Bragg Reflector Research Articles

Design of a dual-channel narrow band filter based on metasurface

We proposed a dual-channel narrow band filter consisting of top and bottom-distributed Bragg reflectors (DBRs) and a dielectric interlayer inserted with a metasurface. Through the design of the metasurface, the two channels of the filter are guaranteed to exhibit high-quality factors with transmittance beyond 90% and full width at half maximum (FWHM) less than 10 nm. We demonstrate that the central wavelengths of each dual-channel filter can be controlled with a total of 50 nm shifts by only changing the width of the metasurface. Compared with the traditional dual-channel filter, our design is easier to fabricate and more convenient to tune the central wavelength, which is promising for ultracompact optical devices.

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.

Integrated microcavity optomechanics with a suspended photonic crystal mirror above a distributed Bragg reflector.

Increasing the interaction between light and mechanical resonators is an ongoing endeavor in the field of cavity optomechanics. Optical microcavities allow for boosting the interaction strength through their strong spatial confinement of the optical field. In this work, we follow this approach by realizing a sub-wavelength-long, free-space optomechanical microcavity on-chip fabricated from an (Al,Ga)As heterostructure. A suspended GaAs photonic crystal mirror is acting as a highly reflective mechanical resonator, which together with a distributed Bragg (DBR) reflector forms an optomechanical microcavity. We demonstrate precise control over the microcavity resonance by change of the photonic crystal parameters. We find that the microcavity mode can strongly couple to the transmissive modes of the DBR. The interplay between the microcavity mode and a guided resonance of the photonic crystal modifies the cavity response and results in a stronger dynamical backaction on the mechanical resonator compared to conventional optomechanical dynamics.

(Invited) tamm Plasmon Resonance Sensors Based on Nanoporous Anodic Alumina Photonic Crystals

Nanoporous Anodic Alumina (NAA) is a material with growing interest in nanotechnology and for biological and medical applications. It is a cost-effective nanostructured material obtained by the electrochemical etching of aluminum in acidic electrolytes at the adequate conditions of applied voltage or current, temperature and electrolyte composition [1-4]. The precise control over the diameter of the nanopore allows to create periodic variations of nanopore’s diameter in deep and obtain different photonic crystals e.g.., Gradient-index filters, microcavities, Distributed Bragg Reflectors, etc [5-6]. The optical properties of NAA depend on its nanoporous structure and of its functionalized surface. NAA can be used to fabricate hybrid photonic structures by gold coating on nanoporous anodic alumina photonic crystals surface (NAA-PCs) [7]. In this metal-dielectric photonic structure, we can observe effects of an enhancement of the surface plasmon resonance due to absorption of the light at the interface of metallic layer and the NAA photonic crystal.Tamm plasmon resonance (TPR) can be tuned by engineering the properties and characteristics of the metal film and the porous photonic structure, providing new opportunities to achieve unique plasmonic−photonic structures for different applications (optical switching, lasing, light emission, surface-enhanced spectroscopy, and sensing). One interesting application of TPR is the use as a sensing platform taking advantage of its exceptional optical properties to confine/amplify the light-matter interactions [8-9]. The sensing performance of TPR-NAA−PCs is assessed by the infiltration of their structure with analytical solutions, producing a spectral shift in the Tamm plasmonic resonance. In this work, we evaluate the structural geometry and the optical properties of TPR-NAA-PCs and the assessment of TPR-NAA-PCs as a sensing platform.Figure 1a shows the reflectance spectrum for a TPR-NAA–PCs structure. The spectrum shows the photonic bandgap and the absorption narrow-line associated with the resonant recirculation of light within the plasmon-photonic system. Figure 1b shows the sensing performance of TPR-NAA-PCS. Red-shift on the position of the TPR-NAA-PCs is observed due to the refractive index variation when the nanopores are infiltrated of different analytical solutions (water- ethylene glycol)AcknowledgmentsThis work was supported by the Spanish Ministerio de Ciencia e Innovación (MICINN/FEDER) PDI2021- 128342OB-I00, by the Agency for Management of University and Research Grants (AGAUR) ref. 2017- SGR-1527, COST Action 20126 - NETPORE and by the Catalan Institution for Research and Advanced Studies (ICREA) under the ICREA Academia Award.

