Resonance Wavelength Research Articles

Highly sensitive microdisk laser sensor for refractive index sensing via periodic meta-hole patterning

Abstract Microdisk lasers have emerged as compact on-chip optical sensors due to their small size, simple structure, and efficient lasing capabilities. However, conventional microdisk laser sensors face challenges in enhancing interactions with external analytes, as their energy remains predominantly confined within the laser material. In this study, we present a novel microdisk laser sensor incorporating periodic meta-hole patterning, designed to enhance external interaction while maintaining the integrity of the whispering gallery mode (WGM). Numerical simulations show that in an InGaAsP microdisk laser (5 μm diameter, 250 nm thickness), the WGM remains stable with periodic meta-holes (period a = 340 nm, diameter d < 0.4a), achieving a resonant wavelength near 1,500 nm. The inclusion of meta-holes led to a substantial improvement in sensitivity, reaching up to 100.8 nm/RIU – a 2.26-fold increase over nonpatterned microdisks. Experimental validation confirmed lasing in structures with a d/a ratio of 0.32, achieving a maximum sensitivity of 74.5 nm/RIU, which represents a 2.02-fold enhancement compared to nonpatterned designs. This advancement in microdisk laser design not only opens new possibilities for high-performance, miniaturized optical sensors but also holds significant potential for integration into next-generation on-chip sensing technologies.

Tunable multiband asymmetric transmission based on flexible chiral metamaterial for refractive index sensing

Tunable multiband asymmetric transmission (AT) effect is effectively demonstrated using a polydimethylsiloxane (PDMS)-based flexible chiral metamaterial (FCM) in the mid-infrared region. The unit cell of the FCM comprises J-shaped and F-shaped gold patterns to achieve three-dimensional (3D) chirality, and a multiband AT effect can be realized. Due to the excitation of enantiomerically sensitive plasmons, the FCM can realize a tunable multiband AT effect that is rarely reported, whose peak values can reach 51.89%, 37.72%, and 28.91% at resonance wavelengths of 9.03 µm, 10.25 µm, and 12.77 µm, respectively. The tunability of the FCM demonstrated that the peaks of AT shift to longer wavelengths when stretching along different directions respectively. Compared with reported refractive index sensors based on chiral metamaterial, FCM has tunable multibands and better refractive index sensitivity, which can reach 7875 nm/RIU, 3375 nm/RIU, and 1625 nm/RIU, respectively. Our proposed FCM opens an avenue to develop refractive index sensors.

Reversibly Alterable Hot-Electron Photodetection Without Altering Working Wavelengths Through Phase-Change Material Sb2S3

Generally, the responsivities of hot-electron photodetectors (HE PDs) are mainly dependent on the device working wavelengths. Therefore, a common approach to altering device responsivities is to change the working wavelengths. Another strategy for manipulating electrical performances of HE PDs is to harness electric bias that can be used to regulate hot-electron harvesting at specified working wavelengths. However, the reliance on bias hampers the flexibility in device operations. In this study, we propose a purely planar design of HE PDs that contains the phase-change material Sb2S3, realizing reversibly alterable hot-electron photodetection without altering the working wavelengths. Optical simulations show that the designed device exhibits strong absorptance (>0.95) at the identical resonance wavelengths due to the excitations of Tamm plasmons (TPs), regardless of Sb2S3 phases. Detailed electrical calculations demonstrate that, by inducing Sb2S3 transitions between crystalline and amorphous phases back and forth, the device responsivities at TP wavelengths can be reversibly altered between 59.9 nA/mW to 128.7 nA/mW. Moreover, when device structural parameters are variable and biases are involved, the reversibly alterable hot-electron photodetection at specified TP wavelengths is maintained.

