title: Adaptive slit beam shaping for direct laser written waveguides.
abstract: We demonstrate an improved method for fabricating optical waveguides in bulk materials by means of femtosecond laser writing. We use an LC spatial light modulator (SLM) to shape the beam focus by generating adaptive slit illumination in the pupil of the objective lens. A diffraction grating is applied in a strip across the SLM to simulate a slit, with the first diffracted order mapped onto the pupil plane of the objective lens while the zeroth order is blocked. This technique enables real-time control of the beam-shaping parameters during writing, facilitating the fabrication of more complicated structures than is possible using nonadaptive methods. Waveguides are demonstrated in fused silica with a coupling loss to single-mode fibers in the range of 0.2 to 0.5 dB and propagation loss <0.4 dB/cm.
authors.affiliation: Department of Engineering Science, University of Oxford, Oxford, United Kingdom. patrick.salter@eng.ox.ac.uk
authors.forename: P S
authors.initials: PS
authors.lastname: Salter
authors.forename: A
authors.initials: A
authors.lastname: Jesacher
authors.forename: J B
authors.initials: JB
authors.lastname: Spring
authors.forename: B J
authors.initials: BJ
authors.lastname: Metcalf
authors.forename: N
authors.initials: N
authors.lastname: Thomas-Peter
authors.forename: R D
authors.initials: RD
authors.lastname: Simmonds
authors.forename: N K
authors.initials: NK
authors.lastname: Langford
authors.forename: I A
authors.initials: IA
authors.lastname: Walmsley
authors.forename: M J
authors.initials: MJ
authors.lastname: Booth
mesh_terms: D004867:Equipment Design; D007834:Lasers; D007909:Lenses; D008027:Light; D055100:Optical Fibers; D055095:Optics and Photonics / Q000295:instrumentation* / Q000379:methods; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D012822:Silicon Dioxide