Double-pass acoustooptic tunable bandpass filter with zero frequency shift and reduced polarization sensitivity

The authors report a zero frequency shift double-pass acoustooptic tunable bandpass filter employing a single acoustic flexural wave to couple light from the core mode to a cladding mode (propagating past a core block) and back again to the core mode. A double pass through the fiber filter yields reduced sidelobe levels and reduced polarization sensitivity. The prototype also exhibited improved dynamic range and a reduction in bandwidth.