Design and analysis of optical devices with ultra-high quality factor based on a plasmonic photonic hybrid structure

Abstract In the present paper, the design of a tunable, high transmitting, and optical ultra-narrow band-pass filter using a plasmonic-photonic hybrid structure comprised of a multilayer stack of dielectrics and a thin sheet of silver is proposed. This current design can create more energy coupling, thus having a higher transmission peak in comparison to prior studies. To obtain a filtering operation, two different topologies are designed to achieve better performance specifications. The materials used in the structure include silicon, silicon-dioxide, and silver. The Drude model is employed for the silver. It has been shown that the geometrical parameters are sensitive to choose such that transmission properties and resonance wavelengths are arbitrarily tunable. The structure's design enables a single-mode as well as a multi-mode spectrum for each topology. We have achieved a maximum quality factor of 432.87 with an ultra-small full-width-at-half-maximum bandwidth of 1.43 nm, while the maximum transmission values are greater than 75%. Most of the various advantages include adjustability, high detection resolution, and integration at the nanoscale for optical applications owing to the basic merits of the hybrid structures of plasmonic and photonic crystals.

Multidimensional Resonance Controlled by Critical Size in Printed Binary Colloidal Crystals for High-Contrast Imaging.

Colloidal crystal engineering enables the precise construction of structures with remarkable properties. However, the flexible and synergistic regulation of multiple properties of colloidal crystals remains a significant challenge. Here, we inspire from Brazilian opals to self-assemble polymer nanoparticles in the gaps of a single-layer opal substrate to fabricate large-scale binary colloidal crystals (BCCs). These BCCs have well-defined sizes, compositions, and dimensions, of which the crystallization process is finely controlled by the Marangoni flow. Notably, we find a critical size for the simultaneous and independent regulation of their lattice resonance wavelength and intensity, forming a full-color palette. Moreover, these BCCs as optical coatings allow for high-contrast imaging of microbials, benefiting from strong spatial confinement. Compared to glass in clinical smearing, they have an order of magnitude improvement in chromatism without dyeing. This work demonstrates that BCCs hold great potential in creating multifunctional devices for various applications including information display, biological detection, and optical imaging.

Micro-ring wavelength selective switch device based on contra-DC

This paper presents, to our knowledge, a novel micro-ring wavelength selective switch device based on a contra-directional coupler (contra-DC), which utilizes the transparent window formed by the contra-DC to select the single resonant wavelength of the micro-ring resonator, avoiding the limitation of free spectral range and realizing the function of wavelength selection/switching. The desired wavelength switching function is achieved by changing the crystal state of the Ge2Sb2Te5 (GST) loaded on the micro-ring resonator. When the device is in the on state, the desired wavelength signal is selectively output from the drop port of the bus waveguide; when the device is in the off state, light is output from the through port. By modifying the GST crystal state, selective routing of light can be achieved, which can be used in optical interconnection networks. The simulation is performed using a 3D finite-difference method. The wavelength selection device achieves a 3 dB bandwidthof 1.6 nm with a side lobe suppression ratio of 20 dB at a length of 230 µm; the switching device achieves the extinction ratio of about 14.7 dB and a side lobe suppression ratio of 18.2 dB between the on/off states.

Silicon photonic modulators with a 2 × 1 Fabry–Perot cavity

Abstract Silicon photonics modulators based on a 2 × 1 Fabry–Perot (FP) cavity, which is circulator-free, are proposed and demonstrated by introducing two asymmetric multimode-waveguide grating (AMWG) reflectors and a short straight modulation section with interleaved PN junctions. In particular, the straight modulation section in the FP cavity is broadened to be far beyond the single-mode regime, alleviating the inherent sensitivity to the variations of waveguide dimensions and thus reducing stochastic resonance-wavelength variations. The Q factor of the FP cavity is manipulated by optimally manipulating the reflection of the AMWGs, and the modulation bandwidth is enhanced to be over 40 GHz by utilizing the optical peaking enhancement effect, which happens when operating at the wavelength slightly detuning to its resonance wavelength. Eye diagrams for high-speed modulation with 50 Gbps are also demonstrated in experiments. Finally, wafer-level measurement is conducted by characterizing the silicon photonic modulators based on the 2 × 1 FP cavity and a conventional microring fabricated on the same chip, experimentally revealing an average improvement of 43 % in minimizing the random resonance-wavelength variation, which is attributed to the implementation of broadening the straight modulation section in the FP cavity.

