Photonic Crystal Cavity Research Articles

Design of bio-alcohol sensor based on waveguide-coupled photonic crystal cavity

Detection of bio-alcohol is crucial in diverse industries, including forensics, medicine, and food production. This paper presents a novel biosensor for bio-alcohol detection in water, integrating three micro-cavities with two waveguides within a hexagonal photonic crystal array. Employing a wavelength interrogation approach and finite-difference time-domain (FDTD) simulations, the proposed biosensor demonstrates a high sensitivity of 610 nm/RIU (nanometers per refractive index unit) and a low detection limit of 7 × 10-3 RIU. Simulation results validate the effectiveness of this photonic crystal biosensor for detecting organic substances in water, showcasing its potential for practical applications.

Optomechanical simulation of a time-dependent parametric oscillator

We explore a finite element model of a standard one-dimensional photonic crystal cavity etched on a nanobeam designed to enhance optomechanical coupling. We theoretically demonstrate that polychromatic driving of the mechanical sidebands produces an effective Hamiltonian model showing optical self- and cross-Kerr terms and parametric interaction between the optical and mechanical modes. For the sake of providing an example, we show that bi-chromating driving, near the first and second red-sidebands, produces an analog simulation of a mechanical parametric oscillator that exhibits a squeezed vacuum ground state in the time-independent case, and in the time-dependent case, the evolution of the mechanical ground state produces displaced squeezed vacuum.

Tunable Localization of Higher‐Order Bound States in Non‐Hermitian Optical Waveguide Lattices

AbstractHigher‐order corner‐bound states in a 2D structure have been found to possess robust and exotic properties beyond the “ordinary” topological edge states, giving rise to a promising applicative potential. For example, the topological nanocavity designed based on the corner states exhibits much better performance than that of the conventional photonic crystal cavity. However, the corner states in the finite Hermitian system are usually coupled with each other, which results in the weakening of their localization. As such, the contradiction between the performance and footprint of topological devices is vexing. Here, it shows that introducing non‐Hermiticity in the higher‐order topological insulators is an effective strategy to enhance the localization of corner states in finite systems. By designing and analyzing the 2D finite Su‐Schriffer‐Heeger optical lattices with two types of non‐Hermitian configuration, the localization degree of higher‐order corner states is found to depend on the gain/loss strength. This is experimentally demonstrated by observing the distribution of corner states in the femtosecond‐laser‐writing loss‐controlled waveguide arrays. This scheme tuning localization of higher‐order corner‐bound states by non‐Hermiticity may offer a new avenue to design robust and compact devices, such as topological nano‐lasers with an ultra‐low threshold.

Silicon-Based Zipper Photonic Crystal Cavity Optomechanical System for Accelerometers.

The cavity optomechanical accelerometer based on photonic crystal microcavities combines mechanical resonators with high-quality factor photonic crystal cavities. The mechanical vibrator is sensitive to weak force/displacement in mechanical resonance modes, which can achieve extremely low noise levels and theoretically reach the standard qillatum noise limit. It is an important development direction for high-precision accelerometers. This article analyzes the principle and structural characteristics of a zipper type photonic crystal cavity optomechanical accelerometer, and designs a silicon-based zipper type photonic crystal cavity and mechanical vibrator structure applied to the accelerometer. The influence of the structural parameters of the zipper cavity on the optical Q factor was analyzed in detail. The resonant frequency of the optical cavity was controlled around 195 THz by adjusting the structural parameters, and the mechanical resonance characteristics of the mechanical vibrator and the optical cavity were analyzed. The effective mass of the optical cavity was 30 pg, and, with the addition of the mechanical vibrator, the effective mass was 3.1 ng. The optical mechanical coupling rate reached the GHz/nm level, providing guidance for the manufacturing and characterization of silicon-based zipper cavity accelerometers.

(Invited) Hybrid Nanodevices for Technology and Fun

Two-dimensional materials like graphene or transition metal dichalcogenides have remarkable properties, making them very attractive from a technological point of view and incredibly fun to work with. The intrinsic properties of 2D materials change drastically when going from the bulk into the true 2D limit, where they exhibit exotic quantum properties. While many groups have focused on studying and exploiting these materials, very little work has been devoted to engineering their intrinsic properties. The “all-surface” nature makes device fabrication complex, and so far, only the most conventional nanofabrication or tailoring routes have been explored. In this talk, I will present novel routes currently under exploration in our group to tailor and exploit the properties of TMDS and MOF devices based on mechanical deformation or physical nanopatterning.Also, the integration of 2D materials into superconducting circuits can lead to novel technological applications of interest for photon and radiation detectors or quantum computing.In this talk, I will present some results concerning the development of retroreflectors based on MoS2 oscillating membranes and how they can be turned into electroluminescent diodes. I will also present the tailoring of conductive channels on MoS2 FET devices. Preliminary results on lateral PN homo-junctions, memristive field-effect transistors and photonic crystal cavities will also be presented. I will present preliminary results on the integration of MOF into Hall bar structures for metrology applications. To finish, I will also present results on the integration of Graphene and MoS2 onto Superconducting nanowire single photon detectors. Figure 1

Site-directed placement of three-dimensional DNA origami.