N-type conducting AlInN/GaN distributed Bragg reflectors with AlGaN graded layers

We obtained a 40-pair Si-doped n-type conducting AlInN/GaN distributed Bragg reflector (DBR) with a low surface pit density, 3.0 × 106 cm−2, by introducing 5 nm Si-doped Al0.39Ga0.61N graded layers grown at high temperature, 1150 °C. A combination of a 0.6 nm GaN cap layer on AlInN and a subsequent thermal cleaning during a temperature increase process up to 1150 °C for the following AlGaN graded layer growth was effective for a suppression of pit/threading dislocation generations at the interfaces of the AlInN layers and the AlGaN graded layers in the DBRs without any additional cleaning processes. We also found that an initial AlN mole fraction of 0.39 in the graded AlGaN layers provided the lowest vertical resistance of the Si-doped AlInN/GaN DBRs with the Si-doped AlGaN graded layers, suggesting that Al0.39Ga0.61N provides the lowest potential spike in the conduction band of the interface with Al0.82In0.18N among AlGaN alloys.

Detection of chemical warfare agent simulants based on luminescent distributed Bragg reflector porous silicon

Detection of chemical warfare agent simulants based on luminescent distributed Bragg reflector porous silicon

Determination of Thermal Damage Threshold in THz Photomixers Using Raman Spectroscopy

The increase of device lifetime and reliability of THz photomixers will play an essential role in their possible future application. Therefore, their optimal work conditions/operation range, i.e., the maximal incident optical power should be experimentally estimated. We fabricated and tested THz photomixer devices based on nitrogen-implanted GaAs integrated with a Bragg reflector. Raman spectroscopy was applied to investigate the material properties and to disclose any reversible or irreversible material changes. The results indicate that degradation effects in the photomixer structures/material could be avoided if the total optical power density does not exceed levels of about 0.7 mW/µm2 for 100 min of operation. Furthermore, the investigations performed during 1000 min of optical exposure on the photomixer devices’ central region comprising interdigitated metal-semiconductor-metal (MSM) structures suggest a reversible “curing” mechanism if the power density level of ~0.58 mW/µm2 is not exceeded. Long-term operation (up to 1000 h) reveals that the photomixer structures can withstand an average optical power density of up to ~0.4 mW/µm2 without degradation when biased at 10 V. Besides the decrease of the position of the A1g (LO) Raman mode from ~291 cm−1 down to ~288 cm−1 with increasing optical power density and operation time, broad Raman modes evolve at about 210 cm−1, which can be attributed to degradation effects in the active photomixer/MSM area. In addition, the performed carrier lifetime and photomixer experiments demonstrated that these structures generated continuous wave sub-THz radiation efficiently as long as their optimal work conditions/operation range were within the limits established by our Raman studies.

Spectrum Extreme Purification and Modulation of DBR Fiber Laser With Weak Distributed Feedback

Highly coherent lasers with spectral hyperpurity can further advance the fields of science and engineering. Especially, a light source with controllable frequency domain parameters can be adapted to a variety of emerging application scenarios. Herein, we report on an implementation of a novel ultra-high spectral purity distributed Bragg reflector (DBR) all-fiber laser based on weak distributed feedback, and its spectrum can be modulated in a certain extent by precisely controlling the intensity of the distributed feedback signal. Eventually, an ultra-high spectral purity laser with a spectral signal-to-noise ratio of 64 dB, a side mode suppression ratio (SMSR) of 83 dB, an output Lorentz linewidth of 115 Hz and a relative intensity noise of less than -122 dB/Hz is successfully obtained under normal conditions. Also, the frequency noise limit of the fiber laser with weak distributed feedback in the high frequency white noise flat region is 4.8 Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Hz, corresponding to a fundamental linewidth of ∼15.1 Hz. In particular, the SMSR and Lorentz linewidth of the laser can be continuously adjusted from 53 dB to 83 dB and 115 Hz to 8.2 kHz, respectively. In addition, we also investigated the effect of different pumping configurations on the performance of the DBR fiber laser. The proposed controllable mechanism of laser spectrum also provides a new perspective for extreme regulation of other laser parameters.