Wavelength-selective nonvolatile optical switch based on periodic Ge2Sb2Se4Te1-assisted racetrack micro-ring

Abstract Integrated silicon photonics based on phase-change materials have the advantages of energy efficiency, ultra-compactness, and nonvolatility, with a promising prospect in reconfigurable photonic systems. A wavelength-selective 1 × 2 nonvolatile optical switch based on a periodic Ge2Sb2Se4Te1 (GSST)-assisted racetrack silicon micro-ring is proposed, where the GSST is embedded in the micro-ring as a one-dimensional photonic crystal. The switch state changes from ‘OFF’ to ‘ON’ by changing the GSST state from amorphous to crystal. The results show that the extinction ratio of the device is 27.99 dB and 19.57 dB at the drop and through ports, respectively. The insertion loss is as low as 1.21 dB at the through port in the crystal state and 0.61 dB at the drop port in the amorphous state. The proposed on-chip optical switch significantly enhances device integration, offers a potential path toward the development of nonvolatile Si-GSST hybrid optical switches, and is crucial to realizing reconfigurable photonic systems. Furthermore, the resonant wavelength of the switch changes very little, by only 0.66 nm between the ‘ON’ and ‘OFF’ states, which is suitable for multichannel wavelength-division-multiplexing systems.

Frequency locked whispering evanescent resonator (FLOWER) for biochemical sensing applications.

Sensitive, rapid and label-free biochemical sensors are needed for many applications. In this protocol, we describe biochemical detection using FLOWER (frequency locked optical whispering evanescent resonator)-a technique that we have used to detect single protein molecules in aqueous solution as well as exosomes, ribosomes and low part-per-trillion concentrations of volatile organic compounds. Whispering gallery mode microtoroid resonators confine light for extended time periods (hundreds of nanoseconds). When light circulates within the resonator, a portion of the electromagnetic field extends beyond the cavity, forming an evanescent field. This field interacts with bound analytes resulting in a change in the cavity's effective refractive index, which can be tracked by monitoring shifts in the resonance wavelength. The surface of the microtoroid can be functionalized to respond specifically to an analyte or biochemical interaction of interest. The frequency-locking feature of frequency locked optical whispering evanescent resonator means that the instruments respond to perturbations in the surface by very rapidly finding the new resonant frequency. Here we describe microtoroid fabrication (4-6 h), how to couple light into these devices using tapered optical fibers (20-40 min) and procedures for coupling antibodies as well as G-protein coupled receptors to the microtoroid's surface (from 1 h to 1 d depending on the target analyte). In addition, we describe our liquid handling perfusion system as well as the use of a rotary selector valve and custom fluidic chamber to optimize sample delivery. Step-by-step details on how to perform biosensing experiments and analyze the data are described; this takes 1-2 d.

Moiré metasurfaces with tunable near-infrared-I chiroptical responses for biomolecular chirality discrimination.

Manipulating circular dichroism in chiral metasurfaces has been increasingly important for a wide range of polarization-sensitive photonic applications. However, simple methods for presenting chiral nanostructures with tunable and considerable chiroptical responses in the near-infrared-I regime remains underexplored. Herein, two sheets of suspended symmetric bilayer metagratings fabricated via single-step electron beam lithography are stacked into a moiré metasurface with its circular dichroism value reaching up to 20.9°. The chirality of the moiré metasurface can be fully tuned in terms of both its sign and magnitude by adjusting the in-plane angle between the two twisted sheets of metagratings. The multilayered design is accessible to the coupling of hybridized plasmons for governing the chiroptical properties in the near-infrared-I regime. The ratio between the resonance wavelength and the grating period is about 1.65, which is much lower compared to that in most existing moiré metasurfaces with strong chiroptical responses. Furthermore, the superchiral fields in the inter-sheet region are further exploited for label-free enantiodiscrimination with ultrahigh sensitivity of 10.17 nm fmol-1 mm2. The proposed moiré metasurfaces with strong near-infrared-I chirality hold great potential for supporting polarization engineering and biomolecular detection, paving a way for advanced applications in medical diagnosis, biomedical imaging, and display technologies.

Localized surface plasmon resonance sensing based on monometallic gold nanoparticles: from material preparation to detection of bioanalytes.

