Silicon Photonic Crystal Cavity Research Articles

Cavity-coupled telecom atomic source in silicon.

Novel T centers in silicon hold great promise for quantum networking applications due to their telecom band optical transitions and the long-lived ground state electronic spins. An open challenge for advancing the T center platform is to enhance its weak and slow zero phonon line (ZPL) emission. In this work, by integrating single T centers with a low-loss, small mode-volume silicon photonic crystal cavity, we demonstrate an enhancement of the fluorescence decay rate by a factor of F = 6.89. Efficient photon extraction enables the system to achieve an average ZPL photon outcoupling rate of 73.3 kHz under saturation, which is about two orders of magnitude larger than the previously reported value. The dynamics of the coupled system is well modeled by solving the Lindblad master equation. These results represent a significant step towards building efficient T center spin-photon interfaces for quantum information processing and networking applications.

Simulation of optomechanical interaction of levitated nanoparticle with photonic crystal micro cavity.

We propose and analyze theoretically a promising design of an optical trap for vacuum levitation of nanoparticles based on a one-dimensional (1D) silicon photonic crystal cavity (PhC). The considered cavity has a quadratically modulated width of the silicon wave guiding structure, leading to a calculated cavity quality factor of 8 × 105. An effective mode volume of approximately 0.16 μm3 having the optical field strongly confined outside the silicon structure enables optical confinement on nanoparticle in all three dimensions. The optical forces and particle-cavity optomechanical coupling are comprehensively analyzed for two sizes of silica nanoparticles (100 nm and 150 nm in diameter) and various mode detunings. The value of trapping stiffnesses in the microcavity is predicted to be 5 order of magnitudes higher than that reached for optimized optical tweezers, moreover the linear single photon coupling rate can reach MHz level which is 6 order magnitude larger than previously reported values for common bulk cavities. The theoretical results support optimistic prospects towards a compact chip for optical levitation in vacuum and cooling of translational mechanical degrees of motion for the silica nanoparticle of a diameter of 100 nm.

Generation of entangled photon pairs from a silicon bichromatic photonic crystal cavity

Integrated quantum photonics leverages the on-chip generation of nonclassical states of light to realize key functionalities of quantum devices. Typically, the generation of such nonclassical states relies on whispering gallery mode resonators, such as integrated optical micro-rings, which enhance the efficiency of the underlying spontaneous nonlinear processes. While these kinds of resonators excel in maximizing either the temporal confinement or the spatial overlap between different resonant modes, they are usually associated with large mode volumes, imposing an intrinsic limitation on the efficiency and footprint of the device. Here, we engineer a source of time-energy entangled photon pairs based on a silicon photonic crystal cavity, implemented in a fully CMOS-compatible platform. In this device, resonantly enhanced spontaneous four-wave mixing converts pump photon pairs into signal/idler photon pairs under the energy-conserving condition in the telecommunication C-band. The design of the resonator is based on an effective bichromatic confinement potential, allowing it to achieve up to nine close-to-equally spaced modes in frequency, while preserving small mode volumes, and the whole chip, including grating couplers and access waveguides, is fabricated in a single run on a silicon-on-insulator platform. Besides demonstrating efficient photon pair generation, we also implement a Franson-type interference experiment, demonstrating entanglement between signal and idler photons with a Bell inequality violation exceeding five standard deviations. The high generation efficiency combined with the small device footprint in a CMOS-compatible integrated structure opens a pathway toward the implementation of compact quantum light sources in all-silicon photonic platforms.

Efficient Frequency Upconversion Photodetection in Heterojunction of InSe and Silicon Photonic Crystal Cavity

