High-resolution grating-assisted acousto-optic tunable filter

Summary form only given. Recent interest in WDM increasingly demands a faster tunable spectral filter with a narrower bandwidth with weak sidelobes to permit a larger number of wavelength channels within the erbium-doped fiber amplifier (EDFA) passband. However, most current acousto-optic tunable filters (AOTFs) have broad spectral bandwidths due to the limited-time-bandwidth product or a refractive-index change of an acousto-optic device at 1.55 /spl mu/m. The spectral bandwidth of an AOTF can be significantly reduced by inserting a diffraction grating in the light path just after the acousto-optic beam deflector (AOBD). Instead, the tuning range is reduced by the same ratio, because the time-bandwidth product is fixed. By optimizing an AOBD with a large bandwidth and a slow acoustic velocity combined with a diffraction grating with a suitable grating period, a narrow bandwidth of 0.2 nm and a broad tuning range of 50 nm-enough to cover the entire EDFA passband-are experimentally obtained. The result implies a significantly increased number of available wavelength channels. The improvement is by a factor of /spl sim/20.