Development Of Thin Film Filters In Hybrid Wavelength Division Multiplexing System

Hybrid wavelength division multiplexing technology, through the combined use of traditional coarse wavelength division multiplexing technology and wide spectrum of erbium doped fiber amplifier technology, had attracted broad attention of optical fiber communication since it appeared due to its long distance of data transmission, high efficiency of communication, anti-interference and secrecy performance, simple construction, and fast formation, etc. However, the technology was strict with the technology of multiplex/demultiplex optical filters and gain flattening filters it used. The two kinds of filters were difficult to develop with current technology of optical thin-film coating preparation, which became the main factor that restricted the development of hybrid wavelength division multiplexing technology. Therefore, based on the use requirements of multiplex/demultiplex optical filters and gain flattening filters in hybrid wavelength division multiplexing technology, through the detailed theoretical analysis and experimental research on alloy target sputtering characteristics, technique of hybrid thin-film deposition, design of film system, preparation technology and testing technology, it simplified the experimental procedure, and developed low-loss CWDM (Coarse Wavelength Division Multiplexing) filter and GFF (Gain Flattering Filter) by making use of less film in this paper.Firstly, Ta-Nb alloy target was used as a sputtering material, O2was used as the reaction gas, and a new type of composite film was prepared by the technique of ion beam reactive sputtering deposition (IBRSD). Respectively, spectrophotometer, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy were used to characterize and analyze the optical properties, crystalline state, composition ratio, the film surface microstructure and surface morphology of the composite film, the experimental results showed that:compared with Ta2O5and Nb2O5, the composite film was more suitable for developing the filters with more layers and lower absorption loss, the composite film could replace Ta2O5and Nb2O5to prepare the thin-film element for hybrid-WDM systems.Secondly, the properties of composite film and SiO2film deposited by ion beam sputtering under different ion beam process parameters were studied, the properties of composite film under different reaction gas parameters were researched, and the uniformity of film layers’thickness was corrected, the necessary conditions for the development of low-loss CWDM filters and gain flattering filters were provided, orthogonal matrix method was used to optimize the process parameters of the ion beam, comparing with the traditional methods, the optimized methods showed that the orthogonal matrix method needed fewer experiments to obtain the desired process parameters, and the great help of simplify the experiment procedures and shorten the development cycles was given.A perfect optimization method for designing filter film was established, the technologies of film stack plus and matching layers optimization were studied, the composite film and SiO2were chosen as the high and low refractive index film material, WMS-13glass was chosen as the substrate material, the film systems of the low-loss CWDM filters and GFF filters were designed by making use of less film and the requirements of hybrid WDM systems had been met.According to the structures of thin film system, the film thickness monitoring strategy of CWDM filters and GFF filters prepared by dual ion beam sputtering methods were studied and developed. In the preparation of the low loss CWDM filters, the optical extreme value method and average time method were used to monitor layers’thickness. In the preparation of the GFF filters, time monitoring method was used to control layers’thickness. The deposition rates of composite and SiO2film were acquired by the least square fitting for results of different deposition experiments. The experimental results showed that the film thickness monitoring precision of ion beam sputtering system could be improved by using those methods, the preparation work of low-loss CWDM and GFF filters could be successfully completed and a better film thickness monitoring scheme was provided for the preparation of high precision thin film devices.The transmission spectrum of the preparation of low-loss CWDM filter had been tested, which demonstration that the center wavelength of filter was1551.1nm, the width of the filter’s pass band was17.1nm and24.2nm in the region of-0.5dB and-35dB respectively, the worst insertion loss within pass band region is-0.09dB, the ripple of the pass band is0.04dB, and the rectangle degree was0.707; the transmission spectrum of the preparation of GFF filter had been tested, which demonstration that the wavelength independent loss of GFF was0.063dB, the difference of maximum and minimum of error function was0.198dB. The results shown that the preparation of the filters met the using requirements of hybrid wavelength division multiplexing system well after testing, the related researches had achieved satisfactory results.