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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

III/V silicon hybrid laser based on a resonant Bragg structure

We demonstrate a laser tunable in intensity with gigahertz tuning speed based on a III/V reflective semiconductor optical amplifier (RSOA) coupled to a silicon photonic chip. The silicon chip contains a Bragg-based Fabry–Perot resonator to form a passive bandpass filter within its stopband to enable single-mode operation of the laser. We observe a side mode suppression ratio of 43 dB, linewidth of 790 kHz, and an optical output power of 1.65 mW around 1530 nm. We also investigate using a micro-ball lens as an alternative coupling method between the RSOA and the silicon chip.

Davis, Jordan A. (ORCID:0000000343483295)↗
NASA NTRS2006

NASA Tech Briefs, May 2006

T-Shaped Emitter Metal Structures for HBTs Rigorous Estimation of SNR of a PSK Communication Link Advanced Ka-Band Transceiver With Monopulse Tracking EMI Filters for Low-Temperature Applications Lightweight Electronic Camera for Research on Clouds Pilot Weather Advisor System Waveguide Power-Amplifier Module for 80 to 150 GHz Better Back Contacts for Solar Cells on Flexible Substrates Topics covered include:Tunable, Highly Stable Lasers for Coherent Lidar; Improved Photon-Emission-Microscope System; Program Synthesizes UML Sequence Diagrams; Aspect-Oriented Subprogram Synthesizes UML Sequence Diagrams; Updated Computational Model of Cosmic Rays Near Earth; Software for Alignment of Segments of a Telescope Mirror; Simulation of Dropping of Cargo With Parachutes; DAVE-ML Utility Program; Robust Control for the Mercury Laser Altimeter; Thermally Stable Piezoelectric and Pyroelectric Polymers; Combustion Synthesis of Ca3(PO4)2 Net-Shape Surgical Implants; Stochastic Representation of Chaos Using Terminal Attractors; Two High-Temperature Foil Journal Bearings; Using Plates To Represent Fillets in Finite-Element Modeling; Repairing Chipped Silicide Coatings on Refractory Metal Substrates; Simplified Fabrication of Helical Copper Antennas; Graded-Index "Whispering-Gallery" Optical Microresonators; Optical Profilometers Using Adaptive Signal Processing; Manufacture of Sparse-Spectrum Optical Microresonators; Exact Tuning of High-Q Optical Microresonators by Use of UV; Automation for "Direct-to" Clearances in Air-Traffic Control; Improved Traps for Removing Gases From Coolant Liquids; and Lunar Constellation of Frozen Elliptical Inclined Orbits.

Source record↗
NASA NTRS2016

Tunable Passive Vibration Suppressor

An apparatus and method for vibration suppression using a granular particle chain. The granular particle chain is statically compressed and the end particles of the chain are attached to a payload and vibration source. The properties of the granular particles along with the amount of static compression are chosen to provide desired filtering of vibrations.

Boechler, Nicholas↗
NASA NTRS1988

The Stable Solar Analyzer

Progress in the development of an instrument with very high (1:10 billion) wavelength stability designed to measure solar surface velocities and magnetic fields is reported. The instrument determines Doppler and Zeeman shifts in solar spectral lines by a 6-point weighted average. It is built around an electrically tunable solid lithium-niobate Fabry-Perot etalon that is stabilized against a diode laser which itself is locked to a resonance line of cesium 133. Key features are the etalon, which acts as a wide-angle 0.017-nm solar filter, the camera with a specially stabilized shutter, and the instrument control and data collection system. Use of the instrument in helioseismological research is emphasized.