The combination of lithographic methods with two-dimensional DNA origami self-assembly has led, among others, to the development of photonic crystal cavity arrays and the exploration of sensing nanoarrays where molecular devices are patterned on the sub-micrometre scale. Here we extend this concept to the third dimension by mounting three-dimensional DNA origami onto nanopatterned substrates, followed by silicification to provide hybrid DNA-silica structures exhibiting mechanical and chemical stability and achieving feature sizes in the sub-10-nm regime. Our versatile and scalable method relying on self-assembly at ambient temperatures offers the potential to three-dimensionally position any inorganic and organic components compatible with DNA origami nanoarchitecture, demonstrated here with gold nanoparticles. This way of nanotexturing could provide a route for the low-cost production of complex and three-dimensionally patterned surfaces and integrated devices designed on the molecular level and reaching macroscopic dimensions.

Amplified spontaneous emission from europium-based molecular complexes coupled to photonic crystal cavities

Rare-earth ion-based materials bear many remarkable optical properties that render them highly appealing for lighting and quantum-related applications. However, their small oscillator strength and weak emission often pose limitations. Here, we synthesize and couple Eu(III)-based molecular complexes to nanobeam photonic crystals supporting air modes. A reasonable spatial overlap between the molecular complexes and cavity modes leads to an average spontaneous emission coupling efficiency of 0.19. Our pump power-dependent photoluminescence measurements evidence amplified spontaneous emission from the molecular complexes with an amplification threshold as low as 4.4 W/cm2, likely benefiting from the efficient coupling. These findings suggest that integrating rare-earth ion-based molecular complexes with photonic structures could be a viable approach for regulating their emission characteristics for particular applications.

High-Sensitivity and Wide Detection-Range Refractive-Index Sensor Based on Amplitude Change in Slotted Photonic Crystal Nanobeam Cavity

High Q-factor is essential for the realization of high sensitivity photonic crystal-based sensors. The Q-factor is usually optimized for a specific refractive-index (RI) value of the ambient background. However, a small change in the RI reduces the Q value, and therefore limits the performance of the sensor to a narrow RI range. Here, we report a high-sensitivity RI sensor with a wide detection-range based on amplitude change of the fundamental mode in slotted photonic crystal nanobeam cavity. Both wavelength and amplitude sensitivity of 333 nm/RIU and 188/RIU are realized in the RI range from 1.3 to 1.6, respectively. To the best of our knowledge, this represents the widest sensing range ever reported in photonic crystal cavities. Owing to the wide sensing range and the insignificance of the Q value, this approach would find applications in various research areas in integrated lab-on-chip systems for optofluidic- and bio-sensing applications.

Notch Microwave Photonic Filter With Narrow Bandwidth and Ultra-High All-Optical Tuning Efficiency Based on a Silicon Nanobeam Cavity

We propose and experimentally demonstrate a narrowband notch microwave photonic filter (MPF) with an ultra-high all-optical tuning efficiency based on an optimized high-quality (Q) nanobeam photonic crystal (PhC) cavity. By optimizing the structural parameters, the hole shapes and the waveguide width of the cavity, a silicon nanobeam cavity with a theoretical high-Q factor of 4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> , a small mode volume (V) of 0.32(λ/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> ) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and a compact size of 6 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> could be obtained. Due to the extremely high Q/V ratio beyond 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> , the nonlinear effects in the cavity could be efficiently excited, which is beneficial for on-chip low-power signal processing. In the experiment, by adjusting the wavelength of the optical carrier, the central frequency of the notch MPF could be widely tuned from 1 GHz to 40 GHz with maintaining the 3dB-bandwidth around 198 MHz and rejection ratios beyond 50 dB. On the other side, the central frequency of the MPF could be all-optically tuned based on the nonlinear effects in the cavity. Owing to the cavity extremely high Q/V ratio, the MPF frequency can be adjusted with an ultra-high tuning efficiency of 308.8 GHz/mW. To the best of our knowledge, whether the notch MPF narrow 3dB-bandwidth of 198 MHz or the all-optical tuning efficiency of 308.8 GHz/mW is a record value among the reported silicon-cavity-based notch MPFs with such a compact device size. With the dominant advantages of sub-gigahertz narrowband, wide tuning range, ultra-high all-optical tuning efficiency and extremely compact cavity size, the proposed MPFs illustrate competitive performance for on-chip microwave signal processing.

