Dr. Xin An Profile

Dr. Xin An

Optical Engineer at Jet Propulsion Lab

SPIE Involvement:

Author

Publications (28)

Proceedings Article | 1 September 2017 Presentation + Paper

Dynamic testbed demonstration of WFIRST coronagraph low order wavefront sensing and control (LOWFS/C)

Fang Shi, Eric Cady, Byoung-Joon Seo, Xin An, Kunjithapatham Balasubramanian, Brian Kern, Raymond Lam, David Marx, Dwight Moody, Camilo Mejia Prada, Keith Patterson, Ilya Poberezhskiy, Joel Shields, Erkin Sidick, Hong Tang, John Trauger, Tuan Truong, Victor White, Daniel Wilson, Hanying Zhou

Proceedings Volume 10400, 104000D (2017) https://doi.org/10.1117/12.2274887

KEYWORDS: Wavefront sensors, Wavefronts, Mirrors, Deformable mirrors, Environmental sensing, Phase shifting, Optical telescopes, Optical fabrication, Device simulation, Space telescopes

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SPIE Journal Paper | 28 October 2015

Demonstration of high contrast with an obscured aperture with the WFIRST-AFTA shaped pupil coronagraph

Eric Cady, Camilo Mejia Prada, Xin An, Kunjithapatham Balasubramanian, Rosemary Diaz, N. Jeremy Kasdin, Brian Kern, Andreas Kuhnert, Bijan Nemati, Ilya Poberezhskiy, A. J. Eldorado Riggs, Robert Zimmer, Neil Zimmerman

JATIS, Vol. 2, Issue 01, 011004, (October 2015) https://doi.org/10.1117/12.10.1117/1.JATIS.2.1.011004

KEYWORDS: Coronagraphy, Photomasks, Planets, Point spread functions, Telescopes, Infrared telescopes, Semiconducting wafers, Reflectivity, Wavefronts, Data modeling

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The coronagraph instrument on the Wide-Field Infrared Survey Telescope-Astrophysics-Focused Telescope Asset (WFIRST-AFTA) mission study has two coronagraphic architectures, shaped pupil and hybrid Lyot, which may be interchanged for use in different observing scenarios. Each architecture relies on newly developed mask components to function in the presence of the AFTA aperture, and so both must be matured to a high technology readiness level in advance of the mission. A series of milestones were set to track the development of the technologies required for the instrument; we report on completion of WFIRST-AFTA coronagraph milestone 2—a narrowband 10−8 contrast test with static aberrations for the shaped pupil—and the plans for the upcoming broadband coronagraph milestone 5.

Proceedings Article | 16 September 2015

Laboratory performance of the shaped pupil coronagraphic architecture for the WFIRST/AFTA coronagraph

Eric Cady, Camilo Mejia Prada, Xin An, Kunjithapatham Balasubramanian, Rosemary Diaz, N. Jeremy Kasdin, Brian Kern, Andreas Kuhnert, Bijan Nemati, Keith Patterson, Ilya Poberezhskiy, A. J. Eldorado Riggs, Daniel Ryan, Hanying Zhou, Robert Zimmer, Neil Zimmerman

Proceedings Volume 9605, 96050B (2015) https://doi.org/10.1117/12.2189113

KEYWORDS: Coronagraphy, Photomasks, Telescopes, Point spread functions, Microscopes, Infrared telescopes, Silicon, Binary data, Infrared radiation, Stars

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One of the two primary architectures being tested for the WFIRST-AFTA coronagraph instrument is the shaped pupil coronagraph, which uses a binary aperture in a pupil plane to create localized regions of high contrast in a subsequent focal plane. The aperture shapes are determined by optimization, and can be designed to work in the presence of secondary obscurations and spiders - an important consideration for coronagraphy with WFIRST-AFTA. We present the current performance of the shaped pupil testbed, including the results of AFTA Milestone 2, in which ≈ 6 × 10^-9 contrast was achieved in three independent runs starting from a neutral setting.