The tunable geometrical properties of gold nanoparticles (AuNPs) endow them with the capacity to exhibit distinct behaviors with respect to both macroscopic (color) and microscopic (resonance wavelength) aspects, which has been extensively utilized in localized surface plasmon resonance (LSPR) sensing platforms. Additionally, functionalizing AuNP surfaces enhances the platforms' capabilities, allowing for the detection of a wide range of molecules related to various aspects of human health. In this review, we comprehensively elucidate the fundamental principles of LSPR biosensing and provide an in-depth survey of the preparation processes for metal nanoparticles, encompassing deposition technology for large-scale particle production as well as ion reduction methods that afford superior control over the particles' physical and chemical attributes. The sensing strategies based on adjustment of the dielectric environment and particle dispersion-aggregation levels are thoroughly reviewed and discussed. The discussion focused on a specific class of nanoparticles, characterized by their uniform shape and size, with each section bifurcated into two parts: a summary of the salient features and recent discoveries pertaining to the sensing strategy, as well as illustrations of representative, cutting-edge applications employing the strategy. We specifically aim to scrutinize analytes commonly encountered in the biomedical realm, encompassing biomarkers that serve as indicators of a wide range of diseases and microbial pathogens, while also prognosticating the future development trends of LSPR optical biosensor platforms within the biomedical field.

Numerical study of tunable terahertz radiation from differential frequency generation in high-<i>Q</i> geometrically perturbed grating waveguide structures

Nonlinear difference frequency generation (DFG) is a key mechanism for realizing terahertz (THz) sources. Utilization of DFG within micro- and nano-structures can circumvent the phase-matching limitations while supporting device miniaturization and integrability, thus the DFG is made a significant area of research. Enhancing the local electric fields through resonant modes in micro- and nano-structures has become a promising approach to achieving efficient and tunable THz sources across a broad wavelength range. In this work, the mechanism of DFG in high-Q-factor grating-waveguide structures for efficientlytuning THz radiation over a wide spectral range is investigated by using numerical simulations based on the finite element method (COMSOL Multiphysics). Theoretical analysis reveals that modulating the positional perturbation of one of the adjacent gratings effectively doubles the grating period, causing Brillouin zone to fold. This folding shifts the dispersion curve of the guided mode (GM) within the waveguide layer above the light cone, forming a guided mode resonance (GMR) with an ultra-high Q-factor, thereby significantly enhancing THz generation in a broad spectral range. Taking a cadmium sulfide (CdS) grating-waveguide structure for example, numerical simulations demonstrate that the THz conversion efficiency reaches an order of 10<sup>–8</sup>W<sup>–1</sup> when both fundamental frequency beams have an intensity of 100 kW/cm<sup>2</sup>, which is 10<sup>9</sup> times higher than the conversion efficiency of a CdS film of the same thickness. Moreover, the fundamental frequency resonance wavelength can be widely tuned by adjusting the incident angle. High-Q-factor resonance modes enable various fundamental frequency combinations by changing the incident angles of the two fundamental frequency beams, facilitating the generation of THz waves with arbitrary frequencies. This approach ultimately enables a highly efficient and tunable THz source in a wide spectral range, providing valuable insights for generating THz sources on micro- and nanophotonic platforms.

Atomic spin precession electro-optic modulation detection based on guided mode resonant lithium niobate metasurfaces.

Low-frequency noise in detection systems significantly affects the performance of ultrasensitive and ultracompact spin-exchange relaxation-free atomic magnetometers. High frequency modulation detection helps effectively suppress the 1/f noise and enhance the signal-to-noise ratio, but conventional modulators are bulky and restrict the development of integrated atomic magnetometer modulation-detection systems. Resonant metasurface-based thin-film lithium-niobate (TFLN) active optics can modulate free-space light within a compact configuration. In this study, we demonstrate a TFLN metasurface platform that leverages guided mode resonance for efficient phase modulation, achieving a modulation amplitude of 0.063 rad at a frequency of 100 kHz. We exploit the resonance in the TFLN waveguide and obtain a high-quality factor of 166 at a resonant wavelength of 795.8 nm. Using the fabricated modulator, we achieve an optical rotation angle measurement sensitivity of 4 × 10-7 rad Hz-1/2 with the modulation. Compared to conventional bulky modulators, the modulator fabricated in this study realizes more than 90% reduction in volume. This study provides a feasible approach for developing miniaturized integrated atomic magnetometers to achieve ultrahigh sensitivity through optical modulation techniques.

