12 May 2011 Light focusing by chirped waveguide grating coupler
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Abstract
Waveguide grating couplers (WGC) are used for input and output coupling in many planar waveguide based sensors. By using a chirped grating, guided light can be decoupled and focused to a desired location. The location and spot size of focused beam depends upon the size and chirp of the grating as well as the wavelength of the light. The locus of the focused beams for different wavelengths lies along a curve. In many applications a planar detector array is used to capture spectral data. Wherever the planar detector array does not intersect this focal curve, images of a point source will be defocused. We develop a theoretical model to calculate the image location and geometric spot size for a given set of grating parameters. In order to experimentally verify the model, chirped waveguide grating couplers were fabricated on HfO2/Quartz planar waveguides using e-beam lithography. The spot size, intensity, and location of diffracted beam was measured at several wavelengths and compared with the theoretical results.
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Pradeep Kumar, Brent Bergner, David Cook, Ivan Avrutsky, "Light focusing by chirped waveguide grating coupler", Proc. SPIE 8032, Next-Generation Spectroscopic Technologies IV, 803203 (12 May 2011); doi: 10.1117/12.884071; https://doi.org/10.1117/12.884071
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