A design study is presented for difference-frequency generation (DFG) in aluminum gallium arsenide (AlGaAs)- on-insulator waveguides. AlGaAs is a mature technology platform with large optical nonlinearities, a high refractive index contrast, and the presence of second-order susceptibility, making it interesting for chip-based frequency conversion. This work targets to efficiently down-convert single-photons to the telecom C-band by DFG. Modal phase-matching (PhM) is used, where the waveguide dimensions are optimized for an efficient and robust conversion of single-photons at 930 nm to around 1550 nm. This paves the way for a single-photon converter that can be integrated on a chip-platform with a single-photon emitters, along other photonic components with standard fabrication techniques. Furthermore, a thorough revision of the DFG theory provides insight into the particular case of a low-powered pump, which is relevant for quantum applications. Finally, a comparison is made with state of the art devices in periodically poled thin film lithium niobate (PPLN). This is, to the best of our knowledge, the first design of a single-photon converter operating in the telecom band that is realized with a III-V material.
This work presents an approach for continuous-wave laser emission in the far-UVC using second-harmonic generation in barium borate (BBO) thin-film waveguides. The crystal orientation is analytically considered for waveguides, and two designs with perfect modal phase matching (PhM) are simulated. The first design includes a BBO ridge-waveguide defined by dry etching. This allows for good confinement and spatial overlap of the relevant optical modes. The second design includes a strip-loaded waveguide, which aims at suppressing the side-wall scattering by confining the optical modes in the BBO thin-film. Showing that the conversion efficiency can be greatly enhanced.
Lasers emitting in the ultraviolet C-band (UVC) have recently attracted considerable attention for germicidal purposes. Combining diode lasers with nonlinear crystals used for second-harmonic generation (SHG) is a promising approach thanks to their relatively low cost, small footprint and long lifetime. The output power in the UVC is limited by the output power of the diode lasers and by the conversion efficiency in the nonlinear crystal. This work compares the SHG conversion efficiency using a bulk approach to values expected using guided modes in waveguides. It discusses the phase-matching (PhM) condition for different input polarizations, the effective nonlinearity, and the Poynting vector walk-off. This last effect is particularly detrimental as it reduces the effective length for the nonlinear interaction in bulk, which ultimately limits the conversion efficiency towards the UVC. Values for the walk-off angle are computed for barium borate (BBO), and a comparison is provided with other nonlinear crystals.
Simulations predict perfect phasematching for difference frequency generation (DFG) in a nonlinear ridge waveguide. It makes use of InGaAsP lattice-matched to InP as a nonlinear ridge waveguide. Both crystals possess high second-order susceptibility χ(2) and low loss, making them ideal for second-order nonlinear effects. The design allows two lasers in the telecom spectrum to interact in the nonlinear waveguide and emit in the mid-infrared (mid-IR). The InGaAsP ridge waveguide heterogeneously integrated on silicon-rich silicon nitride achieves phase-matching, resulting in a conversion efficiency η = 4.5 %/W.
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