Ultralow sidelobe-level integrated acoustooptic tunable filters using tapered-gap surface acoustic wave directional couplers

• Published in: Journal of lightwave technology 1994-06, Vol.12 (6), p.977-982
• Main Authors: Kar-Roy, A., Tsai, C.S.
• Format: Article
• Language: English
• Subjects: Acoustic waveguides; Acoustic waves; Directional couplers; Fabrication; Optical crosstalk; Optical design; Optical filters; Optical surface waves; Optical waveguides; Surface acoustic waves
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/50.296187

We propose a new weighted-coupling scheme using tapered-gap surface acoustic wave directional couplers for realization of ultralow sidelobe-level integrated acoustooptic tunable filters (IAOTF's). Appropriate design analysis has been carried out for 30-mm-long filters operating at an optical wavelength of 1.55 /spl mu/m in an X-cut Y-propagating LiNbO/sub 3/ substrate. New synthesized weighting functions have been used for the improvement of sidelobe level suppression over existing single-stage filters by as much as 27 dB. The -20 dB mainlobe width of the resulting IAOTF's varies from 2.7 to 3.9 nm only for the worst sidelobe levels ranging from -30.6 to -44.7 dB, respectively. It has also been shown that further suppression of sidelobe levels by 3-9 dB is possible if the filter is underdriven at 80% mode-conversion efficiency.< >