Low loss GaN waveguides for visible light on Si substrates

In this work, we present the fabrication and the characterization of an optical waveguide made of AlN and GaN layers grown by MBE on a Si(111) substrate. For the fundamental mode at 633 nm, the propagation losses are in the order of 2 dB/cm, which is a good number for SC waveguides at this wavelength. The propagation losses dramatically increase with the mode order. A careful comparison of measurements and modeling of the complete structure allows identifying the part of the losses due to absorption in the Si substrate, and showing that propagation losses could be further reduced by using well chosen SOI substrates.