Proceedings Article | 2 August 2014

Technology development towards WFIRST-AFTA coronagraph

Ilya Poberezhskiy, Feng Zhao, Xin An, Kunjithapatham Balasubramanian, Ruslan Belikov, Eric Cady, Richard Demers, Rosemary Diaz, Qian Gong, Brian Gordon, Renaud Goullioud, Frank Greer, Olivier Guyon, Michael Hoenk, N. Jeremy Kasdin, Brian Kern, John Krist, Andreas Kuhnert, Michael McElwain, Bertrand Mennesson, Dwight Moody, Richard Muller, Bijan Nemati, Keith Patterson, A. J. Riggs, Daniel Ryan, Byoung-Joon Seo, Stuart Shaklan, Erkin Sidick, Fang Shi, Nicholas Siegler, Rémi Soummer, Hong Tang, John Trauger, J. Kent Wallace, Xu Wang, Victor White, Daniel Wilson, Karl Yee, Hanying Zhou, Neil Zimmerman

Proceedings Volume 9143, 91430P (2014) https://doi.org/10.1117/12.2060320

KEYWORDS: Coronagraphy, Sensors, Wavefronts, Wavefront sensors, Iterated function systems, Photomasks, Space telescopes, Exoplanets, Deformable mirrors, Planets

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NASA’s WFIRST-AFTA mission concept includes the first high-contrast stellar coronagraph in space. This coronagraph will be capable of directly imaging and spectrally characterizing giant exoplanets similar to Neptune and Jupiter, and possibly even super-Earths, around nearby stars. In this paper we present the plan for maturing coronagraph technology to TRL5 in 2014-2016, and the results achieved in the first 6 months of the technology development work. The specific areas that are discussed include coronagraph testbed demonstrations in static and simulated dynamic environment, design and fabrication of occulting masks and apodizers used for starlight suppression, low-order wavefront sensing and control subsystem, deformable mirrors, ultra-low-noise spectrograph detector, and data post-processing.

Proceedings Article | 15 September 2011

Diamond turned high precision PIAA optics and four mirror PIAA system for high contrast imaging of exo-planets

Kunjithapatham Balasubramanian, Eric Cady, Laurent Pueyo, Xin An, Stuart Shaklan, Olivier Guyon, Ruslan Belikov

Proceedings Volume 8151, 815105 (2011) https://doi.org/10.1117/12.892849

KEYWORDS: Mirrors, Manufacturing, Imaging systems, Coronagraphy, Wavefronts, Diamond, Diffraction, Geometrical optics, Precision optics, Optics manufacturing

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Off-axis, high-sag PIAA optics for high contrast imaging present challenges in manufacturing and testing. With smaller form factors and consequently smaller surface deformations (< 80 microns), diamond turned fabrication of these mirrors becomes feasible. Though such a design reduces the system throughput, it still provides 2λ/D inner working angle. We report on the design, fabrication, measurements, and initial assessment of the novel PIAA optics in a coronagraph testbed. We also describe, for the first time, a four mirror PIAA coronagraph that relaxes apodizer requirements and significantly improves throughput while preserving the low-cost benefits.

Proceedings Article | 22 July 2010

Progress on SIM-Lite brassboard interferometer integration and test

I. Hahn, M. Weilert, X. An, G. Kuan, L. Hovland, R. Smythe, E. Hovland, R. Krylo, M. Fisher, Z. Chang, J. Cepeda-Rizo, J. Shields, A. Ahmed, N. Fathpour, J. Carson, F. Nicaise, M. Morales, F. Dekens, R. Goullioud

Proceedings Volume 7734, 77344K (2010) https://doi.org/10.1117/12.858288

KEYWORDS: Interferometers, Stars, Modulation, Mirrors, Telescopes, Metrology, Beam splitters, Cameras, CCD image sensors, Interferometry

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Main brassboard Michelson interferometer components have been recently developed for the future flight phase implementations of SIM Lite mission. These brassboard components include two fine steering mirrors, pathlength modulation and cyclic averaging optics and astrometric beam combiner assembly. Field-independent performance tests will be performed in a vacuum chamber using two siderostats in retro-reflecting positions and a white light stimulus. The brightness and color dependence of the angle and fringe tracking performance will be measured. The performance of filtering algorithms will be tested in a simulated spacecraft attitude control system perturbation. To demonstrate capability of a dim star observation, the angle and fringe tracking CCD sensors are cooled to -110 C using a cold diode heat pipe system. The new feed-forward control (angle and path-length) algorithms for the dim star observation will be tested as well. In this paper, we will report the recent progress toward the integration and performance tests of the brassboard interferometer.

