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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.

Si3N4 is an excellent material for applications of nanophotonics at visible wavelengths due to its wide bandgap and moderately large refractive index (n $\approx$ 2.0). We present the fabrication and characterization of Si3N4 photonic crystal nanobeam cavities for coupling to diamond nanocrystals and Nitrogen-Vacancy centers in a cavity QED system. Confocal micro-photoluminescence analysis of the nanobeam cavities demonstrates quality factors up to Q ~ 55,000, which is limited by the resolution of our spectrometer. We also demonstrate coarse tuning of cavity resonances across the 600-700nm range by lithographically scaling the size of fabricated devices. This is an order of magnitude improvement over previous SiNx cavities at this important wavelength range.

High-index-contrast, wavelength scale texture in thin semiconductor membranes can be used to resonantly enhance a variety of nonlinear optical processes. Several experimental demonstrations in III-V, and silicon membranes incorporating PbSe nanocrystals will be described.

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.

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 in an experimentally feasible geometry, with the operating output power at the point of optimal total conversion efficiency adjustable by varying the mode quality (Q) factors.

We demonstrate tunable frequency-converted light mediated by a chi-(2) nonlinear photonic crystal nanocavity. The wavelength-scale InP-based cavity supports two closely-spaced localized modes near 1550 nm which are resonantly excited by a 130 fs laser pulse. The cavity is simultaneously irradiated with a non-resonant probe beam, giving rise to rich second-order scattering spectra reflecting nonlinear mixing of the different resonant and non-resonant components. In particular, we highlight the radiation at the sum frequencies of the probe beam and the respective cavity modes. This would be a useful, minimally-invasive monitor of the joint occupancy state of multiple cavities in an integrated optical circuit., 4 pages, 4 figures

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.

We demonstrate photonic crystal nanobeam cavities that support both TE- and TM-polarized modes, each with a Quality 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., 4 pages, 4 figures

We describe the design, fabrication, and spectroscopy of coupled, high Quality (Q) factor silicon nanobeam photonic crystal cavities. We show that the single nanobeam cavity modes are coupled into even and odd superposition modes, and we simulate the frequency and Q factor as a function of nanobeam spacing, demonstrating that a differential wavelength shift of 70 nm between the two modes is possible while maintaining Q factors greater than 10^6. For both on-substrate and free-standing nanobeams, we experimentally monitor the response of the even mode as the gap is varied, and measure Q factors as high as 200,000., 4 pages, 3 figures

Wavelength-scale and high-Q photonic crystal resonators made in various materials (Si, Si3N4, III-Vs), as well as their application in novel single-photon sources and nonlinear wavelength conversion at single-photon level, will be discussed.

Using a tapered photonic crysal cavity approach we designed cavities with theoretical Quality factors Q=2 × 107 and measured experimental Q= 7.5 × 105. Non-linear broadening of the cavity resonance has also been observed.

We theoretically demonstrate high fidelity frequency conversion of a photon generated by a dipole-like emitter in a double mode nonlinear cavity irradiated by a classical field, and propose a realistic photonic crystal nanocavity implementation.

We for the first time present designs of high-Q photonic crystal nanocavities in the cases previously rendered “impossible”, including an ultra-high Q dual-polarized nanocavities, high Q/V cavities based on low-index materials, and high-Q air-band-mode cavities.

In order to improve the efficiency of quantum emitters, in particular nitrogen-vacancy (NV) color centers in diamond nanocrystals (NCs), it is important to enhance their photon production rate as well as the collection efficiency of the emitted photons. This can be achieved by embedding the emitters within optical cavities. Here we describe the design and fabrication of 1-D photonic crystal nanocavities in an air-bridge silicon nitride (SiNx) structure. In spite of the low index of silicon nitride (n˜2), we were able to design optical nanocavities with Quality factors as high as Q˜1 × 106. These nanocavities were designed to operate near 637 nm in order to strongly enhance the zero-phonon line (ZPL) emission of an NV center in a diamond NC while suppressing the in-plane emission into the phonon side-band. Simulation results show that a NV center placed near the top of the cavity would experience a reduction of radiative lifetime from ˜15ns to ˜2ps (Purcell factor ˜7000), thus significantly improving the photon production rate. Experimental results show a cavity resonance at ˜630nm, with a linewidth corresponding to Q˜1250, limited by the spectrometer resolution. The presented work is an important step towards the realization of diamond-based single photon devices, including switches.

