Nanobeam Cavities Research Articles

Chip-scale humidity sensor based on a silicon nanobeam cavity.

In this Letter, a novel humidity sensor based on a chip-scale silicon nanobeam cavity with polymethyl methacrylate (PMMA) cladding is demonstrated. This sensor is easy to fabricate and compatible with CMOS technology. It shows a humidity sensing with a linear wavelength dependence of 22.9pm/% relative humidity (RH) in a wide range of RH from 10% to 85%, an ultra-fast response time of 540ms, and high stability. After annealing, the sensor exhibits high reversibility, repeatability, and temperature insensitivity at the range of 25°C-40°C. To the best of our knowledge, this is the first application of integrated photonics in high performance humidity detection. It provides a new way for the chip-scale sensor to integrate with photonic devices and optical systems.

Bloch-surface-wave photonic crystal nanobeam cavity

We theoretically demonstrate a nanobeam cavity based on a photonic crystal ridge that supports localized Bloch surface waves (BSWs) propagating at the truncation interface of a periodic multilayer. Combining the appealing characteristics of a nanobeam cavity (such as flexible geometry, small footprint size, and an etching-free fabrication with the leading lithographic technologies) with the versatility of BSW (whose dispersion relation is finely tunable as compared to other surface waves), this structure may prove to be a customizable visible-to-IR platform, well suited for a number of applications ranging from optical sensing to the control of single-photon emission from embedded nanoemitters such as quantum dots or color centers.

Ultra-low mode volume on-substrate silicon nanobeam cavity.

We design and fabricate an on-substrate bowtie photonic crystal (PhC) cavity in silicon. By optimizing the bowtie shapes in the unit cells of the PhC cavity, the maximum of the electric field can be highly confined in the bowtie tips. Due to such confinement, an ultra-low mode volume of ∼0.1(λ/nSi)3 is achieved, which is more than an order of magnitude smaller than the previous on-substrate nanobeam cavities. An ultra-high quality (Q) factor as large as 106 is predicted by simulation, and up to 1.4×104 is measured in experiment. The observation of pronounced thermo-optic bistability is consistent with the strong confinement of light in the cavities.

Optimal Photonic Crystal Cavities for Coupling Nanoemitters to Photonic Integrated Circuits

AbstractPhotonic integrated circuits that are manufactured with mature semiconductor technology hold great promise for realizing scalable quantum technology. Efficient interfaces between quantum emitters and nanophotonic devices are crucial building blocks for such implementations on silicon chips. These interfaces can be realized as nanobeam optical cavities with high quality factors and wavelength‐scale mode volumes, thus providing enhanced coupling between nano‐scale quantum emitters and nanophotonic circuits. Realizing such resonant structures is particularly challenging for the visible wavelength range, where many of the currently considered quantum emitters operate, and if compatibility with modern semiconductor nanofabrication processes is desired. Here, it is shown that photonic crystal nanobeam cavities for the visible spectrum can be designed and fabricated directly on‐substrate with high quality factors and small mode volumes. Designs are compared based on deterministic and mode‐matching methods and the latter is found advantageous for on‐substrate realizations. The results pave the way for integrating quantum emitters with nanophotonic circuits for applications in quantum technology.

Tuning the coupling between quantum dot and microdisk with photonic crystal nanobeam cavity.

Strong coupling between solid-state quantum emitters and microcavities paves the way for optical coherent manipulation of quantum state and provides opportunities for quantum information processing. However, it is still a challenge to realize strong coupling due to the spectral and spatial mismatch between quantum emitters and cavity modes. Here, we propose a scheme to tune the coupling between a single QD and a microdisk with 1D photonic crystal nanobeam cavity. Based on Finite-Difference Time-Domain (FDTD) method and Green's function expression for the evolution operator, we demonstrate that QDs with emission wavelengths +1.27 nm and -1.44 nm detuned from the bare microdisk mode can be coupled to the system strongly. Particularly, we observe simultaneous coupling between QD and two cavity supermodes, which enriches the optical coherent control methods of quantum states. By adjusting the distance between the two cavities, we can control the coupling between QD and photons. Furthermore, benefiting from the natural integration of nanobeam cavity to waveguide, such a system provides advantages for implementing quantum internet.

