Photonic Crystal Microcavity Research Articles

High-sensitivity nanostructure-based sensor using Fano resonance for noninvasive EEG monitoring

Noninvasive electroencephalogram signal detection with high sensitivity and a high signal-to-noise ratio has attracted much attention. To achieve high-sensitivity electroencephalogram (EEG) sensing, a photonic crystal side-coupled microcavity nanoscale sensor based on Fano resonance is proposed with nano electro-optic sensing technology as the core support. This configuration comprises a nanobeam resonant cavity, a waveguide, and an electrical slab. The substantial overlap between the optical and electric fields within the resonant cavity is analyzed, and the sensor’s electric field sensing performance is assessed. Due to the optically coupled nanoscale sensing structure that is adopted in the sensor, the device has an ultrahigh voltage sensing sensitivity of up to 142.64 nm/V and a compact footprint as small as 4.29 mm2, enabling real-time sensing of EEG signals of 10 μV and below. These improvements overcome the technical challenges of low precision and large size as are associated with existing optical devices used for medical monitoring.

The role of photonic crystal based architectures on tailoring the laser induced fluorescence from green emitting cesium lead bromide nanocrystals

Researchers have long been fascinated by fluorescence and its potential to be boosted as it unlocks a treasure trove of promising applications. In this context, this experimental study investigates the amplification of laser induced fluorescence (LIF) emission from cesium lead bromide (CsPbBr3) perovskite nanocrystals (PNC) using two distinct all-polymer photonic crystal (PC) architectures made of poly 9-vinyl carbazole (PVK) and cellulose acetate (CA) as high and low refractive index (RI) layers, respectively. First structure is a photonic crystal micro cavity (PCMC) where PNC incorporated PVK (PNC:PVK) polymer matrix forms the defect layer sandwiched between two similar PCs. In the second structure, PNC:PVK composite itself functions as high RI layers within the PC. These two designs exploit different mechanisms to achieve fluorescence enhancement. The findings demonstrate the promise of simple, solution processed polymer PCs on applications demanding intensified fluorescence output and pave way to the development of flexible photonic devices capable of manipulating light emission.

Design of a Neural Network Model for Point-Defect Microcavities in Two-Dimensional Silicon-Based Dielectric Column Photonic Crystals

Currently, circuits are becoming more and more highly integrated, but current electronic chip technology has difficulty in meeting the requirements for increased data transmission speed and capacity because of its characteristics of increased energy loss due to interactions between electronic components. In contrast, photonic technology is a promising solution due to its characteristics of high speed, wide bandwidth, and low interaction. Photonic crystals are materials with an artificial periodic dielectric structure, with photonic bandgap and localization properties that are critical to their performance. Photonic crystals, which use photons as an information transfer medium, allow flexible control of photon propagation, just as electrons are controlled in semiconductors, and the study of multifunctional photonic crystals is important for the construction of integrated optical circuits. This paper proposes a neural network-based model to analyze and predict the optical properties of point defect microcavities in 2D silicon-based dielectric column photonic crystals. By modeling the complex relationship between the structural parameters of the photonic crystal and its optical response, a theoretical approach for the design of 2D silicon dielectric column photonic crystals can be provided.

Neural network-based prediction and optimization of optical properties of two-dimensional GaAs dielectric background photonic crystal point-defect microcavities

Neural network-based prediction and optimization of optical properties of two-dimensional GaAs dielectric background photonic crystal point-defect microcavities

Photonic bound states in the continuum governed by heating.

A photonic crystal microcavity with the liquid crystal resonant layer tunable by heating has been implemented. The multiple vanishing resonant lines corresponding to optical bound states in the continuum are observed. The abrupt change in the resonant linewidth near the vanishing point can be used for temperature sensing.

