title: Single-step writing of Bragg grating waveguides in fused silica with an externally modulated femtosecond fiber laser.
abstract: For the first time to our knowledge, high-strength (>30 dB) first-order Bragg grating waveguides were fabricated in bulk fused silica glass in a single-scanning step by modulating a high-repetition-rate femtosecond fiber laser with an external acousto-optic modulator. The modulation induced a waveguide segmentation by delivering controlled bursts of laser pulses to define an array of partially overlapped refractive index voxels. With appropriate choice of modulation frequency and sample scanning speed, low loss waveguides could be formed at high writing speeds to yield sharp Bragg spectral resonances tunable over the 1300 to 1550 nm telecom band. Effects of acousto-optic modulation duty cycle on propagation loss and grating strength are characterized. This modulation method offers facile control and integration of multiwavelength Bragg grating devices to enhance overall functionality of optical circuits in three-dimensional geometries.
authors.affiliation: Department of Electrical and Computer Engineering and Institute for Optical Sciences, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada. haibin.zhang@utoronto.ca
authors.forename: Haibin
authors.initials: H
authors.lastname: Zhang
authors.forename: Shane M
authors.initials: SM
authors.lastname: Eaton
authors.forename: Peter R
authors.initials: PR
authors.lastname: Herman