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(Color online) GaN DCs BPM simulations at a wavelength of 800 nm. (a) Schematic of rib waveguide design using GaN on sapphire with air cladding. The ordinary index of GaN is used due to the restriction to TE operation.7 (b) TE field profile of guided mode at device input. (c) TE field profile of guided mode in coupling region. (d) Plan view BPM simulation of GaN DC design with a 2 -μm gap, cross-sections vary from (b) to (c) in the coupler region.
(Color online) Device length optimization when changing rib width in the coupling region. It shows the minimum device length required to connect a 3.8 -μm wide rib waveguide to the coupling section with a rib width between 1.4 and 2.6 μm for a 0.05 dB taper loss.
(Color online) GaN DC fabrication. (a) Fabrication process flow. (b) Optical plan view micrograph of GaN DCs with (inset) high magnification image of the coupling region. (c) Optical image of cleaved GaN DC facet. (d) oblique SEM of cleaved facet with (inset) inferred facet etch profile. (e) SEM plan view of coupling region. Black regions indicate the waveguides. The coupler gap and waveguide sidewalls are clearly visible.
(Color online) Measured splitting ratio for fabricated GaN DCs with varying coupler length. The curve is a BPM simulation of the power transferred using the parameters shown in Fig. 1 at a wavelength of 800 nm. Inset: optical image of the output facet with an overlay of the measured intensity profile of the guided mode.
(Color online) The Hong-Ou-Mandel dip observed for a 45:55 GaN rib waveguide DC, the signature of quantum interference between two degenerate photons. The fitted visibility is 96%.
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