Bragg Reflector Research Articles

Structural polymorphism, electronic, and optical properties of NaSbS2: A computational approach toward eco-friendly and emerging semiconductor

In this work, the structural polymorphism and electro-optical characteristics of NaSbS2 ternary chalcogenide are realized using density functional theory (DFT). All of the NaSbS2 polymorphs are energetically stable based on the formation energy. The optimized lattice parameters of the monoclinic and triclinic structures and direct electronic bandgap (1.695 eV) of monoclinic structure are consistent with previous studies. Besides, the trigonal and triclinic structures are indirect bandgap (0.916 and 2.015 eV) semiconductors observed from electronic band structure. The higher degree of ionicity between Na and S atoms while strong covalency in the Sb-S bonds are confirmed from the charge and bond analysis. The lower value of electron-hole effective masses indicates higher carrier mobility leading to outstanding electrical conductivity. It was suggested that the polymorphs would be extremely desired to design Bragg reflectors and waveguides based on the reported high value of the real part of the dielectric constant and refractive index. These polymorphs will contribute significantly to being used as absorbers, as evidenced by their high absorption coefficient and photoconductivity and lower transmittance. All the polymorphs reflect significant optical anisotropy and birefringence, rendering them excellent for usage in the fabrication of waveguides, polarizers, and photonic devices. Thus, the projected good features of NaSbS2 polymorphs would play an essential role in the development of lead-free photovoltaic devices, including solar cells and other optoelectronic devices, and would be able to provide practical information for future theoretical and experimental studies.

All-BN distributed Bragg reflectors fabricated in a single MOCVD process

Distributed Bragg Reflectors (DBR) are well-established photonic structures that are used in many photonic applications. However, most of the DBRs are based on different materials or require post-process etching which can hinder integration with other components in the final photonic structure. Here, we demonstrate the fabrication of DBR structures consisting only of undoped boron nitride (BN) layers with high refractive index contrast by using metal–organic chemical vapor deposition (MOCVD). This has been achieved in a single process, without the need for any post-process etching. The difference in the refractive index of the component BN layers stems from different degrees of porosity of the individual BN layers, which is a direct result of a different growth temperature. The fabricated DBR structures consist of 15.5 pairs of BN layers and exhibit a reflectance of 87 ± 1% at the maximum. The wavelength of maximum reflectance can be tuned from 500 nm up to the infrared region (IR), by simply adjusting the growth periods of subsequent BN layers. We also demonstrate that the fabricated structures can be used to create an optical microcavity. The fabricated DBRs are very promising candidates for future applications, for example in combination with single-photon emitters in h-BN, which could allow the building of a cavity-based all-BN single-photon source.

Vertically stacked quantum well diodes for multifunctional applications

Dual-functioning multiple quantum well (MQW) diodes can simultaneously transmit and receive information through visible light. Here, we report vertically stacked red, green, and blue (RGB) MQW diodes for light detection and display applications. Both blue and green MQW diodes are monolithically integrated with distributed Bragg reflector (DBR) filters to realize the separation of light. The versatile RGB MQW transmitter/receiver system not only creates full-color display but also effectively separates RGB light into various colors. These results open feasible routes to generate multifunctional device for the development of full-color display and light receiver.

Multi-Frequency Doppler Velocimetry Based on a Mode-Locked Distributed Bragg Reflector Laser

A differential multi-frequency laser Doppler velocimetry is demonstrated, utilizing the synchronized multimode of a mode-locked distributed Bragg reflector laser. This scheme enables the simultaneous detection of multiple Doppler frequency shifts. Multiple differential Doppler shifts of 0.6 Hz, 1.3 Hz, and 1.9 Hz are obtained, with an average speed of 3.677 mm/s and a standard deviation of 0.122 mm/s, demonstrating a cross-referenced velocity measurement capability. The measurement results are also compared with the dual-frequency laser Doppler velocimetry scheme using electro-optical modulation.

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.

Quasi-TPPs/Fano resonance systems based on an MDM waveguide structure and its sensing application.

