Optical Cavity Structure Research Articles

Cavity-enhanced photo-thermoelectric response in graphene under cyclotron resonance

We investigated the photo-thermoelectric response of Landau-quantized graphene in an infrared optical cavity structure. High-quality graphene/h-BN heterostructure was fabricated on a TiO2/Au optical cavity. We observed a large enhancement of the photo-thermoelectric voltage when the energy of the inter-Landau-level optical absorption, so-called cyclotron resonance, was coincident with that of the cavity mode. This is due to cavity-enhanced cyclotron resonance absorption of mid-infrared light. A maximum photovoltage responsivity of ∼107 V/W was obtained at a wavelength of 9.27 μm under a magnetic field as low as ∼1 Tesla. The obtained responsivity was significantly higher than that of conventional graphene devices. Our results provide an efficient photo-thermoelectric conversion scheme that utilizes Landau-quantized graphene and an optical cavity.

Ultraviolet photodetector improvement based on microspheres

Owing to the ideal optical cavity structure, the microsphere has always played a significant role in micro/nano optoelectronic devices for its high light-confined ability and large surface-volume ratio, which have been applied in lots of areas including intracellular lasers, tunable lasers, and so on. Furthermore, the microsphere cavity will be a useful and efficient means to improve the photodetector (PD) performance by enhancing the light absorption efficiency and light energy in the arrays. Herein, the wide-bandgap semiconductor microspheres are introduced in the PD, which are synthesized by a simple and universal hydrothermal method. The sensitive ultraviolet PD is constructed and obtained with a metal-semiconductor-metal type device structure. The oxide defect concentration in the ZnO microspheres is modulated through thermal treatment to improve the performance, including higher photo-to-dark current ratio near 600, responsivity of 7.6✕10−5 A/W, detectivity of 4.6✕107 Jones, and response speed. Moreover, the microspheres fabricated flexible device presents great detecting performance with different bending degrees. The results display the excellent prospect of semiconductor microspheres to flexible ultraviolet high-performance PDs, which possess the broad and potential development prospect in flexible even on-chip optoelectronic devices.

Optimizing an Optical Cavity-Based Biosensor for Enhanced Sensitivity.

The rapid advancement of biosensor technology has revolutionized healthcare, offering improved sensitivity, specificity, and portability. We have developed an optical cavity-based biosensor (OCB) as a promising solution due to its label-free detection, high sensitivity, real-time monitoring, multiplexing capability, and versatility. The OCB consists of an optical cavity structure (OCS), optical components, and a low-cost camera. The OCS is created by two partially reflective surfaces separated by a small gap, where the interaction between target analytes and immobilized receptors leads to a shift in the resonance transmission spectrum, caused by minute changes in the local refractive index (RI). In our previous work, we successfully detected these small changes with a simple OCS and cost-effective components using a differential detection method. Building upon these achievements, this study focuses on optimizing the OCS, improving the camera settings, and enhancing the differential detection approach. By increasing the reflectance of the surfaces and optimizing the optical cavity widths correspondingly, we achieved an improved limit of detection (LOD). We also investigated how the charge-coupled device (CCD) camera shutter time affects the LOD. Additionally, we introduced a new differential equation to further enhance the sensitivity of our system. Through these advancements, we could improve the LOD of the OCB by 7.2 times, specifically for an OCS with a cavity thickness of 9.881 μm and a silver thickness of 46.87 nm. These findings not only contribute to the ongoing effort of optimizing the OCB, but also pave the way for the development of advanced point-of-care biosensors with enhanced detection capabilities.