Rust, D. M.↗
NASA NTRS1990

Resonant tunneling IR detectors

Researchers propose a novel semiconductor heterojunction photodetector which would have a very low dark current and would be voltage tunable. A schematic diagram of the device and its band structure are shown. The two crucial components of the device are a cathode (InGaAs) whose condition band edge is below the conduction band edge of the quantum wells and a resonant tunneling filter (GaAs-AlGaAs). In a standard resonant tunneling device the electrodes are made of the same material as the quantum wells, and this device becomes highly conducting when the quantum levels in the wells are aligned with the Fermi level in the negatively biased electrode. In contrast, the researchers device is essentially non-conducting under the same bias conditions. This is because the Fermi Level of the cathode (InGaAs) is still well below the quantum levels so that no resonant transport occurs and the barriers (AlGaAs) effectively block current flow through the device. However, if light with the same photon energy as the conduction-band discontinuity between the cathode and the quantum wells, E sub c3-E sub c1, is shone on the sample, free carriers will be excited to an energy corresponding to the lowest quantum level in the well closest to the cathode (hv plue E sub c1 = E sub o). These electrons will resonantly tunnel through the quantum wells and be collected as a photocurrent in the anode (GaAs). To improve the quantum efficiency, the cathode (InGaAs) should be very heavily doped and capped with a highly reflective metal ohmic contact. The thickness of the device should be tailored to optimize thin film interference effects and afford the maximum absorption of light. Because the device relies on resonant tunneling, its response should be very fast, and the small voltages needed to change the responsivity should allow for very high frequency modulation of the photocurrent. In addition, the device is tuned to a specific photon energy so that it can be designed to detect a fairly narrow range of wavelengths. This selectivity is important for reducing the photocurrent due to spurious light sources.

Woodall, Jerry M.↗
NASA NTRS2007

WGM-Based Photonic Local Oscillators and Modulators

Photonic local oscillators and modulators that include whispering-gallery mode (WGM) optical resonators have been proposed as power-efficient devices for generating and detecting radiation at frequencies of the order of a terahertz. These devices are intended especially to satisfy anticipated needs for receivers capable of detecting lowpower, narrow-band terahertz signals to be used for sensing substances of interest in scientific and military applications. At present, available terahertz-signal detectors are power-inefficient and do not afford the spectral and amplitude resolution needed for detecting such signals. The proposed devices would not be designed according to the conventional approach of direct detection of terahertz radiation. Instead, terahertz radiation would first be up-converted into the optical domain, wherein signals could be processed efficiently by photonic means and detected by optical photodetectors, which are more efficient than are photodetectors used in conventional direct detection of terahertz radiation. The photonic devices used to effect the up-conversion would include a tunable optical local oscillator and a novel electro-optical modulator. A local oscillator according to the proposal would be a WGM-based modelocked laser operating at a desired pulserepetition rate of the order of a terahertz. The oscillator would include a terahertz optical filter based on a WGM microresonator, a fiber-optic delay line, an optical amplifier (which could be either a semiconductor optical amplifier or an erbium-doped optical fiberamplifier), and a WGM Ka-band modulator. The terahertz repetition rate would be obtained through harmonic mode locking: for example, by modulating the light at a frequency of 33 GHz and locking each 33d optical mode, one would create a 1.089-THz pulse train. The high resonance quality factors (Q values) of WGM optical resonators should make it possible to decrease signal-generation threshold power levels significantly below those of other optical-signal-generation devices.

Matsko, Andrey↗
DOE OSTI2022

Portable diagnostic package for Thomson scattering and optical emission spectroscopy on Princeton field-reversed configuration 2 (PFRC 2)

An Advanced Research Projects Agency-Energy funded diagnostic system has been deployed to the Princeton field-reversed configuration 2 (PFRC-2) device, located at Princeton Plasma Physics Laboratory. The Portable Diagnostic Package (PDP), designed at Oak Ridge National Laboratory, allows for the measurement of Thomson Scattering (TS) for electron density and temperature and Optical Emission Spectroscopy (OES) for ion temperature, impurity density, and ion velocity. A tunable spectrometer on the PDP with three gratings provides the flexibility to measure low (1 eV) and high (1000 eV) electron temperature ranges from TS. Additionally, using a second spectrometer, the OES diagnostic can survey light emission from various ion excitation levels for wide wavelength ranges. The electron density (<2 × 10 19 m –3 ) of plasmas generated in PFRC-2 has been below the PDP TS discrimination threshold, which has made TS signal detection challenging against a high-background of laser stray light. The laser stray light was iteratively reduced by making modifications to the entrance and exit geometry on PFRC-2. Rayleigh scattering experiments on PFRC have yielded the TS discrimination sensitivity to be >1 × 10 20 m –3 for the PDP. A recently implemented narrow-band notch spectral filter that masks the second harmonic 532 nm Nd:YAG laser wavelength has increased the system’s TS light discrimination sensitivity 65 times compared to the instance when the notch filter was not implemented. The hardware implementation including design changes to the flight tubes and Brewster windows will be discussed, along with results from Rayleigh and rotational Raman scattering sensitivity analyses, which were used to establish a quantitative figure of merit on the system performance. Further, the Raman scattering calibration with the notch filter has improved the PDP electron density threshold to 1 ± 0.5 × 10 18 m –3 .