Proceedings Article | 22 July 2010

Mitigation of angle tracking errors due to color dependent centroid shifts in SIM Lite

Bijan Nemati, Xin An, Renaud Goullioud, Michael Shao, Tsae-Pyng Shen, Udo Wehmeier, Mark Weilert, Xu Wang, Thomas Werne, Janet Wu, Chengxing Zhai

Proceedings Volume 7734, 77344I (2010) https://doi.org/10.1117/12.857778

KEYWORDS: Stars, Interferometers, Metrology, Cameras, Wavefronts, Point spread functions, Charge-coupled devices, Optical alignment, CCD cameras, Beam splitters

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The SIM-Lite astrometric interferometer will search for Earth-size planets in the habitable zones of nearby stars. In this search the interferometer will monitor the astrometric position of candidate stars relative to nearby reference stars over the course of a 5 year mission. The elemental measurement is the angle between a target star and a reference star. This is a two-step process, in which the interferometer will each time need to use its controllable optics to align the starlight in the two arms with each other and with the metrology beams. The sensor for this alignment is an angle tracking CCD camera. Various constraints in the design of the camera subject it to systematic alignment errors when observing a star of one spectrum compared with a start of a different spectrum. This effect is called a Color Dependent Centroid Shift (CDCS) and has been studied extensively with SIM-Lite's SCDU testbed. Here we describe results from the simulation and testing of this error in the SCDU testbed, as well as effective ways that it can be reduced to acceptable levels.

Proceedings Article | 22 July 2010

SIM interferometer testbed (SCDU) status and recent results

Bijan Nemati, Xin An, Renaud Goullioud, Michael Shao, Tsae-Pyng Shen, Udo Wehmeier, Mark Weilert, Xu Wang, Thomas Werne, Janet Wu, Chengxing Zhai

Proceedings Volume 7734, 77341N (2010) https://doi.org/10.1117/12.856300

KEYWORDS: Stars, Calibration, Interferometers, Error analysis, Metrology, Wavefronts, Spectral calibration, CCD cameras, Cameras, Light sources

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SIM Lite is a space-borne stellar interferometer capable of searching for Earth-size planets in the habitable zones of nearby stars. This search will require measurement of astrometric angles with sub micro-arcsecond accuracy and optical pathlength differences to 1 picometer by the end of the five-year mission. One of the most significant technical risks in achieving this level of accuracy is from systematic errors that arise from spectral differences between candidate stars and nearby reference stars. The Spectral Calibration Development Unit (SCDU), in operation since 2007, has been used to explore this effect and demonstrate performance meeting SIM goals. In this paper we present the status of this testbed and recent results.

Proceedings Article | 22 July 2010

SCDU testbed automated in-situ alignment, data acquisition, and analysis

Thomas Werne, Udo Wehmeier, Janet Wu, Xin An, Renaud Goullioud, Bijan Nemati, Michael Shao, Tsae-Pyng Shen, Xu Wang, Mark Weilert, Chengxing Zhai

Proceedings Volume 7734, 77344F (2010) https://doi.org/10.1117/12.857525

KEYWORDS: MATLAB, Computing systems, Cameras, Data storage, Data processing, Data acquisition, Distributed computing, Human-machine interfaces, Control systems, Real-time computing

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In the course of fulfilling its mandate, the Spectral Calibration Development Unit (SCDU) testbed for SIM-Lite produces copious amounts of raw data. To effectively spend time attempting to understand the science driving the data, the team devised computerized automations to limit the time spent bringing the testbed to a healthy state and commanding it, and instead focus on analyzing the processed results. We developed a multi-layered scripting language that emphasized the scientific experiments we conducted, which drastically shortened our experiment scripts, improved their readability, and all-but-eliminated testbed operator errors. In addition to scientific experiment functions, we also developed a set of automated alignments that bring the testbed up to a well-aligned state with little more than the push of a button. These scripts were written in the scripting language, and in Matlab via an interface library, allowing all members of the team to augment the existing scripting language with complex analysis scripts. To keep track of these results, we created an easilyparseable state log in which we logged both the state of the testbed and relevant metadata. Finally, we designed a distributed processing system that allowed us to farm lengthy analyses to a collection of client computers which reported their results in a central log. Since these logs were parseable, we wrote query scripts that gave us an effortless way to compare results collected under different conditions. This paper serves as a case-study, detailing the motivating requirements for the decisions we made and explaining the implementation process.