Design of DMD Nano Logic Gates With Strip Waveguides for Communication System

COMSOL software is used to build and quantify optical logic circuits using plasmonic square ring resonators. An operation utilizing constructive and destructive control along with input port interferences as inputs results in the proposed gates. At 1010 nm resonance wavelength, the transmission threshold is 30% at a single interface, the ratio of input power to output optical power. All plasmonic gates are executed within a singular structure measuring 150 nm by 150 nm. The OR gate and the AND gate exhibit transmission rates exceeding 100%, with both reporting a rate of 221%. The OR and AND gates exhibit modulation depth (MD) values of 96.38 percent, whereas the NOR gate demonstrates a value of 99.8 percent, these optical gates are used in transceivers for communication systems. Index Terms— plasmonic waveguides; optical logic gates; square ring resonator.

Electrically Tuning Quasi‐Bound States in the Continuum with Hybrid Graphene‐Silicon Metasurfaces

AbstractMetasurfaces have become one of the most prominent research topics in the field of optics owing to their unprecedented properties and novel applications on an ultrathin platform. By combining graphene with metasurfaces, electrical tunable functions can be achieved with fast tuning speed, large modulation depth, and broad tuning range. However, the tuning efficiency of hybrid graphene metasurfaces within the short‐wavelength infrared (SWIR) spectrum is typically low because of the small resonance wavelength shift in this wavelength range. In this work, through the integration of graphene and silicon metasurfaces that support quasi‐bound states in the continuum (quasi‐BIC), the critical coupling as well as transmittance spectrum tuning is experimentally demonstrated. The spectrum tuning is substantial even with less than 30 nm resonance wavelength shift thanks to the high quality factor of quasi‐BIC metasurfaces. The tunable transmittance spectrum is measured using Fourier transform infrared spectroscopy (FTIR) with a modified reflective lens to improve the accuracy, and the electrical tuning is realized utilizing the “cut‐and‐stick” method of ion gel. At the wavelength of 3.0 µm, the measured transmittance change (ΔT = Tmax − Tmin) and modulation depth (ΔT/Tmax) can reach 22.2% and 28.9%, respectively, under a small bias voltage ranging from −2 to +2 V. This work demonstrates an effective way of tuning metasurfaces within the SWIR spectrum, which has potential applications in optical modulation, reconfigurable photonic devices, and optical communications.

Narrow Bandwidth and Tunable Mid-Infrared Thermal Emitter Design Based on Double Asymmetric Dielectric Metasurfaces

Thermal emitters working in the mid-infrared (MIR) region are indispensable in many applications, such as sensing, thermophotovoltaics, and imaging. Resonance wavelength tunability, high efficiency, cost-effectiveness, and high quality (Q) factor are desirable properties of thermal emitters. Selective thermal emitters have been realized using metallic metasurfaces, which, due to ohmic losses, do not exhibit very sharp emission peaks. Recently, metasurfaces possessing very high Q factors made of dielectric materials with asymmetric features that exploit quasi-bound states in the continuum are introduced. The dielectric metasurface-based thermal emitters shown in the literature have a single type of asymmetry, such as a difference in the length of resonators or angular separation of resonators. However, resonance wavelength and thermal emissivity could be tuned by having multiple types of asymmetries. This study proposes a structure consisting of a zigzag array of silicon rectangular bars with different lengths as resonators. Gold is the choice of the substrate with a dielectric layer made of Al2O3 sandwiched between gold substrate and silicon bars. Based on the conducted simulations, an emissivity value exceeding 0.99 with a Q factor of 116 at the resonance wavelength of 5.818 µm was obtained when the silicon bars were separated by π/25 from the origin in opposite directions with a length asymmetry factor of 0.3. Additionally, independent tuning of emissivity intensity and resonance wavelength is displayed. Such findings can lead to bespoke thermal emitter designs.