A neural network model for point defect microcavities of two-dimensional GaAs media background photonic crystals

This paper aims to address the challenge of constructing, training, and optimizing a neural network model for the point defect microcavity of a two-dimensional GaAs media background photonic crystal. The objective is to achieve more accurate predictions and analyses of photon modes, thereby enhancing the performance of the microcavity. Due to the structural complexity and multi-parameter nature of point defect microcavities, traditional analysis methods often fail to capture their optical behavior adequately. Consequently, there is a need for a novel approach to establishing an optical model for point defect microcavities, enabling precise predictions of their optical properties and optimal design. In this study, the MPB computing tool developed by MIT, in conjunction with the programming language Scheme, MATLAB, and the Ubuntu virtual machine platform, was utilized for data acquisition. The neural network model was employed to process the input data of the photonic crystal point defect microcavity, leading to predictions and analyses. This interdisciplinary approach results in a high-precision model of the microcavity. The neural network model is capable of nonlinear mapping and prediction by learning the patterns and features of the data. Additionally, this combination holds the promise of enabling more efficient optical information processing and increased data transfer rates. The relationship between the energy band data and the structure of photonic crystals exhibits a high degree of nonlinearity. The neural network model proposed in this paper can infer the structure of photonic crystals based on the photon energy band (dispersion relation ω-K) of micro-cavity structures with point defects in different photonic crystals. This provides a valuable reference for more accurate predictions and analyses of photon modes in complex photonic crystal micro-cavities, ultimately leading to improved micro-cavity performance.

Two-dimensional silicon-based dielectric column photonic crystal point defect microcavity Neural network modelling

In order to solve the problem that it is difficult to predict the microcavity photonic energy bands of point defects in two-dimensional silicon-based dielectric column photonic crystals, this paper proposes a method to predict the microcavity photonic energy bands of point defects in two-dimensional silicon-based photonic crystals by using an artificial neural network model. In this paper, the energy band structure of triangular lattice point defects at different radii is calculated using MPB, and a neural network model is established based on this data and the accuracy of the established model is verified.

Ultrawide-detection-range refractive index sensor based on a two-dimensional mirror-image photonic crystal microcavity

In this work, a refractive index sensor is theoretically proposed based on a two-dimensional mirror-image SiO2/Si photonic crystal microcavity. The introduction of mirror-image microcavity effectively enhances the light localization and the coupling between light and liquid analyte. Results show that the sensor exhibits a high near-linear sensitivity of 493.5 nm RIU−1 with a narrow full-width at half-maximum of ∼20 nm in a broad refractive index range of 1.0 ∼ 1.5. Moreover, the detection resolution for the minimum variation of RI reaches to a level of 0.0002 RIU. For the analyses on the sensor performance (such as sensitivity, full-width at half-maximum), the dependences of all structure parameters are discussed in terms of the cylinder diameter, lattice constant, and microcavity size. This design is expected to detect the refractive index of wide-range liquid analytes in the fields of biology, chemistry, and medicine.

Development of an angle-adjustable photonic crystal fluorescence platform for sensitive detection of oxytetracycline.

We pioneered an angle-adjustable photonic crystal fluorescence platform (APC-Fluor) that integrates PCs, an angular resolution spectrometer and a strategically aligned laser source. This configuration, featuring a coaxial rotating swing arm, allows for precise control over the angles of incidence and emission. The presence of photonic crystal microcavities facilitates the dispersion of fluorescent materials and promotes the transition of electrons from the excited state to the lowest vibrational energy level. The optical resonance effect triggered by modulating the alignment of the reflection peaks of the photonic crystals with the emission peaks of the fluorescent materials can significantly enhance the fluorescence intensity. Compared with the single BSA-AuNCs, the optimized fluorescence intensity can be significantly increased by 11.9-fold. The APC-Fluor system showcases rapid and highly sensitive detection capabilities for oxytetracycline (OTC), exhibiting a response across a concentration range from 2 to 1 × 104 nM and achieving a notably low detection limit of 1.03 nM.

Ultrawide-color-gamut single-pixel dynamic color manipulation based on yarn muscles–graphene MEMS

Herein, the single-pixel color modulation in a composite structure based on a yarn muscles–graphene mechanical system and photonic crystal multimode microcavity is investigated. The position of graphene in the microcavity is changed by varying the stretching of yarn muscles using different current levels. This aids in adjusting the light absorption of graphene to different colors. Hence, red, green, blue, and their mixed colors can be displayed using a single pixel; moreover, the color gamut of this system can reach 96.5% of sRGB space. The proposed system can avoid the spontaneous oscillation caused by large strain energy. This solution can provide insights into the design of low-power, ultrahigh-resolution, and ultrawide-color-gamut interferometric modulator display technologies.