Proceedings Article | 22 July 2010

The SIM Lite Astrometric Observatory: engineering risk reduction activity

Renaud Goullioud, Frank Dekens, Bijan Nemati, Xin An, Larry Hovland

Proceedings Volume 7734, 77341M (2010) https://doi.org/10.1117/12.857721

KEYWORDS: Interferometers, Stars, Telescopes, Metrology, Mirrors, Cameras, Space telescopes, Sensors, Actuators, Calibration

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The SIM Lite Astrometric Observatory is a mission concept for a space-borne instrument to perform micro-arcsecond narrow-angle astrometry to search 60 to 100 nearby stars for Earth-like planets, and to perform global astrometry for a broad astrophysics program. The main enabling technology development for the mission was completed during phases A & B. While the project is waiting for the results of the ASTRO2010 Decadal Survey to proceed into flight implementation, the instrument team is currently converting the developed technology onto flight-ready engineering models. These key engineering tasks will significantly reduce the implementation risks during the flight phases C & D of the mission. The main optical interferometer components, including the astrometric beam combiner (ABC), the fine steering mechanism (FSM), the path-length control and modulation optical mechanisms (POM & MOM), focal plane camera electronics (ATC & FTC), camera cooling cryo-heat pipe, and the siderostat mechanism are currently under development. Main assemblies are built to meet flight requirements and have been or will be subjected to flight qualification level environmental testing (random vibration and thermal cycling) and performance testing. The Spectral Calibration Development Unit (SCDU), a white light interferometer testbed has recently demonstrated how to perform the spectral calibration of the instrument. The Guide 2 Telescope testbed (G2T) has demonstrated the 50 micro-arcsecond angle monitoring capability required by SIM Lite to perform astrometry. This paper summarizes recent progress in engineering risk reduction activities.

Proceedings Article | 22 July 2010

SIM Lite mission spectral calibration sensitivities and refinements

C. Zhai, X. An, R. Goullioud, B. Nemati, M. Shao, J. Shen, X. Wang, U. Wehmeier, M. Weilert, T. Werne, J. Wu

Proceedings Volume 7734, 77341J (2010) https://doi.org/10.1117/12.856336

KEYWORDS: Calibration, Spectral calibration, Error analysis, Stars, Modulation, Ferroelectric materials, Data modeling, Phase shift keying, Fourier transforms, Optical filters

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SIM-Lite missions will perform astrometry at microarcsecond accuracy using star light interferometry. For typical baselines that are shorter than 10 meters, this requires to measure optical path difference (OPD) accurate to tens of picometers calling for highly accurate calibration. A major challenge is to calibrate the star spectral dependency in fringe measurements - the spectral calibration. Previously, we have developed a spectral calibration and estimation scheme achieving picometer level accuracy. In this paper, we present the improvements regarding the application of this scheme from sensitivity studies. Data from the SIM Spectral Calibration Development Unit (SCDU) test facility shows that the fringe OPD is very sensitive to pointings of both beams from the two arms of the interferometer. This sensitivity coupled with a systematic pointing error provides a mechanism to explain the bias changes in 2007. Improving system alignment can effectively reduce this sensitivity and thus errors due to pointing errors. Modeling this sensitivity can lead to further improvement in data processing. We then investigate the sensitivity to a model parameter, the bandwidth used in the fringe model, which presents an interesting trade between systematic and random errors. Finally we show the mitigation of calibration errors due to system drifts by interpolating instrument calibrations. These improvements enable us to use SCDU data to demonstrate that SIM-Lite missions can meet the 1pm noise floor requirement for detecting earth-like exoplanets.

