Distributed Bragg Reflector Mirrors Research Articles

Detection of Volatile Organic Compounds through Spectroscopic Signatures in Nanoporous Fabry-Pérot Optical Microcavities.

Increasingly complex modern gas-monitoring scenarios necessitate advanced sensing capabilities to detect and identify a diverse range of gases under varying conditions. There is a rising demand for individual sensors with multiple responses capable of recognizing gases, identifying components in mixtures, and providing stable responses. Inspired by gas sensors employing multivariable response principles, we develop a nanoporous anodic alumina high-order microcavity (NAA-HOμCV) gas sensor with multiple optical outputs for discriminative gas detection. The NAA-HOμCV architecture, formed by a Fabry-Pérot microcavity with distributed Bragg reflector (DBR) mirrors and an extended-length microcavity layer supporting multiple resonant modes, serves as an effective solid-state fingerprint platform for distinguishing volatile organic compound (VOC) gases. Our research reveals that the coupling strength of light into resonant modes and their evolution depend on the thickness of the DBR mirrors and the dimension of the microcavity layer, which allows us to optimize the discriminative sensing capability of the NAA-HOμCV sensor through structural engineering of the microcavity and photonic crystal mirrors. Gas-sensing experiments conducted on the NAA-HOμCV sensor demonstrate real-time discrimination between physiosorbed VOC gases (isopropanol, ethanol, or acetone) in reversible gas sensing. It also achieves superior ppb-level sensing in irreversible gas sensing of model silane molecules. Our study presents promising avenues for designing compact, cost-effective, and highly efficient gas sensors with tailored properties for discriminative gas detection.

Resonant cavity enhanced InAs/GaAsSb SLS LEDs with a narrow spectral linewidth and a high-spectral intensity operating at 4.6 μm

We investigated the design, growth, fabrication, and characterization of InAs/GaAsSb SLS resonant cavity light emitting diodes (RCLEDs) grown on InAs by molecular beam epitaxy. The structure consists of a 1λ-thick micro-cavity positioned between two lattice-matched AlAsSb/GaAsSb distributed Bragg reflector mirrors (DBRs). A 44-pair InAs/GaAsSb SLS active region is placed at the antinode of the electric field intensity in the center of the cavity. Electroluminescence emission spectra were recorded at room-temperature. Due to the resonant cavity effect, 400 μm-diameter SLS RCLEDs exhibited emission spectra peaked at 4.587 μm with a narrow spectral linewidth of 52 nm. A high-spectral intensity of >3 mW cm−2 nm−1 was achieved for the 400 μm SLS RCLED using 1% duty cycle to avoid Joule heating. Furthermore, temperature dependence of the emission spectra of the RCLED showed excellent temperature stability, with a rate of 0.34 nm/K. Compared to existing mid-infrared 5-stage InAs/GaAsSb SLS ICLEDs operating at ∼4.5 μm, the (400 μm-diameter) InAs/GaAsSb SLS RCLEDs exhibited 10.5× brighter spectral intensity, 14× narrower spectral linewidth, and 8× improvement in the temperature stability. Owing to these attractive features, our SLS RCLEDs could be used to develop the next generation CO gas instruments and active imaging.

Fabrication of InGaN/GaN multiple quantum well embedded on nanoporous GaN mirror under different acid electrolytes

Large-size (2 inch) InGaN/GaN multiple quantum wells (MQW) embedded on nanoporous (NP)-GaN distributed Bragg reflectors (DBR) were fabricated by electrochemical (EC) etching at different acid electrolytes (e.g. HF, oxalic, and HNO3 acids). The sample obtained in HNO3 electrolyte presents the highest reflectance and the strongest photoluminescence (PL) intensity, whereas the sample fabricated by the HF etching has uneven surface, leading to very low reflectance. Compared with the as-deposited sample, the HNO3 etching leads to a 5-fold enhancement of PL intensity of etched sample, probably resulting from two factors which reflection of NP-GaN DBR mirror enhanced the light output, and amplify spontaneous emission (ASE) via a resonant cavity increased PL performance.

