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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

System and method for high power diode based additive manufacturing

The present disclosure relates to a system for performing an Additive Manufacturing (AM) fabrication process on a powdered material (PM) forming a substrate. The system uses a first optical subsystem to generate an optical signal comprised of electromagnetic (EM) radiation sufficient to melt or sinter a PM of the substrate. The first optical subsystem is controlled to generate a plurality of different power density levels, with a specific one being selected based on a specific PM forming a powder bed being used to form a 3D part. At least one processor controls the first optical subsystem and adjusts a power density level of the optical signal, taking into account a composition of the PM. A second optical subsystem receives the optical signal from the first optical subsystem and controls the optical signal to help facilitate melting of the PM in a layer-by-layer sequence of operations.

El-Dasher, Bassem S.↗
DOE OSTI2022

Timing measurement apparatus

Methods, devices and systems for providing accurate measurements of timing errors using optical techniques are described. An example timing measurement device includes an optical hybrid that receives two optical pulse trains and produces two or more phase shifted optical outputs. The timing measurement device further includes two or more optical filters that receive the outputs of the optical hybrid to produce multiple pulse signals with distinctive frequency bands. The device also includes one or more photodetectors and analog-to-digital converters to receive to produce electrical signals in the digital domain corresponding to the optical outputs of the hybrid. A timing error associated with the optical pulse trains can be determined using the electrical signals in digital domain based on a computed phase difference between a first frequency band signal and a second frequency band signal and a computed frequency difference between the first frequency band signal and the second frequency band.

DeVore, Peter Thomas Setsuda↗
DOE OSTI2024

Timing measurement apparatus

Methods, devices and systems for providing accurate measurements of timing errors using optical techniques are described. An example timing measurement device includes an optical hybrid that receives two optical pulse trains and produces two or more phase shifted optical outputs. The timing measurement device further includes two or more optical filters that receive the outputs of the optical hybrid to produce multiple pulse signals with distinctive frequency bands. The device also includes one or more photodetectors and analog-to-digital converters to receive to produce electrical signals in the digital domain corresponding to the optical outputs of the hybrid. A timing error associated with the optical pulse trains can be determined using the electrical signals in digital domain based on a computed phase difference between a first frequency band signal and a second frequency band signal and a computed frequency difference between the first frequency band signal and the second frequency band.

DeVore, Peter Thomas Setsuda↗
NASA NTRS2005

Large diameter refractive Fresnel lenses as low-cost optical communication ground receiver aperture

Feasibility of utilizing large diameter custom designed and fabricated Fresnel lenses as the front optical aperture for Earth-based reception of optical communication signals from remote spacecraft is investigated. This includes preliminary optical designs, investigation of stray-light effects for a particular optical design, effect of temperature variations and mechanical sag on the performance of the photon bucket, and effect of temporal dispersion on the link performance. Experimental results for several commercial off-the-shelf Fresnel lenses with diameters exceeding 1-meter are presented as well as plans for custom diamond turning fabrication of two-meter diameter Fresnel lenses.

Hemmati, Hamid↗
NASA NTRS2001

Apparatus and Method for Effecting Data Transfer Between Data Systems

An apparatus for effecting data transfer between data systems comprising a first transceiver and a second transceiver. The first transceiver has an input for receiving digital data from one of the data systems, an output for serially outputting digital data to one of the data systems, at least one transmitter for converting digital data received at the input into optical signals, and at least one receiver for receiving optical signals and serially converting the received optical signals to digital data for output to the data output. The second transceiver has an input for receiving digital data from another one of the data systems, an output for serially outputting digital data to the another one of the data systems, at least one transmitter for serially converting digital data received at the input of the second transceiver into optical signals, and at least one receiver for receiving optical signals and serially converting the received optical signals to digital data for output to the output of the second transceiver. The apparatus further comprises an optical link connecting the first and second transceivers. The optical link comprising a pair of optical fibers. One of the optical fibers optically links the transmitter of the first transceiver to the receiver of the second transceiver. The other optical fiber optically links the receiver of the first transceiver to the transmitter of the second transceiver.

Kirkpatrick, Joey V.↗
NASA NTRS1993

Reduced electrical bandwidth receivers for direct detection 4-ary PPM optical communication intersatellite links

One of the major sources of noise in a direct detection optical communication receiver is the shot noise due to the quantum nature of the photodetector. The shot noise is signal dependent and is neither Gaussian nor wide sense stationary. When a photomultiplier tube (PMT) or an avalanche photodiode (APD) is used, there is also a multiplicative excess noise due to the randomness of the internal photodetector gain. Generally speaking, the radio frequency (RF) communication theory cannot be applied to direct detection optical communication systems because noise in RF communication systems is usually additive and Gaussian. A receiver structure which is mathematically optimal for signal dependent shot noise is derived. Several suboptimal receiver structures are discussed and compared with the optimal receiver. The objective is to find a receiver structure which is easy to implement and gives close to optimal performance.

