Bragg Reflector Research Articles

High-β lasing in photonic-defect semiconductor-dielectric hybrid microresonators with embedded InGaAs quantum dots

We report an easy-to-fabricate microcavity design to produce optically pumped high-β quantum dot microlasers. Our cavity concept is based on a buried photonic-defect for tight lateral mode confinement in a quasi-planar microcavity system, which includes an upper dielectric distributed Bragg reflector (DBR) as a promising alternative to conventional III–V semiconductor DBRs. The cavities show distinct emission features with a characteristic photonic-defect size-dependent mode separation and Q-factors up to 17 000. Comprehensive investigations further reveal lasing operation with a systematic increase (decrease) of the β-factor (threshold pump power) with the number of mirror pairs in the upper dielectric DBR. Notably, due to the quasi-planar device geometry, the microlasers show high temperature stability, evidenced by the absence of temperature-induced redshift of emission energy and linewidth broadening typically observed for nano- and microlasers at high excitation powers. The device exhibits remarkable lasing performance, maintaining efficacy even under elevated temperatures of up to 260 K.

Photonic engineering of InP towards homoepitaxial short-wavelength infrared VCSELs

Many emerging opportunities, such as three-dimensional (3D) sensing, biophotonics, and optical data links, call for vertical cavity surface-emitting lasers (VCSELs) that operate in the short-wavelength infrared (SWIR) range. In this paper, we report the use of InP distributed Bragg reflector (DBR) mirrors to overcome an impasse in wafer-level mass production of SWIR VCSELs. The DBRs were based on homoepitaxial InP structures and selectively converted through electrochemistry into quarter-wavelength stack structures of alternating nanoporous (NP) and nonporous InP layers with a record index contrast (Δn∼1.0) and near-unity reflectivity. We demonstrated VCSEL operation at both 1380 and 1550 nm from two separate structures prepared on InP substrates using NP–InP DBRs as the bottom mirror and dielectric DBRs as the top mirror. Room temperature continuous-wave (CW) operation of SWIR VCSELs was successfully achieved at both wavelengths with a threshold current density below 2kA/cm2, greater than milliwatt optical output, and a peak power conversion efficiency of 17%. Our work provides strong evidence that the decades-old challenge, in preparing an InP-compatible, high-performance DBR to support the SWIR-emitting vertical cavity, has been addressed and is poised to enable new applications.

Sub-bandgap optical absorption processes in 300-nm-thick Al1−xInxN alloys grown on a c-plane GaN/sapphire template

We investigate the sub-bandgap optical absorption (SOA) in 300-nm-thick Al1−xInxN alloys used in cladding layers of edge-emitting laser diodes and distributed Bragg reflectors of vertical-cavity surface-emitting lasers. Al1−xInxN alloys, with indium content x ranging from 0.114 to 0.185, were grown by metal-organic chemical vapor deposition on a c-plane GaN/sapphire template. SOAs on 300-nm-thick thin films were characterized using photothermal deflection spectroscopy (PDS). Thermal emission, such as nonradiative recombination with phonon emission, is the dominant energy relaxation process occurring after SOA in Al1−xInxN alloys. The absorption coefficient of the SOA was estimated to be 0.6–7.0 × 103 cm−1 in these samples by combining PDS and spectroscopic ellipsometry. The drastic increase in the SOA, when x exceeded the lattice-matched composition of the GaN/sapphire template, indicates that impurities, vacancy-type defects, and their complexes with increasing x are possible candidates that result in SOA in Al1−xInxN alloys.

Development of the hybrid distributed Bragg reflectors for mid-infrared applications

Development of the hybrid distributed Bragg reflectors for mid-infrared applications

Multiple data streams over a single optical path

Quantum well (QW) diodes have the capability to function as a light-emitting diode or a photodiode and inherently feature a partial emission-detection spectral overlap. Therefore, QW diode can sense light emission from another diode sharing the same QW active region. In association with distributed Bragg reflection (DBR) technique, we here present a wavelength-division multiplexing (WDM) visible light communication (VLC) over a single channel by using vertical assembly of red, green, and blue (RGB) QW diodes. The identical QW diodes separately functioning as a transmitter and a receiver establish a wireless communications link. The DBRs enable the transmission of longer-wavelength photons or the reflection of shorter-wavelength photons, creating an optical bandpass filter in conjunction with emission-detection spectral overlap, effectively boosting the capacity of an initially single communication channel. Both the transmitter and the receiver can be switched freely by software, forming time-division multiplexing (TDM) wireless light communication system using single optical path. We unite TDM and WDM together to demonstrate real-time TDM multichannel bidirectional communication using the vertical integration of RGB QW diodes, offering the great potential to establish TDM-WDM VLC.

