Photonic Crystal Nanobeam Cavities Research Articles

Optimizing the quality factor of InP nanobeam cavities using atomic layer deposition

Photonic crystal nanobeam cavities are valued for their small mode volume, CMOS compatibility, and high coupling efficiency-crucial features for various low-power photonic applications and quantum information processing. However, despite their potential, nanobeam cavities often suffer from low quality factors due to fabrication imperfections that create surface states and optical absorption. In this work, we demonstrate InP nanobeam cavities with up to 140% higher quality factors by applying a coating of Al2O3 via atomic layer deposition to terminate dangling bonds and reduce surface absorption. Additionally, changing the deposition thickness allows precise tuning of the cavity mode wavelength without compromising the quality factor. This Al2O3 atomic layer deposition approach holds great promise for optimizing nanobeam cavities that are well-suited for integration with a wide range of photonic applications.

Single nanoparticle detection based on a slotted nanobeam cavity

In this work, a single nanoparticle sensor based on a slot-bridge-slot photonic crystal nanobeam cavity is presented. To investigate the sensor feasibility of a single particle detection, the shift of the resonance wavelength of the cavity mode is calculated by employing perturbation theory and the simulation results of the mode profile. A mode volume of 2.61×10−3λ/n3is realized, which is reduced by a factor of 150 times in comparison with nanobeam cavity. We demonstrate the detection of streptavidin molecules with radius ∼ 2.65 nm with a large resonant wavelength shift (25.4 pm). This represents the largest wavelength shift ever reported in single nanoparticle sensors. Owing to the ultracompact footprint and high sensitivity demonstrated here, the proposed structure holds great potential for lab-on-a-chip biosensing applications.

Fabrication uncertainty guided design optimization of a photonic crystal cavity by using Gaussian processes

We present a fabrication uncertainty aware and robust design optimization approach that can be used to obtain robust design estimates for nonlinear, nonconvex, and expensive model functions. It is founded on Gaussian processes and a Monte Carlo sampling procedure, and assumes knowledge about the uncertainties associated with a manufacturing process. The approach itself is iterative. First, a large parameter domain is sampled in a coarse fashion. This coarse sampling is used primarily to determine smaller candidate regions to investigate in a second, more refined sampling pass. This finer step is used to obtain an estimate of the expected performance of the found design parameter under the assumed manufacturing uncertainties. We apply the presented approach to the robust optimization of the Purcell enhancement of a photonic crystal nanobeam cavity. We obtain a predicted robust Purcell enhancement of F¯P≈3.6. For comparison we also perform an optimization without robustness. We find that an unrobust optimum of FP≈256.5 dwindles to only F¯P≈0.7 when fabrication uncertainties are taken into account. We thus demonstrate that the presented approach is able to find designs of significantly higher performance than those obtained with conventional optimization.

Efficient side-coupling configuration for photonic crystal nanobeam cavities with micro-ring resonators

Efficient side-coupling configuration for photonic crystal nanobeam cavities with micro-ring resonators

Protein sensing using deep subwavelength-engineered photonic crystals.

We demonstrate a higher sensitivity detection of proteins in a photonic crystal platform by including a deep subwavelength feature in the unit cell that locally increases the energy density of light. Through both simulations and experiments, the sensing capability of a deep subwavelength-engineered silicon antislot photonic crystal nanobeam (PhCNB) cavity is compared to that of a traditional PhCNB cavity. The redistribution and local enhancement of the energy density by the 50 nm antislot enable stronger light-molecule interaction at the surface of the antislot and lead to a larger resonance shift upon protein binding. This surface-based energy enhancement is confirmed by experiments demonstrating a nearly 50% larger resonance shift upon attachment of streptavidin molecules to biotin-functionalized antislot PhCNB cavities.

