Distributed Bragg Reflector Cavity Research Articles

Phase change material metasurface loading enables an ultrafast all-optically switchable, compact, narrowband freespace optical filter

Active metasurfaces leveraging phase change materials (PCMs) remain a subject of intense investigation, owing to their inherent tunable properties and successful integration into integrated photonics. By harnessing the ultra-compact form factor of optical metasurfaces, further advancements in switching speeds and reduction in switching energies have the potential to revolutionize applications in free space optical communication, optical signal processing, neuromorphic photonics, quantum photonics, and compact LiDAR. In this context, an ultrafast all-optically switchable narrowband spectral filter employing a distributed Bragg reflector cavity loaded with a PCM-metasurface is proposed. The work involves a comprehensive numerical exploration of its optical properties, encompassing design optimization and anticipating limits in switching speeds and energy requirements. Specifically, focusing on a GST225 metasurface operating in the shortwave-infrared spectrum, the numerical investigations reveal the potential to achieve transmission contrast levels as high as 24 dB, accompanied by Q-factors up to a thousand and less than 1 dB insertion loss. This performance notably outperforms recently reported free-standing PCM metasurfaces and cavities loaded with unstructured PCM thin films. Furthermore, the study predicts full-cycle reconfigurability (transitioning from amorphous to crystalline states and vice versa) with anticipated switching speeds of 91 & 200 MHz and switching fluence of 0.655 & 0.616 mJ/cm2 per cycle for the RESET and SET processes respectively. This investigation holds promise for advancing the state-of-the-art performance of PCM-based metasurfaces.

Compact high-Q Ka-band sapphire distributed Bragg resonator

In a class of high quality (Q-) factor dielectric resonators with low radiative losses, including popular whispering-gallery mode (WGM) resonators with high azimuthal mode numbers, due to high confinement of modal field in dielectric, the Q-factor is limited by the value of inverse dielectric loss tangent of dielectric material. Metal enclosures necessary for device integration only marginally affect the Q-factor while eliminating the residual radiative loss and allowing the optimization of input and output coupling. While very high Q-factors ∼200000 are available in sapphire WGM resonators in X-band, at millimeter wave frequencies increasing dielectric loss limits the Q-factor to much smaller values, e.g. ∼50000 and ∼25000 for quasi-TE and quasi-TM modes, correspondingly, at 36 GHz. The use of distributed Bragg reflection (DBR) principle allows to push modal energy outside dielectric while also isolating it from Joule losses in metallic enclosure walls. Very high Q∼600000>tgδ has been demonstrated in X-band [C. A. Flory and R. C. Taber, IEEE Trans. Ultrason., Ferroelectr., Freq. Control 44, 486–495 (1997).] at the expense of impractically large dimensions. In this work, we report on the assembly and testing of a compact Ka-band sapphire distributed Bragg reflector cavity characterized with Q-factor seven times larger than one predicted by the material’s dielectric loss at the frequency of interest. An intrinsic Q-factor of ∼200000 is demonstrated at 36 GHz for the lowest order TM-mode of a sapphire DBR. The resonator has 50 cm3 volume, smaller than previously demonstrated DBRs.

Tunable multiband THz perfect absorber due to the strong coupling of distributed Bragg reflector cavity mode and Tamm plasma polaritons modes based on MoS2 and graphene

In this work, we propose a multiband terahertz perfect absorber by combining a distributed Bragg reflector (DBR) cavity with molybdenum disulfide (MoS2) and graphene. The absorption peak comes from the strong coupling of the DBR cavity mode and the two Tamm plasma polaritons (TPPs) modes. Our numerical simulations demonstrate that the degree of coupling in this hybrid system is tunable by adjusting the structural parameters, thereby allowing for control over the position and intensity of the absorption peaks. Furthermore, utilizing the tunable Fermi energy level of graphene and controlled variation of the molybdenum disulfide carrier concentration enables active switching between absorption-free, dual-band, and triple-band absorption. Additionally, the high absorption efficiency in a wide angular range and sensitivity make this device highly versatile. The coupled harmonic oscillator model is used to explain the strong coupling phenomena of the system. This simple layered structure provides a hybrid coupling system with a controlled number of bands suitable for potential active terahertz optoelectronic devices.

