| With the rapid development of communication and Internet,optical fiber communication system is advancing towards the trend of large bandwidth,high speed and low loss.However,it is very difficult to detect,analyze and process optical signals with traditional technology.So microwave photonics came into being and various photonic technologies were gradually applied to the RF field.In the application of wideband RF signal detection,the frequency spectrum can be divided into several small frequency bands by different wavelength laser and signal beat frequency,and then processed by down-conversion technology.Frequency scanning laser will directly affect the performance of the whole system,so its research is very important.At present,the common method of frequency division is to first generate an optical frequency comb and then pass through a tunable optical filter.There are some intractable defects in the scheme of frequency-scanning laser.What's more,the bandwidth of the general tunable optical filter is not as narrow as that of the electric filter,and the tuning accuracy and speed are also limited.And the temperature drift is very serious.Therefore,the direct generation of frequency scanning lasers has gradually become an optimal scheme for spectrum detection.However,the scanning step of the existing frequency-scanning laser mainly depends on the modulating frequency of the modulator.Therefore,the scanning frequency is also greatly limited.This paper proposes a scheme of directly generating frequency-scanning lasers,namely frequency-scanning laser based on the principle of vernier caliper,and the influence of frequency scanning laser carrier to noise ratio and the wafer level factors are expounded.The scheme is composed of a phase modulator,an acousto-optic modulator and a FP cavity filter.Frequency scanning is not only determined by modulator or FP cavity filter,but also by cyclic structure to realize frequency scanning laser.Theoretically,the frequency scanning laser with arbitrary step size can be realized.The specific research work of this paper includes the following:1.The generation scheme of optical frequency comb based on cyclic frequency shifter is analyzed theoretically,and its realization principle is elaborated and its numerical simulation is carried out.The high order crosstalk components of the modulated signal,the influence of line width,EDFA and other parameters on the flatness and signal-to-noise ratio of the frequency scanning laser is analyzed theoretically,and the inference is verified by simulation results.The modulation signal is generated by feeding the laser into the MZM modulator and loading the pulse signal.Input this modulation signal into the cyclic frequency shift structure and increase the delay amount,and the generation of frequency scanning laser is realized.2.A new scheme of generating frequency-scanning laser based on the principle of vernier caliper is proposed,and the realization principle of the frequency scanning laser is elaborated and deduced.And it is verified by simulation.3.The influence of laser parameters such as line width and EDFA on the flatness and signal-to-noise ratio of the generated frequency-scanning laser is discussed through theoretical derivation,and simulation results verify the previous inference.The frequency scanning laser based on the principle of vernier caliper has the advantages of low cost,excellent performance and wide tunable frequency range.Its greatest advantage is by changing the modulation depth and FP cavity filter parameters,the frequency scanning laser with arbitrary step size and scanning range can be realized.Compared with other existing technologies,it has certain advantages and provides a new idea and scheme for the research of frequency scanning laser. |
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