Fig. 1. Processing flow charts of the GaN planar optical waveguide obtained by (a) top etching and (b) bock thinning processes. (c) The cross-sectional diagrams of the two types of GaN planar optical waveguide

Fig. 2. Refractive index distribution of GaN planar optical waveguides under the initial model

Fig. 3. Relative light output distribution of GaN planar optical waveguide (in waveguide transmission direction). (a) Initial model; (b) top etching process and (c) back thinning process removing the lower flat layer of ridge waveguide

Fig. 4. GaN waveguide’s transmission loss varying with plate thickness for two different processes

Fig. 5. GaN waveguide’s transmission loss varying with sidewall angle for two different processes

Fig. 6. GaN waveguide’s transmission loss varying with roughness for two different processes

Fig. 7. GaN waveguide’s transmission loss varying with waveguide width for two different processes

Fig. 8. Analysis of light field transmission mode of GaN waveguide (waveguide cross section). (a) Initial model; (b) top etching process and (c) back thinning process removing the flat layer; single-mode transmission achieved by waveguide (d) with width of 150 nm and height of 100 nm, and (e) with width of 100 nm and height of 150 nm

Fig. 9. GaN waveguide’s transmission loss varying with wavelength of the visible light signal for two different processes