Dual-HR-FBG based single-frequency fiber laser at 1030 nm

We demonstrate a single-frequency fiber laser operating at 1030 nm with a distributed Bragg reflector cavity consisting of two high-reflectivity fiber Bragg gratings (HR-FBGs). By proper thermal adjustment, the gain bandwidth of the fiber laser is significantly compressed through the spectral overlap near the edges of the reflection band of two HR-FBGs, and the single-longitudinal-mode lasing is achieved. The effective cavity length of the fiber laser with the proposed cavity configuration is calculated, and its variation with the temperature difference between two HR-FBGs is also verified through the observation of the relaxation oscillation frequency shift. The measured laser linewidth is about 4.45 kHz at a temperature difference of 48.2 °C. The single-frequency output power of 14.4 mW is achieved at a pump power of 540 mW.

Hybrid silicon-tellurium-dioxide DBR resonators coated in PMMA for biological sensing.

We report on silicon waveguide distributed Bragg reflector (DBR) cavities hybridized with a tellurium dioxide (TeO2) cladding and coated in plasma functionalized poly (methyl methacrylate) (PMMA) for label free biological sensors. We describe the device structure and fabrication steps, including reactive sputtering of TeO2 and spin coating and plasma functionalization of PMMA on foundry processed Si chips, as well as the characterization of two DBR designs via thermal, water, and bovine serum albumin (BSA) protein sensing. Plasma treatment on the PMMA films was shown to decrease the water droplet contact angle from ∼70 to ∼35°, increasing hydrophilicity for liquid sensing, while adding functional groups on the surface of the sensors intended to assist with immobilization of BSA molecules. Thermal, water and protein sensing were demonstrated on two DBR designs, including waveguide-connected sidewall (SW) and waveguide-adjacent multi-piece (MP) gratings. Limits of detection of 60 and 300 × 10-4 RIU were measured via water sensing, and thermal sensitivities of 0.11 and 0.13 nm/°C were measured from 25-50 °C for SW and MP DBR cavities, respectively. Plasma treatment was shown to enable protein immobilization and sensing of BSA molecules at a concentration of 2 µg/mL diluted in phosphate buffered saline, demonstrating a ∼1.6 nm resonance shift and subsequent full recovery to baseline after stripping the proteins with sodium dodecyl sulfate for a MP DBR device. These results are a promising step towards active and laser-based sensors using rare-earth-doped TeO2 in silicon photonic circuits, which can be subsequently coated in PMMA and functionalized via plasma treatment for label free biological sensing.

Independent Tuning of Exciton and Photon Energies in an Exciton–Polariton Condensate by Proton Implantation‐Induced Interdiffusion

AbstractThe use of high energy proton implantation is demonstrated to precisely and independently shift the energies of both exciton and photon components of GaAs microcavity exciton–polaritons. The technique applies post‐growth proton implantation and annealing steps in order to create a small local interdiffusion across either the quantum well–barrier material interfaces, or between the layers of the cavity distributed Bragg reflector mirrors to induce energy shifts to the exciton or photon components, respectively. The polariton mode is tunable by an energy exceeding 10 meV with a corresponding increase (decrease) in effective mass for photon (exciton) energy shifts, while maintaining narrow‐linewidth polariton photoemission and condensation for both photonic and excitonic polaritons. This technique uniquely enables new opportunities to explore coherent polariton matter with narrow‐linewidth and heavy masses in tight‐binding, non‐Hermitian, and topological landscapes with sub‐µm feature‐sizes, while also being a simple post‐growth process.

Triple-wavelength laser from a femtosecond laser directly-written fiber cavity for microwave generation.

We report an all-fiber triple-wavelength single-frequency distributed Bragg reflector (DBR) laser for 1-10 GHz microwave (MW) generation. The DBR cavity contains a non-polarization-maintaining Er fiber and a pair of fiber Bragg gratings (FBGs) made using a femtosecond laser line-by-line (LbL) direct-writing method. Such a configuration combining a short cavity and radial asymmetry leads to frequency locking and phase controlling of multi-wavelength fiber lasers. A 1.59-µm triple-wavelength laser with high coherence, spectrum purity, and polarization purity has been demonstrated; 3-6 GHz triple-frequency MW was generated.

