The authors describe the most rectangular passband yet reported for an
acousto-optic wavelength-routing switch. The device is a multicycle S
AW directional-coupler-weighted AOTF, fabricated on XY lithium niobate
, with a -3dB width of 2.52nm and a -20dB width of 0.89nm. For compari
son, an ideal apodised AOTF with the same 3dB width would have a -20dB
width of only 0.33nm.