A scheme of applying high contrast grating hollow waveguide (HCG-HW) to optical phased array (OPA) as the
transmission waveguide and phase shifter is proposed. The phase shift with varied HCG-HW dimensions is deduced in a
theoretical approach and demonstrated by the simulation results. Beam steering in one direction is done by varying the
wavelength. A phase shift range of 18.7 rad and the beam angle shift to 12.62° with varied wavelengths are presented.
We studied the interaction between sub-picosecond laser pulse with fused silica. Breakdown threshold, electron collision time and nonlinear propagation dynamics were investigated to study the ionization dynamics and nonlinear propagation process of laser pulse. Electron collision time was measured to be about 1.7fs when the electron density is about 1019cm-3. Measurements on single shot laser-induced breakdown threshold in bulk fused silica were performed for pulse duration tp ranging from 240fs to 2.5ps when objective with different numerical aperture (NA) were used. It was found that the threshold tendency was depend on effective NA. Numerical simulations based on the nonlinear propagation model revealed that the defocusing effect of the bulk plasma was responsible for the different tendencies. Multi-foci was found at high incident pulse energy and the numerical simulations revealed that it was concomitant with pulse reshaping and refocusing by self-focus.
We present the microfabrication of high refractive index-modulated structures written by line scan inside bulk of fused silica with a femtosecond laser at wavelength of 810 nm. The femtosecond laser beam, with duration between 130 fs and 500 fs at a repetition rate of 1 kHz, was focused through a microscope objective with numerical aperture (NA) of 0.10 or 0.25 into the sample. To fabricate high refractive index-modulated structures in fused silica, we investigated the dependence of refractive index change on laser pulse energy, pulse duration, scan speed, and scanning repetitions. The results showed a "triangle region", with pulse duration of 130 fs to 230 fs and pulse energy of 0.35 μJ to 1.5 μJ, for the fabrication of refractive index modulation structures. The refractive index modulation was increased to 3×10-3 after several scanning passes. Diffractive optical components such as grid, square, circle gratings and Fresnel zone plates have been fabricated by direct writing technique. The structures could be used as diffractive beam splitters, beam shaper and micro-lens.
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