Blue-band slot-enhanced nanobeam cavity with porous-GaN cladding

Traditional photonic crystal cavities are hard to simultaneously attain extreme temporal and spatial confinement of light, which remains a barrier to realize ultimate control of light in a material and maximum performance in photonic devices. Here we demonstrated GaN and porous-GaN based photonic crystal nanobeam cavity by improving the confining light properties with the application of the slot and anti-slot effects. Three dimensional finite-difference time-domain simulations show that the cavity for blue band possesses ultrahigh quality factor as 1.67 × 107, and the mode volume is reduced tenfold compared to nanobeam without slot and anti-slot.

Investigation on photonic crystal nanobeam cavity based on mixed diamond–circular holes

A photonic crystal nanobeam cavity (M-PCNC) with a structure incorporating a mixture of diamond-shaped and circular air holes is proposed. The performance of the cavity is simulated and studied theoretically. Using the finite-difference time-domain method, the parameters of the M-PCNC, including cavity thickness and width, lattice constant, and radii and numbers of holes, are optimized, with the quality factor Q and mode volume Vm as performance indicators. Mutual modulation of the lattice constant and hole radius enable the proposed M-PCNC to realize outstanding performance. The optimized cavity possesses a high quality factor Q = 1.45 × 105 and an ultra-small mode volume Vm = 0.01(λ/n) [Zeng et al., Opt Lett 2023:48;3981–3984] in the telecommunications wavelength range. Light can be progressively squeezed in both the propagation direction and the perpendicular in-plane direction by a series of interlocked anti-slots and slots in the diamond-shaped hole structure. Thereby, the energy can be confined within a small mode volume to achieve an ultra-high Q/Vm ratio.

Simultaneous measurement of relative humidity and temperature using EIT-like effect in photonic crystal cavity coupled system integrated with PVA and graphene

In this work, we propose a sensor based on a photonic crystal nanobeam cavity (PCNC) coupled system integrated with Polyvinyl alcohol (PVA) and graphene, which uses an electromagnetically induced transparency-like (EIT-like) effect for the simultaneous measurement of relative humidity (RH) and temperature (T). The structure consists of a bus waveguide and two types of one-dimensional PCNC supporting the dielectric and air mode resonance, respectively. The RH-sensitive material PVA is used in the dielectric mode cavity to increase the RH sensitivity and anti-interference ability. We demonstrate that the EIT-like transparency window can be actively and flexibly modulated by adjusting the Fermi level of graphene. In addition, the ability of the system to simultaneously detect RH and T is proved by using the three-dimensional finite-difference time-domain (3D-FDTD) method and the sensor matrix. The RH sensitives for the dielectric and air modes are −542.0 pm/%RH and −258.2 pm/%RH, respectively. The T sensitives for the dielectric and air modes are −14.6 pm/K and 35.4 pm/K, respectively. The sensor achieves a strong anti-interference ability and its footprint is only 12 μm × 2.02 μm. Therefore, our proposed sensor has potential applications in food storage, preservation of museum collections, human health, and biological and chemical experiments.

Compact dual-parameter sensor design basedon a photonic crystal nanobeam cavity withchirped slotted annular holes.

A compact photonic crystal nanobeam cavity with a 20µm×0.8µm footprint supporting simultaneous air and dielectric resonant modes is proposed for dual-parameter sensing of refractive index and temperature. The structure consists of a row of chirped annular holes and an air-slot etched in an asymmetrical silicon slab. By tapering the lattice period and hole radius, the bands for air and dielectric modes shift in opposite directions, enabling confinement in a single cavity. Numerical simulations determine refractive index sensitivities of 173.59nm/RIU for the air mode and 286.82nm/RIU for the dielectric mode. Temperature sensitivities are 69.6pm/°C and 78.7pm/°C for the two modes, respectively. The structure demonstrates strong resistance to external interference with refractive index and temperature disturbance resistance coefficients of 2.3×10-5 and 0.07. The high sensitivities in an ultracompact footprint with resistance to crosstalk make this dual-mode nanocavity promising for on-chip biochemical 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.