Photonic crystal nanobeam cavities with optical resonances around 800 nm

We report on the design and the fabrication of 1D photonic crystal (PhC) nanobeam cavities with optical resonances around 800 nm, compatible with Rubidium, Cesium or Argon atomic transitions. The cavities are made of Indium Gallium Phosphide (InGaP) material, a III-V semi-conductor compound which has a large index of refraction ($n \simeq 3.3$) favoring strong optical confinement and small mode volumes. Nanobeam cavities with inline and side coupling have been designed and fabricated, and quality factors up to $2\times 10^4$ have been measured.

Large thermal tuning of a polymer-embedded silicon nitride nanobeam cavity.

Tunable silicon nitride nanophotonic resonators are a critical building block for integrated photonic systems in the visible wavelength range. We experimentally demonstrate a thermally tunable polymer-embedded silicon nitride nanobeam cavity with a tuning efficiency of 44pm/°C and 0.13nm/mW in the near-visible wavelength range. The large tuning efficiency comes from the high thermo-optic coefficient of the SU-8 polymer and the "air-mode" cavity design, where a large portion of the cavity field is confined inside the polymer region. The demonstrated resonator will enable locally tunable cavity quantum electrodynamic experiments in the silicon nitride platform.

Design of a Single Nanoparticle Trapping Device Based on Bow-Tie-Shaped Photonic Crystal Nanobeam Cavities

Photonic crystal (PhC) cavities have been widely utilized for the optical trapping. However, it is still challenging to achieve high-efficiency optical trapping of ultrasmall nanoparticles. In this paper, we show optical trapping of a 3 nm size single nanoparticle by using an ultrahigh Q/V bow-tie-shaped PhC nanobeam cavity. For the trapping of a single polystyrene nanoparticle with the radius as small as 3 nm, a maximum trapping force of 1.2 × 10 5 pN/mW is theoretically obtained, which is at least one order of magnitude higher than the previous results. Furthermore, the calculated sensitivity for the cavity is around 350 nm/RIU, which provides a valid solution for monitoring the trapping process of the nanoparticles with ultrasmall size. We believe that such structure with characteristics of extreme light confinement and high trapping efficiency will be conducive to the development of multifunctional on-chip trapping devices.

Hybrid cavity-antenna systems for quantum optics outside the cryostat?

Abstract Hybrid cavity-antenna systems have been proposed to combine the sub-wavelength light confinement of plasmonic antennas with microcavity quality factors Q. Here, we examine what confinement and Q can be reached in these hybrid systems, and we address their merits for various applications in classical and quantum optics. Specifically, we investigate their applicability for quantum-optical applications at noncryogenic temperatures. To this end we first derive design rules for hybrid resonances from a simple analytical model. These rules are benchmarked against full-wave simulations of hybrids composed of state-of-the-art nanobeam cavities and plasmonic-dimer gap antennas. We find that hybrids can outperform the plasmonic and cavity constituents in terms of Purcell factor, and additionally offer freedom to reach any Q at a similar Purcell factor. We discuss how these metrics are highly advantageous for a high Purcell factor, yet weak-coupling applications, such as bright sources of indistinguishable single photons. The challenges for room-temperature strong coupling, however, are far more daunting: the extremely high dephasing of emitters implies that little benefit can be achieved from trading confinement against a higher Q, as done in hybrids. An attractive alternative could be strong coupling at liquid nitrogen temperature, where emitter dephasing is lower and this trade-off can alleviate the stringent fabrication demands required for antenna strong coupling. For few-emitter strong-coupling, high-speed and low-power coherent or incoherent light sources, particle sensing and vibrational spectroscopy, hybrids provide the unique benefit of very high local optical density of states, tight plasmonic confinement, yet microcavity Q.

Camera detection and modal fingerprinting of photonic crystal nanobeam resonances.

We demonstrate in simulation and experiment that the out-of-plane, far-field scattering profile of resonance modes in photonic crystal nanobeam (PCN) cavities can be used to identify resonance mode order. Through detection of resonantly scattered light with an infrared camera, the overlap between optical resonance modes and the leaky region of k-space can be measured experimentally. Mode order dependent overlap with the leaky region enables usage of resonance scattering as a "fingerprint" by which resonant modes in nanophotonic structures can be identified via detection in the far-field. By selectively observing emission near the PCN cavity region, the resonant scattering profile of the device can be spatially isolated and the signal noise introduced by other elements in the transmission line can be significantly reduced, consequently improving the signal to noise ratio (SNR) of resonance detection. This work demonstrates an increase in SNR of ∼ 19 dB in out-of-plane scattering measurements over in-plane transmission measurements. The capabilities demonstrated here may be applied to improve characterization across nanophotonic devices with mode-dependent spatial field profiles and enhance the utility of these devices across a variety of applications.

