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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

CNOT-based quantum swapping of polarization and modal encoded qubits in photonic Ti:LiNbO{sub 3} channel waveguides

A photonic circuit aimed at implementing a CNOT-based quantum swapping of the modal and polarization qubits, is designed and simulated, using Ti:LiNbO{sub 3} indiffused channel waveguides. A few on-chip optical elements such as the polarization-sensitive odd-mode analyzers and combiners, along with the electrically controllable directional couplers and polarization converters, are incorporated within the circuit and together serve to realize the operation of a deterministic single-photon quantum swap gate. Entanglement generation is realized on-chip by means of two concurrent spontaneous parametric down-conversion processes in the twice periodically poled Ti:LiNbO{sub 3} waveguide, placed at the input section of the circuit. The constituent elements of the circuit are characterized separately using numerical beam propagation method in RSoft program package. Two poling periods of Λ{sub 1}=11.762 μm and Λ{sub 2}=23.667 μm are calculated for the dual periodically perturbed structure in the circuit. The directional couplers operate at V{sub DC}=31.6 V. Maximum polarization conversion efficiency is achieved by applying a constant switching voltage of V{sub EO}=4.52 V.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Qualitative analysis of magnetic waveguides for two-dimensional Dirac fermions

We focus on the confinement of two-dimensional Dirac fermions within the waveguides created by realistic magnetic fields. Understanding of their band structure is of our main concern. We provide easily applicable criteria, mostly depending only on the asymptotic behavior of the magnetic field, that can guarantee existence or absence of the energy bands and provide valuable insight into the systems where analytical solution is impossible. The general results are employed in specific systems where the waveguide is created by the magnetic field of a set of electric wires or magnetized strips.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Distinctive features of fluorescence and waveguides in magnesium aluminate spinel crystals driven by structural discrepancy

Transparent polycrystalline ceramics are of significant importance for a wide range of scientific and industrial applications. Developing a deeper understanding of their thermodynamic behavior is essential for achieving their maximum output performance in technological applications. This study provides a systematic investigation into the thermal excitation-induced fluorescence kinetics and waveguide characteristics of Magnesium Aluminate Spinel (MgAl 2 O 4 ) single crystals, with a focus on the intricate relationship between structure and properties. High-temperature extreme environments through irradiation with swift heavy ions 645.0 MeV Xe and 352.8 MeV Fe ions were created; the atomic deposition energy threshold (E th ) associated with disorder morphologies was assessed between 0.91 and 0.99 eV atom –1 . The track prediction model was developed to support the theoretical prediction of track formation. Electronic energy loss (E ele ) disrupts the balance of the initial structure through the thermal spike effect, leading to the formation of absorption-related F and F + color centers. These defects enhance photoluminescence in the visible spectrum and result in an effective modulation of the intrinsic bandgap. Moreover, as ion beams penetrate into the material, the uneven damage distribution induces the formation of waveguide structures. In conclusion, these findings provide valuable insights into the fabrication of functional devices through irradiation technologies and the structural changes of MgAl 2 O 4 at high temperatures within extreme environments.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Corroborating VNA and thermal measurements of transmission loss on the DIII-D ECH waveguide system

Electron cyclotron heating (ECH) and current drive (ECCD) will play a large role in tokamak-based fusion reactors. At the DIII-D tokamak, 110 GHz microwaves injected into the plasma can provide core heating and current drive as well as impurity control, neoclassical tearing mode mitigation, and breakdown assistance. Understanding the physics of these processes relies on accurate estimates of injected ECH power. DIII-D’s ECH system consists of six MW-class Microwave Power Products (MPP) gyrotron microwave sources. Operating the gyrotrons far from the tokamak removes them from magnetic field interference, so 31.75 mm inner-diameter corrugated waveguides transmit the microwave power the 80 m from the gyrotrons to steerable launchers in the tokamak chamber. Estimates of injected power rely on knowing the generated power at the source and then subtracting transmission loss. Conventional transmission loss measurements based on calorimetric dummy loads are onerous and only possible during extended maintenance periods. This work examines two tools that provide more flexibility for the transmission loss measurements. Furthermore, a resistive temperature detector (RTD) array installed along a waveguide measures heat lost to the transmission line, and low power time domain reflectometry (TDR) measurements with a vector network analyzer (VNA) allows loss measurements without burdensome hardware modifications.