Highly sensitive SERS platform using sub-10-nm Ag nanoparticles on GaN distributed Bragg reflector for detecting organic pollutants

Surface-enhanced Raman scattering (SERS) is crucial for the development of advanced detection technology and achieving high-sensitivity optical signals. Sub-10 nm noble metal nanostructures with high specific surface area and good catalytic activity are suitable for in-situ SERS analysis, while their SERS performance is inferior compared to larger noble metal nanoparticles with sizes of tens of nm. In this study, the weak SERS signals from sub-10 nm Ag nanoparticles (NPs) are greatly enhanced by developing a highly reflective multi-component system, in which monodisperse sub-10 nm Ag NPs are deposited onto a GaN-based distributed Bragg reflector (DBR). This Ag-NP/GaN DBR system exhibits remarkable SERS enhancement, approximately two orders of magnitude. This enhancement effect is further confirmed by SERS mapping over an area of 50 × 50 µm2. Moreover, the Ag-NP/GaN DBR system enables the in-situ monitoring of catalytic reaction processes of R6G and 4-NBT molecules, indicating high analytical sensitivity. To demonstrate practical applications, this Ag-NP/GaN DBR system is exploited to detect the toxic malachite green molecules and polyethylene microplastics, which show strong fingerprint signals. This work provides an effective solution to boost the weak SERS signals of sub-10 nm Ag NPs and paves the way towards practical applications.

Theoretical analysis of bulk acoustic wave resonators with emerging ε -Ga2O3 piezoelectric film

In this paper, the theoretical analysis of 2.3 GHz bulk acoustic wave (BAW) resonators with emerging ε-Ga2O3 piezoelectric films was investigated. By using the finite element method to calculate the dispersion curve of the BAW resonator based on ε-Ga2O3, we designed and optimized the Bragg reflector structure as well as the metal frame to suppress transverse energy leakage. When the width of the raised metal frame is an odd multiple of the quarter wavelength of the S1 Lamb mode, the vibration displacement at the boundary of the resonators is significantly suppressed, and the acoustic energy is concentrated as much as possible in the effective area of the resonators, resulting in improvement of the Qp and Qmax. Therefore, the ε-Ga2O3 based BAW resonators with Bode Qmax (∼1488), electromechanical coupling coefficient k2eff (∼15%), and the figure of merit (FoM) coefficient (∼223) are simulated and designed. Detailed theoretical analysis provides the key theoretical guidance and design scheme for the realization of ε-Ga2O3 BAW filters. The above-mentioned results imply that the emerging ε-Ga2O3 piezoelectric semiconductors have application prospects in BAW resonators and radio frequency front-end fields.

Enhanced photonic spin Hall effect and its sensing application via optical Tamm state based on nanocomposites

In this contribution, by combining the nanocomposite with distributed Bragg reflector, a simple multilayer structure to enhance the photonic spin Hall effect (PSHE) via optical Tamm state (OTS) for both horizontal (H) and vertical (V) polarized lights is presented. The structural parameters of nanocomposite layer (e.g., thickness and filling factor) have a significant influence on PSHE. The maximal spin shifts of 16.2 and 17.8 μm can be achieved for H and V polarized lights, respectively, which are attributed to strong excitation of OTS. Moreover, the spin shift is extremely sensitive to the refractive index changes of sensing medium, and a gas sensor with superior sensing performance is theoretically proposed for both H and V polarized beams. These findings provide an effective method to enhance the PSHE for both H and V polarized lights and therefore open an opportunity for developing PSHE refractive index sensors.