Proceedings Article | 2 September 2008

Broadband white light laser combiner system

Daniel Ryan, Alireza Azizi, Xin An, Hong Tang, Richard Demers

Proceedings Volume 7056, 705623 (2008) https://doi.org/10.1117/12.804262

KEYWORDS: Light, Cameras, Multimode fibers, Calibration, Light sources, Mirrors, Fiber lasers, Photonic crystal fibers, Single mode fibers, Visible radiation

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The SIM-Planetquest (Space Interferometry Mission), currently under development at the Jet Propulsion Laboratory, consists of two 6-meter baseline interferometers on a flexible truss. SIM's science goals require 1μas accuracy in its astrometric measurements[1]. To achieve this level of accuracy for detecting planets SIM built the Spectrum Calibration Development Unit (SCDU) testbed. The testbed requires a white light point source with broadband spectrum. Before each long test the spectrum on the camera must be calibrated. To achieve this task a laser light visible to camera was coupled to the white light source. The light system needed pointing stability of better than 4 micro-radians and a minimum optical power level at the fringe tracking camera. Due to stability requirement of the experiment, the setup, including the point source is in a vacuum chamber. To get a broadband spectrum point source inside the vacuum chamber white light from a multimode fiber was combined with laser light in free space to a photonics crystal fiber (PCF). The output is a single mode, broadband, and Gaussian beam. This paper explains the details of such a design and shows some of the results.

Proceedings Article | 28 July 2008

Achievements of picometer performance from interferometer spectral calibration development unit (SCDU)

Tsae-Pyng Janice Shen, ChengXing Zhai, Xin An, Hong Tang, George Sun, Richard Demers

Proceedings Volume 7013, 701350 (2008) https://doi.org/10.1117/12.790586

KEYWORDS: Spectral calibration, Calibration, Dispersion, Optical coatings, Optical alignment, Interferometers, Metrology, Surface conduction electron emitter displays, Stars, Optical filters

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This paper will present the analysis results taken from a well-designed interferometer SCDU. The objective is to deliver picometer performance to meet the allocated astrometric error budget from SIM PlanetQuest mission. It will describe the validation of optical designs and analysis procedures to achieve high accuracy of the tip-tilt and shear alignments. Then it will enumerate environmental factors essential to the SCDU performances. Finally it will report color-independent 3 picometer Narrow Angle (NA) performance and all-in-one 17 picometer NA performance. The all-in-one pico-performance will require spectral calibration modeling to remove delay differential induced by color.

Proceedings Article | 28 July 2008

Picometer accuracy white light fringe modeling for SIM PlanetQuest spectral calibration development unit

C. Zhai, J. Yu, M. Shao, R. Goullioud, X. An, R. Demers, M. Milman, T. Shen, H. Tang

Proceedings Volume 7013, 70134Z (2008) https://doi.org/10.1117/12.790294

KEYWORDS: Calibration, Spectral calibration, Data modeling, Fourier transforms, Wavefronts, Charge-coupled devices, Optical filters, Monte Carlo methods, Modulation, Signal detection

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The SIM PlanetQuest Mission will perform astrometry to one microarcsecond accuracy using optical interferometers requiring optical path delay difference (OPD) measurements accurate to tens of picometers. Success relies on very precise calibration. Spectral Calibration Development Unit (SCDU) has been built to demonstrate the capability of calibrating spectral dependency of the white light fringe OPD to accuracy better than 20pm. In this article, we present the spectral calibration modeling work for SCDU to achieve the SIM PlanetQuest Engineering Milestone 4. SCDU data analysis shows that the wave front aberrations cause the instrument phase dispersions to vary by tens of nanometers over the bandwidth of a CCD pixel making the previous model inadequate. We include the effect of the wave front aberrations in the white light fringe model and develop a procedure for calibrating the corresponding model parameters using long stroke fringe data based on Discrete Fourier Transform. We make the calibration procedure flight traceable by dividing the whole calibration into the instrument calibration and the source spectral calibration. End-to-end simulations are used to quantify both the systematic and random errors in spectral calibration. The efficacy of the calibration scheme is demonstrated using the SCDU experimental data.

