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Results for “distributed Bragg reflectors”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Multijunction solar cells with graded buffer Bragg reflectors

Distributed Bragg reflectors are incorporated into the compositionally graded buffers of metamorphic solar cells, adding functionality to the buffer without adding cost. The reflection aids in collection in subcells that are optically thin due to low diffusion length, high bulk recombination, radiation hardness, partially-absorbing quantum structures, or simply for cost savings. Performance enhancements are demonstrated in GaAs subcells with QWs, which is beneficial when GaAs is not the ideal bandgap.

France, Ryan Matthew↗
NASA NTRS1990

Unstable-Resonator Distributed-Bragg-Reflector Laser

Proposed distributed-Bragg-reflector (DBR) semiconductor laser has wide curved gratings favoring single-mode operation, even with relatively wide laser stripe, enabling use of higher power. Consists of semiconductor double heterostructure laser bounded at each end by region of passive waveguide.

Lang, Robert J.↗
NASA NTRS1998

Method and Apparatus for Linewidth Reduction in Distributed Feedback or Distributed Bragg Reflector Semiconductor Lasers using Vertical Emission

The linewidth of a distributed feedback semiconductor laser or a distributed Bragg reflector laser having one or more second order gratings is reduced by using an external cavity to couple the vertical emission back into the laser. This method and device prevent disturbance of the main laser beam. provide unobstructed access to laser emission for the formation of the external cavity. and do not require a very narrow heat sink. Any distributed Bragg reflector semiconductor laser or distributed feedback semiconductor laser that can produce a vertical emission through the epitaxial material and through a window in the top metallization can be used. The external cavity can be formed with an optical fiber or with a lens and a mirror of grating.

Cook, Anthony L.↗
NASA NTRS2000

Apparatus For Linewidth Reduction in Distributed Feedback or Distributed Bragg Reflector Semiconductor Lasers Using Vertical Emission

The linewidth of a distributed feedback semiconductor laser or a distributed Bragg reflector laser having one or more second order gratings is reduced by using an external cavity to couple the vertical emission back into the laser. This method and device prevent disturbance of the main laser beam, provide unobstructed access to laser emission for the formation of the external cavity, and do not require a very narrow heat sink. Any distributed Bragg reflector semiconductor laser or distributed feedback semiconductor laser that can produce a vertical emission through the epitaxial material and through a window in the top metallization can be used. The external cavity can be formed with an optical fiber or with a lens and a mirror or grating.

Cook, Anthony L.↗
NASA NTRS1988

GaAs/GaAlAs distributed Bragg reflector laser with a focused ion beam, low dose dopant implanted grating

The performance of a GaAs/GaAlAs distributed Bragg reflector (DBR) laser using a focused ion beam implanted grating (FIB-DBR) is reported for the first time. Stripes of Si(2+) with a period of 2300 A and a dose about 10 to the 14th/sq cm are directly implanted into the passive large optical cavity layer to provide the distributed feedback. Surface-emitting light from the second-order grating is observed. Threshold current of 110 mA and single DBR mode operation from 20 to 40 C are obtained. The wavelength tuning rate with temperature is 0.8 A/C. The coupling coefficient is estimated to be 15/cm. The results show that FIB technology is practical for distributed feedback and DBR lasers and optoelectronic integrated circuits.

Wu, M. C.↗
NASA NTRS1992

High power singlemode GaInAs lasers with distributed Bragg reflectors

High power singlemode strained GaInAs lasers have been fabricated which use buried second order gratings as distributed Bragg reflectors. The lasers operate in an edge emitting fashion with CW powers in excess of 110 mW with single longitudinal and transverse mode operation at 971.9 nm up to 42 mW.

