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NASA NTRS2020

Parabolic Deformable Mirror Testbed for the ExoSpec Project

The ExoSpec Project is a NASA Headquarters directed work package that links four different tasks at Goddard Space Flight Center to enable future missions to more efficiently characterize directly imaged exoplanets. One of the tasks is the development of parabolic deformable mirrors to improve on the current state-of-the-art wavefront sensing and control implementations, which are baselined to have two flat deformable mirrors (DMs) with high actuator count. To effectively control both amplitude and phase aberrations, the flat DMs need to have a large separation, which poses packaging challenges to missions designed to image rocky exoplanets. To eliminate this large separation, the parabolic DM architecture makes the off-axis imaging elements in the optical train controllable. Simulations also show performance enhancements with the architecture change; larger bandwidths have been shown to be controllable with the parabolic DMs and the number of required actuators can be reduced. With a 32×32 pupil flat DM and two 16x16 parabolic DMs, we could obtain a 5 - 12λ/D dark hole at 35%bandwidth. In addition to addressing the packaging challenge faced by future coronagraph missions, reducing the number of actuators reduces both cost and risk of having the entire coronagraph instrument’s performance depend on two high-actuator count DMs. To test these simulations, Goddard is building a testbed and has a vendor developing the parabolic DM. Here we present these simulations, the current testbed performance, and the development plan to incorporate and test the parabolic DMs

Coronagraph↗

NASA NTRS2019

Fast Steering Mirror Disturbance Effects on Overall System Optical Performance for the Large Ultraviolet/optical/infrared Surveyor (LUVOIR) Concept Using a Non-Contact Vibration Isolation and Precision Pointing System

As the optical performance requirements of space telescopes get more stringent, the need to analyze all possible error sources early in the mission design becomes critical. One large telescope with tight performance requirements is the Large Ultraviolet / Optical / Infrared Surveyor (LUVOIR) concept. The LUVOIR concept includes a 15-meter-diameter segmented-aperture telescope with a suite of serviceable instruments operating over a range of wavelengths between 100nm to 2.5um. Using an isolation architecture that involves no mechanical contact between the telescope and the host spacecraft structure allows for tighter performance metrics than current space-based telescopes being flown. Because of this separation, the spacecraft disturbances can be greatly reduced and disturbances on the telescope payload contribute more to the optical performance error. A portion of the optical performance error comes from the disturbances generated from the motion of the Fast Steering Mirror (FSM) on the payload. Characterizing the effects of this disturbance gives insight into the specifications on the FSM needed to achieve the tight optical performance requirements of the overall system. Through analysis of the LUVOIR finite element model and linear optical model given a range of input disturbances at the FSM, the optical performance of the telescope and recommendations for FSM specifications can be determined. The LUVOIR observatory control strategy consists of a multi-loop control architecture including the spacecraft Attitude Control System (ACS), Vibration Isolation and Precision Pointing System (VIPPS), and FSM. This paper focuses on the control loop containing the FSM disturbances and their effects on the telescope optical performance.

Sacks, Lia W.↗

NASA NTRS1986

Optical techniques to feed and control GaAs MMIC modules for phased array antenna applications

A complex signal distribution system is required to feed and control GaAs monolithic microwave integrated circuits (MMICs) for phased array antenna applications above 20 GHz. Each MMIC module will require one or more RF lines, one or more bias voltage lines, and digital lines to provide a minimum of 10 bits of combined phase and gain control information. In a closely spaced array, the routing of these multiple lines presents difficult topology problems as well as a high probability of signal interference. To overcome GaAs MMIC phased array signal distribution problems optical fibers interconnected to monolithically integrated optical components with GaAs MMIC array elements are proposed as a solution. System architecture considerations using optical fibers are described. The analog and digital optical links to respectively feed and control MMIC elements are analyzed. It is concluded that a fiber optic network will reduce weight and complexity, and increase reliability and performance, but higher power will be required.

Bhasin, K. B.↗

NASA NTRS1986

Optical techniques to feed and control GaAs MMIC modules for phased array antenna applications

Bhasin, K. B.↗

NASA NTRS1996

Modified-Signed-Digit Optical Computing Using Fan-Out

Experimental optical computing system containing optical fan-out elements implements modified signed-digit (MSD) arithmetic and logic. In comparison with previous optical implementations of MSD arithmetic, this one characterized by larger throughput, greater flexibility, and simpler optics.

Liu, Hua-Kuang↗

NASA NTRS2008

Efficient Coupler for a Bessel Beam Dispersive Element

A document discusses overcoming efficient optical coupling to high orbital momentum modes by slightly bending the taper dispersive element. This little shape distortion is not enough to scramble the modes, but it allows the use of regular, free-beam prism coupling, fiber coupling, or planar fiber on-chip coupling with, ultimately, 100 percent efficiency. The Bessel-beam waveguide is bent near the contact with the coupler, or a curved coupler is used. In this case, every Bessel-beam mode can be successfully coupled to a collimated Gaussian beam. Recently developed Bessel-beam waveguides allow long optical delay and very high dispersion. Delay values may vary from nanoseconds to microseconds, and dispersion promises to be at 100 s/nm. Optical setup consisted of a red laser, an anamorphic prism pair, two prism couplers, and a bent, single-mode fiber attached to prisms. The coupling rate increased substantially and corresponded to the value determined by the anamorphic prism pair.