Color tuning halide perovskites: Optical amplification and lasing

Light emission with delicate wavelength control generates fundamental colors that are essential for vision-based applications such as displays, information communication, visual and augmented reality. Yet these light emitting technologies critically rely on the development of photonic sources for proper lighting and color matching. Halide perovskites have recently emerged as excellent and efficient photonic sources due to their outstanding photophysical properties, such as low defect trap densities, long carrier lifetime, large absorption coefficient, high quantum yield and optical gain. On a par with the rapid advances of light-emitting diodes (LEDs), perovskite-based optical amplifiers and lasers have made great strides in the past few years, which have much more accurate control of color-matched lighting, high power, spatial and wavevector control of color emission. In this review, we aim to review the recent progress of perovskite lasers at micro-, nano- and subwavelength scales, discuss the properties of halide perovskites and optical cavity structures that benefit color light emission, and examine the remaining challenges in the field for the future development of perovskite-based lasing technologies.

Polarization-independent enhancement of optical absorption in a GaAs quantum well embedded in an air-bridge bull’s-eye cavity with metal electrodes

Electron spins in gate-defined quantum dots (QDs) formed in semiconductor quantum wells (QWs) are promising stationary qubits for implementing large-scale quantum networks in a scalable manner. One key ingredient for such a network is an efficient photon–spin interface that converts any polarization state of a flying photonic qubit to the corresponding spins state of the electron in gate-defined QDs. A bull’s-eye cavity is an optical cavity structure that can enhance the photon absorption of an embedded gate-defined QD without polarization dependence. In this paper, we report the successful fabrication of air-bridge bull’s-eye cavities with metal electrodes and demonstrate the nearly polarization-independent optical absorption of a GaAs QW embedded in the cavities. This work marks an important step toward realizing an efficient photon–spin interface using gate-defined QDs.

Direct Observation of Self-Hybridized Exciton-Polaritons and Their Valley Polarizations in a Bare WS2 Layer.

The strong excitonic properties of transition metal dichalcogenides (TMD) have led to the successful demonstration of exciton-polaritons (EPs) in various optical cavity structures. Recently, self-hybridized EPs have been discovered in a bare TMD layer, but experimental investigation is still lacking because of their nonradiative nature. Herein, the direct observation of self-hybridized EPs in a bare multilayer WS2 via the evanescent field coupling technique is reported. Because of the thickness-dependent Rabi splitting energy, the dispersion curves of the EPs change sensitively with sample thickness. Moreover, continuous tuning of EP dispersion curves is demonstrated by controlling the excitation laser power. Lastly, it is observed that guided EPs retain valley polarization up to 0.2 at room temperature, representing a valley-preserved strong coupling regime. It is believed that the high tunability and valley polarization properties of the guided EPs in bare TMD layers can facilitate new nanophotonic and valleytronic applications.

Plug-and-play QKD architecture with a self-optical pulse train generator.

The commercialization of quantum key distribution (QKD), which enables secure communication even in the era of quantum computers, has acquired significant interest. In particular, plug-and-play (PnP) QKD has garnered considerable attention owing to its advantage in system stabilization. However, a PnP QKD system has limitations on miniaturization owing to a bulky storage line (SL) of tens of kilometers. And, the secure key rate is relatively low because Bob transmits the signal pulses only at the dedicated time slots to circumvent backscattering noise. This study proposes a new method that can eliminate the SL by realizing an optical pulse train generator based on an optical cavity structure. Our method allows Alice to generate optical pulse trains herself by duplicating Bob's seed pulse and excludes the need for Bob's strong signal pulses that trigger backscattering noise as much as the conventional PnP QKD. Accordingly, our method can naturally overcome the miniaturization limitation and the slow secure key rate, as the storage line is no longer necessary. We conducted a proof-of-concept experiment using our method and achieved a key generation rate of 1.6×10-3 count/pulse and quantum bit error rate ≤ 5%.