In this paper, quasi-Tamm plasmon polaritons (TPPs)/Fano resonance systems based on metal-dielectric-metal (MDM) waveguides are proposed. TPPs are surface electromagnetic modes formed at the interface between a metal and a one-dimensional dielectric photonic crystal (PhC). A metal plasmonic Bragg reflector (PBR) in a MDM waveguide is equivalent to a dielectric PhC, which is realized by periodic MDM waveguide width modulation and leads to the photonic bandgap. By introducing a thin Ag baffle and a PBR in MDM waveguide core, the quasi-TPPs are excited at the interface between the Ag baffle and the PBR, when the phase-matching condition is met. The proposed structure can be fabricated with focused ion beam or electron beam direct-writing lithography, avoiding complex fabrication procedures of manufacturing dielectric PhC by filling the MDM waveguide core with different dielectric materials. Furthermore, an MDM waveguide side-coupled resonator system is constructed to generate Fano resonance by placing a PBR on the side of the MDM waveguide and an Ag baffle in the waveguide core. The Fano resonance originates from the interference between a broad continuum state provided by the Ag baffle and a discrete state provided by quasi-TPPs. The sensing performance of the Fano resonance system is investigated. In this design, the open PBR structure replaces the traditional closed resonant cavity, which makes it more convenient to contact with analytes. The numerical simulations demonstrate that a high sensitivity of 1500nm/RIU and figure of merit value of 4.08×105 are achieved.

High Electromechanical Coupling Coefficient of Longitudinally Excited Shear Wave Resonator Based on Optimized Bragg Structure.

In this work, a longitudinally excited shear-wave resonator (YBAR) based on single-crystalline lithium tantalate (LiTaO3, LT) thin film is proposed. The YBAR has a 200 nm X-cut thin film and molybdenum electrode. A high effective electromechanical coupling coefficient (k2eff) of up to 19% for the suspension-type structure was obtained. Furthermore, a Bragg reflector (SiO2/Pt) with optimized layer thickness ratio was employed to improve the performance of the YBAR. Compared to the acoustic wave resonators with the conventional quarter-wave (λ/4) Bragg reflector, the proposed YBAR with an optimized Bragg reflector can reflect both the longitudinal and shear waves efficiently, and resonators with spurious-free response and high quality (Q) value were achieved. This work provides a potential solution to enabling high coupling micro-acoustic resonators with high Q factor in the 5G/6G communication system.

High-performance SiO2-SiNx distributed Bragg reflectors fabricated by ion-assisted reactive magnetron sputtering

With the rapid improvement of photonics, the demand for high-performance distributed Bragg reflectors (DBRs) is increasing. In this study, high-performance DBRs stacked by silica and high refractive index silicon nitride layers were designed and fabricated, which were deposited by ion-assisted reactive magnetron sputtering. TEM, EDX, and XPS were utilized to investigate the crystal properties, elemental composition, and bonding properties of the films. Additionally, AFM, SEM, and Raman spectra were used to analyze the morphology, roughness, and stress of DBRs. The result shows that the films prepared by ion-assisted reactive magnetron sputtering are mainly amorphous. DBRs have extremely smooth surfaces with a root mean square roughness (Rq) of approximately 0.5 nm. No obvious defects are found in their surface and cross-section. And the residual stresses of DBRs are relatively low. The reflectance results show that the maximum reflectance of 6-pair DBR on the silicon substrate is higher than 99.9%. The stopband bandwidth covers approximately 800–1150 nm. In this work, DBRs deposited by ion-assisted reactive magnetron sputtering feature high deposition quality, thinness, and broadband high reflection, which have great application potential in high-performance optical devices.

