A REFLECTION-TYPE SUBSTRATE-MODE GRATING STRUCTURE FOR WAVELENGTH-DIVISION-MULTI-DEMULTIPLEXING

We describe a technique to design and implement a wavelength-division- multi/demultiplexing device with a reflection substrate-mode grating p air in dichromated gelatin. This device is based on a diffraction volu me grating pair, which provides and angularly dispersive function, to separate optical signals at different wavelengths through the dielectr ic substrate with total internal reflection. In this structure, the ch annel separation is enhanced by multiple reflections at substrate-air interfaces with a shorter longitudinal distance. Normally incident cou pling and on-axis output imaging with this structure provide easier al ignment with coupled optical fibers. The device with a polarization-in sensitive high efficiency ( > 80 %) for 76-nm bandwidth has been fabri cated.