Dual-Enhanced Photodetectors Combining Graphene Plasmonic Nanoresonators With Germanium-on-Insulator Optical Cavities

Two-dimensional graphene (2-D graphene) has limited application potential in optoelectronics because of its low light absorptivity and gapless property. This work presents photodetectors with increased light absorption efficiency, which couple 3-D graphene with the optical cavity structure of germanium-on-insulator (GeOI). Multiple reflections are generated at the 3-D graphene/GeOI heterojunction due to the unique plasmonic nanoresonator and optical cavity structures. The photodetectors exhibit excellent responsivity (R=0.9x10⁴ mAW⁻¹) and specific detectivity (D*= 3.96x10¹⁰ cmHz <formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex>$^{1/2}$</tex> </formula> W⁻¹) under 1550-nm illumination with fast response rates, excellent reproducibility, and long-term stability. The technique paves the way for creating novel high-performance graphene-based photodetectors with hybrid architectures.

Resonant nanocavity-enhanced graphene photodetectors on reflecting silicon-on-insulator wafers

The weak light absorption and zero-bandgap properties of two-dimensional graphene negatively affect electron–hole recombination and quantum yield, restricting its usefulness in practical optoelectronic applications. In this work, plasma-assisted chemical vapor deposition is used to synthesize three-dimensional graphene (3D-graphene) in situ on the surface of silicon-on-insulator (SOI) wafers, thereby creating high-performance broadband photodetectors. The nanocavity structure of the 3D-graphene integrates with the optical cavity structure of the SOI to enhance the interaction that occurs between the 3D-graphene and incident light. The resulting device has excellent performance in the near-infrared (NIR). The mechanism by which the light absorption of the photodetector is enhanced is explored in detail via experimental analysis and theoretical calculation. Photodetectors based on the 3D-graphene/SOI Schottky heterojunction exhibit a broad detection range (from 440 to 1550 nm), ultrahigh responsivity (27.4 A/W), and excellent detectivity (1.37 × 1011 Jones) at a wavelength of 1550 nm. The Schottky heterojunctions combine two structures (nanocavity and optical cavity) that enhance light absorption. They are also compatible with complementary metal-oxide-semiconductor technology, providing a strategy for manufacturing high-performance NIR photodetectors.

Optical cavity structure design and optical path simulation for rapid nitric oxide detection

Optical cavity structure design and optical path simulation for rapid nitric oxide detection

Monolithic Integrated Semiconductor Optical Amplifier With Broad Spectrum, High Power, and Small Linewidth Expansion

Semiconductor optical amplifiers (SOAs) offer direct electrical injection, power consumption, integration, and anti-radiation advantages over optical fiber amplifiers. However, saturation output power and gain bandwidth have been limited in traditional structure SOAs. We demonstrate a monolithic integrated SOA with broad spectrum, high power, high gain, and small spectral linewidth expansion. The device adopts a two-stage amplified large optical cavity structure, and a lower optical field confinement factor is obtained by adjusting the thickness of the waveguide layer. The lower optical field confinement factor is conducive to improving the coupling efficiency and the maximum output power. Our device, fabricated only by standard i-line lithography with micron-scale precision, obtains excellent and stable performance. When the input power is set to 1 mW, the output power is 419 mW with a gain of 26.23 dB. When the input power is set to 25 mW at 25 °C, the output power increases to 600 mW with a gain of 13.8 dB. The corresponding gain bandwidth of 3 dB measures at least 70 nm. The spectral linewidth after the SOA is 1.15 times wider than that of the seed laser.

Demonstration of a Label-Free and Low-Cost Optical Cavity-Based Biosensor Using Streptavidin and C-Reactive Protein.

An optical cavity-based biosensor (OCB) has been developed for point-of-care (POC) applications. This label-free biosensor employs low-cost components and simple fabrication processes to lower the overall cost while achieving high sensitivity using a differential detection method. To experimentally demonstrate its limit of detection (LOD), we conducted biosensing experiments with streptavidin and C-reactive protein (CRP). The optical cavity structure was optimized further for better sensitivity and easier fluid control. We utilized the polymer swelling property to fine-tune the optical cavity width, which significantly improved the success rate to produce measurable samples. Four different concentrations of streptavidin were tested in triplicate, and the LOD of the OCB was determined to be 1.35 nM. The OCB also successfully detected three different concentrations of human CRP using biotinylated CRP antibody. The LOD for CRP detection was 377 pM. All measurements were done using a small sample volume of 15 µL within 30 min. By reducing the sensing area, improving the functionalization and passivation processes, and increasing the sample volume, the LOD of the OCB are estimated to be reduced further to the femto-molar range. Overall, the demonstrated capability of the OCB in the present work shows great potential to be used as a promising POC biosensor.

