SF1D.4.pdf CLEO:2015 © OSA 2015 Signal Gain from Four-Wave Mixing in Anomalous AlGaAs nanowaveguides Pisek Kultavewuti 1 , Vincenzo Pusino 2 , Marc Sorel 2 , J. Stewart Aitchison 1 1 Dept. of Electrical and Computer Engineering, Univ. of Toronto, 10 King’s College Road, Toronto, Ontario, Canada M5S 3G4 2 School of Engineering, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom pisek.kultavewuti@mail.utoronto.ca Abstract: We experimentally demonstrate efficient four-wave mixing with a net signal gain of 4.1 dB and a conversion efficiency of 5.3 dB in low-loss AlGaAs nanowaveguides in an anomalous dispersion regime. OCIS codes: (230.3120) Integrated optics devices; (190.3270) Kerr effect; (130.7405) Wavelength conversion devices. 1. Introduction Parametric processes such as four-wave mixing (FWM) could be a solution to realizing all-optical signal processing and secure quantum communications. FWM allows functionalities such as frequency conversion and signal regeneration in an all-optical domain that avoids latency in optical-electrical-optical conversion in current networks. In addition, FWM can generate entangled photon pairs, which are important for quantum communications. Integrated FWM-based devices for, but not exclusive to, these applications are highly sought after due to their additional advantages of robustness, compactness, and reduced power requirement. Several materials have been proposed for efficient FWM interactions. These materials include silicon [1], silicon nitride [2], chalcogenide [3], and AlGaAs [4–6]. Among them, AlGaAs exhibits a large third-order Kerr nonlinearity and low two-photon absorption and has the potential for direct integration with on-chip lasers, promising a truly integrated solution. Furthermore, it has been shown that AlGaAs nanowaveguides have zero- dispersion wavelength (ZDW) near 1550 nm that favors the FWM phase matching condition [7]. These waveguides have nanoscale dimensions that concentrate optical intensity in a small area and significantly enhance nonlinearity, effectively reducing power requirement. The challenge in using such nanowaveguides for efficient FWM is the large loss associated with sidewall scattering, which limits the optical power in the waveguide [8]. Recently, low-loss waveguides have been fabricated and exhibited very efficient FWM even with continuous-wave (cw) lights [5,6]. In this work, we report for the first time a positive conversion efficiency of 5.3 dB and a signal gain of 4.1 dB in anomalous AlGaAs nanowaveguides from FWM interactions between a pulsed pump and cw signals. 2. Device and Experiment Device patterns were fabricated by electron-beam lithography with an HSQ mask and ICP-RIE dry etching onto a multi-layered AlGaAs wafer. The wafer structure, from bottom to top, consists of a GaAs substrate followed by MOVPE-grown AlGaAs layers with aluminum molar concentrations of 0.75, 0.25, and 0.75 and with thicknesses of 4,200, 600, and 300 nm respectively, and was capped by a 10-nm-thick GaAs. The fabrication process yields deeply etched, high-contrast waveguides. Waveguides consisted of a 5-mm-long nanowaveguide central section whose ends are connected to adiabatic tapers to 2-μm-wide waveguides for efficient end-fire coupling. The widths of the nanowaveguides were varied from 600 to 1200 nm in 50 nm increments. The devices were cleaved at the wide waveguide section near the taper such that loss in these segments is relatively small. Propagation losses of these waveguides were measured using the Fabry-Perot technique and for TE modes at 1550 nm they are 9, 7, and 5.8 dB/cm for 700-, 800-, and 900-nm-wide waveguides, respectively. Note that the 700- nm-wide waveguide is expected to have ZDW near 1550 nm and becomes anomalously dispersive at longer wavelengths. The devices were excited using a pump derived from an optical parametric oscillator delivering 3-ps pulses at a repetition rate of 76 MHz. A signal source was a tunable CW laser. Both the pump and the signal were coupled into and out of the waveguides by objective lenses. The output light could be directed to a power meter or an optical spectrum analyzer (OSA). The wavelength of the pulsed pump was fixed at 1600 nm throughout the experiment whereas the wavelength of the cw-signal was varied between 1510 nm to 1590 nm. Free-space-to-fiber coupling efficiency at the OSA was around 20%. Note that our OSA has an increasing detection noise from 1650 nm making analysis error-prone when the idler falls beyond this wavelength.