47 OTHER INSTRUMENTATION↗
NASA NTRS1996

High Spectral Resolution Lidar Measurements Using an I2 Absorption Filter

The University of Wisconsin high spectral resolution lidar (HSRL) measures optical properties of the atmosphere by separating the Doppler-broadened molecular backscatter return from the unbroadened aerosol return. The HSRL was modified to use an I2 absorption cell The modified HSRL transmitter uses a continuously pumped, Q-switched, injection seeded, frequency doubled Nd:YAG laser operating at a 4 kHz pulse repetition rate. This laser is tunable over a 124 GHz frequency range by temperature tuning the seed laser under computer control.

Eloranta, E. W.↗
NASA NTRS2003

Tunability and synthetic lineshapes in high-Q optical whispering gallery modes

We demonstrate novel techniques to manipulate spectral properties of high quality factor (Q>107) whispering-gallery modes (WGM) in optical dielectric microresonators. These include permanent frequency trimming of WGM frequencies by means of UV photosensitivity of germanium doped silica resonators electro-optical tuning of WGM in lithium niobate resonators, and cascading of microresonators for obtaining second-order filtering function. We present theoretical interpretation of experimental results, and application example of techniques for photonic microwave filtering.

optical filters↗
NASA NTRS1990

Compensating For Doppler Shift In Laser Instrumentation

Electronic tuning system continually adjusts frequency of tunable diode laser to compensate for Doppler shift caused by motion of transmitter or receiver containing laser. Doppler-shift-compensating system intended primarily for use in transmitter or receiver of laser remote-sensing or communication system to keep frequency of received signal within frequency range of narrow-band-pass filter. By use of narrow-band filter (instead of wide-band filter required in absence of Doppler compensation), signal-to-noise ratio of laser system increased. Thus, less-powerful transmitter usable.

Schwemmer, Geary K.↗
DOE OSTI2020

Widely tunable, heterogeneously integrated quantum-dot O-band lasers on silicon

Heterogeneously integrated lasers in the O-band are a key component in realizing low-power optical interconnects for data centers and high-performance computing. Quantum-dot-based materials have been particularly appealing for light generation due to their ultralow lasing thresholds, small linewidth enhancement factor, and low sensitivity to reflections. Here, we present widely tunable quantum-dot lasers heterogeneously integrated on silicon-on-insulator substrate. The tuning mechanism is based on Vernier dual-ring geometry, and a 47 nm tuning range with 52 dB side-mode suppression ratio is observed. These parameters show an increase to 52 nm and 58 dB, respectively, when an additional wavelength filter in the form of a Mach–Zehnder interferometer is added to the cavity. The Lorentzian linewidth of the lasers is measured as low as 5.3 kHz.

Malik, Aditya (ORCID:0000000334487577)↗
NASA NTRS1985

Wave motions in the upper atmospheric sodium layer observed with a lidar technique

Since the middle of 1980, the vertical profile of the atmospheric sodium layer was observed with a tunable laser radar at Mt. Zao Observatory in northern Japan. The principal characteristics of the lidar system are summarized. The output wavelength is continuously monitored by using a sodium resonance cell, a spectrometer, and a Fabry-Perot interferometer provided with the reference spectrum of the sodium lamp. Owing to the strict temperature control of the filters, the tuning is sufficiently stable throughout the night. The calibration of the absolute sodium density was carried out by adopting the method established by previous works.