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.

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.

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.

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.

Transverse Magnetic Mode Laser in Photonic Crystal Nanobeam Cavity

We experimentally demonstrate a transverse magnetic (TM) mode laser in a photonic crystal (PhC) slab structure at room temperature. This study proposes a PhC nanobeam (NB) cavity to support a high-quality-factor ($Q$-factor) TM mode. For a large and complete photonic band gap, the PhC NB structures consist of large air holes in a thick dielectric slab. The PhC NB cavity is optimized numerically for a high-$Q$-factor TM mode of over 1 000 000 by reducing the radii of the air holes quadratically from the center to the edge of the PhC NB. A single-TM-mode lasing action is observed in an In-Ga-As-P quantum well (QW)-embedded optimized PhC NB cavity structure at room temperature via optical pulse pumping, where the QW layer is lightly etched. We believe that the TM mode lasers in PhC NB cavities with a lightly etched QW can be good candidates for a surface plasmon excitation source or a highly sensitive optical sensor.

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.

Cubic-wavelength mode volume photonic crystal nanobeam cavities in a monolithic CMOS platform.

We report on the design, fabrication, and experimental characterization of photonic crystal (PhC) nanobeam cavities with the smallest footprint, largest intrinsic quality factor, and smallest mode volume to be demonstrated to date in a monolithic CMOS platform. Two types of cavities were designed, with opposite spatial mode symmetries. The opposite mode symmetry, combined with evanescent coupling, allows the nanobeam cavities to be used in reflectionless topologies, desirable in complex photonic integrated circuits (PICs). The devices were implemented and fabricated in a 45 nm monolithic electronics-photonics CMOS platform optimized for silicon photonics (GlobalFoundries 45CLO) and do not require any post-processing. Quality factors exceeding 100 000 were measured for both devices, the highest, to the best of our knowledge, among fully cladded PhC nanobeam cavities in any silicon-on-insulator (SOI) platform. Additionally, the ability of the cavities to confine light into small mode volumes, of the order of (λ/n)3, was confirmed experimentally using near-field scanning optical microscopy (NSOM). These types of cavities are an important step toward realizing ultra-low energy active devices required for the next generation of integrated optical links beyond the current microring resonator-based links and other CMOS PICs.

Assisted Microring Resonator Based on One-Dimensional Photonic Crystal Nanobeam Cavity

Assisted Microring Resonator Based on One-Dimensional Photonic Crystal Nanobeam Cavity

Integrated device for electro-optic modulation and wavelength-mode division hybrid multiplexing based on graphene and photonic crystal

An integrated device for graphene electro-optic (EO) modulation and wavelength-mode division hybrid multiplexing (WMDM) is proposed. The device is composed of three parts: EO modulator, wavelength division multiplexer (WDM), and mode division multiplexer (MDM). The EO modulator and WDM consist of a one-dimensional photonic crystal nanobeam cavity coupled with a nanowire waveguide. The modulation of a certain wavelength can be achieved by utilizing the characteristic that the chemical potential of graphene can be adjusted with voltage. The MDM adopts nanowire waveguides to realize mode conversion. The performance parameters of the integrated device are analyzed using the three-dimensional finite-difference time-domain method of numerical analysis. The results show that the integrated device can simultaneously complete the modulation and WMDM of the fundamental transverse electric (TE0) modes and first-order TE (TE1) modes at 1570.0 and 1573.2 nm, respectively. The extinction ratio is greater than 23.2 dB, the insertion loss is <0.36 dB, and the channel crosstalk is < − 22.7 dB. In addition, the modulation speed reaches 18 GHz.

Ultrafast all-optical switching in a silicon-polymer compound slotted photonic crystal nanobeam cavity

Ultrafast all-optical switching in a silicon-polymer compound slotted photonic crystal nanobeam cavity