Pissadakis, S., Zervas, M.N., Sager, D.A. and Wilkinson, J.S.
Superstrate index control of waveguide grating reflectivity
Optics Letters, 27, (5), . (doi:10.1364/OL.27.000327).
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Control of reflectivity of a relief grating in a high-index film overlaid on a monomode glass waveguide was achieved by adjustment of the superstrate refractive index with liquids. Weak gratings reflecting at 1531nm were inscribed by UV laser ablation. The grating reflectivity was measured as the ratio of the transmission outside the reflection band, at 1536 nm, to that at the Bragg wavelength. Reflectivity with an air superstrate was 0.3 dB for both polarizations. In the TE polarization the grating strength increased to 20.5dB after application of a liquid of index 1.45. In the TM polarization the strength increased to 27dB with a superstrate index of 1.50. Good agreement was found with a theoretical model based on beam propagation.
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