Coupling of QD-based PhC nanocavity with two mechanical modes: an approach to tunable optical switching and sensing applications

We theoretically study the dynamical change in the amplification of the output probe field spectra of a hybrid optomechanical system consisting of double mechanical modes coupled to a photonic crystal (PhC) nanocavity. The PhC cavity is also embedded with a quantum dot (QD) (two-level system) and simultaneously driven by an external pump and a probe field. We show that multiple number of transparency windows that appear can be controlled by the QD-cavity coupling strength and also the Fano profiles are directly measured by the resonant frequency of the mechanical mode. We also show the optical transition from bistability to tristability/multistability by adjusting the switching threshold of the system parameters. These results can also be used to study frequency optical nonreciprocity and all-optical switches in multi-resonator photonic devices.

Determining the transfer function of a reconstructive spectrometer using measurements at two wavelengths.

The transfer function is the characteristic function of the dispersive element of a reconstructive spectrometer. It maps the transmitted spatial intensity profile to the incident spectral intensity profile of an input. Typically, a widely tunable and narrowband source is required to determine the transfer function across the entire operating wavelength range, which increases the developmental cost of these reconstructive spectrometers. In this Letter, we utilize the parabolic dispersion relation of a planar one-dimensional photonic crystal cavity, which acts as the dispersive element, to determine the entire transfer function of the spectrometer using measurements made at only two wavelengths. Using this approach, we demonstrate reliable reconstruction of input spectra in simulations, even in the presence of noise. The experimentally reconstructed spectra also follow the spectra measured using a commercial spectrometer.

Deterministic Fabrication of a Coupled Cavity-Emitter System in Hexagonal Boron Nitride.

Light-matter interactions in optical cavities underpin many applications of integrated quantum photonics. Among various solid-state platforms, hexagonal boron nitride (hBN) is gaining considerable interest as a compelling van der Waals host of quantum emitters. However, progress to date has been limited by an inability to engineer simultaneously an hBN emitter and a narrow-band photonic resonator at a predetermined wavelength. Here, we overcome this problem and demonstrate deterministic fabrication of hBN nanobeam photonic crystal cavities with high quality factors over a broad spectral range (∼400 to 850 nm). We then fabricate a monolithic, coupled cavity-emitter system designed for a blue quantum emitter that has an emission wavelength of 436 nm and is induced deterministically by electron beam irradiation of the cavity hotspot. Our work constitutes a promising path to scalable on-chip quantum photonics and paves the way to quantum networks based on van der Waals materials.

An electroluminescent and tunable cavity-enhanced carbon-nanotube-emitter in the telecom band

Emerging photonic information processing systems require chip-level integration of controllable nanoscale light sources at telecommunication wavelengths. Currently, substantial challenges remain in the dynamic control of the sources, the low-loss integration into a photonic environment, and in the site-selective placement at desired positions on a chip. Here, we overcome these challenges using heterogeneous integration of electroluminescent (EL), semiconducting carbon nanotubes (sCNTs) into hybrid two dimensional – three dimensional (2D-3D) photonic circuits. We demonstrate enhanced spectral line shaping of the EL sCNT emission. By back-gating the sCNT-nanoemitter we achieve full electrical dynamic control of the EL sCNT emission with high on-off ratio and strong enhancement in the telecommunication band. Using nanographene as a low-loss material to electrically contact sCNT emitters directly within a photonic crystal cavity enables highly efficient EL coupling without compromising the optical quality of the cavity. Our versatile approach paves the way for controllable integrated photonic circuits.

Two-dimensional heterostructure quasi-BIC photonic crystal surface-emitting laser with low divergence

Abstract High beam quality, large-area output, and small footprint are significant pursuing goals for vertical-cavity surface-emitting lasers (VCSELs), which impose strict requirements on tight light confinements with minimized radiation losses. To achieve this, bound states in the continuum (BICs) have been demonstrated as an effective way of trapping light. Here, we combine BICs and photonic bandgaps to realize a quasi-BIC single-mode photonic crystal (PhC) laser on a colloidal quantum dots (CQDs)/silicon oxide (SiO2) hybrid integrated platform. The PhC cavity is a defect-free hexagonal heterostructure with three regions, and the thin CQDs film is embedded within the SiO2 nanopillar planar array as both an optical gain material and a backbone for the PhC. The mode gaps between different regions provide the lateral confinement while the quasi-BICs near the Γ-point generate the small-divergence vertical radiation coupling, resulting in a well-defined emission concentrating within ±1.85° of the normal surface direction and an optical pumping energy density threshold of 216.75 μJ/cm2. Our results demonstrate the design flexibility and versatility of the quasi-BIC laser even with a low contrast of a refractive index between the PhC slab and the substrate, which has potential applications in cavity quantum electrodynamics, nonlinear optics, and integrated photonics.

