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Register a new userTemperature dependence of the Kerr nonlinearity and two-photon absorption in a silicon waveguide at 1.55{mu}m
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We measure the temperature dependence of the two-photon absorption and optical Kerr nonlinearity of a silicon waveguide over a range of temperatures from 5.5 to 300 K at a wavelength of 1.55 {mu}m. The two-photon absorption coefficient is calculated from the power dependent transmission of a 4.9 ps pulse. We observed a nearly two-fold decrease in the two-photon absorption coefficient from 0.76 cm/GW at 300K to 0.42 cm/GW at 5.5 K. The Kerr nonlinearity is inferred from the self-phase modulation induced spectral broadening of the transmitted pulse. A smaller reduction in Kerr nonlinearity from 5.2E-18 m^2/W at 300 K to 3.9E-18 m^2/W at 5.5 K is found. The increased ratio of Kerr to absorptive nonlinearity at low temperatures indicates an improved operation of devices that make use of a nonlinear phase shift, such as optical switches or parametric photon-pair sources. We examine how the heralding efficiency of a photon-pair source will change at low temperature. In addition, the modelling and experimental techniques developed can readily be extended to other wavelengths or materials of interest.
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A fast silicon-graphene hybrid plasmonic waveguide photodetectors beyond 1.55 {mu}m is proposed and realized by introducing an ultra-thin wide silicon-on-insulator ridge core region with a narrow metal cap. With this novel design, the light absorption in graphene is enhanced while the metal absorption loss is reduced simultaneously, which helps greatly improve the responsivity as well as shorten the absorption region for achieving fast responses. Furthermore, metal-graphene-metal sandwiched electrodes are introduced to reduce the metal-graphene contact resistance, which is also helpful for improving the response speed. When the photodetector operates at 2 {mu}m, the measured 3dB-bandwidth is >20 GHz (which is limited by the experimental setup) while the 3dB-bandwith calculated from the equivalent circuit with the parameters extracted from the measured S11 is as high as ~100 GHz. To the best of our knowledge, it is the first time to report the waveguide photodetector at 2 {mu}m with a 3dB-bandwidth over 20 GHz. Besides, the present photodetectors also work very well at 1.55 {mu}m. The measured responsivity is about 0.4 A/W under a bias voltage of -0.3 V for an optical power of 0.16 mW, while the measured 3dB-bandwidth is over 40 GHz (limited by the test setup) and the 3 dB-bandwidth estimated from the equivalent circuit is also as high as ~100 GHz, which is one of the best results reported for silicon-graphene photodetectors at 1.55 {mu}m.
Using a compact optically-pumped silicon nanophotonic chip consisting of coupled silicon microrings, we generate photon pairs in multiple pairs of wavelengths around 1.55 mu m. The wavelengths are tunable over several nanometers, demonstrating the capability to generate wavelength division multiplexed photon pairs at freely-chosen telecommunications-band wavelengths.
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Topological matter and topological optics have been studied in many systems, with promising applications in materials science and photonics technology. These advances motivate the study of the interaction between topological matter and light, as well as topological protection in light-matter interactions. In this work, we study a waveguide-interfaced topological atom array. The light-matter interaction is nontrivially modified by topology, yielding novel optical phenomena. We find topology-enhanced photon absorption from the waveguide for large Purcell factor, i.e., $Gamma/Gamma_0gg 1$, where $Gamma$ and $Gamma_0$ are the atomic decays to waveguide and environment, respectively. To understand this unconventional photon absorption, we propose a multi-channel scattering approach and study the interaction spectra for edge- and bulk-state channels. We find that, by breaking inversion and time-reversal symmetries, optical anisotropy is enabled for reflection process, but the transmission is isotropic. Through a perturbation analysis of the edge-state channel, we show that the anisotropy in the reflection process originates from the waveguide-mediated non-Hermitian interaction. However, the inversion symmetry in the non-Hermitian interaction makes the transmission isotropic. At a topology-protected atomic spacing, the subradiant edge state exhibits huge anisotropy. Due to the interplay between edge- and bulk-state channels, a large topological bandgap enhances nonreciprocal reflection of photons in the waveguide for weakly broken time-reversal symmetry, i.e., $Gamma_0/Gammall 1$, producing complete photon absorption. We show that our proposal can be implemented in superconducting quantum circuits. The topology-enhanced photon absorption is useful for quantum detection. This work shows the potential to manipulate light with topological quantum matter.
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