Kamiyama, H.↗
NASA NTRS2006

A Compact 600 GHz Electronically Tunable Vector Measurement System for Submillimeter Wave Imaging

The design of a complete vector measurement system being tested over 560-635 GHz is presented. The topics include: 1) Current State-of-the-Art in Vector Measurements; 2) Submillimeter Active Imaging Requirements; 3) 600 GHz Vector Measurement System; 4) 450 MHz IF Signal; 5) 450 MHz IF signal @ 1 kHz Res. BW; 6) 450 MHz IF Signal Mixed with Shifted 450 MHz Reference Signal; 7) Reference Signal Offset Generator; 8) Cavity Bandpass Filter; 9) Miniature Multistage Helical Filter; 10) X36 450 MHz Multiplier; 11) 600 GHz Test Setup; 12) 600 GHz Transmit Module; 13) 600 GHz Receive Module; 14) Performance Tests: Amplitude Stability & Dynamic Range; 15) Performance Tests: Phase Stability; 16) Stability at Imaging Bandwidths; 17) Phase Measurement Verification; and 18) The Next Step: Imaging.

phase measurements↗
DOE OSTI2021

Bound States in the Continuum on a Silicon Chip with Dynamic Tuning

Expanding bound states in the continuum (BIC) beyond photonic crystal systems may enable broader applications benefiting from the unique properties of BIC states. We use photonic integrated circuit to realize a Fabry-Pérot BIC on a silicon chip. The devices consist of cascaded ring resonators with tunable resonance frequencies and phase delays. As a result, the BIC state is dynamically tuned with electrical I/O. We analyze the mechanism of the formation of BIC states in this waveguide system and point out the fundamental differences between the BIC states and electromagnetically induced transparency states in integrated photonics. The high transmission protected by the BIC state enables versatile optical filters, which are capable of independent control over switching, peak position, and quality factor. We also demonstrate the scalability of this platform. As a result, this integrated silicon photonic platform brings opportunities for practical BIC applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1983

High-resolution lidar system for measuring the spatial and temporal structure of the mesospheric sodium layer

The design of a high-resolution tunable-dye laser-based lidar system for the study of the mesospheric sodium layer is presented and results of sodium measurements are indicated. The lidar system comprises a tunable flashlamp-pumped dye laser operating at the sodium D2 resonance line at 589.0 nm with a pulse width of 2 microsec FWHM and pulse frequency of 10 Hz and a telescope with a 1.22=m diameter Fresnel lens. Sodium profiles are obtained from the integration of 100 to 250 laser shots, with spatial and temporal resolution enhanced by two-dimensional filtering techniques. Measurements obtained over a 9-hour nighttime period illustrate the highly dynamic nature of the sodium layer, which was observed with a spatial resolution of 2 km and temporal resolution of 30 min. Observations made with a steerable apparatus have confirmed a presunrise enhancement of over 100 percent in sodium column abundance.

Gardner, C. S.↗
DOE OSTI2024

In situ oxidation of reduced graphene oxide membranes by peracetic acid for dye desalination

Graphene oxide (GO) membranes with tunable interlayer spacings are of interest for dye removal from salty textile wastewater, and the membranes are often reduced to improve their stability, which inevitably lowers water permeance. Herein, we demonstrate that reduced GO (rGO) membranes can be facilely modified using peracetic acid (PAA) in situ to dramatically enhance water permeance while retaining dye rejection. Specifically, PAA-modified membranes (PrGO) are synthesized by vacuum-filtering hydrazine-reduced rGO nanosheets onto Nylon substrate and then exposing them to PAA solutions. The effects of the rGO layer thickness, PAA content, and PAA exposure time on the membrane chemistry, nanostructures, and salt/dye separation properties are thoroughly examined. For example, the PAA oxidation of a 100 nm-thick rGO membrane for 10 min increases water permeance by 180 %, from 35 to 93 Liter m −2 h −1 bar −1 , and decreases Na 2 SO 4 rejection from 10 % to 3.3 % while retaining the rejection of Congo red at ≈99.7 %. The PrGO membranes exhibit stable water permeance and >99 % dye rejection in multi-cycle tests in a crossflow system, surpassing state-of-the-art GO membranes and showcasing their potential for practical applications.

