Stretchable photonic crystal cavity with wide frequency tunability.

We report a new approach for realizing a flexible photonic crystal (PC) cavity that enables wide-range tuning of its resonance frequency. Our PC cavity consists of a regular array of silicon nanowires embedded in a polydimethylsiloxane (PDMS) matrix and exhibits a cavity resonance in the telecommunication band that can be reversibly tuned over 60 nm via mechanical stretching-a record for two-dimensional (2D) PC structures. These mechanically reconfigurable devices could find potential applications in integrated photonics, sensing in biological systems, and smart materials.

Integrated diamond networks for quantum nanophotonics.

We demonstrate an integrated nanophotonic network in diamond, consisting of a ring resonator coupled to an optical waveguide with grating in- and outcouplers. Using a nitrogen-vacancy color center embedded inside the ring resonator as a source of photons, single photon generation and routing at room temperature is observed. Furthermore, we observe a large overall photon extraction efficiency (10%) and high quality factors of ring resonators (3200 for waveguide-coupled system and 12,600 for a bare ring).

Fabrication and characterization of high-quality-factor silicon nitride nanobeam cavities.

We present the fabrication and characterization of high-quality-factor (Q) Si3N4 photonic crystal nanobeam cavities at visible wavelengths for coupling to nitrogen-vacancy centers in a cavity QED system. Confocal microphotoluminescence analysis of the nanobeam cavities demonstrates quality factors up to Q ~ 55,000, which are limited by the resolution of our grating spectrometer. This is a 1-order-of-magnitude improvement over previous SiNx cavities at this important wavelength range. We also demonstrate coarse tuning of cavity resonances across 600-700 nm by lithographically scaling the size of fabricated devices.

Programmable photonic crystal nanobeam cavities.

We present dynamically reconfigurable photonic crystal nanobeam cavities, operating at ~1550 nm, that can be continuously and reversibly tuned over a 9.5 nm wavelength range. The devices are formed by two coupled nanobeam cavities, and the tuning is achieved by varying the lateral gap between the nanobeams. An electrostatic force, obtained by applying bias voltages directly to the nanobeams, is used to control the spacing between the nanobeams, which in turn results in tuning of the cavity resonance. The observed tuning trends were confirmed through simulations that modeled the electrostatic actuation as well as the optical resonances in our reconfigurable geometries.

Broadband frequency conversion and shaping of single photons emitted from a nonlinear cavity.

Much recent effort has focused on coupling individual quantum emitters to optical microcavities in order to produce single photons on demand, enable single-photon optical switching, and implement functional nodes of a quantum network. Techniques to control the bandwidth and frequency of the outgoing single photons are of practical importance, allowing direct emission into telecommunications wavelengths and "hybrid" quantum networks incorporating different emitters. Here, we describe an integrated approach involving a quantum emitter coupled to a nonlinear optical resonator, in which the emission wavelength and pulse shape are controlled using the intra-cavity nonlinearity. Our scheme is general in nature, and demonstrates how the photonic environment of a quantum emitter can be tailored to determine the emission properties. As specific examples, we discuss a high Q-factor, TE-TM double-mode photonic crystal cavity design that allows for direct generation of single photons at telecom wavelengths (1425 nm) starting from an InAs/GaAs quantum dot with a 950 nm transition wavelength, and a scheme for direct optical coupling between such a quantum dot and a diamond nitrogen-vacancy center at 637 nm.

Design of an efficient terahertz source using triply resonant nonlinear photonic crystal cavities.

We propose a scheme for efficient cavity-enhanced nonlinear THz generation via difference-frequency generation (DFG) processes using a triply resonant system based on photonic crystal cavities. We show that high nonlinear overlap can be achieved by coupling a THz cavity to a doubly-resonant, dual-polarization near-infrared (e.g. telecom band) photonic-crystal nanobeam cavity, allowing the mixing of three mutually orthogonal fundamental cavity modes through a chi((2)) nonlinearity. We demonstrate through coupled-mode theory that complete depletion of the pump frequency - i.e., quantum-limited conversion - is possible. We show that the output power at the point of optimal total conversion efficiency is adjustable by varying the mode quality (Q) factors.

Difference-frequency generation with quantum-limited efficiency in triply-resonant nonlinear cavities.

We present a comprehensive study of second-order nonlinear difference frequency generation in triply resonant cavities using a theoretical framework based on coupled-mode theory. We show that optimal "quantum-limited" conversion efficiency can be achieved at any pump power when the powers at the pump and idler frequencies satisfy a critical relationship. We demonstrate the existence of a broad parameter range in which all triply-resonant DFG processes exhibit monostable conversion. We also demonstrate the existence of a geometry-dependent bistable region.

Ultra-high-Q TE/TM dual-polarized photonic crystal nanocavities.

We demonstrate photonic crystal nanobeam cavities that support both TE- and TM-polarized modes, each with a Q factor greater than one million and a mode volume on the order of the cubic wavelength. We show that these orthogonally polarized modes have a tunable frequency separation and a high nonlinear spatial overlap. We expect these cavities to have a variety of applications in resonance-enhanced nonlinear optics.

Design of a silicon nitride photonic crystal nanocavity with a Quality factor of one million for coupling to a diamond nanocrystal.

A photonic crystal nanocavity with a Quality (Q) factor of 1.4 x 10(6), a mode volume of 0.78(lambda/n)(3), and an operating wavelength of 637 nm is designed in a silicon nitride (SiN(x)) ridge waveguide with refractive index of 2.0. The effect on the cavity Q factor and mode volume of single diamond nanocrystals of various sizes and locations embedded in the center and on top of the nanocavity is simulated, demonstrating that Q > 1 x 10(6) is achievable for realistic parameters. An analysis of the figures of merit for cavity quantum electrodynamics reveals that strong coupling between an embedded diamond nitrogen-vacancy center and the cavity mode is achievable for a range of cavity dimensions.

Emission spectrum of electromagnetic energy stored in a dynamically perturbed optical microcavity.

An ultrafast pump-probe experiment is performed on wavelength-scale, silicon-based, optical microcavities that confine light in three dimensions with resonant wavelengths near 1.5 mum, and lifetimes on the order of 20 ps. A below-bandgap probe pulse tuned to overlap the cavity resonant frequency is used to inject electromagnetic energy into the cavity, and an above-bandgap pump pulse is used to generate free carriers in the silicon, thus altering the real and imaginary components of the cavity's refractive index, and hence its resonant frequency and lifetime. When the pump pulse injects a carrier density of ~ 5 x10(17) cm(-3) before the resonant probe pulse strikes the sample, the emitted radiation from the cavity is blue-shifted by 16 times the bare cavity linewidth, and the new linewidth is 3.5 times wider than the original. When the pump pulse injects carriers, and thus suddenly perturbs the cavity properties after the probe pulse has injected energy into the cavity, we show that the emitted radiation is not simply a superposition of Lorentzians centred at the initial and perturbed cavity frequencies. Under these conditions, a simple model and the experimental results show that the power spectrum of radiation emitted by the stored electromagnetic energy when the cavity frequency is perturbed during ring-down consists of a series of coherent oscillations between the original and perturbed cavity frequencies, accompanied by a gradual decrease and broadening of the original cavity line, and the emergence of the new cavity resonance. The modified cavity lifetime is shown to have a significant impact on the evolution of the emission as a function of the pump-probe delay.