Broadband Wavelength-division Multiplexing Multi-channel Filters Based On Sampled Fiber Bragg Gratings

Broadband wavelength-division multiplexing multi-channel filters based on sampled fiber Bragg gratings and an accurate wavelength spacing equation have been proposed for the first time. Firstly, taking advantage of Coupled Mode Theory, the reflection spectrum expression of Fiber Bragg Grating (FBG) can be derived from Maxwell Equations. Sampling on the fiber core index modulation of FBG with square wave, Sampled Fiber Bragg Grating (SFBG) can be produced for the application of comb filter. Secondly, the analyzing approach for the reflection spectrum of SFBG are based on the reflection spectrum expression of FBG.. SFBG can be partitioned into several segments and each segment can be express as optical matrix of uniform FBG. Using Piecewise-uniform Approach, the reflection spectrum of SFBG can be calculated. Thirdly, the accurate analytical expression for reflection-peak wavelengths of SFBG can be derived by Fourier Analysis Approach. With this expression, the details of reflection spectrum of SFBG, such as the location of reflection-peak wavelength and the spacing of reflection-peak wavelengths, can be indicated. In conclusion, these three steps are the basis of design of broadband wavelength-division multiplexing multi-channel filters.Taking advantage of the accurate expressions of the location of reflection-peak wavelength and the spacing of reflection-peak wavelengths, the concrete parameters that influence the spectrum properties of SFBG can be calculated. The location of reflection-peak wavelength and the spacing of reflection-peak wavelengths should satisfy the ITU-T Recommendation. The location of reflection spectrum varies with the grating period (corresponding to the Bragg wavelength of FBG), thus, by changing the grating period, the reflection spectrum of SFBG can be shifted by one wavelength spacing or more.