AbstractFrequency upconversion photodetection by two‐dimensional (2D) materials with nonlinear optical response is an appealing technique for applications such as extending photodetection wavelength range, autocorrelation measurement, and high‐efficiency single photon detection. However, the frequency upconversion efficiency in 2D materials is limited due to the low efficiency of nonlinear optical processes and atomic light‐matter interaction length. Here, the efficient frequency upconversion photodetection is realized by van der Waals (vdW) integration of a few‐layer InSe with a silicon photonic crystal cavity (Si‐PPC). With the large second‐order nonlinearity of InSe and enhanced light‐matter interaction by Si‐PCC, continuous wave (CW) pumped second harmonic generation (SHG) is demonstrated with pump power down to 100 µW. Further, InSe and Si absorb the SHG photons and generate photocarriers which are separated and collected by the n‐InSe/p‐Si heterojunction. A frequency upconversion photoresponsivity of 16 µA W−1 with a CW laser at 1467 nm is obtained. More efficient SHG with pulsed laser improves the responsivity to 3.9 mA W−1 with quadratic power dependence, which is record‐high among the frequency upconversion photodetectors based on 2D materials. This work opens up opportunities for a high‐efficiency 2D material nonlinear photodetector integrated on photonic integrated circuits.

Stark Tuning of Telecom Single-Photon Emitters Based on a Single Er3+

The implementation of scalable quantum networks requires photons at the telecom band and long-lived spin coherence. The single Er3+ in solid-state hosts is an important candidate that fulfills these critical requirements simultaneously. However, to entangle distant Er3+ ions through photonic connections, the emission frequency of individual Er3+ in solid-state matrix must be the same, which is challenging because the emission frequency of Er3+ depends on its local environment. Herein, we propose and experimentally demonstrate the Stark tuning of the emission frequency of a single Er3+ in a Y2SiO5 crystal by employing electrodes interfaced with a silicon photonic crystal cavity. We obtain a Stark shift of 182.9±0.8 MHz, which is approximately 27 times of the optical emission linewidth, demonstrating promising applications in tuning the emission frequency of independent Er3+ into the same spectral channels. Our results provide a useful solution for construction of scalable quantum networks based on single Er3+ and a universal tool for tuning emission of individual rare-earth ions.

Ultrahigh thermal-efficient all-optical silicon photonic crystal nanobeam cavity modulator with TPA-induced thermo-optic effect.

We propose and experimentally demonstrate an on-chip all-optical silicon photonic crystal nanobeam cavity (PCNBC) modulator. With the advantages of the strong two-photon absorption (TPA)-induced thermo-optic (TO) effect, ultrahigh thermal-efficient tuning with π phase shift temperature difference ΔTπ of 0.77°C and power Pπ of 0.26 mW is implemented. Moreover, the all-optical modulation is carried out by a pulsed pump light with an average switching power of 0.11 mW. The response times for the rising and falling edges are 7.6 µs and 7.4 µs, respectively. Such a thermal-efficient modulator is poised to be the enabling device for large-scale integration optical signal control systems.

Quantization of Mode Shifts in Nanocavities Integrated with Atomically Thin Sheets

AbstractThe unique optical properties of 2D layered materials are attractive for achieving increased functionality in integrated photonics. Owing to the van der Waals nature, these materials are ideal for integrating with nanoscale photonic structures. Here a carefully designed air‐mode silicon photonic crystal nanobeam cavity for efficient control through 2D materials is reported. By systematically investigating various types and thicknesses of 2D materials, the authors are able to show that enhanced responsivity allows for giant shifts of the resonant wavelength. With atomically precise thickness over a macroscopic area, few‐layer flakes give rise to quantization of the mode shifts. The dielectric constant of the flakes is extracted and found to be independent of the layer number down to a monolayer. Flexible reconfiguration of a cavity is demonstrated by stacking and removing ultrathin flakes. With an unconventional cavity design, these results open up new possibilities for photonic devices integrated with 2D materials.

Evidence for near-unity radiative quantum efficiency of bright excitons in carbon nanotubes from the Purcell effect

The efficiencies of photonic devices are primarily governed by radiative quantum efficiency, which is a property given by the light-emitting material. Quantitative characterization for carbon nanotubes, however, has been difficult despite being a prominent material for nanoscale photonics. Here we estimate the radiative quantum efficiency of bright excitons in carbon nanotubes by modifying the exciton dynamics through cavity quantum electrodynamical effects. Silicon photonic crystal nanobeam cavities are used to induce the Purcell effect on individual carbon nanotubes. Spectral and temporal behavior of the cavity enhancement is characterized by photoluminescence microscopy and the fraction of the radiative decay process is evaluated. We find that the radiative quantum efficiency can reach near unity for bright excitons in long air-suspended carbon nanotubes at room temperature.Received 19 March 2021Revised 27 February 2022Accepted 23 March 2022DOI:https://doi.org/10.1103/PhysRevResearch.4.L022011Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCavity quantum electrodynamicsExcitonsPhysical SystemsNanotubesOptical microcavitiesTechniquesPhotoluminescenceCondensed Matter, Materials & Applied Physics

Single Virus Detection on Silicon Photonic Crystal Random Cavities.