Optimization and characterization of a PCF-based SPR sensor for enhanced sensitivity and reliability in diverse chemical and biological applications

This paper presents the meticulous design and characterization of a photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor, analyzed using finite element method (FEM) simulations. The sensor’s superior performance is demonstrated by its exceptional sensitivity to minute changes in the refractive index (RI) of various analytes. The optimized structure reveals a peak resonance at 0.78898 µm with a maximum confinement loss of 546.34 dB/cm. Detailed investigations show resonance wavelength red shifts of up to 0.93% with a 5% increase in air hole diameter and blue shifts of up to 0.88% with a 5% decrease. Additionally, variations in the plasmonic gold layer thickness result in resonance shifts of up to 0.76% longer or 0.87% shorter wavelengths. The sensor achieves remarkable wavelength sensitivity (WS) of up to 13,000 nm/RIU and amplitude sensitivity (AS) of up to 1538.90RIU−1, underscoring its high precision in detecting analyte concentration changes. The design’s robustness against fabrication errors, evidenced by minimal variations in resonance characteristics, highlights its practical reliability. Furthermore, the use of a polynomial regression model with an R2 value near unity accurately approximates the relationship between resonance wavelength and analyte RI, ensuring precise sensing capabilities without overfitting. Comparative analysis with existing designs confirms the sensor’s superior performance, rendering it highly suitable for a wide range of applications, including biosensing of glucose, water contaminated by cholera germs, mucosa of the human intestine, important components of human blood, and detection of chemicals like acetone, ethanol, benzene, propanol, glycerol, and expired transformer oil.

Non-invasive in-situ monitoring of deep etching processes using terahertz metasurfaces

This study presents an in-situ and non-invasive process control and monitoring (PCM) method for deep silicon etching, leveraging terahertz metasurfaces. The technique addresses the challenges for monitoring deep and high aspect ratio etching processes, which are prevalent in semiconductor microfabrication. By incorporating metasurfaces with identical geometric shapes and sizes as crucial components of targeted devices, the method enables accurate monitoring of the etching depth in the process. Continuous shifts of terahertz reflection spectra provide information on etching depth, while abrupt change in the curves highlights the etching endpoint, preventing over-etching. For the commonly used comb-finger structure, numerical simulations demonstrate a strong linear relationship between etching depth and terahertz resonant wavelengths (nonlinearity < 1%) and an abrupt resonant frequency change (> 0.6 THz) at the endpoint. Experimental validations confirm the accuracy of the PCM method, with an etching depth estimation error below 2 µm. This approach enhances the precision of PCM in microfabrication, offering the potential for widespread applications in the production of micromechanical sensors, actuators, and other microelectronic devices.

Dual polarization-independent quasi-bound states in the continuum in a hetero-out-of-plane dielectric metasurface.

Symmetry-protected quasi-bound states in the continuum (qBICs) in metasurfaces with broken in-plane symmetry are extensively investigated to achieve high quality-factor (Q-factor) resonances. Herein, we propose the hetero-out-of-plane (H-OP) dielectric metasurface, which is composed of Si cuboids tetramer broken out-of-plane symmetry by adding a layer of silica. Dual polarization-independent qBICs are realized. The multipolar decomposition of scattering powers and near-field distributions reveal the physical mechanism of dual qBICs modes, which are dominated by the magnetic quadrupole and the toroidal dipole. The two symmetry-protected qBICs in the H-OP metasurface have robust Q-factors and stable resonance wavelengths compared with these in the out-of-plane metasurface. Our results provide a route to achieve the high Q-factor resonator with better performance applied in many optical and optoelectronic devices.

Observation of edge bound states in the continuum at truncated silicon pillar photonic crystal

Bound states in the continuum are optical modes with extremely high-quality factors and narrow resonances, which exist in the dispersion spectrum of the radiative region above the light line. A unique bound state in the continuum is supported at the edge of truncated photonic crystals, which is a type of a Fabry-Pérot type bound state in the continuum, but has never been observed in experiments. Here, we demonstrate the bound states in the continuum supported at the edge array of silicon (Si) pillars whose diameter is bigger than that of the rest of a Si-pillar two-dimensional photonic crystal. We also show the tunability of the resonance and surface sensitivity of the mode when Si pillars are conformally coated with nanometer-thick aluminium oxide films. The presence of an oxide nanofilm improves the quality factor by over 60 % and shifts the resonance wavelength. Such behavior signifies the substantial potential of the bound states in the continuum on two-dimensional photonic crystals for post-fabrication tuning of the quality factor and surface sensing applications.