KEYWORDS: Space operations, Telescopes, Signal processing, Receivers, Transmitters, Laser safety, Interfaces, Sensors, Deep space optical communications, Actuators
The National Aeronautics and Space Administration’s (NASA) Deep Space Optical Communications (DSOC) payload, launched with the Psyche spacecraft on October 13, 2023, is facilitating an ongoing Technology Demonstration (TD) of Free-Space Optical Communications (FSOC), from beyond the earth-moon system. The DSOC Flight Laser Transceiver (FLT), can acquire a 1064 nm uplink laser from earth, and return a 1550 nm, Serially Concatenated Pulse Position Modulated (SCPPM) signal, to earth. The FLT uses a 22 cm diameter unobscured optical transceiver assembly, coupled to a 4 W average power laser transmitter, supplemented with actuators, sensors, electronics and software. A 5-7 kW average power, multi-beam 1064 nm uplink laser assembly integrated to the Optical Communications Telescope Laboratory (OCTL) near Wrightwood, CA serves as the Ground Laser Transmitter (GLT). The DSOC Ground Laser Receiver (GLR) at the Palomar Observatory, Hale telescope (operated by Caltech Optical Observatories), consists of a Superconducting Nanowire Single Photon Detector (SNSPD) array, connected to a ground signal processing assembly. Signal photon arrivals are detected and processed to extract information codewords at the GLR. A Mission Operations System (MOS) co-located with the Psyche Project Mission Operations Center, at the Jet Propulsion Laboratory (JPL), coordinates DSOC technology demonstration activities. This paper presents a system overview, mission description and operations architecture for the TD. Early results that include downlink at maximum downlink data-rate of 267 Mb/s from 0.37 Astronomical Units (AU) or 55 million kilometers are presented.
The MSTAR sensor (Modulation Sideband Technology for Absolute Ranging) is a new system for measuring absolute distance, capable of resolving the integer cycle ambiguity of standard interferometers, and making it possible to measure distance with subnanometer accuracy. The sensor uses a single laser in conjunction with fast phase modulators and low frequency detectors. We describe the design of the system - the principle of operation, the metrology source, beam-launching optics, and signal processing - and show results for target distances up to 1 meter. We then demonstrate how the system can be scaled to kilometer-scale distances and used for space-based applications.
"Exo-C" is NASAs first community study of a modest aperture space telescope mission that is optimized for high contrast observations of exoplanetary systems. The mission will be capable of taking optical spectra of nearby exoplanets in reflected light, discovering previously undetected planets, and imaging structure in a large sample of circumstellar disks. It will obtain unique science results on planets down to super-Earth sizes and serve as a technology pathfinder toward an eventual flagship-class mission to find and characterize habitable Earth-like exoplanets. We present the mission/payload design and highlight steps to reduce mission cost/risk relative to previous mission concepts. Key elements are an unobscured telescope aperture, an internal coronagraph with deformable mirrors for precise wavefront control, and an orbit and observatory design chosen for high thermal stability. Exo-C has a similar telescope aperture, orbit, lifetime, and spacecraft bus requirements to the highly successful Kepler mission (which is our cost reference). Much of the needed technology development is being pursued under the WFIRST coronagraph study and would support a mission start in 2017, should NASA decide to proceed. This paper summarizes the study final report completed in March 2015.
“Exo-C” is NASA’s first community study of a modest aperture space telescope designed for high contrast observations of exoplanetary systems. The mission will be capable of taking optical spectra of nearby exoplanets in reflected light, discover previously undetected planets, and imaging structure in a large sample of circumstellar disks. It will obtain unique science results on planets down to super-Earth sizes and serve as a technology pathfinder toward an eventual flagship-class mission to find and characterize habitable exoplanets. We present the mission/payload design and highlight steps to reduce mission cost/risk relative to previous mission concepts. At the study conclusion in 2015, NASA will evaluate it for potential development at the end of this decade.
We present an overview of the ongoing progress towards flight readiness of the SIM project. We summarize the
engineering milestones that have been completed in the last two years, namely: the Brass-Board Internal and
External Metrology Beam Launchers, the Brass-Board Metrology Source, and the Instrument Communication
Hardware/Software Architecture Demonstration. We also show other progress such as: the life test of the bass-screw
and PZT actuators, building the Metrology Fiducials and the Single Strut Test Article. We status the
ongoing work on the Brass-Board Fast Steering Mirror and the Brass-Board Astrometric Beam Combiner. We
end with a proposed path towards finishing the Brass-Board suite.
Point-to-point laser metrology systems can be used to stabilize large structures at the nanometer levels required for
precision optical systems. Existing sensors are large and intrusive, however, with optical heads that consist of several
optical elements and require multiple optical fiber connections. The use of point-to-point laser metrology has therefore
been limited to applications where only a few gauges are needed and there is sufficient space to accommodate them.
Range-Gated Metrology is a signal processing technique that preserves nanometer-level or better performance while
enabling: (1) a greatly simplified optical head - a single fiber optic collimator - that can be made very compact, and (2) a
single optical fiber connection that is readily multiplexed. This combination of features means that it will be
straightforward and cost-effective to embed tens or hundreds of compact metrology gauges to stabilize a large structure.
In this paper we describe the concept behind Range-Gated Metrology, demonstrate the performance in a laboratory
environment, and give examples of how such a sensor system might be deployed.
We propose and have demonstrated a prototype high-reliability pump module for pumping a Non-Planar Ring Oscillator
(NPRO) laser suitable for space missions. The pump module consists of multiple fiber-coupled single-mode laser diodes
and a fiber array micro-lens array based fiber combiner. The reported Single-Mode laser diode combiner laser pump
module (LPM) provides a higher normalized brightness at the combined beam than multimode laser diode based LPMs.