On-chip silicon microcavity sensors are advantageous for the detection of virus and biomolecules due to their compactness and the enhanced light-matter interaction with the analyte. While their theoretical sensitivity is at the single-molecule level, the fabrication of high quality (Q) factor silicon cavities and their integration with optical couplers remain as major hurdles in applications such as single virus detection. Here, label-free single virus detection using silicon photonic crystal random cavities is proposed and demonstrated. The sensor chips consist of free-standing silicon photonic crystal waveguides and do not require pre-fabricated defect cavities or optical couplers. Residual fabrication disorder results in Anderson-localized cavity modes which are excited by a free space beam. The Q≈105 is sufficient for observing discrete step-changes in resonance wavelength for the binding of single adenoviruses (≈50nm radius). The authors' findings point to future applications of CMOS-compatible silicon sensor chips supporting Anderson-localized modes that have detection capabilities at the level of single nanoparticles and molecules.

A Novel Photonic Crystal BioNEMS Sensing Platform Based on Fano resonances

A novel optical BioNEMS (Bio Nano-Electro-Mechanical-Systems) sensor based on a tunable 2D photonic crystal (PhC) cavity is proposed in this paper. The present device includes a functionalized BioNEMS cantilever and a tunable PhC structure. This optical detection system is a rod-type silicon photonic crystal cavity in which a designed defect allows the transmission of highly confined wave modes. While the immobilized capture probes are exposed to a solution containing the target biomarkers (i.e., DNA, mRNA or proteins), binding events cause a stress on the surface of the nanocantilever because of biological interactions. Therefore, the NEMS movable part is displaced as a result of an induced differential surface stress. This changes the position of the defect nanorods in the PhC cavity which leads to the transmitted wavelength variations. Finally, the concentration of biological quantities is measured by detecting the optical spectrum changes of the proposed biosensor. Furthermore, the presented BioNEMS sensor is analyzed by numerical and analytical approaches to obtain its functional characteristics as follows: optical sensitivity of 5140 nm/RIU, FOM of 10280 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , Q-factor of 3078, mechanical sensitivity of 1.05 µm/Nm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and resonant frequency of 23.45 kHz. Based on the obtained results, the proposed structure relied on Fano resonances provides a high-precision biosensor which has a great potential for highly sensitive detection of biomarkers in early diseases diagnosis as well as drug delivery test.

Study of the Effects of Cavity Mode Spacing on Mode-Hopping in III–V/Si Hybrid Photonic Crystal Lasers

We present a design methodology for hybrid lasers to realise mode-hop free operation by controlling the cavity mode spacing. In this study, a compact hybrid photonic crystal laser (H-PhCL) was employed which allowed a reduction of the Fabry–Perot length of the laser cavity and eliminated the need for an active mode stabilisation mechanism in order to realise mode-hop free operation. The H-PhCL was formed by butt-coupling a reflective semiconductor optical amplifier (RSOA) with a two-dimensional silicon (Si) photonic crystal (PhC) cavity. Continuous stable single frequency operation with &gt;40 dB side-mode suppression ratio (SMSR) of the laser was achieved for gain currents of up to 100 mA, i.e., up to four times the threshold current. The shorter length of the laser cavity enabled single frequency operation due to the selection of a single longitudinal mode by the PhC narrowband reflector. Various longitudinal mode spacing regimes were studied to explain the mode-hop free characteristics of the H-PhCL. The proposed hybrid laser design methodologies can be adapted to eliminate mode-hopping in laser wavelength.

