OPTIMIZATION OF FIBER BRAGG GRATING FOR DENSE WDM TRANSMISSION-SYSTEM

A fiber Bragg grating, which has periodical perturbation of the refrac tive index in the fiber core, acts as a wavelength selective reflectio n filter and steep optical spectrum can be realized by forming more th an ten thousand of gratings along the fiber core. Owing to capability of making steep optical spectrum, fiber Bragg gratings has been expect ed to be introduced practical use as multiplexing or demultiplexing fi lters in dense WDM transmission systems. On the other hand, radiation mode loss, reflection side mode and temperature dependence of Bragg wa velength, should be improved to put the fiber Bragg grating to practic al use in dense WDM transmission systems. In this paper, an optimum de sign and performance of the fiber Bragg grating for dense WDM systems are described. The photosensitive cladding fiber realized less than 0. 2 dB insertion loss at transmitted signal channels and less than 0.1 d B splicing loss with standard single-mode fibers. An adequate apodizat ion technique in the refractive index distribution suppressed reflecti on side modes. A temperature compensating package, which gives longitu dinal strain with negative temperature dependence to a fiber Bragg gra ting, minimized temperature dependence of Bragg wavelength less than 0 .001 nm/degrees C. Thermal decay of Bragg grating was also investigate d and adequate annealing condition was estimated to obtain sufficient stability for practical use in dense WDM transmission.