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Diffraction grating couplers milled in Si3N4 rib waveguides with a focused ion beam

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Abstract

Focused ion beam milling is a processing technology which allows flexible direct writing of nanometer scale features efficiently substituting electron beam lithography. No mask need results in ability for patterns writing even on fragile micromechanical devices. In this work we studied the abilities of the tool for fabrication of diffraction grating couplers in silicon nitride waveguides. The gratings were fabricated on a chip with extra fragile cantilevers of sub micron thickness. Optical characterization of the couplers was done using excitation of the waveguides in visible range by focused Gaussian beams of different waist sizes. Influence of Ga+ implantation on the device performance was studied.

©2005 Optical Society of America

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Figures (6)

Fig. 1.
Fig. 1. Excitation of the waveguide by out of plane incident beam with diameter w
Fig. 2.
Fig. 2. (a) A photograph of a chip with waveguides and cantilevers (the waveguides in the cavities are the cantilevers of sub-micron thickness). (b) A magnified photo of the chip area with gratings (marked by the frame in fig. 2(a)). The gratings are 40×40 μm2 in size
Fig. 3.
Fig. 3. (a) The profile of the grating 1 obtained with AFM. (b) The spatial spectrum obtained by Fourier transform of the profile.
Fig. 4.
Fig. 4. (a) Schematic view of the experiment. (b) Measured coupling efficiencies of the DGCs versus incident beam spot size.
Fig. 5.
Fig. 5. Optimised coupling length versus corrugation depth for the grating couplers.
Fig. 6.
Fig. 6. Normalised depth profile of Ga inside the coupler.

Tables (1)

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Table 1. Parameters of the diffraction grating couplers

Equations (1)

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dP ( x ) dx = A ( x ) η P ( x ) α rad P ( x ) α abs
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