Savchenkov, Anatoliy↗

NASA NTRS1995

Prototype Focal-Plane-Array Optoelectronic Image Processor

Prototype very-large-scale integrated (VLSI) planar array of optoelectronic processing elements combines speed of optical input and output with flexibility of reconfiguration (programmability) of electronic processing medium. Basic concept of processor described in "Optical-Input, Optical-Output Morphological Processor" (NPO-18174). Performs binary operations on binary (black and white) images. Each processing element corresponds to one picture element of image and located at that picture element. Includes input-plane photodetector in form of parasitic phototransistor part of processing circuit. Output of each processing circuit used to modulate one picture element in output-plane liquid-crystal display device. Intended to implement morphological processing algorithms that transform image into set of features suitable for high-level processing; e.g., recognition.

Fang, Wai-Chi↗

NASA NTRS2016

Active Full-Shell Grazing-Incidence Optics

MSFC has a long history of developing full-shell grazing-incidence x-ray optics for both narrow (pointed) and wide field (surveying) applications. The concept presented in this paper shows the potential to use active optics to switch between narrow and wide-field geometries, while maintaining large effective area and high angular resolution. In addition, active optics has the potential to reduce errors due to mounting and manufacturing lightweight optics. The design presented corrects low spatial frequency error and has significantly fewer actuators than other concepts presented thus far in the field of active x-ray optics. Using a finite element model, influence functions are calculated using active components on a full-shell grazing-incidence optic. Next, the ability of the active optic to effect a change of optical prescription and to correct for errors due to manufacturing and mounting is modeled.

Full-shell↗

NASA NTRS1989

Development of fiber-based laser anemometer for SSME application

A recent study by Rocketdyne for NASA identified laser anemometry, using a compact optical head, as a feasible diagnostic instrument for the Space Shuttle Main Engine (SSME) Model Verification experiments. Physical Research, Inc. (PRI) is presently under contract from NASA Lewis to develop and deliver such a laser anemometer system. For this application, it is desired to place the laser at a remote distance from the engine, and use single mode polarization preserving fiber optics for the transmission of the laser light to and from the measurement head. Other requirements are given. Analytical and experimental tools are being used to develop the technologies required for the laser anemometer. These include finite element analysis of the optical head and vibration tests for various optical and mechanical components. Design of the optical head and the fiber optic connectors are driven by the temperature and vibration requirements for the measurement environment. Results of the finite element analysis and the vibration tests of the components are included. Conceptual design of the fiber optic launcher and the optical probe has also been complete. Detailed design of the probe as well as the fabrication and assembly of the components is in progress.

Modarress, Dariush↗

NASA NTRS1992

Acousto-optic filtering of lidar signals

The predominant part of the noise in lidar receivers is created by the background radiation; therefore, one of the most important elements of the receiving optics is a spectrally selecting filter placed in front of the photodetector. Interference filters are usually used to transmit a given wavelength. Specific properties of the interference filters, such as simple design, reliability, small size, and large aperture, combined with high transmission coefficient and narrow spectral band, make them the preferred spectral device in many cases. However, problems arise in applications such as the Differential Absorption Lidar (DIAL) technique, where fast tuning within a wide spectral region is necessary. Tunable acousto-optical filters (TAOF), used recently in astrophysical observations to suppress the background radiation, can be employed with success in lidar sounding. They are attractive due to the possibility for fast spectral scanning with a narrow transmission band. The TAOF's advantages are fully evident in DIAL lidars where one must simultaneously receive signals at two laser frequencies.

Kolarov, G.↗

NASA NTRS1992

Developments on high temperature fiber optic microphone

A fiber optic microphone, based on the principle of the fiber optic lever, features small size, extended bandwidth, and capability to operate at high temperatures. These are requirements for measurements in hypersonic flow. This paper describes the principles of operation of fiber optic sensors, a discussion of the design of a fiber optic microphone, the functional elements and packaging techniques of the optoelectronic circuitry, and the calibration techniques used in the development of the high temperature fiber optic microphone.

Wright, Kenneth D., II↗

NASA NTRS1991

Spatiospectral and picosecond spatiotemporal properties of a broad area operating channeled-substrate-planar laser array

Spatiospectral and spatiotemporal properties of an eight-element channeled-substrate-planar laser array are investigated in both CW and pulsed operating conditions. The closely spaced CSP array with strong optical coupling between array elements is characterized by a broad area laserlike operation determined by its spatial mode spectra. The spatiotemporal evolution of the near and far field exhibits complex dynamic behavior in the picosecond to nanosecond domain. Operating parameters for the laser device have been experimentally determined. These results provide important information for the evaluation of the dynamic behavior of coherent semiconductor laser arrays.