AlGaAs photocathode with enhanced response at 532 nm

The AlGaAs photocathode can be used in the field of underwater optical communication because of its fast response speed and adjustable spectral response range. In order to solve the problem that the low light absorption of the AlGaAs emission layer limits the improvement of its quantum efficiency, the distributed Bragg reflector (DBR) structure is used to reflect the light at a specific wavelength back to the emission layer to further increase the absorption rate, thus improving the response capability of the photocathode at 532 nm. The spectral response model of the AlGaAs photocathode with DBR structure is obtained by solving one-dimensional continuity equation. The optical model of the AlGaAs photocathode with enhanced response at 532 nm is established by the finite-difference time-domain method. The effects of the sublayer periodic pairs, the sublayer material and the thickness of emission layer and buffer layer on the absorption rate of emission layer are analyzed. The light absorption distributions of AlGaAs photocathode with and without DBR structure are compared, and the influence mechanism of DBR structure on the blue-green light absorption capacity of AlGaAs photocathode emission layer is clarified, which can provide a theoretical basis for designing its structural parameters. The results show that the DBR structure with a periodic pair of 20 and Al<sub>0.7</sub>Ga<sub>0.3</sub>As/AlAs has the best reflection effect on 532 nm light. Based on the DBR structure, when the thickness of the emission layer and buffer layer are 495 nm and 50 nm, respectively, the emission layer has the best absorption rate of 532 nm light. Furthermore, two kinds of AlGaAs photocathodes with and without DBR structure are prepared by the metal-organic chemical vapor deposition technology, and the reflectivity and profile structure of the grown samples are characterized. Then the Cs/O activation experiments are performed to compare the spectral response curves. It is found that the spectral response of the AlGaAs photocathode sample with DBR structure at 532 nm wavelength is about twice that of the sample without DBR structure.

A synergetic enhancement strategy of light utilization and carrier transfer for UV photodetection associated with artificial resonance nano-cavities

Light confinement can be significantly boosted with the artificial resonance nano-cavities between MXene nanosheets and distributed Bragg reflectors. The carrier separation and transfer processes are simultaneously enhanced by the construction of the electron pathway with those nanosheets.

Photonic crystal gas sensors based on metal-organic frameworks and polymers.

A photonic crystal (PC) is an optical microstructure with an adjustable dielectric constant. The PC sensor was deemed a powerful tool for gas molecule detection due to its excellent sensitivity, stability, online use and tailorable optical performance. The detection signals are generated by monitoring the changes of the photonic band gap when the sensing behavior occurs. Recently, many efforts have been devoted to improving the PC sensor's detection performance and reducing technical costs by selecting and refining functional materials. In this case, metal-organic frameworks (MOFs) with a large specific surface, tunable structural properties and polymers with unique swelling properties have attracted increasingly attention. In this review, a systematic review of PC gas sensors based on MOFs and polymers was carried out for the first time. Firstly, the optical properties and gas sensing mechanism of PCs were briefly summarized. Secondly, a detailed discussion of the structural properties and rapid preparation methods of distributed Bragg reflectors (DBRs), opals and inverse opals (IOPCs) was presented. Thirdly, the recent advances in MOF, polymer and MOF/polymer-based PC sensors over the past few years were summarized. It should be noted that the sensitivity and selectivity enhancement strategy by appropriate material species selection, organic ligand functionalization, metal-ion doping, diverse functional material arrays, and multi-component compounding were analyzed in detail. Finally, prospects on PC gas sensors are given in terms of preparation methods, material functionalization and future applications.

Intracavity frequency-doubled external-cavity surface-emitting blue laser with high conversion efficiency

Blue laser with high power and high beam quality has many applications such as in laser display, underwater communication and imaging, and non-ferrous metal processing. Optically pumped external-cavity surface-emitting laser combines the advantages of both surface-emitting semiconductor lasers and solid-state disk lasers, and can produce high output power and good beam quality simultaneously. Its high intracavity circulating power is more conducive to intracavity frequency doubling, achieving high-power and high beam quality blue light through fundamental laser in the near-infrared waveband. This paper reports an efficient intracavity frequency doubled 490 nm high power blue light by using a 980 nm fundamental laser in an external-cavity surface-emitting laser. The V-type resonant cavity is formed by the high reflectivity distributed Bragg reflector (DBR) at the bottom of gain chip, a folded flat concave mirror (high reflectivity coated for 980 nm and anti-reflectivity coated for 490 nm), and a flat concave end mirror (high reflectivity coated for 980 nm and 490 nm). By inserting a nonlinear crystal LBO into the cavity at the beam waist formed by the folded mirror and end mirror, and employing a birefringent filter (BRF) to polarize the fundamental laser and narrow the linewidth of the laser, a high power and high beam quality blue laser with high conversion efficiency is obtained. The effects of different factors including the length of nonlinear crystal, the linewidth of fundamental laser, and the compensation of walk off angle on the output power of the blue laser are studied experimentally. The length of the nonlinear crystal is optimized based on the size of the fundamental laser beam waist at the position of the crystal in the resonant cavity. Under the type-I phase matching condition of LBO, over 6 W output power at 491 nm wavelength is obtained when the crystal length is 5 mm and the BRF thickness is 1 mm. The beam quality <i>M</i><sup>2</sup> factor in the <i>x</i> direction and the <i>y</i> direction are both 1.08, and the conversion efficiency of frequency doubling is 63%. The experimental results also show that symmetrically placed nonlinear crystals can compensate for the walk-off angle during frequency doubling to a certain extent, thereby clearly improving the conversion efficiency of the frequency doubled blue laser.

