Low-loss InGaP-on-insulator waveguides for high-efficiency entangled pair generation and nonlinear photonics

Nonlinear photonic platforms underpin applications ranging from spectroscopy to quantum communication, yet often face trade-offs between efficiency, loss, and scalability. An emerging platform, thin-film InGaP-on insulator, combines high χ² nonlinearity with wafer-scale fabrication. Here, we demonstrate second-harmonic generation pumped at 1550 nm with a normalized efficiency of 50±1 /W in a single-pass III–V waveguide and up to 50 mW of generated signal power. Conversely, devices enable high-brightness generation of time-energy entangled photon pairs with a per-bandwidth generation rate of 7.5 GHz/(mW·THz). Using InGaP grown via molecular beam epitaxy (MBE), we show losses below 1 dB/cm at 1550 nm and stable phase matching across fabrication runs. An absolute measurement of the nonlinear response yields d₁₄=106±4 pm/V for InGaP grown via both MBE and metalorganic chemical vapor deposition. These results demonstrate the scalability and efficiency of InGaP-on-insulator for entangled photon-pair sources and nonlinear photonic systems such as mid-infrared frequency conversion.