Yu, NU↗

NASA NTRS1985

Design, performance investigation and delivery of a miniaturized Cassegrainian concentrator solar array

A miniaturized Cassegrainian concentrator (MCC) solar array concept is being developed with the objective of significantly reducing the recurring cost of multikilowatt solar arrays. The desired cost reduction is obtained as a result of using very small high efficiency solar cells in conjunction with low-cost optics. In the MCC single element concept and panel concept, incident solar radiation is reflected from a primary parabolic reflector to a secondary hyperbolic reflector and finally to a 4-millimetr diameter solar cell. A light catcher cone is used to improve off-axis performance. An element is approximately 13-millimeters thick which permits efficient launch stowage of the concentrator system panels without complex optical component deployments or retractions. The MCC elements are packed in bays within graphite epoxy frames and are electrically connected into appropriate series-parallel circuits. A MCC single element with a 21 sq cm entrance aperture and a 20 percent efficient, 0.25 sq cm gallium arsenide solar cell has the same power output as 30-sq cm of 11-percent efficiency (at 68 C) silicon solar cells. The MCC concept provides the potential for a significant reduction in array cost due to a 99 percent reduction in required cell area and a 30 percent reduction in array area relative to planar array of equivalent power.

Patterson, R. E.↗

NASA NTRS2006

Holographic Plossl Retroreflectors

Holographic retroreflectors that function equivalently to Plossl eyepieces have been developed and used in free-space optical communication systems that utilize laser beams. Plossl eyepieces are well known among telescope designers. They have been adopted for use a retroreflectors and as focusing elements (for reception) and collimating elements (for transmission) in optical communication systems. A retro-reflector that incorporates a Plossl eyepiece is termed a cat's-eye retroreflector.

Waluschka, Eugene↗

NASA NTRS1993

First oxygen from lunar basalt

The Carbotek/Shimizu process to produce oxygen from lunar soils has been successfully demonstrated on actual lunar samples in laboratory facilities at Carbotek with Shimizu funding and support. Apollo sample 70035 containing approximately 25 percent ilmenite (FeTiO3) was used in seven separate reactions with hydrogen varying temperature and pressure: FeTiO3 + H2 yields Fe + TiO2 + H2O. The experiments gave extremely encouraging results as all ilmenite was reduced in every experiment. The lunar ilmenite was found to be about twice as reactive as terrestrial ilmenite samples. Analytical techniques of the lunar and terrestrial ilmenite experiments performed by NASA Johnson Space Center include iron Mossbauer spectroscopy (FeMS), optical microscopy, SEM, TEM, and XRD. The Energy and Environmental Research Center at the University of North Dakota performed three SEM techniques (point count method, morphology determination, elemental mapping), XRD, and optical microscopy.

Gibson, M. A.↗

NASA NTRS1983

Beam Splitter Introduces Little Aberration

Placing beam splitter inside existing lens minimizes aberrations. Six channel beam splitter has optical paths of lengths equal to distances traveled by rays. Lens element cemented to each of exit faces of beam splitter is optically concentric with element cemented to entrance face and with center of curvature of monocentric optical system. Beam splitter makes it possible to form separate image in each wavelength channel of interest.

Evans, N. L., Jr.↗

NASA NTRS2008

Dispersion-Enhanced Laser Gyroscope

We analyze the effect of a highly dispersive element placed inside a modulated optical cavity on the frequency and amplitude of the output modulation to determine the conditions for enhanced gyroscopic sensitivities. The element is treated as both a phase and amplitude filter, and the time-dependence of the cavity field is considered. Both atomic gases (two-level and multi-level) and optical resonators (single and coupled) are considered and compared as dispersive elements. We find that it is possible to simultaneously enhance the gyro scale factor sensitivity and suppress the dead band by using an element with anomalous dispersion that has greater loss at the carrier frequency than at the side-band frequencies, i.e., an element that simultaneously pushes and intensifies the perturbed cavity modes, e.g. a two-level absorber or an under-coupled optical resonator. The sensitivity enhancement is inversely proportional to the effective group index, becoming infinite at a group index of zero. However, the number of round trips required to reach a steady-state also becomes infinite when the group index is zero (or two). For even larger dispersions a steady-state cannot be achieved, and nonlinear dynamic effects such as bistability and periodic oscillations are predicted in the gyro response.

Smith, David D.↗

NASA NTRS2001

Integrated Modeling of Optical Systems (IMOS): An Assessment and Future Directions

Integrated Modeling of Optical Systems (IMOS) is a finite element-based code combining structural, thermal, and optical ray-tracing capabilities in a single environment for analysis of space-based optical systems. We'll present some recent examples of IMOS usage and discuss future development directions. Due to increasing model sizes and a greater emphasis on multidisciplinary analysis and design, much of the anticipated future work will be in the areas of improved architecture, numerics, and overall performance and analysis integration.

Moore, Gregory↗