Tunable ultraviolet laser based on intracavity third harmonic generation of external cavity surface emitting laser

Ultraviolet laser has high frequency, short wavelength, large single-photon energy, and high spatial resolution, and has wide applications in many fields such as fine processing, life sciences, and spectroscopy. In this work, a wavelength tunable ultraviolet laser based on intracavity third harmonic generation from an external-cavity surface-emitting laser is reported. The W-type resonant cavity of the laser is composed of a distributed Bragg reflector (DBR) at the bottom of the gain chip, three plane-concave mirrors, and a rear plane mirror. On the arm containing the gain chip, a birefringent filter is inserted at the Brewster angle as the polarization and wavelength tuning element, which can also narrow the linewidth of the fundamental laser to a certain extent. A type-I phase-matched LBO crystal is placed on the beam waist between the folding mirrors M2 and M3 to convert the 980 nm fundamental laser into 490 nm blue light, and a type-I phase-matched BBO crystal is inserted in the beam waist near the rear mirror to produce a 327 nm ultraviolet output from the remained 980 nm fundamental laser and the frequency-doubled 490 nm second harmonic. Before the BBO crystal, a half-wave plate at 980 nm is employed to change the polarization of the fundamental laser, so as to meet the type-I phase-matching condition of the used BBO crystal. Owing to the larger nonlinear coefficient of the type-I phase-matched BBO crystal, and its obviously higher transmittance at 327 nm wavelength than the usually used LBO crystal, the output power is obtained to be 538 mW at 327 nm ultraviolet wavelength, corresponding to a conversion efficiency of 1.1% from pump light to ultraviolet laser. The experiment is performed under conditions of 15 ℃ temperature, 47 W absorbed pump power, 5 mm-length LBO and 5 mm-length BBO crystals. By using a 2 mm-thick birefringent filter as the tuning element, 34.1 nm tuning range of the 980 nm fundamental laser, 14.3 nm tuning range of the 490 nm second harmonic, and 8.6 nm tuning range of the 327 nm third harmonic are obtained. The ultraviolet laser exhibits good beam quality as well as acceptable power stability with the maximum power fluctuation less than 2% within 4.5 h.

All-plastics distributed Bragg reflectors for sensing and thermal shielding applications

Year by year, the importance of plastic nanostructures in photonics is increasing. Indeed, polymers represent an interesting alternative to more traditional metal oxides, being easily processable and allowing for light, free-standing and flexible structures. In the field of energy efficiency and sustainability, we bring in two positive examples of the use of plastic photonic crystals: sensing and thermal shielding. In sensing they allow for easy detection of analytes, such as the byproducts of food degradation; a colour change identifies the spoilage, with possible application of these plastic sensors in smart packaging applications. On the other hand, they can be of interest for thermal shielding applications. Indeed, they can be engineered as thin, transparent films able to reduce indoor heating by sunlight and in turn the energy consumption related to the use of air conditioning.

Over 300 mW Single-frequency Distributed Bragg Reflector Fiber Laser at 2.04 μm Based on Tm:YAG/Ho:YAG Co-derived Silica Fiber

Over 300 mW Single-frequency Distributed Bragg Reflector Fiber Laser at 2.04 μm Based on Tm:YAG/Ho:YAG Co-derived Silica Fiber

Enhanced DBR mirror design via D3QN: A reinforcement learning approach.

Modern optical systems are important components of contemporary electronics and communication technologies, and the design of new systems has led to many innovative breakthroughs. This paper introduces a novel application based on deep reinforcement learning, D3QN, which is a combination of the Dueling Architecture and Double Q-Network methods, to design distributed Bragg reflectors (DBRs). Traditional design methods are based on time-consuming iterative simulations, whereas D3QN is designed to optimize the multilayer structure of DBRs. This approach enabled the reflectance performance and compactness of the DBRs to be improved. The reflectance of the DBRs designed using D3QN is 20.5% higher compared to designs derived from the transfer matrix method (TMM), and these DBRs are 61.2% smaller in terms of their size. These advancements suggest that deep reinforcement learning, specifically the D3QN methodology, is a promising new method for optical design and is more efficient than traditional techniques. Future research possibilities include expansion to 2D and 3D design structures, where increased design complexities could likely be addressed using D3QN or similar innovative solutions.