Inverse design of distributed bragg reflector targeting a sharp reflectivity spectrum

Distributed Bragg reflectors (DBRs) have found applications in various fields, including optical communications, light generation, solar cells, and sensors. DBRs are also crucial in open-access Fabry‐Pérot microcavities for enhanced and spectrally tunable light-matter interactions. This document presents the inverse design, fabrication, and optical characterization of aperiodic Ta2O5/SiO2 multilayer DBR mirrors targeting a sharp reflectivity spectrum. The results were confirmed through simulations and experimental measurements. The proposed inverse design methodology can be used to develop DBRs for important technologies such as single-photon sources, polaritonic systems, and random laser generation.

Improved Characteristics of Fluorene‐Type Polymer Light‐Emitting Devices Based on Multilayer Formation from Polymers and Solution‐Processable Wide‐Bandgap Inorganic Copper(I) Thiocyanate with p‐Type Conduction and High Refractive Index

The functional solution‐processable multilayer formation is a significant factor in the improved characteristics of polymer light‐emitting devices. The improved characteristics of direct current and alternating current (AC)‐driven fluorene‐type polymer light‐emitting devices based on multilayer structures utilizing polymers and solution‐processable inorganic wide‐bandgap semiconductor, copper(I) thiocyanate, CuSCN, which exhibits p‐type conduction and high refractive index, are investigated. For the polymer light‐emitting diodes based on poly(9,9‐dioctylfluorene‐co‐benzothiadiazole), F8BT with CuSCN, the plateau of current efficiency indicates the carrier injection and transport to be balanced at lower current density and the balance to be maintained through the wide current range. CuSCN acts as the hole transport and electron‐blocking layer, although CuSCN acts as a fluorescence quencher for F8BT. The introduction of inorganic/organic hybrid dielectric mirrors, which consists of the alternating layers of inorganic CuSCN and insulating poly(vinylidene fluoride‐trifluoroethylene), P(VDF‐TrFE), into the AC voltage‐driven polymer electroluminescent device (ACEL) structure, is an effective way to achieve both the spectral narrowing and color tunability. Using high‐refractive‐index CuSCN, the color‐tunable emission for ACEL with distributed Bragg reflector mirrors and the electroluminescent (EL) emission from a weak microcavity effect are achieved.

Photonic Characterization and Modeling of Highly Efficient Color Conversion Layers With External Reflectors

We propose a new method for fabricating arrays of colloidal quantum dots for color conversion layers (CCLs) with atomic layer deposited (ALD) encapsulation. Semiconductor processes were used to transfer the CCL onto a transparent glass substrate. This method enables pixels as small as 5 μm, and the pixel's size and pitch can be controlled through the semiconductor process and mask layout. A dual-color array with a red-and-green CCL was also demonstrated to be suitable for microdisplay applications in experiments. The best color conversion efficiency of a single color CCL reached as high as 20.7%. A set of distributed Bragg reflector mirrors was used to increase photon recycling, and these mirrors yielded an increase in peak intensity of 35.7%. We formulated a model of incoherent reflection and transmission to calculate the changes in CCL properties when mirrors are added; this model had close fit with results from experiments in which mirrors of different reflection coefficients were used. Through the use of ALD, the CCL can be stored at a normal room-temperature environment for more than 9000 hours, and the projected lifetime is linearly extrapolated to be 44,041 hours.

Room-Temperature Continuous-Wave Microcavity Lasers from Solution-Processed Smooth Quasi-2D Perovskite Films with Low Thresholds

Continuous-wave (CW) lasing in quasi-two-dimensional (2D) perovskite-based distributed feedback cavities has been achieved at room temperature; however, CW microcavity lasers comprising distributed Bragg reflectors (DBRs) have rarely been prepared using solution-processed quasi-2D perovskite films because the roughness of perovskite films significantly increases intersurface scattering loss in the microcavity. Herein, high-quality spin-coated quasi-2D perovskite gain films were prepared using an antisolvent to reduce roughness. The highly reflective top DBR mirrors were deposited via room-temperature e-beam evaporation to protect the perovskite gain layer. Lasing emission of the prepared quasi-2D perovskite microcavity lasers under CW optical pumping was clearly observed at room temperature, featuring a low threshold of ∼1.4 W cm-2 and beam divergence of ∼3.5°. It was concluded that these lasers originated from weakly coupled excitons. These results elucidate the importance of controlling the roughness of quasi-2D films to achieve CW lasing, thus facilitating the design of electrically pumped perovskite microcavity lasers.