Infrared Light Absorbance: a New Method for Temperature Compensation in Nondispersive Infrared CO2 Gas Sensor

Nondispersive infrared CO2 gas sensor was developed after the simulation of optical cavity structure and assembling the optical components: IR source, concave reflectors, Fresnel lens, a hollow disk, and IR detectors. By placing a hollow disk in front of reference IR detector, the output voltages are almost constant value, near to 70.2 mV. The absorbance of IR light, Fa, shows the second order of polynomial according to ambient temperatures at 1,500 ppm. The differential output voltages and the absorbance of IR light give a higher accuracy in estimations of CO2 concentrations with less than ± 1.5 % errors. After implementing the parameters that are dependent upon the ambient temperatures in microcontroller unit (MCU), the measured CO2 concentrations show high accuracies (less than ± 1.0 %) from 281 K to 308 K and the time constant of developed sensor is about 58 sec at 301 K. Even though the estimation errors are relatively high at low concentration, the developed sensor is competitive to the commercial product with a high accuracy and the stability.

Self‐Assembled, 10 nm‐Tailored, Near Infrared Plasmonic Metasurface Acting as Broadband Omnidirectional Polarizing Mirror

AbstractPlasmonic metasurfaces tailored at the few‐nanometers scale and fabricated by high‐throughput lithography‐free methods are needed to efficiently produce optical components with optimal performance and small footprint. Herein, the design of such metasurfaces and their fabrication over cm2 areas by self‐assembly are reported. They present an optical cavity structure, in which a 2D array of parallel Au nanorods is coupled to a metal mirror through a thin spacer. The nanorods present a quasi‐monodisperse ≈10 nm diameter and separation, and a broad polydisperse length distribution. These remarkable nanostructural features, combining periodicity in one direction with randomness in another, endow the nanorod array with unconventional plasmonic and anisotropic effective optical properties. Thanks to these properties, for light polarized along the nanorods, the metasurface displays strong destructive optical interference and thus near‐perfect absorption over a broad range of angles of incidence and of wavelengths in the near infrared. In contrast, for light polarized perpendicular to the nanorods, no such interference occurs and thus the metasurface behaves as a metal mirror. In sum, the metasurface can be used as broadband omnidirectional polarizing mirror, an original thin and monolithic optical component merging the functionalities of a metal mirror and of a wire‐grid polarizer.

Multi-frequency radiation of dissipative solitons in optical fiber cavities

New resonant emission of dispersive waves by oscillating solitary structures in optical fiber cavities is considered analytically and numerically. The pulse propagation is described in the framework of the Lugiato-Lefever equation when a Hopf-bifurcation can result in the formation of oscillating dissipative solitons. The resonance condition for the radiation of the dissipative oscillating solitons is derived and it is demonstrated that the predicted resonances match the spectral lines observed in numerical simulations perfectly. The complex recoil of the radiation on the soliton dynamics is discussed. The reported effect can have importance for the generation of frequency combs in nonlinear microring resonators.

Toggling between active and passive imaging with an omni-resonant micro-cavity.

While passive illumination schemes often utilize a broadband spectral acceptance, the performance of active illumination with a laser is improved by narrowband spectral filtering at the sensor. We present an experimental demonstration of an optical cavity structure that is capable of toggling between two performance limits: narrowband resonant and broadband omni-resonant transmission. To achieve omni-resonance without modifying the cavity, the incident optical field is pre-conditioned by associating each wavelength with a particular incidence angle that enables a broad continuous spectrum to resonate with the cavity. This strategy can help seamlessly combine passive and active illumination in the same system.