Photonic generation of a tunable multi-band linearly frequency-modulated waveform

A photonic-assisted tunable multi-band linearly frequency-modulated (LFM) waveform generator based on optical heterodyne detection is proposed and experimentally demonstrated. The multi-band LFM waveform is generated from a photodetector (PD), where a broadband LFM optical pulse and a multi-wavelength optical signal with the same magnitude at different wavelengths are heterodyne-detected. The LFM optical pulse is generated from a three-electrode distributed Bragg reflector laser diode (DBR-LD). The multi-wavelength optical signal is produced through a Mach-Zehnder modulator (MZM), in which a light wave from an optical fiber laser (OFL) is nonlinearly intensity-modulated by a radio frequency (RF) signal. By tuning the wavelength of the LFM optical pulse lower than that of the multi-wavelength optical signal, a multi-band LFM waveform is generated at the PD. The center frequency of the generated LFM waveform can be adjusted by manipulating the wavelength of the OFL. The versatility in the bandwidth and temporal duration of the LFM waveform is attained through the precise tuning of the LFM optical pulse. The tuning of the center frequency difference between frequency bands is performed by altering the frequency of the RF signal. Experimental results have corroborated the realization of a tunable multi-band LFM waveform generator. The bandwidth and temporal duration of each band and the center frequency difference between frequency bands have tuning ranges from 0.7 to 6.7 GHz, 1 to 50 μs, and 2 to 6.7 GHz, respectively. The demonstration shows new avenues to implement high-performance multi-band LFM waveform generators for applications in multi-functional modern radar systems.

Tunable Tamm plasmon cavity as a scalable biosensing platform for surface enhanced resonance Raman spectroscopy

Surface enhanced Resonance Raman spectroscopy (SERRS) is a powerful technique for enhancing Raman spectra by matching the laser excitation wavelength with the plasmonic resonance and the absorption peak of biomolecules. Here, we propose a tunable Tamm plasmon polariton (TPP) cavity based on a metal on distributed Bragg reflector (DBR) as a scalable sensing platform for SERRS. We develop a gold film-coated ultralow-loss phase change material (Sb2S3) based DBR, which exhibits continuously tunable TPP resonances in the optical wavelengths. We demonstrate SERRS by matching the TPP resonance with the absorption peak of the chromophore molecule at 785 nm wavelength. We use this platform to detect cardiac Troponin I protein (cTnI), a biomarker for early diagnosis of cardiovascular disease, achieving a detection limit of 380 fM. This scalable substrate shows great promise as a next-generation tunable biosensing platform for detecting disease biomarkers in body fluids for routine real-time clinical diagnosis.

Tuning strong coupling towards the deep ultraviolet region realized through Tamm-plasmon exciton-polaritons

Light-matter interactions at the nanoscale have attracted considerable attention due to its features of high optical-field confinement and large electromagnetic-field enhancement. Herein, we theoretically demonstrate strong coupling between Tamm plasmon (TP) and exciton polaritons towards the deep ultraviolet (DUV) region in metal Al/distributed Bragg reflector (DBR)-molecular structures. By adjusting the thickness of the spacer layer and the angle of incident light, the obvious anti-crossing phenomena can be observed with a Rabi splitting of 38.4 meV. Moreover, through varying the period number of the DBR structure, the coupling strength can be effectively manipulated from weak to strong. These findings may extend the operating wavelength of strong coupling to the DUV region, and benefit the development of new-style optical filters.

Research On Etching of Distributed Bragg Reflector

This study investigated the effect of etching process parameters on the sidewall morphology and bottom metal etching damage of Distributed Bragg Reflector (DBR), and analyzed the underlying mechanisms. By comparing the etching morphology under different RF power and pressure conditions, it was found that increasing RF power and reducing pressure can solve the problem of sidewall fracture and obtain a smooth sidewall morphology. By comparing the effect of different process gases on the sidewall angle, it was found that adding O2 can reduce the DBR/Photoresit selectivity and sidewall angle while adding BCl3 can increase the DBR/Photoresit selectivity and sidewall angle. Therefore, the sidewall angle can be adjusted by controlling the type and flow rate of the etching gas. By comparing the DBR/metal selectivity under different RF power, it was found that as the RF power decreases, the DBR/metal selectivity increases, which can prevent metal splashing caused by over-etching of metal. Therefore, in DBR etching, high RF power is used for main etching to obtain a smooth sidewall morphology and the sidewall angle can be adjusted by varying the gas type and flow rate, while low RF power is used for over-etching to improve the DBR/metal selectivity and prevent metal over-etching. This study has reference significance for the development of the inverted chip DBR process.

Monolithic VECSEL for stable kHz linewidth.

