| We present the first experimental study of the optical properties of HELP InGaAsP (InGaAsP grown by He-plasma-assisted molecular beam epitaxy) relevant to all-optical switching, and the first demonstration of picosecond switching using this material.;We observed an optical response time of 15 ps, a nonlinear index change as large as 0.077, a sharp absorption band edge, and a small absorption tail in HELP InGaAsP. The unique coexistence of ultrafast response, large interband nonlinearity, and small band-tail absorption, never before reported, makes HELP InGaAsP particularly suitable for ultrafast all-optical switching. Additionally, faster response (subpicosecond) was achieved by doping the material with beryllium, and moderate doping (up to ∼1018 cm−3) did not significantly alter the absorption edge.;We systematically studied the response time variations with doping concentration, annealing temperature, carrier density, and wavelength. We conclude that, (a) Be doping reduces the response time by compensating for donor-like mid-gap states, thus increasing the electron trap concentration; (b) annealing removes defects responsible for fast carrier trapping; (c) the response time increases with carrier density due to limited trap states; (d) the response time varies with wavelength due to difference in electron and hole trapping cross-sections, which were determined based on experimental results and a phenomenological two-trap-level rate equation model.;We investigated two types of HELP-InGaAsP-based all-optical switching devices, the nonlinear directional coupler (NLDC) and the asymmetric Fabry-Pérot (AFP) switch.;Based on numerical modelling and waveguide loss measurements, we conclude that, while HELP-InGaAsP-based passive NLDCs are in principle viable, practical devices will tend to require high switching energy, and will likely experience low contrast and high insertion loss.;We demonstrated that AFP devices will outperform NLDCs in contrast ratio, throughput, bandwidth, switching time, and polarization-sensitivity. We designed and fabricated three prototype AFP devices, and achieved polarization-independent switching with a 5 ps switching window, 20 dB contrast ratio, ≥10% throughput, 25–40 nm bandwidth (at ≥10 dB contrast ratio), and 0.5–1.4 pJ/μm2 switching energy density.;HELP InGaAsP is a promising material for ultrafast switching and other applications requiring ultrafast nonlinear operations. The HELP-InGaAsP-based AFP device we demonstrated is well suited for demultiplexing high-bit-rate data in practical optical communications systems. |