Tunable Bloch surface wave constructed by two-dimensional lithium niobate grating for biosensor

In this study, a Bloch surface wave (BSW) biosensor coupled with a two-dimensional lithium niobate grating was designed. The influence of the nonlinear characteristics of lithium niobate on the BSW sensor was theoretically investigated, and the tunability of the BSW was studied using the excitation schemes of n e and n o. To confine the energy on the surface of the solution in contact with the sensor, we introduce a distributed Bragg reflector mirror (DBR) consisting of four pairs of 76% and 42% porosity porous silicon films. A layer of lithium niobate grating is deposited on top of DBR to excite Bloch surface waves(BSW) and introduce the concept of azimuth detection in the study of the tunable properties of lithium niobate. Then, the azimuth angle of the resonance peaks excited along the n e and n o directions of lithium niobate varied by approximately 5°.

Design, Modeling, and Characterization of Hot Electron Light Emission and Lasing in Semiconductor Heterostructure-VCSOA with Optical Gain up to 36 dB

Vertical-cavity semiconductor optical amplifiers (VCSOAs) are interesting devices for optical communication applications. In this work, we have studied the characteristics of gain spectra and amplifier bandwidth in reflection mode at 1300 nm GaInNAs/GaAs hot electron light emission and lasing in semiconductor heterostructure-VCSOA structure using MATLAB program. The device contains 16 Ga0.7In0.3N0.038As0.962 multiple quantum wells (QWs) in its intrinsic region; the active region is bounded between eight pairs of GaAs/AlAs top distributed Bragg reflectors (DBRs) mirror and 25 pairs of AlAs/GaAs bottom DBRs mirror. Simulation results suggest that the resonance cavity of QW of HILLISH-VCSOA is varied with temperature and number of DBRs periods. We compare the relation between the wavelength and gain at a different single-pass gain in both reflection and transmission modes. The highest gain at around 36 dB is observed in reflection mode. Moreover, we calculated the amplifier bandwidth at different periods of top mirror’s reflectivity, in which when the peak reflection gains increases, the amplifier bandwidth decreases.

A Comparison of Top Distributed Bragg Reflector for 1300 nm Vertical Cavity Semiconductor Optical Amplifiers Based on III–V Compound

In this work, the design of GaAs/AlGaAs distributed Bragg reflector (DBR) has been implemented for 1300 nm vertical cavity semiconductor optical amplifiers (VCSOAs) for optical fiber communication applications. The top DBR period and Al concentration are varied, the peak reflectivity of the DBR is increasing from 50% to 97.5% for 13 periods with increasing Al concentration, whereas the reflectivity bandwidth is increased to almost 190 nm. The relation between wavelength and incidence angle variation on DBR reflectivity is increasing with the incident angle (0°, 20°, 30°, and 50°), the resonant wavelength and bandwidth of the measured reflectance spectra shifts to shorter wavelength and wider bandwidth, respectively. In addition, a comparison between the linear, the graded, and the parabolic DBRs has been achieved with transfer matrix method using MATLAB software to show the influence of layer in DBRs and its effect on lasing wavelength. It is shown that using grading DBR mirror is much more beneficial compared to abrupt DBR, whereas it has lower reflectivity of almost 10% due to VCSOAs device which needs less number of top layers until prevent reaching lasing threshold.

Design of monolithic distributed Bragg reflector-integrated photodiode using a tapered waveguide with InP and polymer cladding layer

We propose a monolithic distributed Bragg reflector (DBR) integrated photodiode using a tapered waveguide with InP and polymer cladding layers for achieving a high efficiency bandwidth product. In the proposed photodiode, a DBR mirror is formed at the end of the waveguide, thereby increasing the effective absorption length of the device. Furthermore, to reduce the coupling loss, the InP and polymer cladding layers are formed under and on top of the core layer, respectively. Consequently, the mutual tradeoff between the bandwidth and quantum efficiency of the photodetector could be alleviated.

