An experimental acousto-optic tunable filter that has a narrow spectra
l bandwidth (0.2 nm at 1550 nm) and a fast (10-mu s) tuning capability
with a continuous tuning range of approximately 50 nm is described. T
he tunable filter consists of an acousto-optic beam deflector with a d
iffraction grating whose grating vector is transverse to the direction
of light propagation.