Engineering Quantum Nanophotonic Components from Hexagonal Boron Nitride

AbstractIntegrated quantum photonics (IQP) provides a path to practical, scalable quantum computation, communications and information processing. Realization of an IQP platform requires controlled engineering of many nanophotonic components. However, the range of materials for monolithic platforms is limited by the simultaneous need for high‐quality quantum light sources, high optical performance, and availability of scalable nanofabrication techniques. Here, the fabrication of IQP components from the recently emerged material hexagonal boron nitride (hBN), including tapered waveguides, microdisks, and 1D and 2D photonic crystal cavities, is demonstrated. Resonators with quality factors greater than 4000 are achieved, and proof‐of‐principle complex, free‐standing IQP circuitry fabricated from single‐crystal hBN is engineered. The results show the potential of hBN for scalable integrated quantum technologies.

Scalable high Q-factor Fano resonance from air-mode photonic crystal nanobeam cavity

Abstract Fano resonance from photonic crystal nanobeam cavity (PCNC) is important building block for large-scale photonic integrated circuits (PICs) to enable photonic switches and sensors with superior characteristics. Nevertheless, most state-of-the-art demonstrations rely on electron beam lithography (EBL) and operate in dielectric mode. Hence, we theoretically, numerically and experimentally present the characteristics of Fano resonance from optical interference between the discrete state of air-mode PCNC and the continuum mode of side-coupled line-defect waveguide with partially transmitting element (PTE) using deep ultraviolet (DUV) lithography for the first time. Experimentally high average Q-factor of ∼1.58 × 104 is achieved for 30 measured devices, which indicates the feasibility of mass manufacture of high-Q Fano resonance from air-mode PTE-PCNC. Additionally, the thermo-optic bi-stability and thermal tuning characterizations of the proposed device are discussed. This work will contribute to building ultra-compact lab-on-chip resonance-based photonic components.

Realization of spinning mode with maximum chirality in photonic-crystal defect cavity at exceptional point

Optical modes spinning with maximum chirality in cavities at the chip level are essential for quantum and biomedical applications. The coalescent chiral mode at the exceptional point (EP) due to non-Hermicity is the one in demand. Yet, approaching EPs require fine balances between the loss/gain and the dielectric perturbation, which are typically nontrivial. In this paper, by elevating the reliability of fine-tuning, we realize circularly-polarized-like lasing modes with maximum chirality at the EP of photonic-crystal one-hole cavities. Such an EP is of intracavity type in the subwavelength scale and reaching it requires more reliable strategies than those for its forerunners. We adopt the in-plane tunneling loss that is well controlled with the layer number of air holes in the photonic-crystal slab. By removing and relocating holes in blocks, we systematically elevate the chirality of the radiation field. The collective variations of holes render the EP robust against the uncertainty in fabrications. Without auxiliary non-Hermitian and chiral structures, our works promote coherent chiral light sources at the chip level.

Optomechanically induced optical trapping system based on photonic crystal cavities.

Optical trapping has proven to be a valuable experimental technique for precisely controlling small dielectric objects. However, due to their very nature, conventional optical traps are diffraction limited and require high intensities to confine the dielectric objects. In this work, we propose a novel optical trap based on dielectric photonic crystal nanobeam cavities, which overcomes the limitations of conventional optical traps by significant factors. This is achieved by exploiting an optomechanically induced backaction mechanism between a dielectric nanoparticle and the cavities. We perform numerical simulations to show that our trap can fully levitate a submicron-scale dielectric particle with a trap width as narrow as 56 nm. It allows for achieving a high trap stiffness, therefore, a high Q-frequency product for the particle's motion while reducing the optical absorption by a factor of 43 compared to the cases for conventional optical tweezers. Moreover, we show that multiple laser tones can be used further to create a complex, dynamic potential landscape with feature sizes well below the diffraction limit. The presented optical trapping system offers new opportunities for precision sensing and fundamental quantum experiments based on levitated particles.

Frequency comb generation in rod type 2D photonic crystal coupled cavity waveguide

Frequency comb generation in rod type 2D photonic crystal coupled cavity waveguide

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.