Proceedings Article | 28 July 2008

Brassboard Astrometric Beam Combiner (ABC) development for the Space Interferometry Mission (SIM)

Muthu Jeganathan, Gary Kuan, Mike Rud, Sean Lin, Kristen Sutherland, James Moore, Xin An

Proceedings Volume 7013, 70134X (2008) https://doi.org/10.1117/12.789520

KEYWORDS: Mirrors, Simulation of CCA and DLA aggregates, Cameras, Camera shutters, Optical alignment, Staring arrays, Interferometry, Metrology, Mechanical engineering, Off axis mirrors

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The Astrometric Beam Combiner (ABC) is a critical element of the Space Interferometry Mission (SIM) that performs three key functions: coherently combine starlight from two siderostats; individually detect starlight for angle tracking; and disperse and detect the interferometric fringes. In addition, the ABC contains: a stimulus, cornercubes and shutters for in-orbit calibration; several tip/tilt mirror mechanisms for in-orbit alignment; and internal metrology beam launcher for pathlength monitoring. The detailed design of the brassboard ABC (which has the form, fit and function of the flight unit) is complete, procurement of long-lead items is underway, and assembly and testing is expected to be completed in Spring 2009. In this paper, we present the key requirements for the ABC, details of the completed optical and mechanical design as well as plans for assembly and alignment.

Proceedings Article | 28 July 2008

Spectral calibration at the picometer level on SCDU (spectral calibration development unit)

Richard Demers, Xin An, Alireza Azizi, Gary Brack, Oliver Lay, Daniel Ryan, Janice Shen, George Sun, Hong Tang, Chengxing Zhai

Proceedings Volume 7013, 70132H (2008) https://doi.org/10.1117/12.790653

KEYWORDS: Spectral calibration, Metrology, Calibration, Wavefronts, Stars, Beam splitters, Servomechanisms, Mirrors, Optical filters, Interferometers

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SCDU (Spectral Calibration Development Unit) is a vacuum test bed that was built and operated for the SIM-Planetquest Mission and has successfully demonstrated the calibration of spectral instrument error to an accuracy of better than 20 picometers. This performance is consistent with the 1 micro-arc second goal of SIM. The calibration procedure demonstrated in the test bed is traceable to the SIM flight instrument. This article is a review of all aspects of the design and operation of the hardware as well as the methodology for spectral calibration. Spectral calibration to better than 20 picometers and implications for flight are discussed.

Proceedings Article | 23 June 2006

Demonstration of spectral calibration for stellar interferometry

Richard Demers, Xin An, Hong Tang, Mayer Rud, Andrew Kissil, Eug-Yun Kwack

Proceedings Volume 6268, 62682H (2006) https://doi.org/10.1117/12.672604

KEYWORDS: Beam splitters, Calibration, Interferometers, Optical coatings, Glasses, Spectral calibration, Metrology, Mirrors, Optical alignment, Fourier transforms

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A breadboard is under development to demonstrate the calibration of spectral errors in microarcsecond stellar interferometers. Analysis shows that thermally and mechanically stable hardware in addition to careful optical design can reduce the wavelength dependent error to tens of nanometers. Calibration of the hardware can further reduce the error to the level of picometers. The results of thermal, mechanical and optical analysis supporting the breadboard design will be shown.

Proceedings Article | 14 February 2005

Laser metrology in the micro-arcsecond metrology testbed

Xin An, David Marx, Renaud Goullioud, Feng Zhao

Proceedings Volume 5634, (2005) https://doi.org/10.1117/12.580030

KEYWORDS: Metrology, Interferometers, Laser metrology, Heterodyning, Stars, Sensors, Mirrors, Electronics, Optical alignment, Diffraction

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The Space Interferometer Mission (SIM), scheduled for launch in 2009, is a space-born visible light stellar interferometer capable of micro-arcsecond-level astrometry. The Micro-Arcsecond Metrology testbed (MAM) is the ground-based testbed that incorporates all the functionalities of SIM minus the telescope, for mission-enabling technology development and verification. MAM employs a laser heterodyne metrology system using the Sub-Aperture Vertex-to-Vertex (SAVV) concept. In this paper, we describe the development and modification of the SAVV metrology launchers and the metrology instrument electronics, precision alignments and pointing control, locating cyclic error sources in the MAM testbed and methods to mitigate the cyclic errors, as well as the performance under the MAM performance metrics.