From Bloch surface waves to cavity-mode resonances reaching an ultrahigh sensitivity and a figure of merit

We report on a new sensing concept based on resonances supported by a one-dimensional photonic crystal (1DPhC) microcavity resonator in the Kretschmann configuration. For a 1DPhC comprising six bilayers of TiO2/SiO2 with a termination layer of TiO2 employed to form a microcavity, we show that when the angle of incidence is changed, the Bloch surface waves (BSWs) can be transformed into cavity-mode resonances exhibiting an ultrahigh sensitivity and a figure of merit. Using wavelength interrogation, we demonstrate that Bloch surface TE wave excitation shows up as a sharp dip in the reflectance spectrum with a sensitivity and a figure of merit (FOM) of 70 nm per refractive index unit (RIU) and 19.5 RIU−1, respectively. When the angle of incidence decreases, cavity-mode resonances for both TE and TM waves are resolved for RI in a range of 1.0001–1.0005. The sensitivity and FOM can reach 52,300 nm/RIU and 402,300 RIU−1 for the TE wave, and 14,000 nm/RIU and 2154 RIU−1 for the TM wave, respectively. In addition, resonances are confirmed experimentally for a humid air with a sensitivity of 0.073 nm per percent of the relative humidity (%RH) for BSW resonance and is enhanced to 1.367 nm/%RH for the TM cavity-mode resonance. This research, to the best of the authors’ knowledge, is the first demonstration of a new BSW-like response that can be utilized in a simple sensing of a wide range of gaseous analytes.

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.

Integrated Flexible Microscale Mechanical Sensors Based on Cascaded Free Spectral Range-Free Cavities.

Photonic mechanical sensors offer several advantages over their electronic counterparts, including immunity to electromagnetic interference, increased sensitivity, and measurement accuracy. Exploring flexible mechanical sensors on deformable substrates provides new opportunities for strain-optical coupling operations. Nevertheless, existing flexible photonics strategies often require cumbersome signal collection and analysis with bulky setups, limiting their portability and affordability. To address these challenges, we propose a waveguide-integrated flexible mechanical sensor based on cascaded photonic crystal microcavities with inherent deformation and biaxial tensile state analysis. Leveraging the advanced multiplexing capability of the sensor, for the first time, we successfully demonstrate 2D shape reconstruction and quasi-distributed strain sensing with 110 μm spatial resolution. Our microscale mechanical sensor also exhibits exceptional sensitivity with a detected force level as low as 13.6 μN in real-time measurements. This sensing platform has potential applications in various fields, including biomedical sensing, surgical catheters, aircraft and spacecraft engineering, and robotic photonic skin development.

Strain Engineering of the Electronic States of Silicon‐Based Quantum Emitters

AbstractLight‐emitting complex defects in silicon have been considered a potential platform for quantum technologies based on spin and photon degrees of freedom working at telecom wavelengths. Their integration in complex devices is still in its infancy and has been mostly focused on light extraction and guiding. Here the control of the electronic states of carbon‐related impurities (G‐centers) is addressed via strain engineering. By embedding them in patches of silicon on insulator and topping them with SiN, symmetry breaking along [001] and [110] directions is demonstrated, resulting in a controlled splitting of the zero phonon line (ZPL), as accounted for by the piezospectroscopic theoretical framework. The splitting can be as large as 18 meV, and it is finely tuned by selecting patch size or by moving in different positions on the patch. Some of the split, strained ZPLs are almost fully polarized, and their overall intensity is enhanced up to 7 times with respect to the flat areas, whereas their recombination dynamics is slightly affected accounting for the lack of Purcell effect. This technique can be extended to other impurities and Si‐based devices such as suspended bridges, photonic crystal microcavities, Mie resonators, and integrated photonic circuits.

