Phase-Sensitive Amplification in Integrated Kerr Media

Abstract

Phase-sensitive amplification (PSA) is an attractive function for a wide range of applications such as optical regeneration, noiseless amplification and generation of squeezed state of light. Integrated PSA potentially leads to optical performance improvement and cost reduction in future all-optical signal processing. Silicon and chalcogenide provide compelling platforms for nonlinear photonic integration because of their large nonlinearity and potential CMOS compatible properties. However, demonstration of on-chip PSA remains a challenge due to the power handling and the presence of large losses compared to low-loss bulk optical fibers. This thesis theoretically and experimentally explores PSA in on-chip χ(3) silicon and chalcogenide waveguides from different aspects, including experimental performance, analytical modelling, and multi-wave nonlinear effects. First, we provide an analytic solution of PSA to explain the roles of the linear and nonlinear absorptions on PSA gain in general semiconductor materials. This analytic method can predict the PSA gain with a pulsed or continuous wave pump. Then, we demonstrate the first silicon PSA in a record-short photonic crystal (PhC) waveguide. A maximum and minimum gain contrast (or extinction ratio) of 11 dB is demonstrated by taking advantage of the slow-light enhancement and dispersion engineering technique. We find that although the maximum gain of PSA is limited by two-photon absorption (TPA), the important parameter of PSA extinction ratio is not significantly degraded by TPA. In the next experiment, a relatively large positive gain of 12 dB and an extinction ratio of 18 dB are observed in chalcogenide waveguides with negligible TPA. Finally, the cross-nonlinear absorption and cross-phase modulation (XPM) accompanying the silicon PSA process are investigated using a pump-probe scheme. We provide analytic solutions accounting for the TPA-only and a numerical solution to consider the free-carrier effects. We found the relative effect of free carriers on the pump is stronger than that on the probe, and the expected ratio of two between XPM-induced and self phase modulation-induced spectral broadening in pure Kerr media does not hold with either TPA or free carriers. This analysis furthers our understanding of XPM-induced crosstalk and cross-nonlinear absorption of photonic functions in silicon photonic chips. To sum up, we show that χ(3) on-chip PSA with large gain and large extinction ratio is achievable in silicon and chalcogenide waveguides, which can be used for optical classical and quantum signal processing.