Regulative control and enhancement of multi-color upconversion luminescence with DBR cavities

Upconversion luminescence (UCL) of lanthanide-doped materials (e.g. NaYF4:Yb3+/Er3+) involves multi-step, multi-channel transitions (corresponding to multi-color emissions) in a multi-level system, and is a low-efficiency nonlinear process. Usually, the UCL is enhanced by local enhancement of the excited field or one of its multi-color emissions is promoted by matching with a resonance cavity mode based on Purcell effect. Here, we propose to regulatively control and enhance the UCL by fostering one color of the UCL emissions with a resonance mode and inhibiting the other with an anti-resonance or nonresonance mode in forbidden band in an optical cavity, so that excited-state ions (e.g. Er3+) transit to the ground state more via the fostered UCL emission channel, rather than the inhibited one. As such, high-contrast single-color UCL emission can be achieved with an enhancement beyond that of Purcell effect. For the purpose, superior mode properties of distributed Bragg reflector (DBR) cavities can be applied, whose forbidden band of the DBR layers and resonance cavity mode in the forbidden band can be independently tuned in positions to match with the UCL emissions for them to be inhibited and fostered respectively. In experimental implementation, multi-color UCL (e.g. red and green) of NaYF4:Yb3+/Er3+ nanoparticles embedded in such DBR cavities are studied. And high-contrast single-color UCL emissions are demonstrated with enhancements factors beyond Purcell factors calculated in numerical simulations. A hypothesis on modifications of intermediate transitions in the UCL processes, as feedbacks to influences of mode characteristics in the DBR cavities for regulative control, is also proposed to explain the phenomena. The work suggests a way to regulatively control multi-channel photon emissions in multi-level systems for enhanced single-channel photon emission.

Single- and Twin-Photons Emitted from Fiber-Coupled Quantum Dots in a Distributed Bragg Reflector Cavity.

In this work, we develop single-mode fiber devices of an InAs/GaAs quantum dot (QD) by bonding a fiber array with large smooth facet, small core, and small numerical aperture to QDs in a distributed Bragg reflector planar cavity with vertical light extraction that prove mode overlap and efficient output for plug-and-play stable use and extensive study. Modulated Si doping as electron reservoir builds electric field and level tunnel coupling to reduce fine-structure splitting (FSS) and populate dominant XX and higher excitons XX+ and XXX. Epoxy package thermal stress induces light hole (lh) with various behaviors related to the donor field: lh h1 confined with more anisotropy shows an additional XZ line (its space to the traditional X lines reflects the field intensity) and larger FSS; lh h2 delocalized to wetting layer shows a fast h2–h1 decay; lh h2 confined shows D3h symmetric higher excitons with slow h2–h1 decay and more confined h1 to raise h1–h1 Coulomb interaction.

Symmetric Excitons in an (001)-Based InAs/GaAs Quantum Dot Near Si Dopant for Photon-Pair Entanglement

The sacrificed-QD-layer method can well control the indium deposition amount to grow InAs quantum dots (QDs) with isotropic geometry. Individual Si dopant above an (001)-based InAs QD proves a new method to build a local electric field to reduce fine structure splitting (FSS = X1−X2) and show D3h symmetric excitons. The lowest FSS obtained is 3.9 μeV with the lowest energy X state (LX) anticlockwise rotate from [1–10] (i.e., zero FSS will be crossed in a proper field). The lateral field projection induces a large eh separation and various FSS, LX, and emission intensity polarization. The lateral field along [1–10] breaks the X1–X2 wavefunction degeneracy for independent HH and VV cascade emissions with robust polarization correlation. With FSS ~4 μeV and T1 ~0.3 ns fastened in a distributed Bragg reflector cavity, polarization-resolved XX–X cross-correlations show fidelity ~0.55 to a maximal entangled state |HH> + |VV>. A higher fidelity and zero FSS will be obtained in the hybrid QD structure with a junction field integrated to tune the FSS and a sub-bandgap excitation to avoid influences from electrons in the barrier.

Diode-pumped 1.15 W linearly polarized single-frequency Yb3+-doped phosphate fiber laser.

Compact and robust high-power single-frequency laser oscillators are in great demand for some specific applications where narrow-linewidth lasers with extremely low noise are required. In this paper, we report a single-mode-diode-pumped watt-level single-frequency Yb3+-doped phosphate fiber laser at 1050 nm based on an all-fiber distributed Bragg reflector cavity. A maximum output power of 1.15 W with a slope efficiency of 66% was achieved with 18-mm-long 8 wt.% Yb3+-doped phosphate fiber. Stable, single-longitudinal-mode lasing with a spectral linewidth of 9.6 kHz and polarization extinction ratio of ∼30 dB was obtained.