O'Brien, S.↗
NASA NTRS1992

High power GaInAs lasers with distributed Bragg reflectors

Single-mode strained-layer lasers have been fabricated which use buried second-order gratings for distributed Bragg reflectors. The lasers contain a strained GaInAs quantum well in the active region and operate in an edge emitting fashion with CW powers in excess of 110 mW. Single longitudinal and transverse mode operation is maintained at about 971.9 nm up to 42 mW. Total power conversion efficiencies as high as 28 percent have been observed. The longitudinal and transverse mode behavior is stable under 90 percent amplitude modulation with 50 percent duty cycle pulses at 10 kHz and 10 MHz. Preliminary life-test data at 40 C also indicate room temperature lifetimes in excess of 45,000 hours.

O'Brien, S.↗
DOE OSTI2024

High-intensity polarized electron gun featuring distributed Bragg reflector GaAs photocathode

The polarized electron source is a critical component in accelerator facilities such as the electron–ion collider, which requires a polarized electron gun with higher voltage and higher bunch charge than existing sources. One challenge we faced was the surface charge limit of the distributed Bragg reflector GaAs/GaAsP superlattice (DBR-SL-GaAs) photocathode. We suppressed this effect by optimizing the surface doping and heat cleaning procedures. We achieved up to 11.6 nC bunch charge of polarized electron beam. In this report, we discuss the performance of tests of a DBR-SL-GaAs photocathode in the high voltage direct current gun. Possible reasons for the observed peak quantum efficiency wavelength shift are analyzed, and we addressed it by using a wavelength tunable laser. In addition, the impact of the DBR layer and laser on the lifetime is investigated in this paper. The optimal DBR-SL-GaAs operating zone has been proposed, which gave us a long lifetime and high polarization at 30 μA operation. Finally, the success of this polarized gun will be key to the future of the nuclear sciences.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1999

Electrically-Tunable Group Delays Using Quantum Wells in a Distributed Bragg Reflector

There is a growing interest in the fabrication of semiconductor optical group delay lines for the development of phased arrays of Vertical-Cavity Surface-Emitting Lasers (VCSELs). We present a novel structure incorporating In(x)GA(1-x)As quantum wells in the GaAs quarter-wave layers of a GaAs/AlAs distributed Bragg reflector (DBR). Application of an electric field across the quantum wells leads to red shifting and peak broadening of the el-hhl exciton peak via the quantum-confined Stark effect. Resultant changes in the index of refraction thereby provide a means for altering the group delay of an incident laser pulse. We discuss the tradeoffs between the maximum amount of change in group delay versus absorption losses for such a device. We also compare a simple theoretical model to experimental results, and discuss both angle and position tuning of the BDR band edge resonance relative to the exciton absorption peak. The advantages of such monolithically grown devices for phased-array VCSEL applications will be detailed.

Nelson, Thomas R., Jr.↗
NASA NTRS2014

DBR and DFB Lasers in Neodymium- and Ytterbium-Doped Photothermorefractive Glasses

The first demonstration, to the best of our knowledge, of distributed Bragg reflector (DBR) and monolithic distributed feedback (DFB) lasers in photothermorefractive glass doped with rare-earth ions is reported. The lasers were produced by incorporation of the volume Bragg gratings into the laser gain elements. A monolithic single-frequency solid-state laser with a line width of 250 kHz and output power of 150 mW at 1066 nm is demonstrated.

Photo-Thermal Refractive Glasses↗
DOE OSTI2025

Linewidth narrowing and wideband frequency modulation of a DBR laser

We present a scheme to phase-lock a 240 mW, 852 nm distributed Bragg reflector (DBR) laser to a fixed-frequency narrow-linewidth laser with a rapidly tunable frequency offset near 9 GHz. The phase-lock is accomplished by electronic feedback on the beatnote between the two lasers. The frequency offset can be swept 200 MHz in 300 us, limited by the feedback loop bandwidth, allowing for its use in complex cooling and state preparation schemes needed in atomic physics experiments. Here, we find that the phase-lock reduces the linewidth of the DBR laser below its natural linewidth of ~400 kHz to ~100 kHz

47 OTHER INSTRUMENTATION↗
NASA NTRS1989

DBR laser with nondynamic plasma grating formed by focused ion beam implanted dopants

