Study On All-fiber Optical Comb Filters

As one of the most revolutionary technologies in the twentieth century, optical fibercommunication exhibits great superiority and potential in3U (Ultra-High Speed, Ultra-LongHaul, Ultra-Large Capacity) communications. DWDM (Dense Wavelength DivisionMultiplexing) could increase optical communication capacity to a large extent and is also themainstream method for capacity increasing. All-fiber components are essential in all-opticalnetworks since they are simple, compatible, with small size and immune from EMI(Electromagnetic Interference). So far, all-fiber comb filters has been used in realizingmulti-wavelength source, multi-channel dispersion compensation, gain flattening, high-speedimpulse sequence, fiber sensors and so on.Firstly, basic theories and analyzing methods for fiber grating and HBF (HighBirefringence Fiber) Sagnac loop are introduced. Specifically, we deduce the transfer matrixmethod based on coupled-mode theory to address problems regarding nonuniform fibergratings. Also, Jones calculus is introduced in detail to perform research on HBF Sagnacloop.Secondly, the novel optical multichannel filter based on full-duty-cycle sampled fiberBragg grating with spectral Talbot effect is proposed for the first time to our knowledge.Based on analysis and numerical simulations, it is shown that high-performance comb filterscan be realized with the proposed structure. Moreover, it is found that channel count scaleslinearly with the number of samples and that high-quality filtering is still available with stepchirp or some fabrication errors.Lastly, the relationship between parameters of HBF Sagnac loop and comb spectrum isstudied. We also demonstrate one-order and multi-order HBF Sagnac loop both numericallyand experimentally. The results indicate that HBF Lyot-Sagnac loop is suitable for realizingnarrow-band comb filtering as it could reduce the line width and increase the isolationeffectively.