Davidson, Frederic M.↗
NASA NTRS2017

Hemispherical Optical Dome for Underwater Communication

For many years, acoustic systems have been used as the primary method for underwater communication; however, the data transfer rate of such systems is low because sound propagates slowly through the water. A higher throughput can be achieved using visible light to transmit data underwater. The first issue with using this approach is that there is generally a large loss of the light signal due to scattering and absorption in water even though there is an optimal wavelength for transmission in the blue or green wavelengths of the visible spectrum. The second issue is that a simple system consisting only of a highly directional source transmitter and small optical detector receiver has a very narrow field of view. The goal of this project is to improve an optical, underwater communication system by increasing the effective field of view of the receiving optics. To this end, we make two changes to the simple system: (1) An optical dome was added near the receiver. An array of lenses is placed radially on the surface of the dome, reminiscent of the compound eye of an insect. The lenses make the source and detector planes conjugate, and each lens adds a new region of the source plane to the instrument's total field of view. (2) The receiver was expanded to include multiple photodiodes. With these two changes, the receiver has much more tolerance to misalignments (in position and angle) of the transmitter.Two versions of the optical dome (with 6 and 8 diameters) were designed using the CREO CAD software and modeled using the CODE V optical design software. A series of these transparent hemispherical domes, with both design diameters, were manufactured using a 5-axis mill. The prototype was then retrofitted with lenses and compared with the computer-generated model to demonstrate the effectiveness of this solution. This work shows the dome design improves the optical field of view of the underwater communication system considerably. Furthermore, with the experimental test results, a geometric optimization model was derived providing insights to the design performance limits.

Design↗
NASA NTRS1998

A Fiber-Optic Coupled Telescope for Water Vapor DIAL Receivers

A fiber-optic coupled telescope of low complexity was constructed and tested. The major loss mechanisms of the optical system have been characterized. Light collected by the receiver mirror is focused onto an optical fiber, and the output of the fiber is filtered by an interference filter and then focused onto an APD detector. This system was used in lidar field measurements with a 532-nm Nd:YAG laser beam. The results were encouraging. A numerical model used for calculation of the expected return signal agreed with the lidar return signal obtained. The assembled system was easy to align and operate and weighed about 8 kg for a 30 cm (12") mirror system. This weight is low enough to allow mounting of the fiber-optic telescope receiver system in a UAV. Furthermore, the good agreement between the numerical lidar model and the performance of the actual receiver system, suggests that this model may be used for estimation of the performance of this and other lidar systems in the future. Such telescopes are relatively easy to construct and align. The fiber optic cable allows easy placement of the optical detector in any position. These telescope systems should find widespread use in aircraft and space home DIAL water vapor receiver systems.

DeYoung, Russell J.↗
NASA NTRS1998

Fiber-Optic Coupled Lidar Receiver System to Measure Stratospheric Ozone

The measurement of ozone in the atmosphere has become increasingly important over the past two decades. Significant increases of ozone concentrations in the lower atmosphere, or troposphere, and decreases in the upper atmosphere, or stratosphere, have been attributed to man-made causes. High ozone concentrations in the troposphere pose a health hazard to plants and animals and can add to global warming. On the other hand, ozone in the stratosphere serves as a protective barrier against strong ultraviolet (UV) radiation from the sun. Man-made CFC's (chlorofluorocarbons) act as a catalyst with a free oxygen atom and an ozone molecule to produce two oxygen molecules therefore depleting the protective layer of ozone in the stratosphere. The beneficial and harmful effects of ozone require the study of ozone creation and destruction processes in the atmosphere. Therefore, to provide an accurate model of these processes, an ozone lidar system must be able to be used frequently with as large a measurement range as possible. Various methods can be used to measure atmospheric ozone concentrations. These include different airborne and balloon measurements, solar occulation satellite techniques, and the use of lasers in lidar (high detection and ranging,) systems to probe the atmosphere. Typical devices such as weather balloons can only measure within the direct vicinity of the instrument and are therefore used infrequently. Satellites use solar occulation techniques that yield low horizontal and vertical resolution column densities of ozone.

Harper, David Brent↗
NASA NTRS1993

A Prototype Quasi-Optical SIS Array Receiver

We report measurements on a prototype SIS array receiver consisting of a ten-element dipole antenna array with half square micron niobium SIS junctions.