Dynamic-Metasurface-Based Cavity Structures for Enhanced Absorption and Phase Modulation

Metasurface-based optical cavity structures consist of a metallic metasurface realized on top of a dielectric slab backed with a metal plane. Such structures have been employed in the design of optical devices such as flat lenses, wave plates, and holograms at frequencies from microwave to mid-infrared. Recently, such structures with dynamically reconfigurable optical characteristics have been explored for electrically tunable optical absorption and reflection phase modulation. To date, absorption modulation and phase modulation have been realized with large insertion loss. In this work, we employ an analytical approach based on transmission line theory where the metasurface is represented by a surface admittance. We extend the above approach for the design and analysis of under- and overcoupled resonance regimes in the metasurface cavity structure. This enables a mutual design of cavity thickness and individual metasurface for large amplitude or phase modulation. A dynamic-metasurface-based optical cavity is experimentally demonstrated at terahertz frequencies where the dynamic metasurface consists of metallic resonators embedded with thin-film vanadium dioxide patches. By driving an insulator to metal transition in vanadium dioxide, the terahertz optical response of the metasurface-based cavity structure is modulated. The fabricated device exhibits perfect absorption modulation and reflection phase modulation up to 180°. The reported results demonstrate the potential of such structures for realizing novel devices such as tunable holograms, high-efficiency modulators, and frequency-tunable filters at terahertz. The analytical approach presented here can be applied to the analysis and design of metasurface cavity structures based on other material systems at frequencies ranging from terahertz to mid-infrared.

Large‐Area Hybrid Plasmonic Optical Cavity (HPOC) Substrates for Surface‐Enhanced Raman Spectroscopy

AbstractSurface‐enhanced Raman spectroscopy (SERS) is receiving increasing interests owing to its high sensitivity and molecular fingerprint information. The practical application of SERS relies on the highly enhancing, uniform, reproducible, and affordable substrates. A novel gap‐free 3D SERS substrate with unique hybrid plasmonic and optical cavity (HPOC) structures to improve the uniformity and reduce the fabrication cost while maintaining the high SERS enhancement is introduced here. The gold HPOC structures are fabricated by the tunable holographic lithography followed by gold deposition and can be conveniently optimized for a specific excitation wavelength by tuning the cavity length. The substrate shows average enhancement factor larger than 106 and excellent uniformity with a standard deviation smaller than 6.7%. Together with the capability to be fabricated on a flexible polyethylene substrate, the HPOC SERS substrate is promising for practical applications.

Label-free real-time detection of biotinylated bovine serum albumin using a low-cost optical cavity-based biosensor.

We have developed a low-cost optical cavity-based biosensor with a differential detection method for point-of-care medical diagnostics. To experimentally demonstrate its label-free real-time biosensing capability, we performed the detection of biotinylated bovine serum albumin (BSA). Streptavidin is introduced into the optical cavity structure and immobilized on 3-aminopropyltriethoxysilane (APTES) coated surface. After rinsing out unbound streptavidin with DI water, biotinylated BSA without any labeling is introduced. A CMOS camera captures the transmitted light of two different wavelengths passing through the optical cavity sensing area in real-time. Then, the differential values are calculated to enhance the responsivity. We successfully demonstrated the label-free real-time detection of biotinylated BSA, and the measurement results matched well with the simulation results. The limit of detection of the optical cavity-based biosensor for the biotinylated BSA detection with the sensing area of 180 μm × 180 μm is estimated to be 2.82 pM, which could be reduced further for a smaller sensing area with the tradeoff of a longer sensing time.

Investigation of lasers based on coupled waveguides by near-field scanning optical microscopy

We have investigated near field intensity distributions of InGaAs/GaAs/AlGaAs lasers possessing broadened waveguides based on coupled large optical cavity structures (CLOC) by scanning near-field optical microscopy (SNOM). The concept allows effective suppressing of the transverse high-order mode lasing. The obtained results can be considered to be the direct proof of pure transverse single-mode emission of the CLOC lasers.