VCSEL Cavity Loss and Gain Measurement for High-Speed Optical Interconnects

Over 100 Gb/s Four-level Pulse-Amplitude Modulation (PAM4) Vertical-Cavity Surface-Emitting Laser (VCSEL) based optical interconnects require high speed, damped, and low relative intensity noise (RIN) VCSELs. Measurement techniques for intrinsic parameters are essential for optimizing VCSEL designs. The proposed VCSEL cavity round-trip loss and gain coefficient measurement provides the insight of VCSEL distributed Bragg reflectors (DBRs) and quantum well (QW) design. A simple VCSEL cavity model is described and excellent matching between the model and measurement is achieved.

Anapole-Assisted Low-Power Optical Trapping of Nanoscale Extracellular Vesicles and Particles.

This study addresses the challenge of trapping nanoscale biological particles using optical tweezers without the photothermal heating effect and the limitation presented by the diffraction limit. Optical tweezers are effective for trapping microscopic biological objects but not for nanoscale specimens due to the diffraction limit. To overcome this, we present an approach that uses optical anapole states in all-dielectric nanoantenna systems on distributed Bragg reflector substrates to generate strong optical gradient force and potential on nanoscale biological objects with negligible temperature rise below 1 K. The anapole antenna condenses the accessible electromagnetic energy to scales as small as 30 nm. Using this approach, we successfully trapped nanosized extracellular vesicles and supermeres (approximately 25 nm in size) using low laser power of only 10.8 mW. This nanoscale optical trapping platform has great potential for single molecule analysis while precluding photothermal degradation.

Preparation and Increased Optical Properties of Large-Area AlInGaN LEDs with Mesoporous AlGaN-Distributed Bragg Reflectors

Preparation and Increased Optical Properties of Large-Area AlInGaN LEDs with Mesoporous AlGaN-Distributed Bragg Reflectors

Flexible multi-layered coloring transparent electrode composed of AZO–based materials

Color implementation in flexible photovoltaics (PVs) is aesthetically important in modern vehicles and buildings. To implement color in flexible PVs using conventional distributed Bragg reflector (DBR) methods, it is necessary to reduce its brittleness and minimize the light loss due to refractive index differences (Δn). Here, color-implemented transparent front electrodes for flexible and transparent solar cells (FTSCs) have been proposed using an aluminum-doped zinc oxide (AZO)–based multilayer with periodic hydrogenation (AZO:H). The hydrogenation of AZO causes passivation in vacancies of oxygen and zinc and strengthening of the O–H bonds, resulting in improved of electrical and optical properties and a very low Δn of ∼5%. Using the AZO:H DBR–diffuser electrodes, we demonstrate three primary colors and colored FTSCs made of silicon thin film. The FTSCs show little change in power conversion efficiencies for the different colors owing to low return loss by the very low Δn. They are lightweight for their high specific power and exhibit excellent flexibility that enables them to endure the bending stress of 600 cycles at a 6 mm bending radius. The developed device can be used for vehicle and building-integrated PV applications, and the methodology can be used for other thin-film solar cells that require color and flexibility.

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.

Record quantum efficiency from strain compensated superlattice GaAs/GaAsP photocathode for spin polarized electron source

Photocathodes based on GaAs and other III–V semiconductors are capable of producing highly spin-polarized electron beams. GaAs/GaAsP superlattice photocathodes exhibit high spin polarization; however, the quantum efficiency (QE) is limited to 1% or less. To increase the QE, we fabricated a GaAs/GaAsP superlattice photocathode with a Distributed Bragg Reflector (DBR) underneath. This configuration creates a Fabry–Pérot cavity between the DBR and GaAs surface, which enhances the absorption of incident light and, consequently, the QE. These photocathode structures were grown using molecular beam epitaxy and achieved record quantum efficiencies exceeding 15% and electron spin polarization of about 75% when illuminated with near-bandgap photon energies.

Mode Selection of a Lateral Waveguide for Single-Mode Operation of Lasers with a Distributed Bragg Reflector

Mode Selection of a Lateral Waveguide for Single-Mode Operation of Lasers with a Distributed Bragg Reflector

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.

