Wavelength-sized silicon disk cavities in superfluid helium exhibit blue-shifted bistability near the λ-point when subject to high optical input power. At lower temperature, we observe symmetric lineshapes and obtain a large intracavity photon number of 40,000.
Photonic nanocavities are a key component in many applications because of their capability of trapping and storing photons and enhancing interactions of light with various functional materials and structures. The maximal number of photons that can be stored in silicon photonic cavities is limited by the free-carrier and thermo-optic effects at room temperature. To reduce such effects, we performed the first experimental study of optical nonlinearities in ultrahigh-Q silicon disk nanocavities at cryogenic temperatures in a superfluid helium environment. At elevated input power, the cavity transmission spectra exhibit distinct blue-shifted bistability behavior when temperature crosses the liquid helium lambda point. At even lower temperatures, the spectra restore to symmetric Lorentzian shapes. Under this condition, we obtain a large intracavity photon number of about 40,000, which is limited ultimately by the local helium phase transition. These new discoveries are explained by theoretical calculations and numerical simulations.
Silica microspheres behave as efficient optical microresonators when small-volume whispering-gallery modes (WGMs) are used. We have realized a cryogenic set-up to work with microspheres immersed in a superfluid helium bath. Quality factors up to 109 have been obtained at 2 K. In this environment, we have been able to observe a dispersive bistable behavior of the WGM resonances, due to the weak intrinsic Kerr optical nonlinearity of silica, with a threshold power of 10 (mu) W only. This result opens the way to the realization of thresholdless microlaser, based on a rare-earth doped silica microsphere and to other Cavity-QED projects with microspheres at low temperatures.
Resonance shift and bistability in a silicon microring resonator operating at higher optical power levels pose serious difficulties, especially in nonlinear four wave mixing process. A solution of parking a laser wavelength around any of the resonances of a microring resonator and operating at any power levels is explored by integrating a microheater. We have shown with the existing theoretical model that the previous history of phase detuning in a silicon microring resonator determines the effective gain in stimulated four wave mixing process. The experimental results have been shown to be closely matching with the simulation results. For a microring resonator of radius 50 μm, an improved stimulated four wave mixing gain of ~ 11.6 dB has been observed while thermo-optically blue-shifting resonances in comparison to that of red-shifting resonances, for a launched pump power of 8.4 mW operating at a slightly off-resonant wavelength λp. The proposed technique can be used in designing actively controlled efficient photon sources in a large-scale integrated quantum photonic circuit operating at λ ~ 1550 nm.
Over the past few decades, optical ring resonators have attracted a considerable amount of attention as versatile elements for a wide range of applications ranging from telecommunication and sensing to basic scientific research [1,2]. The silicon-on-insulator (SOI) material system is a mature fabrication technique and provides the ability to implement microring resonators. In addition, the high confinement of light and the large third-order nonlinearity of silicon at wavelengths in the near infrared, typically around 1.4-1.6 µm, can be utilized for a number of applications by microring resonator devices [3,4]. The optical bistability observed in silicon-based microring resonators have been theoretically investigated and numerically simulated through various sophisticated techniques [5-9]. However, only recently unifying analytical theories regarding nonlinear effects of optical bistability in microring resonators in terms of a slowly varying envelope approach have been reported [10,11]. Previously, we analytically described the nonlinear response of microring resonators consisting of an add-drop filter with feedback and showed that Fano lineshapes can be adjusted by the resonator parameters [12]. In this chapter, we extend our work to examine the optical bistabililty in such microring resonators and test the analytical results with those predicted by the OptiFDTD software package.
Micro- and nanocavities allow for strong light confinement in very small volume. They give opportunities for new experiments such as cavity quantum electrodynamics, waveguiding, light slowing or trapping. The increase of the electromagnetic (EM) field in the cavity enhances the interaction between light and matter, resulting in the possible observation of nonlinear effects. Several studies have recently been published on the observation and characterisation of nonlinear silicon cavities. As a step further, the authors propose and demonstrate the feasibility of an innovative way to mechanically control the bistable operating regime of a nanocavity. Using a near-field tip, the nanocavity operating regime was switched between monostable and bistable behaviours.