Vertical-external-cavity surface-emitting semiconductor lasers (VECSELs) are of increasing interest for applications requiring ultra-coherence and/or low noise at novel wavelengths; performance that is currently achieved via high-Q, air-spaced resonators to achieve long intra-cavity photon lifetimes (for the so-called class-A low noise regime), power scaling and high beam quality. Here, we report on the development of a compact, electronically tunable, monolithic-cavity, class-A VECSEL (monolithic VECSEL) for ultra-narrow free-running linewidths. A multi-quantum-well, resonant periodic gain structure with integrated distributed Bragg reflector (DBR) was optically-bonded to an air-gap-free laser resonator created inside a right-angle fused-silica prism to suppress the influence of environmental noise on the external laser oscillation, thus achieving high stability. Mode-hop-free wavelength tuning is performed via the stabilized temperature; or electronically, and with low latency, via a shear piezo-electric transducer mounted on the top of the prism. The free-running linewidth, estimated via the frequency power spectral density (PSD), is sub-kHz over ms timescales and <1.9 kHz for time sampling as long as 1s, demonstrating at least two orders-of-magnitude improvement in noise performance compared to previously reported single frequency VECSELs. The stable, total internal reflection resonator concept is akin to the prevalent monolithic non-planar ring oscillator (NPRO), however the monolithic VECSEL has several important advantages: tailored emission wavelength (via semiconductor bandgap engineering), no relaxation oscillations, no applied magnetic field, and low requirements on the pump beam quality. This approach is power-scalable in principle and could be applied to VECSELs at any of the wavelengths from the visible to the mid-infrared at which they are already available, to create a range of robust, ultra-coherent laser systems with reduced bulkiness and complexity. This is of particular interest for remote metrology and the translation of quantum technologies, such as optical clocks, from research laboratories into real world applications.

On‐Demand Indistinguishable and Entangled Photons Using Tailored Cavity Designs

AbstractThe biexciton‐exciton emission cascade commonly used in quantum‐dot systems to generate polarization entanglement yields photons with intrinsically limited indistinguishability. In the present work, it focuses on the generation of pairs of photons with high degrees of polarization entanglement and simultaneously high indistinguishability. It achieves this goal by selectively reducing the biexciton lifetime with an optical resonator. It demonstrates that a suitably tailored circular Bragg reflector fulfills the requirements of sufficient selective Purcell enhancement of biexciton emission paired with spectrally broad photon extraction and twofold degenerate optical modes. The in‐depth theoretical study combines (i) the optimization of realistic photonic structures solving Maxwell's equations from which model parameters are extracted as input for (ii) microscopic simulations of quantum‐dot cavity excitation dynamics with full access to photon properties. It reports non‐trivial dependencies on system parameters and use the predictive power of the combined theoretical approach to determine the optimal range of Purcell enhancement that maximizes indistinguishability and entanglement to near unity values, here specifically for the telecom C‐band at 1550 nm.

Thermal management of tungsten by spectrally selective thin film optical filters under laser illumination

Surface temperature management of refractory metals, such as Tungsten, is crucial for their use in high-temperature applications like aerospace, defense, and laser instruments. In this study, distributed Bragg reflectors (DBR) were utilized to reduce the temperature caused by intense laser illumination. To address this problem, we developed a coupled optical and thermal model and investigated multiple factors, including material composition, morphology, architecture, and source-related parameters, such as wavelength. Our results indicate that our DBR coating designs can significantly decrease the temperature of the Tungsten.