ECH↗
DOE OSTI2017

Controlling propagation and coupling of waveguide modes using phase-gradient metasurfaces

Here, research on two-dimensional designer optical structures, or metasurfaces, has mainly focused on controlling the wavefronts of light propagating in free space. Here, we show that gradient metasurface structures consisting of phased arrays of plasmonic or dielectric nanoantennas can be used to control guided waves via strong optical scattering at subwavelength intervals. Based on this design principle, we experimentally demonstrate waveguide mode converters, polarization rotators and waveguide devices supporting asymmetric optical power transmission. We also demonstrate all-dielectric on-chip polarization rotators based on phased arrays of Mie resonators with negligible insertion losses. Our gradient metasurfaces can enable small-footprint, broadband and low-loss photonic integrated devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Passive wavelength tuning and multichannel photonic coupling using monolithically integrated vertical microresonators on ridge waveguides

The passive tuning of the resonant coupling wavelength in a SiN x vertical microring coupler (VμRC) monolithically integrated on a ridge waveguide by engineering the structural parameters of the VμRCs is experimentally demonstrated and theoretically verified. Multi-channel photonic coupling is achieved by integrating two different VμRCs on a single ridge waveguide. This work represents here a critical step to 3D photonic integration using VμRCs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Laser-heated capillary discharge plasma waveguides for electron acceleration to 8 GeV

A plasma channel created by the combination of a capillary discharge and inverse Bremsstrahlung laser heating enabled the generation of electron bunches with energy up to 7.8 GeV in a laser-driven plasma accelerator. The capillary discharge created an initial plasma channel and was used to tune the plasma temperature, which optimized laser heating. Although optimized colder initial plasma temperatures reduced the ionization degree, subsequent ionization from the heater pulse created a fully ionized plasma on-axis. The heater pulse duration was chosen to be longer than the hydrodynamic timescale of ≈ 1 ns, such that later temporal slices were more efficiently guided by the channel created by the front of the pulse. Here, simulations are presented which show that this thermal self-guiding of the heater pulse enabled channel formation over 20 cm. The post-heated channel had lower on-axis density and increased focusing strength compared to relying on the discharge alone, which allowed for guiding of relativistically intense laser pulses with a peak power of 0.85 PW and wakefield acceleration over 15 diffraction lengths. Electrons were injected into the wake in multiple buckets and times, leading to several electron bunches with different peak energies. To create single electron bunches with low energy spread, experiments using localized ionization injection inside a capillary discharge waveguide were performed. A single injected bunch with energy 1.6 GeV, charge 38 pC, divergence 1 mrad, and relative energy spread below 2% full-width half-maximum was produced in a 3.3 cm-long capillary discharge waveguide. This development shows promise for mitigation of energy spread and future high efficiency staged acceleration experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Factor of spontaneous emission into the optical dielectric waveguide mode

Within the framework of a complete vector analysis, an expression for the factor of spontaneous emission into the transverse mode of a dielectric waveguide is found. The results are compared with those previously obtained in the framework of the scalar approximation. It is shown that their most significant quantitative difference is possible for waveguides used in diode lasers and amplifiers in which the transverse beam size is commensurable with the wavelength. The conditions for the applicability of the scalar approximation for calculating the spontaneous emission factor are obtained. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Anharmonic Bloch oscillations in a waveguide array

Using the coupled-wave method, we consider anharmonic Bloch oscillations of light in an array of waveguides, taking into account the coupling between waveguides up to the third order. It is shown that the beam trajectory is periodic, with the trajectory oscillating within a single period. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Effect of the waveguide layer thickness on output characteristics of semiconductor lasers with emission wavelength from 1500 to 1600 nm

The effect of the waveguide layer thickness on output characteristics of AlGaInAs/InP quantum-well semiconductor lasers is analysed. The samples of semiconductor lasers with narrow and wide waveguides are experimentally fabricated. Their comparison is carried out and the advantages of particular constructions depending on the current pump are demonstrated. (lasers and amplifiers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Power characteristics of lasers with quantum-well waveguides and blocking layers

The power characteristics of lasers with a quantum-well (QW) waveguide are calculated based on a complex model taking into account the diffusion and drift of charge carriers, capture of electrons and holes at the QW levels, spatial distribution of radiation in the cavity, intraband absorption, and heating of the active region. Structures with doped blocking barrier layers are proposed, which allow one to decrease leakage currents to a few percent. The calculated average output power of a laser based on the GaInAs/GaAs QW heterostructure (aperture 100 μm) with a QW waveguide and a GaAsP doped blocking layer in a pulsed regime was 29 W at 80-A current pulses with a duration of 5 μs. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Planar waveguide structures based on SrF{sub 2}: Ho, Er, Tm. Dependence of the refractive index on the dopant concentration

Refractive indices of SrF{sub 2} crystals doped with holmium, erbium, and thulium ions are measured. These crystals are used as active laser media, in particular, as materials for planar waveguides. The presence of active ions in these crystals may create a difference between the refractive indices of the cladding and the doped core of a planar waveguide. At dopant concentration to 4 %, the difference Δn between the refractive indices of the doped core and undoped reflective layer can reach 0.007.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Simulation of an electro-optic modulator based on the quantum-confined Stark effect in a two-layer InAlGaAs rib waveguide on an InP substrate