Transmission enhancement effect of distributed Bragg reflector structure covered with metal grating

In order to observe the extraordinary optical transmission (EOT) through a metal gratings, induced by Tamm plasmon polaritons (TPPs), a layered structure consisting of a distributed Bragg reflector covered with a one-dimensional metal grating is proposed in this work. When an incident light wave passes through DBR regime and impinges on the DBR-metal interface normally, the generation of TPPs and the resulting highly localized energy on the metal-DBR interface are simulated in detail by the finite element method. As a result, the surface plasmon polariton (SPPs) modes accommodated inside the slits of metal gratings can be excited more effectively by the enhanced electromagnetic field associated with TPPs located on the interface. Furthermore, the enhanced transmission of incident light waves in the structure can be achieved when the SPP mode inside the grating slits satisfies the Fabry-Perot (FP)-like resonance condition, which reveals that the EOT in this structure comes from a TPPs-FP hybrid resonance. This inference can be confirmed by the relationships between the central wavelength and the grating height for the two transmission peaks, and the magnetic field modal profiles associated with the two peaks. Quantitative effects of the slit width and duty cycle on the transmission peak of the metal grating are analyzed numerically, and the results demonstrate that when the period is determined, as the slits width increases, the two peak transmittances first increase and then decrease. On the other hand, when the slit widths are chosen to be 40 nm, 50 nm, and 60 nm respectively, the peak transmittance first increases and then decreases with the duty cycle increasing. Meanwhile, it is found that the center wavelengths of the transmission peaks are related to the duty cycle in a nearly linear manner for three slit widths, which can be used to flexibly adjust the center wavelength of extraordinary optical transmission.

Investigating the Spectral Response of Fiber Bragg Grating for Strain Sensor Applications

Abstract: The optical fibre sensor (OFS) has become quite well-known and prominent in the sensor technology industry. It is often used to react to outputs from other systems, like those in industrial, monitoring, and chemical analysis applications, and to detect changes in the environment. A Bragg reflector starts to grow and transmit all other wavelengths while a short section of optical fibre with a specific wavelength is reflected with light in a device called a Fibre Bragg Grating. The current study focuses on the evolving characteristics and behaviours of strain and temperature sensors operating on Fibre Bragg Gratings (FBG) through software modelling. This work's primary goal is to investigate the characteristics and behaviour of strain sensor that are used with fibre bragg gratings. A strain sensor can be used to determine the strain in an object whose resistance changes when force is applied.

Investigating The Spectral Response of Fiber Bragg Grating (FBG) for Temperature Sensor Applications

Abstract: In the field of sensor technology, the optical fibre sensor (OFS) has gained a lot of notoriety and prominence. It is frequently utilised to detect changes in the environment and react to outputs from other systems, such as those used in chemical analysis, industrial, and monitoring applications. A Fibre Bragg Grating (FBG) is a type of device in which a brief segment of optical fibre with a particular wavelength is reflected with light, while the Bragg reflector begins to grow and transmit all other wavelengths. The developing features and behaviours of temperature and strain sensors working on Fibre Bragg Grating using computer modelling are the focus of the current project. The main objective of this work is to examine the behaviour and properties of temperature sensors operating on Fibre Bragg Grating. The temperature sensor is utilised to measure and identify any temperature anomalies operating on the Fibre Bragg Grating that may cause mishaps or fires. This will reveal how temperature sensors may be demonstrated using Fibre Bragg Grating.

Design and Simulation of InGaN-Based Red Vertical-Cavity Surface-Emitting Lasers.

We propose a highly polarized vertical-cavity surface-emitting laser (VCSEL) consisting of staggered InGaN multiple quantum wells (MQWs), with the resonance cavity and polarization enabled by a bottom nanoporous (NP) n-GaN distributed Bragg reflectors (DBRs), and top TiO2 high-index contrast gratings (HCGs). Optoelectronic simulations of the 612 nm VCSEL were systematically and numerically investigated. First, we investigated the influences of the NP DBR and HCG geometries on the optical reflectivity. Our results indicate that when there are more than 17 pairs of NP GaN DBRs with 60% air voids, the reflectance can be higher than 99.7%. Furthermore, the zeroth-order reflectivity decreases rapidly when the HCG's period exceeds 518 nm. The optimal ratios of width-to-period (52.86 ± 1.5%) and height-to-period (35.35 ± 0.14%) were identified. The staggered MQW design also resulted in a relatively small blue shift of 5.44 nm in the emission wavelength under a high driving current. Lastly, we investigated the cavity mode wavelength and optical threshold gain of the VCSEL with a finite size of HCG. A large threshold gain difference of approximately 67.4-74% between the 0th and 1st order transverse modes can be obtained. The simulation results in this work provide a guideline for designing red VCSELs with high brightness and efficiency.