| With the development of the data service, the bandwidth requirements of users are growing day by day, and the capacity of optical communication system increases rapidly. How to make use of existing optical fiber transmission system to improve the optical communication capacity and meet the growing demands has become a hot area of optical communication research. WDM(Wavelength Division Multiplexing) technology can meet such requests. One of the core devices of WDM is OADM(Optical Add/Drop Multiplexer). OADM can multiplex the intensive and interval wavelength to an optical fiber for transmission, or separate the various multiplexed wavelengths by using optical methods. WDM thin-film filter which is a film element, is developed in recent years and has become one of the most popular devices of OADM.This research is based on a new type of reversible two-way broadband wavelength division multiplexing / demultiplexer. The structures and performance of parallel plate thin-film filter and wedge thin-film filter of WDM, which are parts of that OADM, are designed and analyzed. The film structures and transmittance of the two wideband WDM thin-film filters curve is simulated. A WDM thin-film filer testing system is designed, which is made up of Tunable laser, ASE, Optical Spectrum Analyzer(OSA), Optical Power Meter, etc.. The center wavelength, transmittance, insertion loss, bandwidth, transmittance spectrum, and other performances are tested and analyzed. Through this research, hope that this research will become reference of development and application of a WDM thin-film filter.First, this study provides an overview of technology, development and the present situation of WDM thin-film filter, including the application of the thin-film filters, preparation techniques, measurement techniques, etc.. At the same time, the study elaborates the subject content and significance.Second, around the topic of this research, the theoretical foundations of the key technologies in this paper are briefly introduced, including the basic principles of WDM technology and its main characteristics; the basic principles of thin-film filter and its application in WDM systems. Two typical structures of the thin-film filter, F-P thin-film filter and all dielectric F-P thin-film filter, are elucidated as key points, and center wavelength, transmittance of peak wavelength, half bandwidth, and calculation of each parameters are elucidated.Third, various design requirements of WDM thin-film filter are introduced, including center wavelength, bandwidth of channel, peak insertion loss, incident angle, polarization dependent loss, etc.. And the film layer structures of high refractive index spacing layer thin-film filter and low refractive index spacing layer one are designed, and their transmittance curves are simulated. The influences on filter's performance of spacing layer thickness are analyzed. At the same time, a new type of reversible two-way broadband wavelength division multiplexing / demultiplexer is given. This OADM uses two thin-film filters-Device I parallel plate thin-film filter and Device II wedge thin-film filter-to complex wave and partial wave. In this paper, the structure of two filters are designed and simulated, getting transmittance spectrum of C+L wave band, transmittance of peak wavelength, wavelength interval, and etc. of each thin-film filter.Fourth, this research designs and analyses the testing system of WDM thin-film filter, which can test center wavelength, transmittance, insertion loss, bandwidth, transmittance spectrum, and other performances of thin-film filter samples. It is made up of Tunable laser, ASE, Optical Spectrum Analyzer(OSA), Optical Power Meter, and other instruments of Optical communications. The advantages of the system are air direct coupling, simple structure, convenient measurement, measurement and high accuracy, and etc.. Through multiple testing, coupling rate of the system is 95%, insertion loss is 0.22dB, the stability of system is less than 0.05dB, and system stability is well. At the same time, ASE broadband light source and tunable laser involved in the experiment are designed. They are both use optical fiber loop mirror structure, which can effectively increase the output power. The output power can reach more than 20mW. In addition, various notes of testing samples in the use of the system are summarized.At last, samples of thin-film filter are tested and the performances are analyzed. The sample of WDM parallel plate thin-film filter is tested by the ASE broadband light source, transmission spectrum of different scanning points are got. The thickness of F-P cavity spacing layer can be calculated, d = 0.104mm. And there are 29 channel wavelengths. With the same method, the sample of wedge thin-film filter is also tested, the thickness of F-P cavity spacing layer is 0.859mm. 24 channel wavelengths are got. At the same time, the transmittance and insertion loss of are tested. According to the result of the testing, fringe spacing is 0.5mm, and the angle of wedge is calculated, it isθ= 3.98′′.Thin-film filter technology can be widely used in WDM, it has the advantages of wide bandwidth, good stability, low cost, easy to be realized, and so on. The advantages of the WDM thin film filter testing system are air direct coupling, simple structure, convenient measurement, measurement and high accuracy, system stability being well, and etc..In summary, this research detailed structural design, simulation, testing of laboratory devices, and summed up the results of testing and analysis of the WDM thin-film filter and its testing systems. The study is very detailed and in-depth. I hope these results can provide valuable technical support for research and development of WDM thin-film filters. |
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