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Single Mode LiNbO3 Waveguides at 4.7 μm by Proton Exchange: Addressing the Atmospheric M-Band

In this paper we present new infrared waveguides based on proton-exchanged Lithium Niobate samples. Characterization of the waveguides in the visible and near infrared allows to develop a wavelength dependence function for refractive index and birefringence that predicts a single mode behaviour at 4.7 μm. This was confirmed by Fourier Transform Spectroscopy and compared to beam propagation simulations. We have obtained the first single mode planar waveguide at 4.7 μm, based on a simple technique that could be interesting for developing integrated optics beam combiners for astronomy.