title: Sidelobe suppression in all-fiber acousto-optic tunable filter using torsional acoustic wave.
abstract: We propose two techniques to suppress intrinsic sidelobe spectra in all-fiber acousto-optic tunable filter using torsional acoustic wave. The techniques are based on either double-pass filter configuration or axial tailoring of mode coupling strength along an acousto-optic interaction region in a highly birefringent optical fiber. The sidelobe peak in the filter spectrum is experimentally suppressed from -8.3 dB to -16.4 dB by employing double-pass configuration. Axial modulation of acousto-optic coupling strength is proposed using axial variation of the fiber diameter, and the simulation results show that the maximum side peak of -9.3 dB can be reduced to -22.2dB. We also discuss the possibility of further spectral shaping of the filter based on the axial tailoring of acousto-optic coupling strength.
authors.affiliation: Department of Physics, Chonnam National University, 300 Yongbong-dong, Buk-gu, Gwangju 500-757, Korea. kjl@kaist.ac.kr
authors.forename: Kwang Jo
authors.initials: KJ
authors.lastname: Lee
authors.forename: In-Kag
authors.initials: IK
authors.lastname: Hwang
authors.forename: Hyun Chul
authors.initials: HC
authors.lastname: Park
authors.forename: Byoung Yoon
authors.initials: BY
authors.lastname: Kim