MoTe2 PN Homojunction Constructed on a Silicon Photonic Crystal Cavity for High-Performance Photodetector

We demonstrate a straightforward construction of MoTe2 PN homojunction on a silicon photonic crystal cavity, which promises the realizations of cavity-enhanced optoelectronic devices integrated on silicon photonic chips. The employed silicon photonic crystal cavity has an air-slot in the middle to split it into two parts, which directly function as two individual back-gate electrodes of the top-coated few-layer MoTe2. Beneficial from MoTe2’s ambipolar property, reconfigured (PN, NN, PP, NP) homojunctions are realized by controlling the gate voltages of the two separated silicon electrodes. For instance, on/off ratios exceeding 104 are obtained from the PN or NP homojunctions, and the ideality factors could approach 1.00. On the other hand, the silicon photonic crystal cavity could enhance light absorption in the coated MoTe2, promising high-performance photodetection. By coupling the resonant mode with the MoTe2 PN junction, a high photoresponsivity of 156 mA/W is obtained at the wavelength of 1353.7 nm, though it is the limit of MoTe2’s absorption bandedge. As attributes of the PN junction, the photodetector has a dark current as low as 0.14 nA and a response bandwidth exceeding 1.1 GHz. The proposed device geometry has advantages of employing silicon photonic crystal cavity as the back gates of MoTe2 PN junction directly and simultaneously to enhance light–MoTe2 interactions, which might open a new avenue to construct MoTe2-based laser diodes and electro-optic modulators on silicon photonic chips.

Multifunctional optoelectronic device based on graphene-coupled silicon photonic crystal cavities.

We present a hybrid device based on graphene-coupled silicon (Si) photonic crystal (PhC) cavities, featuring triple light detection, modulation, and switching. Through depositing single-layer graphene onto the PhC cavity, the light-graphene interaction can be enhanced greatly, which enables significant detection and modulation of the resonant wavelength. The device is designed to generate a photocurrent directly by the photovoltaic effect and has an external responsivity of ∼14 mA/W at 1530.8 nm (on resonance), which is about 10 times higher than that off-resonance. Based on the thermo-optical effect of silicon and graphene, the device is also demonstrated in electro-optical and all-optical modulation. Also, due to the high-quality (Q) factor of the resonate cavity, the device can implement low threshold optical bistable switching, and it promises a fast response speed, with a rise (fall) time of ∼0.4 μs (∼0.5 μs) in the all-optical switch and a rise (fall) time of ∼0.5 μs (∼0.5 μs) in the electro-optical hybrid switch. The multifunctional photodetector, modulator, and optical bistable switch are achieved in a single device, which greatly reduces the photonic overhead and provides potential applications for future integrated optoelectronics.

Highly Sensitive and Tunable Fano-Like Rod-Type Silicon Photonic Crystal Refractive Index Sensor

A highly sensitive and tunable 2D rod-type silicon photonic crystal cavity based biosensor configuration has been designed and numerically analyzed. The structure is optimized so that the light-matter interaction is maximized in the cavity region. Out-of-plane light confinement is achieved by sandwiching the rods between metal plates, and tuning is achieved by introducing an air-gap between on top of the rods and the metal plate. A single rod is positioned in the middle of the waveguide so that the cavity Q-factor is enhanced by obtaining a Fano-like resonance. The air-gap between the rods and the metal plate acts as a slot structure, confining E-field in that small region and simultaneously decreasing mode-volume while making the resonance characteristics highly dependent on the gap size. This creates the opportunity to tune the resonance characteristics by electrostatic actuation via applying voltage to the top and bottom metal plates. The proposed structure has a sensitivity value of 1039 nm/RIU, a mode volume of 0.214 ( $\lambda $ /n)3, flexible tuning capabilities, and is the first tunable 2D PhC rod-type refractive index sensor.

Fundamental Thermal Noise Limits for Optical Microcavities

We present a joint theoretical and experimental characterization of thermo-refractive noise in high quality factor ($Q$), small mode volume ($V$) optical microcavities. Analogous to well-studied stability limits imposed by Brownian motion in macroscopic Fabry-Perot resonators, microcavity thermo-refractive noise gives rise to a mode volume-dependent maximum effective quality factor. State-of-the-art fabricated microcavities are found to be within one order of magnitude of this bound. We confirm the assumptions of our theory by measuring the noise spectrum of high-$Q/V$ silicon photonic crystal cavities and apply our results to estimate the optimal performance of proposed room temperature, all-optical qubits using cavity-enhanced bulk material nonlinearities.