Surface-acoustic-wave-controlled optomechanically induced transparency in a hybrid piezo-optomechanical planar distributed Bragg-reflector-cavity system

We propose a scheme that can generate tunable optomechanically induced transparency in a hybrid piezooptomechanical cavity system. The system is composed of a high-quality planar distributed Bragg reflector cavity modified with an embedded Gaussian-shaped defect. Moreover, interdigitated transducers are fabricated on the surface of the cavity to generate surface acoustic waves. Under the actuation of the surface acoustic wave, the upper Bragg mirrors can be vibrated as a bulk acoustic resonator, and the distributed Bragg reflector cavity becomes a standard three-level optomechanical system. In this situation, we show that when a strong pump optical field and a weak probe optical field are simultaneously applied to the hybrid optomechanical cavity system, optomechanically induced transparency occurs under the quantum interference between different energy-level pathways. Our scheme can be applied in the fields of optical switches and quantum information processing in solid-state quantum systems.

Design of resonant cavity thin film structures with complex active layers

A systematic approach to designing resonant cavity distributed Bragg reflector (DBR) structures with complex-index active regions is developed in this paper. The technique is based on the effective reflectance index of multilayer thin films. While the design of DBR structures with real refractive index films is quite straightforward, the use of a complex refractive index in the cavity requires a different approach. In this paper, we show that a complex active region requires an asymmetric reflector geometry along with a separate phase compensator. This technique is illustrated using phase change materials and metals in the resonant cavity.

Tuning of the polariton modes induced by longitudinal strong coupling in the graphene hybridized DBR cavity.

In this Letter, we construct a graphene hybridized distributed Bragg reflector (DBR) cavity, where spatially longitudinal strong coupling occurs between the Tamm plasmon polaritons (TPPs) existing around the graphene layer and the cavity mode (CM) existing in the DBR cavity. As a result, two hybrid polariton modes emerge, which contain both the TPP and the CM components. In the simulation, we demonstrate that the resonant frequencies and the damping rates of the polariton modes can be actively tuned by the graphene Fermi level and the incident angle of light. Besides, the coupling strength and the damping rates are also passively tuned by the pair number of the layers in the DBR. Theoretically, we analyze the TPP-CM strong coupling by the coupled harmonic oscillator equations, which help to explain the regulation process. The controllable TPP-CM longitudinal strong coupling with two absorption bands may achieve potential applications in developing graphene-based active optoelectronic and polaritonic devices in terahertz waves.

Enhancement of acoustic spin pumping by acoustic distributed Bragg reflector cavity

Surface acoustic waves (SAWs) in the GHz frequency range can inject spin currents dynamically into adjacent non-magnetic layers via the spin pumping effect associated with ferromagnetic resonance. Here, we demonstrate an enhancement of acoustic ferromagnetic resonance and spin current generation by a pair of SAW reflector gratings, which form an acoustic analog of the distributed Bragg reflector cavity. In the experiment, we confirmed 2.04 ± 0.02 times larger SAW power absorption in a device with cavity than in the case of no acoustic cavity. We confirmed up to 2.96 ± 0.02 times larger spin current generation by measuring electric voltages generated by the inverse Edelstein effect at the interface between Cu and Bi2O3. The results suggest that acoustic cavities would be useful to enhance the conversion efficiency in SAW driven coupled magnon–phonon dynamics.

Tamm plasmons in metal/nanoporous GaN distributed Bragg reflector cavities for active and passive optoelectronics.

We theoretically and experimentally investigate Tamm plasmon (TP) modes in a metal/semiconductor distributed Bragg reflector (DBR) interface. A thin Ag (silver) layer with a thickness (55 nm from simulation) that is optimized to guarantee a low reflectivity at the resonance was deposited on nanoporous GaN DBRs fabricated using electrochemical (EC) etching on freestanding semipolar (2021¯) GaN substrates. The reflectivity spectra of the DBRs are compared before and after the Ag deposition and with that of a blanket Ag layer deposited on GaN. The experimental results indicate the presence of a TP mode at ∼ 454 nm on the structure after the Ag deposition, which is also supported by theoretical calculations using a transfer-matrix algorithm. The results from mode dispersion with energy-momentum reflectance spectroscopy measurements also support the presence of a TP mode at the metal-nanoporous GaN DBR interface. An active medium can also be accommodated within the mode for optoelectronics and photonics. Moreover, the simulation results predict a sensitivity of the TP mode wavelength to the ambient (∼ 4-7 nm shift when changing the ambient within the pores from air with n = 1 to isopropanol n = 1.3), suggesting an application of the nanoporous GaN-based TP structure for optical sensing.

Wavelength-Tunable Mid-Infrared Lasing from Black Phosphorus Nanosheets.

