Phase-sensitive amplification in a χ<sup>(3)</sup> photonic chip

Abstract

Summary form only given. Four-wave mixing and other parametric nonlinear processes have been the subject of much research over the last decades. In particular phase sensitive amplification in optical parametric amplifiers holds great potential for signal processing in optical telecommunications, e.g. for the regeneration of phase encoded signals [1] or as potentially broadband, noiseless amplifiers [2].While there are some demonstrations of phase-sensitive amplification and regeneration in chip-like architectures based on the second-order χ(2) nonlinearity [3] in periodically-poled Lithium Niobate waveguides, most demonstrations thus far have been using highly nonlinear fibre with the associated limitations on bandwidth and integrability. In particular there has not been a demonstration of phase-sensitive amplification inside a χ(3)-based integrated platform such as Silicon or highly nonlinear glasses. In this submission we demonstrate for the first time phase-sensitive amplification inside a χ(3) photonic chip using a highly nonlinear chalcogenide waveguide. Our demonstration is based on an elegant spectral control technique that slices the pump and signal waves from the same broadband spectrum of a mode-locked laser, thus significantly simplifying the challenges of ensuring synchronization of the waves while enabling accurate control of the relative phase of the interacting waves.The experimental setup is depicted in Fig. 1(a). A mode-locked laser (repetition rate 38.6 MHz, 300 fs pulse duration, 160 W peak power), is spectrally sliced using a spectral pulse shaper (SPS 1), to yield two pump waves at 1550.1 nm and 1564.5 nm (spectral width ~70 GHz) and a degenerate signal/idler at 1557.7 nm (width ~130 GHz). After amplification all waves are polarisation aligned and coupled to the TM-mode of the chalcogenide waveguide. A second SPS provides filtering of excess noise and the required phase control. The output of the waveguide is measured with an optical spectrum analyser (OSA). The phase-sensitive gain is characterised by changing the relative phase of the interacting waves using SPS 2 and measuring the power of the signal relative to the unamplified signal. The approximate on-chip peak powers were 4.8 W and 2.5 W for the two pumps and 4 mW for the signal. Figures 1(b) and (c) depict output spectra and the on-chip signal gain as a function of relative phase. We can see a clear periodic dependence of the gain on the relative phase. The period of the variation is π and the ratio of maximum gain to minimum gain, i.e the main performance indicator often denoted the phase-sensitive gain, was 9.9 dB. The experimental results agree well with numerical simulations of the underlying nonlinear Schrodinger equation using a split-step Fourier method. In conclusion we have for the first time shown phase-sensitive amplification on a χ(3) photonic chip. We achieved a phase-sensitive gain of 9.9 dB which is comparable to previous demonstrations, and is sufficient to perform other processing functions such as regeneration of phase-encoded communication signals. Prospects for extending our experiment to continuous or quasicontinuous wave operation are promising and currently ongoing.