Proceedings Article | 24 May 2000

Optically programmable gate array

Jose Mumbru, George Panotopoulos, Demetri Psaltis, Xin An, Fai Mok, Suat Ay, Sandor Barna, Eric Fossum

Proceedings Volume 4089, (2000) https://doi.org/10.1117/12.386900

KEYWORDS: Logic, Sensors, Photodetectors, Field programmable gate arrays, Interfaces, Signal detection, Optical arrays, Holograms, Optical storage, Holography

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The Optically Programmable Gate Array (OPGA), an optical version of a conventional FPGA, benefits from a direct parallel interface between an optical memory and a logic circuit. The OPGA utilizes a holographic memory accessed by an array of VCSELs to program its logic. An active pixel sensor array incorporated into the OPGA chip makes it possible to optically address the logic in a very short time allowing for rapid dynamic reconfiguration. Combining spatial and shift multiplexing to store the configuration pages in the memory, the OPGA module can be made compact. The reconfiguration capability of the OPGA can be applied to solve more efficiently problems in pattern recognition and database search.

Proceedings Article | 22 November 1999

Holographic optical disc

Gan Zhou, Xin An, Allen Pu, Demetri Psaltis, Fai Mok

Proceedings Volume 3802, (1999) https://doi.org/10.1117/12.370229

KEYWORDS: Holography, Holograms, Sensors, Data storage, Pulsed laser operation, Multiplexing, Optical discs, Computing systems, Spatial light modulators, Signal detection

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The holographic disc is a high capacity, disk-based data storage device that can provide the performance for next generation mass data storage needs. With a projected capacity approaching 1 terabit on a single 12 cm platter, the holographic disc has the potential to become a highly efficient storage hardware for data warehousing applications. The high readout rate of holographic disc makes it especially suitable for generating multiple, high bandwidth data streams such as required for network server computers. Multimedia applications such as interactive video and HDTV can also potentially benefit from the high capacity and fast data access of holographic memory.

Proceedings Article | 1 October 1999

Optical memory for computing and information processing

Jose Mumbru, Gan Zhou, Xin An, Wenhai Liu, George Panotopoulos, Fai Mok, Demetri Psaltis

Proceedings Volume 3804, (1999) https://doi.org/10.1117/12.363963

KEYWORDS: Vertical cavity surface emitting lasers, Logic, Field programmable gate arrays, Optical storage, Holograms, Data processing, Holography, Neural networks, Interfaces, Photodetectors

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The high data transfer rate achievable in page-oriented optical memories demands for parallel interfaces to logic circuits able to process efficiently the data. The Optically Programmable Gate Array, an enhanced version of a conventional FPGA, utilizes a holographic memory accessed by an array of VCSELs to program its logic. Combining spatial and shift multiplexing to store the configuration pages in the memory, the OPGA module is very compact and has extremely short configuration time allowing for dynamic reconfiguration. The reconfiguration capability of the OPGA can be applied to solve more efficiently problems in pattern recognition and digit classification.

Proceedings Article | 2 June 1999

Optically reconfigurable processors

Jose Mumbru, Gan Zhou, Suat Ay, Xin An, George Panotopoulos, Fai Mok, Demetri Psaltis

Proceedings Volume 10296, 102960D (1999) https://doi.org/10.1117/12.365910

KEYWORDS: Optical arrays, Field programmable gate arrays, Holography, Vertical cavity surface emitting lasers, Logic, Pattern recognition, Image classification

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Reconfigurable processors bring a new computational paradigm where the processor modifies its structure to suit a given application, rather than having to modify the application to fit the device. The Optically Programmable Gate Array, an enhanced version of a conventional FPGA, utilizes a holographic memory accessed by an array of VCSELs to program its logic. Combining spatial and shift multipexing to store the configuration pages in the memory, the OPGA module is very compact and has extremely short configuration time allowing for dynamic reconfiguration. The reconfiguration capability of the OPGA can be applied to solve more efficiently problems in pattern recognition and digit classification.

