A passband-flattened acousto-optic filter

We have demonstrated a passband-flattened LiNbO/sub 3/ guided-wave acousto-optic tunable filter (AOTF). Passband flattening is achieved by approximating the predicted flattened-filter decaying-sine acoustic intensity drive function by two half cycles of a sine wave of successively lower intensity. These filters have a cross-state 3-dB passband of /spl sim/1.75 nm, equal to that of the apodized filters on which they are based, an approximately 1 nm wide flat region with <0.5 dB variation of transmission, and correspondingly broadened depletion in the bar state, with a maximum rejection ratio of better than 17 dB. Worst-case sidelobes are /spl sim/13 dB. The typical acoustic power required for complete switching is 40 mW, only 20-40% greater than that needed in the apodized filter.<>