Dye desalination↗
DOE OSTI2025

Orientation-Driven Chirality Funnels in Chiral Low-Dimensional Lead-Halide Perovskite Heterostructures

Chiral hybrid metal-halide perovskites show low-symmetry crystal structures, large Rashba splitting, spin-filtering, and strong chiroptical activity. Circular dichroism and circularly polarized photoluminescence have been investigated in chiral perovskites with increasingly distorted chiral structures. Here, we report the fabrication of chiral (R/S)-EBAPbI3 (EBA = α-ethylbenzylamine) single crystals, which possess highly distorted octahedral structures with a high angle variance value of ∼68 degree2. Using control in the fabrication conditions, we transfer chiral single crystals to thin films and achieve different crystal orientation preferences that induce tunable chiroptical properties to their heterostructures with PbI2 nanodomains, which we characterize with in situ X-ray diffraction and grazing-incidence wide-angle X-ray scattering measurements. Using transient chiroptical spectroscopies, we resolve photoexcited charge carrier dynamics and chirality transfer processes in such heterostructures down to cryogenic temperatures. We observe rapid carrier transfer along the in-plane (002) facets in chiral perovskite phases to PbI2 nanostructures within the initial few picoseconds, while carrier transfer along the out-of-plane (002) facets occurs at a slower rate. This fast transfer process leads to high photoluminescence intensities and large degrees of circular polarization in the emission from PbI2 nanodomains at cryogenic temperatures. Our findings report a multidimensional chiral-achiral heterostructure which takes advantage of controllable chirality transfer and offers new routes for future spintronic and chiroptical applications.

Liu, Shangpu↗
DOE OSTI2022

Silicon nitride stress-optic microresonator modulator for optical control applications

Modulation-based control and locking of lasers, filters and other photonic components is a ubiquitous function across many applications that span the visible to infrared (IR), including atomic, molecular and optical (AMO), quantum sciences, fiber communications, metrology, and microwave photonics. Today, modulators used to realize these control functions consist of high-power bulk-optic components for tuning, sideband modulation, and phase and frequency shifting, while providing low optical insertion loss and operation from DC to 10s of MHz. In order to reduce the size, weight and cost of these applications and improve their scalability and reliability, modulation control functions need to be implemented in a low loss, wafer-scale CMOS-compatible photonic integration platform. The silicon nitride integration platform has been successful at realizing extremely low waveguide losses across the visible to infrared and components including high performance lasers, filters, resonators, stabilization cavities, and optical frequency combs. Yet, progress towards implementing low loss, low power modulators in the silicon nitride platform, while maintaining wafer-scale process compatibility has been limited. Here we report a significant advance in integration of a piezo-electric (PZT, lead zirconate titanate) actuated micro-ring modulation in a fully-planar, wafer-scale silicon nitride platform, that maintains low optical loss (0.03 dB/cm in a 625 µm resonator) at 1550 nm, with an order of magnitude increase in bandwidth (DC - 15 MHz 3-dB and DC - 25 MHz 6-dB) and order of magnitude lower power consumption of 20 nW improvement over prior PZT modulators. The modulator provides a >14 dB extinction ratio (ER) and 7.1 million quality-factor (Q) over the entire 4 GHz tuning range, a tuning efficiency of 162 MHz/V, and delivers the linearity required for control applications with 65.1 dB·Hz 2/3 and 73.8 dB·Hz 2/3 third-order intermodulation distortion (IMD3) spurious free dynamic range (SFDR) at 1 MHz and 10 MHz respectively. We demonstrate two control applications, laser stabilization in a Pound-Drever Hall (PDH) lock loop, reducing laser frequency noise by 40 dB, and as a laser carrier tracking filter. This PZT modulator design can be extended to the visible in the ultra-low loss silicon nitride platform with minor waveguide design changes. This integration of PZT modulation in the ultra-low loss silicon nitride waveguide platform enables modulator control functions in a wide range of visible to IR applications such as atomic and molecular transition locking for cooling, trapping and probing, controllable optical frequency combs, low-power external cavity tunable lasers, quantum computers, sensors and communications, atomic clocks, and tunable ultra-low linewidth lasers and ultra-low phase noise microwave synthesizers.

Wang, Jiawei (ORCID:0000000257965220)↗