Van der Waals layered semiconductor materials own unique physical properties and have attracted intense interest in developing high-performance electronic and photonic devices. Among them, black phosphorus (BP) is distinct for its layer number-tuned direct band gap which spans from near- to mid-infrared (MIR) waveband. In addition, the puckered honey comb crystal lattice endows the material with highly linear-polarized emission and marked anisotropy in carrier transportation. These unique material properties render BP as an intriguing and promising building block for constructing mid-infrared-ranged coherent light sources. Here, a room temperature surface-emitting MIR laser based on single crystalline BP nanosheets coupled with a distributed Bragg reflector cavity is reported. MIR stimulated emission at 3611 nm is achieved with a near-unity linear polarization, which exhibits robust thermal stability up to 360 K. Most importantly, the lasing wavelength can be tuned from 3425 to 4068 nm by varying the cavity length via thickness control of BP layer. The demonstrated highly polarized lasing output and wavelength-tunable capacity of the proposed device scheme in MIR spectral range opens up promising opportunities for a broad array of applications in polarization-resolved IR imaging, range-finding, and free space quantum communications.

Waveguide integrated GaN distributed Bragg reflector cavity using low‐cost nanolithography

This work presents the design, fabrication and measurement of gallium nitride (GaN) distributed Bragg reflector cavities integrated with input and output grating couplers. The devices are fabricated using a new, low-cost nanolithography technique: displacement Talbot lithography combined with direct laser writing lithography. The finite-difference time-domain method has been used to design all the components and measured and modelled results show good agreement. Such devices have applications in GaN integrated photonics and biosensing.

Light-Matter Interaction and Lasing in Lead Halide Perovskites.

Lead halide perovskites (LHPs) are attractive material systems for light emission, thanks to the ease and diverse routes of synthesis, the broad tunability in color, the high emission quantum efficiencies, and the strong light-matter coupling which may potentially lead to exciton-polariton condensation. This account contrasts the laser-like coherent light emission from highly lossy Fabry-Perot cavities, formed naturally from LHP nanowires (NWs) and nanoplates (NPs), with highly reflective cavities made of LHP gain media, sandwiched between two distributed Bragg reflector (DBR) mirrors. The mechanism responsible for the operation of conventional semiconductor lasers involves stimulated emission of electron and hole pairs bound by the Coulomb potential, i.e., excitons or, at excitation density above the so-called Mott threshold, an electron-hole plasma (EHP). We discuss how lasing from LHP NWs or NPs likely originates from stimulated emission of an EHP, not excitons or exciton-polaritons. A character central to this kind of lasing is the dynamically changing photonic properties in the naturally formed cavity. In contrast to the more static conditions of a DBR cavity, lasing modes and gain profiles are extremely sensitive to material properties and excitation conditions in an NW/NP cavity. While such unstable photonic cavities pose engineering challenges in the application of NW/NP lasers, they provide excellent probes of many-body physics in the LHP material. For sufficiently strong light-matter coupling expected for LHPs in DBR cavities, an exciton-polariton, i.e., the superposition state between the exciton and the cavity photon, can form. An exciting prospect of strong light-matter coupling is the potential formation of an exciton polariton condensate, which possesses many interesting quantum and nonlinear effects, such as superfluidity, long-range coherence, and laserlike light emission. However, it is difficult to distinguish coherent light from an exciton-polariton condensate and that from conventional stimulated laser emission. Several reports have established the condition of strong coupling for LHPs in DBR cavities. We stress, however, that these studies have not included necessary experiments to unambiguously establish the formation of exciton-polariton condensation, and several experiments and routes of analysis are needed to make a more convincing case for exciton-polariton condensation in LHP based systems. The potential of exciton-polariton condensation expands the horizon of LHP materials from conventional optoelectronics to quantum devices.

Single-frequency fibre laser at 1030 nm based on gain bandwidth compression

We demonstrate a single-frequency linear cavity fiber laser at 1030 nm with a distributed Bragg reflector cavity configuration. Despite the fact that the combination of the cavity length of the fiber laser and the reflection band of the output FBG cannot satisfy the condition of single-longitudinal mode oscillation, the single-frequency lasing is still realized by the proper temperature control of two FBGs to narrow the gain bandwidth. Under the respective temperature of two FBGs of 43.4 °C and 9 °C, the laser linewidth of around 9.6 kHz is achieved at a pump power of 113 mW. The relative noise intensity for frequencies of above 1.5 MHz is about −140 dB Hz−1. The maximum output power of 126.2 mW is obtained with the slope efficiency of about 28%.