Design and calculation of type-II superlattice resonant cavity-enhanced photodetector with high quantum efficiency and low dark current

The type-II superlattice (T2SLs) infrared detector with distributed Bragg reflector (DBR) on the basis of unipolar barrier structure is investigated. The traditional binary material InAs/GaSb is used in the device, and two kinds of unipolar barrier structures, nBn and pBp, are used to reduce the generation-recombination (GR) dark current of the device. 6 periods of AlAs0.09Sb0.91/GaSb is selected as the DBR mirror. The target wavelength of DBR mirror is 3.3 μm, which is used as methane detector. The supercell is 7 ML InAs/4 ML GaSb, which has a 50% cutoff wavelength of 4 μm. The quantum efficiency (QE) of the detector with DBR mirror can reach ~ 90% at the target wavelength of 3.3 μm, and is significantly higher than that of the device without DBR mirror. The peak detectivity of pBp RCE PD is about ~1 × 1013 Jones.

A Comparative Study of Electrical Characterization of P-Doped Distributed Bragg Reflectors Mirrors for 1300 nm Vertical Cavity Semiconductor Optical Amplifiers

This paper presents an electrical analysis of various diameters of two p-types of GaAs/Al0.9Ga0.1As and two p-types of GaAs/Al0.3Ga0.7As/Al0.9Ga0.1As distributed Bragg reflectors (DBRs) mirrors structure grown on undoped and on p-doped GaAs, which affects the characteristics of 1300 nm vertical cavity surface emitting lasers (VCSELs) and vertical cavity semiconductor optical amplifiers (VCSOAs). Electrical characterizations and Hall measurements of current−voltage (IV) for GaAs/Al0.9Ga0.1As linear DBRs and GaAs/Al0.3Ga0.7As/Al0.9Ga0.1 As graded DBRs were also performed at temperatures between 13 and 300 K. Consequently, p-type DBRs are designed with graded composition interfaces technique. The smaller mesa diameters are used to reduce vertical and longitudinal resistances and to limit the heating effect and improve the characteristics of VCSEL/VCSOA devices.

(Invited) Development of Blue Vertical Cavity Surface Emitting Lasers (VCSELs) with Nanoporous GaN

Blue and green vertical cavity surface emitting lasers (VCSELs) are expected to be used in future generation display and lighting applications. Applications in virtual reality (VR), augmented reality (AR), retinal scanning display (RSD), and portable projection devices are only a few of the anticipated applications. However, in spite of vigorous pursuit for more than two decades, GaN VCSELs have yet reached commercialization.The main challenge in the technology of III-nitride VCSELs is the fabrication of distributed Bragg reflectors (DBRs) that can provide near-unity reflection and thus support the formation of high-quality vertical cavity. Several groups reported VCSEL operations using epitaxial DBRs (using AlGaN/GaN or AlInN/GaN) and dielectric DBRs (involving lift-offs or epitaxial lateral overgrowth). In this talk, we will discuss an alternative approach to this challenging problem by using electrochemistry to create nanoporous GaN as a low-index medium, toward a manufacturable DBR mirror technology to support blue and green VCSELs. This nano-engineering based on electrochemistry can help to circumvent impasses and creates new dimensions in the exploration of optoelectronic devices using GaN.We acknowledge research support from US Department of Energy, National Science Foundation, DARPA, and IP Group.

(Invited) Development of Blue Vertical Cavity Surface Emitting Lasers (VCSELs) with Nanoporous GaN

Blue and green vertical cavity surface emitting lasers (VCSELs) are expected to be used in future generation display and lighting applications. Applications in virtual reality (VR), augmented reality (AR), retinal scanning display (RSD), and portable projection devices are only a few of the anticipated applications. However, in spite of vigorous pursuit for more than two decades, GaN VCSELs have yet reached commercialization. The main challenge in the technology of III-nitride VCSELs is the fabrication of distributed Bragg reflectors (DBRs) that can provide near-unity reflection and thus support the formation of high-quality vertical cavity. Several groups reported VCSEL operations using epitaxial DBRs (using AlGaN/GaN or AlInN/GaN) and dielectric DBRs (involving lift-offs or epitaxial lateral overgrowth). In this manuscript, I will discuss an alternative approach to this challenging problem by using electrochemistry to create nanoporous GaN as a low-index medium, toward a manufacturable DBR mirror technology to support blue and green VCSELs. This nano-engineering based on electrochemistry can help to circumvent impasses and creates new dimensions in the exploration of optoelectronic devices using GaN.