An electro-optic Mach – Zehnder modulator based on the quantum-confinement Stark effect in layered multiple-quantum-well InAlGaAs structures on InP substrate is numerically simulated. The novelty of the modulator design is the use of a two-layer rib optical waveguides, which provide technologically efficient (loss of 1.5 dB per element) coupling of the modulator with optical fibre. It is shown that, changing the electrode width and the distance between two waveguides in two Mach – Zehnder interferometer arms, one can match the impedance of the modulator with an external 50-Ω load and the velocities of microwave and optical waves in the modulator. The results of the study can be used in integrated optics, optical communication, and radiophotonics devices. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Conversion of light polarisation in asymmetric plasmonic waveguides

Hybrid plasmonic waveguides with an embedded conducting oxide layer can be used for producing fast and compact electro-optical modulation devices. However, due to constraints, which plasmon modes impose on light polarisation, modulators of this class are not compatible with high-efficiency modern diffraction gratings used for coupling light into a waveguide. In the present work we demonstrate how a simple structuring of a modulation sandwich makes it possible to produce a compact polarisation converter that eliminates the mentioned incompatibility. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Dual-wavelength generation of picosecond pulses with 9.8 GHz repetition rate in Nd : YAG waveguide laser with graphene

We report a new solid-state waveguide laser generating picosecond pulses with a GHz repetition rate, based on the use of graphene as a saturable absorber. Lasing at the main transverse mode is provided by the geometry of a cylindrical waveguide formed in the active crystal volume by the method of direct writing with a femtosecond laser beam. Fine tuning of the intracavity interferometer formed between the active medium and output mirror makes it possible to control the spectral-temporal parameters of output radiation and to smoothly tune the repetition rate of pulses having a duration of less than 20 ps. In particular, the possibility of dual-wavelength generation in the regime of continuous passive mode locking using a single saturable absorber based on graphene is demonstrated. By amplifying laser output radiation in the ytterbium fibre amplifier, an average output power of 530 mW is obtained. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

AlGaInAs/InP semiconductor lasers with an ultra-narrow waveguide and an increased electron barrier

Semiconductor lasers based on AlGaInAs/InP heterostructures with an ultra-narrow waveguide and an increased electron barrier layer are developed. It is shown that the use of this waveguide in conjunction with profiled doping ensures a balance between internal optical losses and heat resistance. Additional use of strained wide-bandgap layers as blocking barriers limiting electron leakage from the active region makes it possible to increase the output power at the same pump current. The developed lasers with a stripe contact 100 μm wide demonstrate at room temperature an output optical power of 4.0 – 4.4 W (pump current 14 A) in a continuous-wave regime and 15 – 17 W (100 A) in a pulsed regime (100 ns, 1 kHz) at wavelengths of 1450 – 1500 nm. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Analysis of the ITER ECH Waveguide Transmission Line Expansion Unit

The ITER Electron Cyclotron Heating (ECH) system consists of transmission lines made up of individual sections of evacuated, aluminum, circularly corrugated waveguides. The high-intensity beam of electromagnetic radiation, necessary for plasma heating, heats the waveguides and other components in the transmission lines causing the lines to expand and contract. To maintain the structural integrity and the required straightness in the transmission lines, expansion units have to be incorporated into the ECH transmission line system. Calculations of several models of expansion units have been completed in this paper to evaluate the effect of the design and materials on the functionality of the expansion unit. Finally, models have been evaluated assuming three different expansion ranges and several different materials.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Larmor power limit for cyclotron radiation of relativistic particles in a waveguide

Cyclotron radiation emission spectroscopy (CRES) is a modern technique for high-precision energy spectroscopy, in which the energy of a charged particle in a magnetic field is measured via the frequency of the emitted cyclotron radiation. The He6-CRES collaboration aims to use CRES to probe beyond the standard model physics at the TeV scale by performing high-resolution and low-background beta-decay spectroscopy of 6 He and 19 Ne. Having demonstrated the first observation of individual, high-energy (0.1–2.5 MeV) positrons and electrons via their cyclotron radiation, the experiment provides a novel window into the radiation of relativistic charged particles in a waveguide via the time-derivative (slope) of the cyclotron radiation frequency, df c /dt. We show that analytic predictions for the total cyclotron radiation power emitted by a charged particle in circular and rectangular waveguides are approximately consistent with the Larmor formula, each scaling with the Lorentz factor of the underlying e ± as γ 4 . This hypothesis is corroborated with experimental CRES slope data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