Electronic Structure and Optical Spectra of Halide Perovskites A2BCl6[(A = Cs; B = Se, Sn, Te, Ti, Zr) and (A = K; B = Pd, Pt, Sn)] for Photovoltaic and Optoelectronic Applications

A precise and systematic analysis for A2BCl6[(A = Cs; B = Se, Sn, Te, Ti, Zr) and (A = K; B = Pd, Pt, Sn)] is performed to investigate structural stability as well as optical and electrical properties using pseudopotential plane wave method. The calculated lattice constants show consistency with the experimental results that ensure their structural stability. From the electronic band structure results, Cs2BCl6(B = Se, Sn, Te, Ti, Zr) and K2BCl6(B = Pd, Pt, Sn) are established to be within an energy bandgap that varies between 1.131 and 3.731 eV. The metallic behavior of the materials for Cs2BCl6(B = Ta, W) and K2BCl6(B = Ta, W, Mn, Mo, Os, Re, Ru, Ta, Tc) is confirmed showing the presence of conducting characteristics. The dielectric function is large in the near‐ultraviolet region (3.10–4.13 eV). The extinction coefficient of A2BCl6has the ability to work for implementations like Bragg's reflectors, optical and optoelectronic devices. The optical parameters of A2BCl6disclose that the working constructions have an elevated dielectric constant. Analysis of the electronic and optical properties demonstrates that these double‐perovskite materials are suitable for photovoltaic and optoelectronic applications.

High-Directionality Silicon Nitride Antenna Based on Distributed Bragg Reflector for Optical Phased Array

Optical phased arrays (OPAs) have great potential in the fields of integrated solid-state light detection and ranging. The ranging distance of an OPA can be further enlarged by improving the directionality of the grating antenna. A high-directionality silicon nitride grating antenna with a distributed Bragg reflector (DBR) is proposed. The DBR consists of a stack of silicon nitride and silicon dioxide layers, which are utilized as the bottom reflectors to further reduce downward radiation. In a simulation, the directionality of the antenna exceeded 71.6% within the wavelength range of 1420–1740 nm. Additionally, the directionality of the antenna can achieve 97.6% at 1550 nm. Compared to a grating antenna without a DBR, the directionality is improved by 1.52 dB. Moreover, the proposed silicon nitride grating antenna has a large fabrication tolerance and is compatible with CMOS fabrication techniques, showing great potential for enhancing the performance of the integrated optical phased array.

High‐Efficiency Structural Coloration Enabled by Defect‐Free Block Copolymer Self‐Assembly for a Solar Cell Distributed Bragg Reflector

AbstractSolar cell coloration with minimum optical loss is increasingly required for building‐integrated photovoltaics (BIPV) in modern urban areas because of its importance in harmonizing the exterior of zero‐energy buildings and surroundings. A simple strategy for developing a distributed Bragg reflector (DBR) is designated with 1D lamella‐forming polystyrene‐b‐poly(2‐vinylpyridine) (PS‐b‐P2VP) films. An optimized thermal annealing process produces defect‐free lamellar microdomains oriented parallel to the substrate throughout the film. The selective crosslinking in the P2VP block and swelling of these films in a methanol solution with methanesulfonic acid facilitate the formation of highly asymmetric gigantic lamellae, enabling the entire visible‐wavelength spectrum of DBR structural colors. Three representative red (R), green (G), and blue (B) DBR films are produced on a Si solar cell. Coloration from high‐reflectance and narrow‐width DBR films results in vividly colored Si solar cells with a minor or negligible reduction in power conversion efficiency. The approach for photovoltaics, in terms of both the attractive esthetic and technical aspects of BIPV application, offers a viable method for fabricating high‐performance DBR films based on block copolymer self‐assembly.

Flexible GaN-based ultraviolet microdisk lasers on PET substrate.

Flexible optoelectronics is a technique for fabricating optoelectronic devices on a flexible substrate. Compared with conventional devices, flexible optoelectronic devices can be used in more complex working environments benefiting from the mechanical flexibility. Herein, for the first time to the best of our knowledge, a flexible GaN-based microdisk laser on a polyethylene terephthalate (PET) substrate in the ultraviolet A (UVA) range was demonstrated by using thin film transfer process based on laser lift-off (LLO). The lasing wavelength is 370.5 nm with a linewidth of 0.15 nm and a threshold power density of 200 kW/cm2. Additionally, a distributed Bragg reflector (DBR) was deposited on the backside of the microdisk as the bottom mirror between GaN microdisk and PET substrate, which can provide better mode confinement inside the microdisk and increases the oscillation intensity. The lasing wavelength of the flexible laser shows a 2-nm redshift under different bending curvature of the substrate, which is promising for applications such as mechanical sensing.