Study On Novel Passive Compound Resonator Filtering And Its Application In Single-Longitudinal-Mode Fiber Laser

With the maturity and development of laser technology,single-longitudinal-mode(SLM)fiber lasers have been deeply studied by scholars due to their potential applications in fiber sensing,LIDAR,microwave photonics,optical atomic clocks and other fields.At present,one of the research focuses of SLM fiber lasers is to achieve multi-performance output of ultra-narrow line width,single / dual / multi-wavelength switchable,wavelength tunable /scan,etc.This article is based on the work of a new type of passive compound resonator filtering and its application in single longitudinal mode fiber laser.The main innovations and research contents include:1.The theoretical modeling and simulation analysis of cascade and nested passive compound resonator cavity filters are performed.The simulation methods involved include the conventional research method based on transmission matrix and the research method based on signal flow chart in automatic control theory.The variation rules of transmission spectrum under different parameters are analyzed in detail for the two structures.By studying the main parameters such as the free spectral range and full width at half maximum,it is found that the filter effect of the nested "8" cavity filter structure has obvious advantages among the two kinds of compound resonator filters.2.A four-wavelength switchable and tunable SLM fiber laser based on "8" structure filter was developed.Based on the characteristics of the laser main cavity and the reflection spectrum characteristics of the cascaded polarization-maintaining fiber Bragg grating(PM-FBG),with the realization of SLM laser as the goal,the "8" structure filter has been theoretically researched and experimentally produced.The cascade PM-FBG with 45-degree axial deviation fusion was used as a four-channel wavelength initial filter for the first time in a multi-wavelength switchable fiber laser.By introducing enhanced polarization hole burning effect and polarization-dependent loss,switchable operation of four single-wavelength operations,six dual-wavelength operations,four three-wavelength operations and one four-wavelength operation(fifteen lasing states)is realized,all with high stability.In single-wavelength operation,the four SLM lasing outputs measured are all with an optical signal-to-noise ratio of >82 dB,a side-mode suppression ratio of >67 dB,a laser linewidth<600 Hz,a relative intensity noise(frequency >3 MHz)?-154.58 dB/Hz,a power fluctuation?0.311 dB(7.93%),no jump mode within 30 min and excellent polarization characteristics.In addition,the feasibility of tunable wavelength interval and generation of microwave signals in different dual-wavelength operation modes was verified,and the frequency of 23.10 GHz microwave signal was successfully generated when the wavelength interval was 0.184 nm.