Parameter investigations on lithium-niobate-based photonic crystal optomechanical cavity

In this paper, to fully understand the influence of nanofabrication error issues on the lithium-niobate-based device, the systematic simulations and optimizations of lithium-niobate-based photonic crystal (PhC) optomechanical cavity considering the material dispersion and inclination angle of PhC air hole are investigated in details. The structural parameter influences on the PhC band gap, the line defected waveguide transmission characteristics, the optical resonant wavelength of the PhC microcavity, and the mechanical resonant frequency are all discussed. The effects of the simulation methods on the PhC band gap are investigated as well. And finally, the opto-mechanical coupling rate of the lithium-niobate-based PhC optomechanical cavity structure is calculated. Such obtained results can help researchers to precisely design the required optomechanical cavity for specific applications.

Voltage-tunable Q factor in a photonic crystal microcavity.

A photonic crystal microcavity with a tunable quality factor (Q factor) has been implemented on the basis of a bound state in the continuum using the advanced liquid crystal cell technology platform. It has been shown that the Q factor of the microcavity changes from 100 to 360 in the voltage range of 0.6 V.

Reflective-to-absorptive THz switchable bifunctionality through phase transition of vanadium dioxide in a 1D defective photonic crystal microcavity

Reflective-to-absorptive THz switchable bifunctionality through phase transition of vanadium dioxide in a 1D defective photonic crystal microcavity

Enhancement of spontaneous emission from CdSe/ZnS quantum dots through silicon nitride photonic crystal cavity based on miniaturized bound states in the continuum.

Colloidal CdSe/ZnS quantum dots (QDs) exhibit excellent optical properties for wide potential applications in light-emitting diodes, solar concentrators, and single-photon sources. However, the ultra-thin films with low concentration of QDs still encounter inefficient photoluminescence (PL) and poor directionality of radiation, which need to be enhanced using nanophotonics device designs. Here we design and experimentally demonstrate an on-substrate silicon nitride (SiN) photonic crystal (PhC) microcavity encapsulated by a layer of PMMA hosting CdSe/ZnS QDs. The miniaturized bound states in the continuum (BIC) supported by our structures, provide high-Q resonant modes with highly-directional emission patterns. Experimental results show that the BIC mode in the microcavity has a Q-factor up to 7000 owing to the symmetric refractive index distribution along the Z-direction, rendering 8.5-fold enhancement of PL intensity and 8.4-fold acceleration of radiative emission rate. Our work provides a practical way for constructing efficient on-chip surface-emitting light sources on silicon-based integrated photonic devices.

High-Time-Resolution Microspectrometer Based on Phase-Change Materials

The application of graphene--photonic crystal microcavity structures with phase-change-material layers in spectral analysis is studied. It is found that selective absorption of different wavelengths of light can be realized by changing the crystallinity of the phase-change material, so that different wavelengths of light can be separated and measured in the time domain to perform spectral analysis. Since the phase-transition time of phase-change materials is very fast, this spectral analysis can be done with submicrosecond time resolution. This kind of spectral-analysis device has a simple structure and can be integrated with a chip. It has important prospects for application in the fields of biological molecular recognition, biological sensing, and chemical analysis.

Spontaneous emission enhancement based on thin-film chalcogenide/fluoride one dimensional photonic crystal

We report the fabrication of a one-dimensional photonic crystal microcavity via co-evaporation with electron beam/thermal evaporation process, which, to the best of our knowledge, is the first rare-earth doped one-dimensional photonic crystal based on chalcogenide/fluoride thin films. The microcavity was made of a half-wave dysprosium doped Ga2Se3 layer sandwiched between two embedded Ga2Se3/YF3 distributed Bragg reflectors. Near infrared transmittance spectra indicated that the stopband region from 1090 nm to 1515 nm was formed and a cavity resonance centered at 1342 nm. A cavity quality factor of 153 was achieved resulting in a 53-fold enhancement in spontaneous emission intensity. This photonic crystal microcavity configuration offers a new route to mid-wavelength and long-wavelength infrared fluorescence enhancement, which has attracted considerable interest for potential applications, such as fluorescence-based imaging and biomedical sensing.