SIS array antenna array mixer array SIS receiver w↗
NASA NTRS1990

Direct detection optical intersatellite link at 220 Mbps using AlGaAs laser diode and silicon APD with 4-ary PPM signaling

A newly developed 220 Mbps free-space 4-ary pulse position modulation (PPM) direct detection optical communication system is described. High speed GaAs integrated circuits were used to construct the PPM encoder and receiver electronic circuits. Both PPM slot and word timing recovery were provided in the PPM receiver. The optical transmitter consisted of an AlGaAs laser diode (Mitsubishi ML5702A, lambda=821nm) and a high speed driver unit. The photodetector consisted of a silicon avalanche photodiode (APD) (RCA30902S) preceded by an optical interference filter (delta lambda=10nm). Preliminary tests showed that the self-synchronized PPM receiver could achieve a receiver bit error rate of less than 10(exp -6) at 25 nW average received optical signal power or 360 photons per transmitted information bit. The relatively poor receiver sensitivity was believed to be caused by the insufficient electronic bandwidth of the APD preamplifier and the poor linearity of the preamplifier high frequency response.

Sun, Xiaoli↗
NASA NTRS2006

Coherent Optical Focal Plane Array Receiver for PPM Signals: Investigation and Applications

The performance of a coherent optical focal plane array receiver for PPM signals under atmospheric turbulence is investigated and applications of this system are addressed. The experimental demonstration of this project has already been explained in previous publications [1]. This article shows a more exhaustive analysis of the expressions needed to obtain the Bit Error Rate (BER) for the real system under study in the laboratory. Selected experimental results of this system are described and compared with theoretical BER expressions, and array combining gains are presented. Receiver sensitivity in terms of photons per bit (PPB) is examined; BER results are shown as a function of signal to noise ratios, (SNR), as well as a function of photons per symbol, and photons per bit.

shot noise limited↗
DOE OSTI2024

MODELING AND METHOD FOR OPTICAL PERFORMANCE OF A RECEIVER COATING AND ITS DEGRADATION DUE TO OPERATION

The optical properties of the coating used on a concentrated solar power (CSP)’s receiver directly impact the performance of the power plant. Receiver coatings are designed to absorb as much heat as possible and transfer it to the circulating fluid. Over time, the absorptivity of the receiver coating degrades due to environmental and operational conditions. This project aims to (1) create a test apparatus that allows coatings to undergo accelerated lifetime testing under conditions that mimic what the coating will experience on-tower; and (2) develop a mathematical model that based on the test data predicts absorptivity over time. To create the mathematical model, samples of BrightSource Energy’s Gen1 and Gen2 coatings were tested first looking at individual failure modes (such as high temperature cycling) and then for combined failure modes in the newly developed apparatus. In addition to taking optical measurements, the samples were destroyed to allow for metalogical evaluation to understand what was happening on a microscopic level. Pre-existing models from the literature that describe accelerated testing as well as individual phenomena observed in the coating were then combined to create the model. Additionally, the Gen2 and Gen3 coatings are being testing at the Plataforma Solar de Almería (PSA) facility in Almeria, Spain to confirm that the apparatus test results are similar to those received on-sun. (PSA’s facility closely mimics on-tower conditions). The goal is to enable industry players to test coatings using the new apparatus, gather absorptivity measurements (without needing to destroy samples), and input the information into the model to determine how the coating will perform over time, thus allowing the optical performance of coatings to be compared even before they are used on-tower. The model will be publicly available by the end of the project (currently projected as December 2024).

14 SOLAR ENERGY↗
NASA NTRS1974

Optical antenna gain. II - Receiving antennas

Expressions are developed for the gain of a centrally obscured, circular optical antenna used as the collecting and focusing optics in a laser receiver, involving losses due to (1) incoming light blockage by central obscuration, (2) energy spillover at the detector, and (3) the effect of local oscillator distribution in the case of heterodyne or homodyne detection. Numerical results are presented for direct detection and for three types of local oscillator distribution (uniform, Gaussian, and matched).

Degnan, J. J.↗
DOE OSTI2022

Solar optical performance of SiC receiver tubes

As part of a DOE Small Business Innovative Research (SBIR) project, CTP explored options to enhance the solar optical properties of its solar receiver tube. Sandia National Laboratories (Sandia) working with CTP, performed high-flux solar simulator tests on several receiver-tube specimens. Furthermore, the results demonstrated the excellent durability and optical performance of SiOC composite receiver tubes at 800°C surface temperatures.

14 SOLAR ENERGY↗
NASA NTRS1993

A 250 GHz planar low noise Schottky receiver

A planar quasi-optical Schottky receiver based on the quasi-integrated horn antenna has been developed and tested over the 230-280 GHz bandwidth. The receiver consists of a planar GaAs Schottky diode placed at the feed of a dipole-probe suspended on a thin dielectric membrane in an etched-pyramidal horn cavity. The diode has a 1.21 micron anode diameter and a low parasitic capacitance due to the use of an etched surface channel. The antenna-mixer results in a measured DSB conversion loss and noise temperature at 258 GHz of 7.2 dB +/- 0.5 dB and 1310 K +/- 70 K, respectively, at room temperature. The design is compatible with SIS mixers, and the low cost of fabrication and simplicity makes it ideal for submillimeter-wave imaging arrays requiring a 10-20 percent bandwidth.

Ali-Ahmad, Walid Y.↗