Novel compact dual-channel all-fiber Bragg grating multiplexer

Due to the excellent spectral characteristics, fiber Bragg gratings are widely considered as filters for wavelength-division multiplexed (WDM) systems. Because Bragg gratings are stopband filters they have to be combined with other components such as circulators or couplers in order to work as optical multiplexers. Recently, we analyzed the characteristics of an all-fiber add-drop multiplexer with a Bragg grating within the coupling zone of a fiber coupler. We have shown that the position of the grating has to be chosen carefully for proper device operation. Here we demonstrate a novel dual-channel all-fiber Bragg grating multiplexer. The device is based on a polished fiber coupler. Two 2.8-mm-long Bragg gratings at different wavelengths of 1531.6 nm and 1535.3 nm were written at the same position identically into both fibers of the coupler. This was done easily by using a phase mask and stretching the fibers before writing the gratings. After embedding the fibers in separate glass substrates using an epoxy resin, the fiber claddings were polished off. Because we improved the polishing process, a long and homogenous coupling length of ~14 mm could be reached. Thus, the actual grating position within the coupling zone is less critical, which makes manufacturing easier. The dependency of the grating position on the Bragg wavelength can be neglected