Investigation And Design Of Band-Pass Filter Based On Cascaded Mach-Zehnder Interfermeters

Optical filter is an indispensable component in optical communication and photoelectron fields. It has been widely adopted in wavelength locking, wavelength multiplexer/demultiplexer, wavelength routers, dispersion compensators, and gain equalizers etc. With the increasing number of channels and decreasing channel spacing in wavelength division multiplexing (WDM) system, novel optical filters with excellent characteristics have become a leading trend presently. Particularly, the Mach-Zehnder interferometer (MZI) based filters have attracted considerable attention in the WDM system, because of their excellent characteristics, such as simple structure, low insertion loss, multi-level series, comb and band-pass filtering etc.To improve the filtering performance of caccaded MZIs and to design a band-pass filter with required performance index, combining with the comb filtering property of cascaded MZIs, the band-pass filter based on cascaded MZIs has been investigated by both theoretical study and numerical analysis.Firstly, the principle of filter based on cascaded MZIs is studied by the method of transfer matrix. Then the similarity of interferometer principle between cascaded MZIs and that of ladder-type optical filter (LTOF) is analyzed. The results show that the LTOF can be regarded as a filter based on cascaded MZIs with fixed path differences. Then, to obtain optimal sets of coupling angles and phase shift, a scheme combining some optimal algorithms commonly in digital filter and the comb filter based on cascaded MZIs is analyzed. It is indicated that the methods of digital filter not only can obtain perfect results, but also improve the design efficiency. Compared with genetic algorithm (GA) scheme, the particle swarm optimizationalgorithm (PSO) scheme is characterized by less calculation time, higher approximation accuracy, flater pass-bands and stop-bands.In the band-pass filter investigation section, a novel theoretical model of optical band-pass filter based on cascaded MZIs with chirped path differences is established...