A volume diffraction grating having a substrate and an optically active
layer has a structure formed in the optically active layer. The structure
is operational to diffract optical signals in two selected spectral bands.
The grating may be formed in a high dispersion embodiment suitable for
separating individual signals from composite signals of both spectral
bands. Alternatively, the grating may be formed in a low dispersion
version which can separate the composite signals from each other. In
another embodiment, a second structure is formed in the optically active
layer. Each of the structures is configured to be operational in one of
the spectral bands, allowing signals in each band to be diffracted
independently of one another. In another embodiment, the structure(s) may
have a curved profile allowing the diffracted beams to be shaped or
focused without the need for external lenses.
