel frequency sweeping of high-resolution real-time spectrum analyzer. The linear frequency swept signal can help to improve the resolution of laser radar and the sweeping rate of above spectrum analyzer.In this paper, on one hand, OFC system based on the continuous wave modulation technology is analyzed and optimized by numerical simulation. On the other hand, a new method which is used to generate linear frequency swept signal with quadratic phase modulation is proposed and studied in theory and experiment. At last, based on the experiment, broadband linear frequency swept signal system with swept range of 200 GHz and sweep rate of 10 THz/ms is designed. The main contents of this paper are as follows:1. The applications of OFC based on continuous wave and linear frequency swept optical signal in dense wavelength division multiplexing(DWDM) communication system, high-resolution laser radar imaging system and high-resolution real-time spectrum analyzer are introduced briefly. And several methods in OFC and linear frequency swept optical signal generating are summarized and compared.2. The fundamentals of time lens are introduced. The influence of cascaded modulator quantity and the change of driven electrical signal on the OFC quality(flatness and lines number) are analyzed with numerical simulation. Also, the influence of quadratic profile signal drifting and higher-order harmonics on the OFC quality are studied. The tolerated offsets of each parameter are obtained, which provides the credible evidence for optimization of experiment system and the chosen of devices.3. The principle of frequency shift with sawtooth wave and quadratic profile phase modulation are induced and studied in experiment. The results shown that in the case of sawtooth wave phase modulation, side-mode suppression ratio(SMSR) of fixed frequency shift reaches 20 dB, and the influence factors are discussed by experiments finding. In the case of quadratic profile phase modulation, we get the linear frequency swept optical signal successfully, the linearity of it is observed by real-time spectrum analyzer, and the influence factors of linearity are analyzed qualitatively.4. On the basis of above experiment, broadband linear frequency swept signal system with swept range of 200 GHz and sweep rate of 10 THz/ms is designed, which provides the credible evidence for realization of high-resolution laser radar imaging system.