High-power narrow spectrum GaSb-based DBR lasers emitting near 2.1 µm

Stable high-power narrow-linewidth operation of the 2.05-2.1 µm GaSb-based diode lasers was achieved by utilizing the sixth-order surface-etched distributed Bragg reflector (DBR) mirrors. The DBR multimode devices with 100 µm wide ridge waveguides generated ∼850mW in the continuous wave (CW) regime at 20°C. The device CW output power was limited by thermal rollover. The laser emission spectrum was defined by Bragg reflector reflectivity at all operating currents in a wide temperature range. The devices operated at DBR line with detuning from gain peak exceeding 10 meV.

Study of surface roughness of lifted-off epitaxial lateral overgrown GaN layers for the n-DBR mirror of a III-nitride vertical-cavity surface emitting laser

In this work, we propose using the low defect density wing region arising from epitaxial lateral overgrowth (ELO) for the development of Group III-nitride flip-chip vertical-cavity surface emitting lasers (VCSELs). The ELO wing is intended to be incorporated within the VCSEL cavity, supporting the n-side distributed Bragg reflector (DBR) mirror, and must therefore be very smooth. We measure the surface morphology of the interface surface of the ELO material after separation from the growth substrate, finding that the interface roughness changes with the composition and thickness of the ELO mask. Sub-nanometer surface roughness suitable for the placement of the DBR mirror is achieved using mask layers terminating in Si3N4, or via 300 nm thick sputtered SiO2.

High Performance Wide Angle DBR Design for Optoelectronic Devices

To improve the performance of optoelectronic devices, a high performance wide angle SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> Distributed Bragg Reflector (DBR) mirror was designed and fabricated on double polished sapphire substrate. 17-pairs gradually varied DBR structure was applied in order to acquire a broad stopband reflectivity over 95% from 400 nm to 800 nm, covering the whole visible light region. The DBR mirrors deposited at the backside of optoelectronics devices are also demonstrated to remain a high reflectivity at wide incident angles, which improves the emission efficiency of LEDs and light absorption efficiency of InGaN/GaN photoelectrochemical cell (PEC).

Highly Angular Tolerant Transmission Filters for Narrow-Band Image Sensors

A dielectric transmittance filter composed of subwavelength grating sandwiched between two few-layers distributed Bragg reflectors (DBRs) is proposed with the aim of being compatible with CMOS technology and to be tunable by lithographic means of the grating pattern without the need of thickness changes, in the broad spirit of metamaterials. The DBR mirrors form a Fabry-Perot (FP) cavity whose resonant frequency can be tuned by changing the effective refractive index of the cavity, here, by tailoring the in-plane filling factor of the grating. The structure has been studied and designed by performing numerical simulations using Fourier Modal Method (FMM). This filter proves to have high broad angular tolerance up to ±30˚. This feature is crucial for evaluating the spectral performance of narrow-band filters especially the so-called Ambient light sensors (ALS). By analyzing the transmittance spectral distributions in the band diagram, it is found that the angular tolerance is due to coupling between the FP and the guided mode inside the cavity in analogy to resonances occurring within multimode periodic waveguides in a different context.

Mid-infrared resonant cavity light emitting diodes operating at 4.5 µm.

We report on a mid-infrared resonant cavity light emitting diode (RCLED) operating at the wavelength of 4.5 µm with a narrow spectral linewidth at room temperature. Compared to a reference LED without a resonant cavity, our RCLED exhibits (85x) higher peak intensity, (13x) higher integrated output power, (16x) narrower spectral linewidth and (7x) superior temperature stability. The device consists of a one-wavelength thick micro-cavity containing an Al0.12In0.88As/InAs0.85Sb0.15 quantum well active region sandwiched between two high contrast AlAs0.08Sb0.92/GaSb distributed Bragg reflector mirrors, grown lattice-matched on GaSb by molecular beam epitaxy. The high spectral brightness, narrow linewidth and superior temperature stability are attractive features, enabling these devices to be used for detection of N2O at 4.5 µm. We show that with only minor adjustments the gases CO2 (4.2 µm) and CO (4.6 µm) are also readily accessible.