Optical characteristics of cavity structures with Al0.2Ga0.8As/Al0.9Ga0.1As distributed Bragg reflectors and In0.37Ga0.63As quantum dots as the active region

Optical characteristics of cavity structures with Al0.2Ga0.8As/Al0.9Ga0.1As distributed Bragg reflectors and In0.37Ga0.63As quantum dots as the active region

Near-infrared tunable Tamm plasmons high-performance hot electron photodetector based on Ag/Ge2Sb2Te5 low Schottky barrier

Hot electron photodetector is a typical hot electron optoelectronic device, which can realize the narrow band photoelectric detection with high tunability and sensitivity. The Tamm plasmons (TPs) based on the planar metal film/distributed Bragg reflector (DBR) has the advantages of simple structure, low manufacturing cost, and high absorption efficiency. A multilayer thin film device structure for high-performance near-infrared hot electron metal-semiconductor-metal photodetectors is proposed. The structure is based on Ag/Ge2Sb2Te5 (GST) Schottky barrier and TPs formed by SiO2/MoS2 DBR. The simulation results of hot electron emission theory show that DBR can effectively extend the absorption spectrum of Ag film and the response spectrum of the device, and enhance the absorption rate of Ag film and the response of the device. The responsivity which is up to 53 mA/W can be obtained by adjusting the structure parameters of the DBR, the thickness of the Ag film, and the GST layer. At the same time, we also propose a digital display system based on the arrangement of crystalline GST and amorphous GST. It provides a new way for the realization of high-performance near-infrared hot electronic devices and is conducive to expanding the application field of hot electronic photodetectors.

Controlled Cavity Length and Wide-Spectrum Lasing in FAMACsPb(BrI)3 Ternary Perovskite Vertical-Cavity Surface-Emitting Lasers with an All-Dielectric Dielectric Bragg Reflector

In this study, we utilized a dielectric Bragg reflector (DBR) as a mirror and positioned a wide-spectrum FAMACsPb(BrI)3 halide perovskite film between two DBRs to construct a vertical-cavity surface-emitting laser (VCSEL) structure. The top and bottom DBRs were connected using optical adhesive, allowing us to control the cavity length by applying external force. Through this approach, we achieved operation at the desired wavelength. Due to the exceptional optical gain provided by FAMACsPb(BrI)3, we successfully observed multimode and lasing phenomena at room temperature under continuous-wave (CW) laser excitation. The outcomes of this study provide valuable insights for the application of novel VCSEL structures and highlight the potential of using FAMACsPb(BrI)3 halide perovskites in optical gain. This work holds significant implications for the fields of optical communication and laser technology.

Exploring the potential of broadband Tamm plasmon resonance for enhanced photodetection.

Tamm plasmon polaritons (TPPs) have emerged as a promising platform for photodetector applications due to their strong light-matter interaction and potential for efficient light absorption. In this work, a design for a broadband photodetector (PD) based on the optical Tamm plasmon (OTS) state generated in a periodic metal-semiconductor-distributed Bragg reflector (DBR) geometry is proposed. The transfer matrix method (TMM) was used to study the propagation of electromagnetic waves through the proposed structure. By exciting the structure with incident light and analyzing the electric field profile within the multilayer structure at the resonant wavelength, we observe a distinctive electric field distribution that indicates the presence of Tamm plasmon modes. A comparative study was conducted to investigate the optical properties of a photodetector in the near-infrared (NIR) range by varying parameters such as thickness. By optimizing the thickness, we successfully achieved a broadband photoresponse in the photodetector, with a maximum responsivity of 21.8mA/W at a wavelength of 1354nm, which falls within the photonic bandgap region. FWHM was found to be 590nm for the responsivity spectrum. The geometry also presents maximum absorption with FWHM calculated to be about 871.5nm. The proposed geometry offers a broadband photoresponse, which is advantageous for the advancement of Tamm-based detector technologies. The ability to detect light over a wide operation range makes this mechanism highly beneficial for various applications.

High-performance gas sensor with symmetry-protected quasi-bound states in the continuum.

A high-performance optical sensor with a vertical cavity structure comprising high-contrast gratings (HCGs) and a distributed Bragg reflector was designed. The structure has two peaks with different mechanisms, among which the first peak is formed by breaking the symmetry of the structure and coupling between the incident wave and the symmetric protection mode. The joint action of the HCG resonance and Fabry-Perot resonance formed a second peak. Moreover, changing the structural parameters, such as the grating width, period, and cavity length, can tune the spectral reflection dips. The sensitivity of the designed structure was as high as 674 nm/RIU, and the corresponding figure of merit was approximately 34741. The presented gas sensor provides a method for applying a vertical cavity structure to the sensing domain.