We report a simple post-process technique that harnesses a hybrid chalcogenide/silicon-germanium system for the control of waveguide dispersion. By adding a chalcogenide top cladding to a SiGe/Si waveguide, we can substantially change the dispersive properties, which underpin the generation of a supercontinuum. In our particular example, we experimentally show that a shift from anomalous to normal dispersion takes place. We numerically study the dispersion dependence on the chalcogenide thickness and show how to use this additional degree of freedom to control the position of the zero dispersion wavelengths and hence the spectral span of the supercontinuum. Finally, we compare our approach with more traditional techniques that use geometry for dispersion tailoring.
One of the challenges in laser direct writing with a high numerical-aperture objective is the severe axial focal elongation and the pronounced effect of the refractive-index mismatch aberration. We present the simultaneous compensation for the refractive-index mismatch aberration and the focal elongation in three-dimensional laser nanofabrication by a high numerical-aperture objective. By the use of circularly polarized beam illumination and a spatial light modulator, a complex and dynamic slit pupil aperture can be produced to engineer the focal spot. Such a beam shaping method can result in circularly symmetric fabrication along the lateral directions as well as the dynamic compensation for the refractive-index mismatch aberration even when the laser beam is focused into the material of a refractive index up to 2.35.
Long-period gratings in highly nonlinear chalcogenide glass (As 2 S 3 ) rib waveguides are fabricated. A strong resonance of $17 dB depths and 3 dB width of $15 nm is obtained at a wavelength of 1525 nm by coupling the fundamental mode to the HE 02 mode in good agreement with theory. The 20 mm grating is produced by a simple shadow mask technique and has a pitch of L ¼ 80 mm. the Australian Research Council (ARC). The Centre for Ultrahighbandwidth Devices for Optical Systems is an ARC Centre of Excellence. K. Finsterbusch is a research fellow of the German Research Foundation (DFG).
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