Design of cascaded volume holographic gratings to increase the number of channels for an optical demultiplexer.

The design and demonstration of a holographic optical demultiplexer based on cascaded volume holographic gratings are presented. By serially adding a second holographic grating, which has a different grating period, slant angle, and center wavelength compared with those of the first grating, the operating wavelength range of the optical demultiplexer could be expanded, and, therefore, the number of channels of the holographic demultiplexer is doubled. As a result of the experiment, a 0.4 nm spaced 130- channel demultiplexer with a channel uniformity of 3.5 dB, a 3 dB bandwidth of 0.12 nm, and channel cross talk of -20 dB is experimentally achieved.