The second harmonic radiation emitted into the top half space from three dimensionally localized modes of L3 defect cavities in InP-based planar photonic crystals is studied using both CW and pulsed excitation. The far field harmonic radiation patterns observed from modes with resonant wavelengths ~ 1550 nm, excited by a tunable CW laser with less than 1 mW power, reveal strong local field enhancement (> 1000 X). A detailed comparison with FDTD modeling allows us to conclude that the bulk InP second order susceptibility tensor dominates the second order response of these microcavities. When a broadband, sub picoseconds source is used to simultaneously excite two of the microcavity modes, the harmonic spectrum in general consists of three contributions, the second harmonic from each of the excited modes, and a third peak due to the second order (sum frequency) mixing of the two modes. By using short and long pulse excitation simultaneously, we demonstrate how the emission frequency due to sum frequency processes can be used to continuously tune the harmonic emission frequency dependent on the occupation of various cavity modes.

A high Q mode in a silicon planar photonic crystal microcavity is dynamically perturbed by injection of free carriers, and modelled by a damped harmonic oscillator which undergoes an instantaneous frequency and lifetime shift.

The far-field second-order radiation pattern from a wavelength-scale, InP-based photonic crystal microcavity that confines light in three dimensions is measured when excited on resonance by $300\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{W}$ of continuous-wave power from a laser diode. The measurements are accurately simulated using the finite-difference time-domain method, showing that both absorption and scattering play significant roles in determining the pattern of the radiation. The results show that the bulk second-order nonlinear susceptibility mediates the nonlinear process. In a separate set of experiments, a short-pulse laser is used to simultaneously populate two distinct modes of a similar microcavity. The detected second-order spectra show features due to the second harmonic generated by each mode, as well as the sum-frequency generation due to nonlinear intermode mixing. The key phenomena that determine the second-order response of these fundamentally small optical cavities are identified.

Polarization-resolved second-harmonic spectra are obtained from the resonant modes of a two-dimensional planar photonic crystal microcavity patterned in a free-standing InP slab. The photonic crystal microcavity is comprised of a single missing-hole defect in a hexagonal photonic crystal host formed with elliptically-shaped holes. The cavity supports two orthogonally-polarized resonant modes split by 60 wavenumbers. Sum-frequency data are reported from the nonlinear interaction of the two coherently excited modes, and the polarization dependence is explained in terms of the nonlinear susceptibility tensor of the host InP., Comment: 7 pages, 8 Postscript figures, to be presented at Photonics West Jan. 25

Sum frequency data are reported from the nonlinear interaction of two coherently excited resonant modes of a two-dimensional planar photonic crystal microcavity patterned in a free-standing InP slab.

The resonant modes of two-dimensional planar photonic crystal microcavities patterned in a free-standing InP slab are probed in a novel fashion using a long working distance microscope objective to obtain cross-polarized resonant scattering and second-harmonic spectra. We show that these techniques can be used to do rapid effective assays of large arrays of microcavities that do not necessarily contain resonant light-emitting layers. The techniques are demonstrated using microcavities comprised of single missing-hole defects in hexagonal photonic crystal hosts formed with elliptically shaped holes. These cavities typically support two orthogonally polarized resonant modes, and the resonant scattering and harmonic spectra are well fitted using a coherent sum of Lorentzian functions. The well-defined coherence between the two resonant features is explained in terms of a microscopic harmonic oscillator model. The relative merits of these techniques are quantitatively compared with the more commonly used cavi...

We experimentally demonstrate high quality factor dual-polarized photonic crystal nanobeam cavities. The free-standing nanobeams are fabricated in a 500 nm thick silicon layer, and are probed using both tapered optical fiber and free-space resonant scattering set-ups. We measure Q factors greater than 104 for both transverse magnetic (TM) and transverse electric modes, and observe fiber transmission drops as large as 1−T=0.8 at the TM mode resonances.

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.

We investigate the design, fabrication and experimental characterization of high Quality factor photonic crystal nanobeam cavities in silicon. Using a five-hole tapered 1D photonic crystal mirror and precise control of the cavity length, we designed cavities with theoretical Quality factors as high as 14 million. By detecting the cross-polarized resonantly scattered light from a normally incident laser beam, we measure a Quality factor of nearly 750,000. The effect of cavity size on mode frequency and Quality factor was simulated and then verified experimentally., Comment: 3 pages, 4 figures, submitted to APL. One change: added 1 author to version v1

The unidirectional coupling of a microcavity mode to a ridge waveguide in a slab photonic crystal structure was investigated for the first time. Experimental observation of the coupling efficiency for the signal coupled out of the structure is in good agreement with the result of three-dimensional finite-difference time-domain simulations. The coupling efficiency of the cavity mode to the output channel is ∼60%.

Wavelength-scale and high-Q photonic crystal nanobeam resonators, made in Si, III–Vs, and Si 3 N 4 , and their applications in reconfigurable photonics, optoelectronics, biochemical sensing and quantum information processing are presented.