A static plasma grating has been demonstrated experimentally (Wu et al., 1988) in a large-optical-cavity focused-ion-beam-distributed-Bragg-reflector (FIB-DBR) GaAlAs/GaAs laser diode. The grating is formed by implanting stripes of dopants with a focused ion beam. The dopants ionize to form periodic fluctuations in the carrier concentration which, through the Kramers-Kronig relations, form an index grating. A model of the grating strength for optimizaton of the laser design is developed and presented. The computed results show that the coupling coefficient k can be increased by more than an order of magnitude over the 15/cm experimentally. Therefore, FIB-DBR or FIB-distributed-feedback (DFB) lasers with performance comparable to that of conventional DBR (or DFB) lasers can be expected.

Boenke, Myra M.↗
DOE OSTI2025

Spatial quantum-interference landscapes of multi-site-controlled quantum dots coupled to extended photonic cavity modes

Abstract A compact platform to integrate emitters in a cavity-like support is to embed quantum dots (QDs) in a photonic crystal (PhC) structure, making them promising candidates for integrated quantum photonic circuits. The emission properties of QDs can be modified by tailored photonic structures, relying on the Purcell effect or strong light-matter interactions. However, the effects of photonic states on spatial features of exciton emissions in these systems are rarely explored. Such effect is difficult to access due to random positions of self-assembled QDs in PhC structures, and the fact that quantum well excitons’ wavefunctions resemble photonic states in a conventional distributed Bragg reflector cavity system. In this work, we instead observe a spatial signature of exciton emission using site-controlled QDs embedded in PhC cavities. In particular, we observe the detuning-dependent spatial repulsion of the QD exciton emissions by polarized imaging of the micro-photoluminescence, dependent on the controlled QD’s position in a spatially extended photonic pattern. The observed effect arises due to the quantum interference between QD decay channel in a spatially-extended cavity mode. Our findings suggest that integration of site-controlled QDs in tailored photonic structures can enable spatially distributed single-photon sources and photon switches.

Physics↗
DOE OSTI2026

Polariton Control of Molecular Charge Transfer in Perylene Diimide Semiconductors

We report the modulation of molecular charge transfer in a bay-substituted perylene diimide derivative embedded in a planar distributed Bragg reflector microcavity. Angle-resolved reflectance spectra confirm the formation of upper and lower polaritons with clear Rabi splitting, indicating strong coupling between the cavity mode and molecular excitons. Using broadband transient absorption spectroscopy, we compare the ultrafast dynamics of cavity and non-cavity films. While excited-state absorption and stimulated emission pathways remain largely unchanged, kinetic modeling reveals a moderate increase in the charge transfer rate and yield under strong coupling. This enhancement is attributed to a reduction in the effective driving force via the formation of the lower polariton, placing the system deeper into the Marcus inverted regime. Our results demonstrate a promising non-chemical method leveraging cavity quantum electrodynamics to modulate charge separation processes in molecular semiconductors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Encoding hierarchical 3D architecture through inverse design of programmable bonds

The ability to fabricate materials and devices at small scales by design has resulted in tremendous technological progress. However, the need for engineered three-dimensional (3D) nanoscale materials requires new strategies for organizing nanocomponents. Here we demonstrate an inverse design approach for the assembly of nanoparticles into hierarchically ordered 3D organizations using DNA voxels with directional, addressable bonds. By identifying intrinsic symmetries in repeating mesoscale structural motifs, we prescribe a set of voxels, termed a mesovoxel, that are assembled into target 3D crystals. The relationship between different degrees of encoded information used for voxel bonds and the fidelity of assembly is investigated using experimental and computational methods. We apply this assembly strategy to create periodic 3D nanoparticle ordered organizations, including structures with low-dimensional elements, helical motifs, a nanoscale analogue of a face-centred perovskite crystal and a distributed Bragg reflector based on a crystal with plasmonic and photonic length-scale regimes.

36 MATERIALS SCIENCE↗
DOE OSTI2023

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.

47 OTHER INSTRUMENTATION↗