Hybrid III-V Silicon Photonic Crystal Cavity Emitting at Telecom Wavelengths.

Photonic crystal (PhC) cavities are promising candidates for Si photonics integrated circuits due to their ultrahigh quality (Q)-factors and small mode volumes. Here, we demonstrate a novel concept of a one-dimensional hybrid III-V/Si PhC cavity which exploits a combination of standard silicon-on-insulator technology and active III-V materials. Using template-assisted selective epitaxy, the central part of a Si PhC lattice is locally replaced with III-V gain material. The III-V material is placed to overlap with the maximum of the cavity mode field profile, while keeping the major part of the PhC in Si. The selective epitaxy process enables growth parallel to the substrate, and hence in-plane integration with Si, and in-situ in-plane homo- and heterojunctions. The fabricated hybrid III-V/Si PhCs show emission over the entire telecommunication band from 1.2 to 1.6 μm at room temperature validating the device concept and its potential towards fully integrated light sources on silicon.

All-Optical Spiking Neuron Based on Passive Microresonator

Neuromorphic photonics that aims to process and store information simultaneously like human brains has emerged as a promising alternative for next generation intelligent computing systems. The implementation of hardware emulating the basic functionality of neurons and synapses is the fundamental work in this field. However, previously proposed optical neurons implemented with SOA-MZIs, modulators, lasers or phase change materials are all dependent on active devices and pose challenges for integration. Meanwhile, although the nonlinearity in nanocavities has long been of interest, the previous theories are intended for specific situations, e.g., self-pulsation in microrings, and there is still a lack of systematic studies in the excitability behavior of the nanocavities including the silicon photonic crystal cavities. Here, we report for the first time a universal coupled mode theory model for all side-coupled passive microresonators. The excitability of microresonators resulting from the subcritical Andronov-Hopf bifurcation is categorized as Class 2 neural excitability and can be used to mimic the Hodgkin-Huxley neuron model. We demonstrate that the microresonator-based neuron can exhibit the typical characteristics of spiking neurons: excitability threshold, leaky integrating dynamics, refractory period, cascadability and inhibitory spiking behavior, paving the way to realize all-optical spiking neural networks.

Enhancement of Radiative Transitions by Silicon Photonic Crystal Cavities

Enhancement of Radiative Transitions by Silicon Photonic Crystal Cavities

Comparison Between the Linear and Nonlinear Homogenization of Graphene and Silicon Metasurfaces

In this article, we use a versatile homogenization approach to model the linear and nonlinear optical response of two metasurfaces: a plasmonic metasurface consisting of graphene patches and a dielectric photonic nanostructure consisting of silicon photonic crystal (PhC) cavities. The former metasurface is resonant at wavelengths that are much larger than the graphene elements of the metasurface, whereas the resonance wavelengths of the latter one are comparable to the size of its resonant components. By computing and comparing the effective permittivities and nonlinear susceptibilities of the two metasurfaces, we infer some general principles regarding the conditions under which homogenization methods of metallic and dielectric metasurfaces are valid. In particular, we show that in the case of the graphene metasurface the homogenization method describes very well both its linear and nonlinear optical properties, whereas in the case of the silicon photonic nanostructure the homogenization method is only qualitatively accurate, especially near the optical resonances.

Frequency modulated hybrid photonic crystal laser by thermal tuning.

We demonstrate frequency modulation (FM) in an external cavity (EC) III-V/silicon laser, comprising a reflective semiconductor optical amplifier (RSOA) and a silicon nitride (SiN) waveguide vertically coupled to a 2D silicon photonic crystal (PhC) cavity. The PhC cavity acts as a tunable narrowband reflector giving wavelength selectivity. The FM was achieved by thermo-optical modulation of the reflector via a p-n junction. Single-mode operation was ensured by the short cavity length, overlapping only one longitudinal laser mode with the reflector. We investigate the effect of reflector modulation theoretically and experimentally and predict a substantial tracking of the resonator by the laser frequency with very small intensity modulation (IM).