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Proceedings Article | 5 November 1998

Interpixel grating noise in holographic memories

Xin An, George Panotopoulos, Demetri Psaltis

Proceedings Volume 3468, (1998) https://doi.org/10.1117/12.330422

KEYWORDS: Holograms, Diffraction gratings, Signal to noise ratio, Phase modulation, Spatial light modulators, Holography, Phase shift keying, Diffraction, Interference (communication), Modulation

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We have experimentally discovered that the Signal-to-Noise Ratio (SNR) of holograms initially remains constant as the number of holograms stored increases and drops significantly only after a large number of holograms are recorded. This suggests that in a large-scale memory, the limiting noise source is not crosstalk between holograms but holographic noise due to the prolonged exposure of the signal beam. We have carried out experiments to investigate the formation and influence of the inter-pixel grating noise and shown that it is a very important form of holographic noise. We also proposed and demonstrated the use of random-phase modulation in the signal to suppress the inter-pixel grating noise.

Proceedings Article | 22 May 1998

Volume holographic optical correlation for digital word recognition

Pierpaolo Boffi, Xin An

Proceedings Volume 3490, (1998) https://doi.org/10.1117/12.308968

KEYWORDS: Holography, Digital holography, Volume holography, Holograms, Optical correlators, Multiplexing, Fractal analysis, Spatial light modulators, Phase shift keying, Optical filters

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Optical byte recognition using volume holographic correlator is presented. The storage of 256 multiplexed holograms is performed and the phase-coded byte discrimination in real- time is experimented.

Proceedings Article | 22 September 1997

Holographic memories

Demetri Psaltis, Geoffrey Burr, Xin An, Michael Levene, George Barbastathis, Allen Pu

Proceedings Volume 3137, (1997) https://doi.org/10.1117/12.287773

KEYWORDS: Multiplexing, Holograms, Holography, Spatial light modulators, Fourier transforms, Optical correlators, 3D image reconstruction, Spherical lenses, Modulation, Content addressable memory

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Holographic memories can be read-out either with the reference or the signal beam. Reference beam read-out reconstructs the stored data whereas signal beam read-out performs a search of the stored data base. This dual mode of holographic memories is explored for the various methods that have been developed for multiplexing holograms.

Proceedings Article | 9 August 1996

Nonvolatile holographic storage in photorefractive materials

Demetri Psaltis, Xin An, George Barbastathis, Ali Adibi, Ernest Chuang

Proceedings Volume 10287, 102870C (1996) https://doi.org/10.1117/12.259691

KEYWORDS: Holography, Holographic materials

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We review methods of nonvolatile storage in photorefractive materials, namely thermal and electrical fixing, two-lambda readout, two photon recording, and periodic refreshing. For each method, we briefly review the physical processes that are responsible for counteracting photorefractive erasure, and present recent experimental results.

Proceedings Article | 8 September 1995

Large-scale rapid-access holographic memory

Geoffrey Burr, Xin An, Fai Mok, Demetri Psaltis

Proceedings Volume 2514, (1995) https://doi.org/10.1117/12.218729

KEYWORDS: Holograms, Mirrors, Multiplexing, Crystals, Holography, Scanners, Spatial light modulators, Signal to noise ratio, Segmented mirrors, Fractal analysis

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We describe a page-formatted random-access holographic memory capable of storing up to 160,000 holograms. A segmented mirror array allows a 2D angle scanner to provide access to any of the stored holograms. High-speed random access can be achieved with a nonmechanical angle scanner. We demonstrate holographic storage and high-speed retrieval using an acousto- optic deflector.

Proceedings Article | 9 November 1993

Image processing applications of optical neural networks

Demetri Psaltis, Hsin-Yu Li, Xin An

Proceedings Volume 2026, (1993) https://doi.org/10.1117/12.163597

KEYWORDS: Spatial light modulators, Neural networks, Image processing, 3D image processing, Optical networks, Switching, Holography, Holograms, Crystals, Information operations

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In this paper we explore the use of 3D disks for the construction of networks with extremely large storage capacity. 3D disks can store up to 10¹² weights per disk. In this paper we discuss how 3D disks are used to implement an optical neural network and then derive the capacity and speed of the resulting architecture.

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