Reduced sidelobe integrated acousto-optic filter with birefringence apodization

Abstract

A two-section integrated acousto-optic tunable filter with significantly reduced sidelobes has been fabricated. The sidelobe reduction was achieved with birefringence apodization in the form of variable-width Ti-stripe waveguides. The design and fabrication of the device, which includes integrated proton-exchanged TE and TM-pass polarizers, are described. Experimental tuning curves for each filter section and the overall device are presented and compared with calculated results. The largest sidelobes were found to be 24 dB below the peak transmission, which represents a 5.3-dB improvement over an ideal filter without birefringence apodization. The FWHM of the filter is 1.36 nm, which is only 16% larger than predicted for its interaction length of 17 mm/section.