| Nowadays, with the development and application of fiber gratings, optical fiber grating penetrates into various branches of optical fiber communication system gradually, including wavelength division multiplexed system/demultiplexer, the dispersion compensation, the fiber amplifier gain flatness,etc., the research on fiber Bragg grating technology and device can solve many key technological problems in optical communication system.Fiber grating with features of good coupling and wavelength selectivity, large bandwidth, small size, polarization insensitive, ease of use and maintain, and good connectivity with other optic fiber systems has a complete production process, can form large scale production and reduce cost.Therefore fiber grating and devices occupy a crucial position in the all-optical network. because of the optical fiber transmission loss, it makes the optical signal cannot transmit far more distance than 50-100km for the receiver to identify. In WDM and DWDM systems, the need of wider bandwidth and a plurality of cascaded amplifiers to work that result in the choosing of a wider and flatter range of gain spectrum of erbium-doped fiber amplifier (EDFA) is inevitable.Chirped phase shifted grating can be formed by introducing phase shift in chirped fiber grating, it contains some important properties of both chirped fiber grating and phase-shift grating, including a wider range of reflection bandwidth and transmission window. To achieve practical application needed more wide band specific reflection bandwidth and transmission window, a special EDFA Gain flattening filter based on chirped phase-shifted fiber grating excellent filter features is designed by Cascading apodized chirped phase-shifted fiber grating and chirp fiber grating in the paper.Main work done and achievements are as follows:1. A detailed derivation of the phase-shifted fiber grating coupled mode equations and a solution have been carried out, and the transfer matrix method of phase-shifted fiber grating was analyze.2. The transfer matrix method was applied to analyze the reflective spectrum of chirped phase-shifted FBG and apodized chirped phase-shifted FBG. Some regular characteristics between these two kinds of structure of grating were summarized at the different phase shift parameter and different grating parameters, which provided a solid theoretical basis for subsequent design cascaded apodized chirped phase-shifted FBG filter.3.Two kinds of cascaded fiber gratings were discussed and analyzed,the role of different raster bands overlap phenomenon does not exist, the independent role of the grating and no interfere with each other were verified by the simulation analysis of the reflection spectrum when there were no overlap in the two reflection spectrum.4.The working principle of erbium-doped fiber amplifier (EDFA) and its three kinds of pumping modes were analyzed in detail, and the experiment of EDFA was built to measure the gain spectrum and make a comparison among the three kinds of pumping modes.5. The simulation analysis of filter based on cascaded chirped phase-shift FBG and chirped FBG for flattening BIP-EDFA gain spectrum was carried out by using matlab and origin8.1, after the comparison of the effect of filter with existing literature and journal article on EDFA gain flattening, the filter based on the cascaded chirped phase-shifted grating and chirped grating adopted in this paper made the gain variation in an EDFA within about ±0.3 dB over bandwidth of 35.8 nm. In addition, the simulation analysis of the designed cascaded chirped phase shifted grating showed it played a certain role in fiber dispersion compensation. |
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