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Simulation and fabrication of slow light suspended air-bridge AlGaAs photonic crystal waveguide

Photonic crystals can exhibit interesting optical properties such as peculiar dispersion, small group velocity, negative refraction and diffraction. Group velocity engineering in a certain wavelength range allows for enhanced nonlinear optical interactions, while higher light confinement achievable in photonic crystal waveguides leads to a reduced footprint for integrated photonic components. Silicon-based photonic crystals are relatively well studied,1–3 however, they are not suitable for a monolithic integration with active devices. III-V semiconductors exhibit light-emitting properties, large Kerr nonlinearity and negligible two-photon absorption in the telecommunication regime, and therefore are more suitable for frequency conversion, all-optical signal processing, laser absorption spectroscopy and microcomb generation for correlation spectroscopy applications. In this work, we theoretically investigate the design and fabrication of photonic crystal waveguides based on an airbridge Al0.18Ga0.82 slab for frequency conversion using FWM. We demonstrate a suspended Al0.18Ga0.82 layer fabricated by HF-controlled wet etching of an AlGaAs heterostructure, which selectively etched top and bottom claddings of higher aluminum concentration AlGaAs leaving behind the core suspended in air. We show, by simulations, that the group-index values of 25 over a bandwidth of 22 nm around 1590 nm in a dispersion-engineered W1 photonic crystal defect waveguide are possible enabling this device to operate in the slow-light regime where we also demonstrate a phase mismatch of nearly zero. Future designs can be optimized for longer wavelengths in the mid-infrared (MIR) as a promising platform to realize compact, slow-light enhanced integrated photonic components for sensing and wavelength conversion, thanks to the low propagation loss of AlGaAs in the MIR regime.