Tailoring mode splitting and degeneracy in silicon triply resonant nanobeam cavities

We investigate the use of coupled silicon nanobeam cavities for achieving multiple resonances as a photonic dedicated platform for nonlinear signal processing and sensing. The transmission spectra of the triple-coupled cavities were measured, and high quality factors, up to about 80,000, have been experimentally reported. By precisely varying the positions of three cavities vertically and horizontally, evolutions of the supermodes were fully mapped, in good agreement with the simulation designs. Some specific and interesting properties such as the dark state of the system, leading to unique transmission spectra, have been clearly observed. Based on a geometrical control of the structure, the three resonances can be tuning independently, and degeneracy modes emerge in some configurations when the distance parameters are properly chosen. This triple-resonant device is expected to enable the adjustment of third-order nonlinear properties in silicon photonics, and it is also a candidate for sensing or reconfigurable and programmable photonics.

Ultra-compact low loss electro-optical nanobeam cavity modulator embedded photonic crystal

In this paper, a hybrid electro-optical modulator based on a one-dimensional photonic crystal nanobeam cavity is proposed. The main component of the cavity builder is the indium–tin–oxide that is a transparent conductive oxide. The proposed structure is used to minimize optical losses and also to have a high-quality factor with a tunability from the distributed feedback system. The proposed modulator has a wide range of resonant tunable in a footprint of 1.892 μm2. This structure has the ability to shift the wavelength of 1.55 μm using a very small voltage 0.1 V. Simulation results show that the proposed structure has an insertion loss of 0.027 dB, extension ratio 3.484 dB, 119.89 GHz modulation speed, and 0.59 aJ/bit modulation energy. By comparing the proposed method parameters and other modulators based on the one-dimensional photonic crystal nanobeam cavity, a significant improvement in modulation voltage, insertion losses, energy consumption, and footprint have been observed.

Low-index-mode photonic crystal nanobeam cavity for refractive index sensing at the 2 μm wavelength band.

We present the design, fabrication, and characterization of a one-dimensional photonic crystal (1D-PhC) low-index-mode nanobeam cavity on the silicon-on-insulator platform for refractive index sensing at the 2μm wavelength band. A Q-factor of 4.35×105 and an effective mode volume of Veff∼1.95(λ/nSi)3 are theoretically achieved. The measured transmission spectrum of the device immersed in NaCl solutions with different mass concentrations demonstrates a sensitivity of 326.1nm/RIU and a Q-factor of ∼1144.

Compact design of a gallium phosphide nanobeam cavity for coupling to diamond germanium-vacancy centers

A design for an ultrahigh Q/V nanobeam cavity engineered to interact with Germanium-vacancy (GeV) centers is presented. The nanobeam cavity supports a mode with Q/V>108 with transmission over 70%. The proposed design is based on a new scalable approach developed to reduce the footprint of nanobeam cavities by more than 50% without losing the cavity Q/V value and transmission. Cavity quantum electrodynamics analysis reveals that strong coupling between the zero-phonon line transition of GeV centers and the cavity mode can be achieved for a range of nanobeam dimensions.

High-Sensitive TM Modes in Photonic Crystal Nanobeam Cavity with Horizontal Air Gap for Refractive Index Sensing

We propose a new type of refractive index sensing based on the transverse magnetic (TM) modes in the photonic crystal (PhC) nanobeam (NB) cavity with a horizontal air gap. The electric field of the resonant TM mode is strongly confined within the horizontal air gap present at the PhC NB cavity. In order to increase the quality (Q) factor and the sensitivity (S) of the refractive index change in the air simultaneously, the cavity structure is fully optimized. Because of the trade-off between the Q-factor and S of the TM mode in the PhC NB cavity with an air gap, there is an optimal thickness of the air gap in the dielectric slot. From the numerical simulation results, S can exceed 1000 nm/RIU with Q > 40,000. When the dielectric slot becomes thin, S could be higher than 1200 nm/RIU. For practical applications, we suggest an Si-based PhC NB cavity with a horizontal SiO2 slot structure which can also provide high S with a high Q-factor after a very fine selective wet etching process. This new type of TM resonant mode in the PhC NB cavity can be an ideal platform for compact sensors in photonic integrated circuits for TM waveguide systems.

