Compact and monolithic coarse wavelength-division multiplexer-demultiplexer fabricated by use of a high-spatial-frequency transmission grating buried in a slab waveguide.

A compact and monolithic four-channel demultiplexer with 20-nm spacing was fabricated by use of a high-spatial-frequency transmission grating buried in a silica waveguide. The grating was successfully buried in a silica slab waveguide by overcladding by plasma-enhanced chemical-vapor deposition. The device's size was approximately 5.1 mm x 9.2 mm. The average insertion loss was 13 dB. The average cross talk was -15 dB for adjacent channels and -19 dB for nonadjacent channels. The polarization-dependent loss was estimated to be as low as 0.7 dB.