Flat-field spectrograph in SiO/sub 2//Si

The operation of a flat-field spectrograph in silica glass on silicon (SiO/sub 2//Si) as a demultiplexer with 4-nm channel spacing in the 1.5- mu m waveguide length region is demonstrated. The concept allows fabrication tolerances to be compensated simultaneously with the adjustment of fan-out. Fiber-to-fiber insertion loss of 10.1 dB and crosstalk attenuation >15 dB have been achieved.>