High-Q Slot-Mode Photonic Crystal Nanobeam Cavity Biosensor With Optomechanically Enhanced Sensitivity

A biosensor design based on a photonic crystal nanobeam cavity with an optomechanical positive feedback mechanism is proposed. Design of the cavity and optomechanical sensitivity enhancement method are numerically analyzed and the results show that fourfold improvement is possible without any degradation of the Q -factor.

Anti-External Interference Sensor Based on Cascaded Photonic Crystal Nanobeam Cavities for Simultaneous Detection of Refractive Index and Temperature

In this paper, we present an anti-external interference sensor based on cascaded silicon-on-insulator ellipse stack major axis modulated photonic crystal (PC) nanobeam cavities. Two PC nanobeam cavities, one covered with SU-8 cladding (cav1) and the other exposed to air directly (cav2), are cascaded to detect refractive index (RI) and temperature simultaneously. Three-dimensional finite-difference time-domain simulations are used for our analysis. We prove the feasibility to obtain RI and temperature simultaneously, obtaining an RI sensitivity of 0 nm/RIU (refractive index unit) and a temperature sensitivity of –107.9 pm/K for cav1, whereas an RI sensitivity of 354.6 nm/RIU and a temperature sensitivity of 46.7 pm/K for cav2. Particularly, the proposed sensor not only achieves competitive RI sensitivities and temperature sensitivities, but also increases the differences between the sensitivity ratios of RI sensing and temperature sensing, which makes the dual-parameter detection easier. Furthermore, we propose the concept and analysis of anti-external interference to describe the ability to resist the external interferences. Based on this analysis method, the proposed sensor achieves a strong anti-external interference ability. Therefore, the proposed sensor is potentially a promising platform for future application of dual-parameter sensing.

Efficient side-coupling to photonic crystal nanobeam cavities via state-space overlap

We present design guidelines for realizing side-coupled photonic crystal nanobeam (PCN) cavities with efficient coupling to low order resonances through adjusting the overlap of the PCN cavity mode and a feeding bus waveguide in both physical and k-space. We show that optimal side-coupled configurations function at a non-zero k-vector offset between the bus waveguide and PCN cavity modes. The straightforward design of side-coupled PCNs with high contrast resonances opens the door to their practical implementation in multiplexed, on-chip photonic devices.

High-contrast and low-power all-optical switch using Fano resonance based on a silicon nanobeam cavity.

We experimentally demonstrate an ultra-compact all-optical switch involving Fano resonance based on a side-coupled Fabry-Perot (F-P) resonator and a silicon photonic crystal (PhC) nanobeam cavity, with an area of only 11 μm2. By optimizing the structure of the nanobeam cavity to increase its intrinsic quality factor (Q), we achieve a sharp asymmetric transmission spectrum, with an extinction ratio (ER) as high as 40dB and a peak loss as low as 0.6dB. As far as we know, this is the highest measured ER in PhC-based Fano resonance. These excellent properties enable us to realize an all-optical switch with shorter switching recovery time, lower power consumption, and higher contrast, compared to that involving Lorentzian resonance. For example, under signal trains of 2.5Gb/s, switching energy with a contrast of 3dB for the Fano case is 113fJ, which is 8dB smaller than that for the Lorentzian case. Furthermore, by performing blue-detuned filtering on the 15-Gb/s output signal light, the switching contrast of the all-optical switch based on Fano resonance is significantly improved from 0.67dB to 9.53dB.

Photonic crystal elliptical-hole tapered low-index-mode nanobeam cavities for sensing.

A one-dimensional photonic crystal elliptical-hole tapered low-index-mode nanobeam cavity sensor fully encapsulated in a water environment is proposed. In the proposed structure, to confine the light in the low-index region and enhance the light-matter interaction, a tapered major axis of the elliptical hole away from the nanobeam cavities center is optimized. Through a three-dimensional finite-difference time-domain simulation, the results show that the low-index-mode of the middle geometry cell is confined in the photonic bandgap of two-sided cells. The highest quality factor of 6.04×105 is achieved when 13 tapered segments and 5 mirror segments are placed at both sides of the host waveguide. The proposed nanobeam structure theoretically possesses a sensitivity of 244.7nm/RIU (refractive index unit) in a water environment. Moreover, an ultra-compact footprint of 6.4 μm×0.85 μm is achieved, which is only half of the size compared to the best value reported for the nanobeam structure. The results indicate that it is a promising sensor for excellent on-chip sensing with respect to the very small footprint.