A higher brightness from the pump source is essential for efficient NPRO laser pumping and leads to higher reliability
because higher efficiency requires a lower operating power for the laser diodes, which in turn increases the reliability
and lifetime of the laser diodes. Single-mode laser diodes with Fiber Bragg Grating (FBG) stabilized wavelength permit
the pump module to be operated without a thermal electric cooler (TEC) and this further improves the overall reliability
of the pump module. The single-mode laser diode LPM is scalable in terms of the number of pump diodes and is capable
of combining hundreds of fiber-coupled laser diodes. In the proof-of-concept demonstration, an e-beam written
diffractive micro lens array, a custom fiber array, commercial 808nm single mode laser diodes, and a custom NPRO
laser head are used. The reliability of the proposed LPM is discussed.
KEYWORDS: Polarization, Phase modulation, Polarizers, Temperature metrology, Space operations, Data modeling, Interferometry, Space telescopes, Connectors, Optical spheres
For precision displacement measurements, laser metrology is currently one of the most accurate measurements. Often, the measurement is located some distance away from the laser source, and as a result, stringent requirements are placed on the laser delivery system with respect to the state of polarization. Such is the case with the fiber distribution assembly (FDA) that is slated to fly aboard the Space Interferometry Mission (SIM) next decade. This system utilizes a concatenated array of couplers, polarizers and lengthy runs of polarization-maintaining (PM) fiber to distribute linearly-polarized
light from a single laser to fourteen different optical metrology measurement points throughout the spacecraft. Optical power fluctuations at the point of measurement can be traced back to the polarization extinction ratio (PER) of the concatenated components, in conjunction with the rate of change in phase difference of the light along the slow and fast axes of the PM fiber. Thermal variations are one of the major contributors to this change and can lead to tight spacecraft design requirements. In this presentation, we will discuss our experimentally-validated model which predicts
the polarization behavior for various distribution designs, as well as present the thermal performance of various PM components and how this levies thermal control requirements on the spacecraft.
Laser metrology systems are a key component of stellar interferometers, used to monitor path lengths and dimensions internal to the instrument. Most interferometers use 'relative' metrology, in which the integer number of wavelengths along the path is unknown, and the measurement of length is ambiguous. Changes in the path length can be measured relative to an initial calibration point, but interruption of the metrology beam at any time requires a re-calibration of the system.
The MSTAR sensor (Modulation Sideband Technology for Absolute Ranging) is a new system for measuring absolute distance, capable of resolving the integer cycle ambiguity of standard interferometers, and making it possible to measure distance with sub-nanometer accuracy. We describe the design of the system, show results for target distances up to 1 meter, and demonstrate how the system can be scaled to kilometer-scale distances. In recent experiments, we have used white light interferometry to augment the 'truth' measurements and validate the zero-point of the system.
MSTAR is a general-purpose tool for conveniently measuring length with much greater accuracy than was previously possible, and has a wide range of possible applications.
This overview paper is a progress report about the system design and technology development of two interferometer concepts studied for the Terrestrial Planet Finder (TPF) project. The two concepts are a structurally-connected interferometer (SCI) intended to fulfill minimum TPF science goals and a formation-flying interferometer (FFI) intended to fulfill full science goals. Described are major trades, analyses, and technology experiments completed. Near term plans are also described. This paper covers progress since August 2003 and serves as an update to a paper presented at that month's SPIE conference, "Techniques and Instrumentation for Detection of Exoplanets."
The nulling interferometers proposed for planet detection are arrays of collector telescopes whose amplitudes and phases are carefully controlled to generate a null response at the star. Perturbations in the amplitude and phase response of the instrument lead to time-dependent fluctuations in the stellar leakage that can mimic a planet signal. Understanding these non-linear systematic errors is important, since they drive most of the instrument requirements for missions such as the Terrestrial Planet Finder and Darwin.
We show that 'amplitude-phase' errors are the dominant source of instrument noise. They are unaffected by the technique of phase chopping, increase rapidly at short wavelengths, are largely independent of the size and transmission efficiency of the collector optics, and depend only weakly on the nulling configuration and distance to the target system. Detection of an Earth around a G-type star like the sun requires ~1.5 nm of path control and ~0.1% control of the amplitude, integrated over all frequencies, including DC.
This paper also introduces the X-Array - a new nulling configuration with 4 collectors and a central combiner arranged in an X pattern. This has a number of advantages over the standard dual Bracewell layout, and over other configurations that have been proposed.
A number of stellar systems that can be searched for presence of Earth-like planets in a given mission lifetime is a key figure of merit for planet hunting stellar interferometers. We have developed a method to calculate the number of stellar systems that can be searched and characterized. Using this method we have evaluated the performance of a number of architectures. We conclude that simpler second-order null architectures outperform more complicated fourth-order null architectures. We also quantify the advantages of the variable length formation-flying configurations vs. fixed length structurally connected configurations.
Absolute metrology measures the actual distance between two optical fiducials. A number of methods have been employed, including pulsed time-of-flight, intensity-modulated optical beam, and two-color interferometry. The rms accuracy is currently limited to ~5 microns. Resolving the integer number of wavelengths requires a 1-sigma range accuracy of ~0.1 microns. Closing this gap has a large pay-off: the range (length measurement) accuracy can be increased substantially using the unambiguous optical phase.
The MSTAR sensor (Modulation Sideband Technology for Absolute Ranging) is a new system for measuring absolute distance, capable of resolving the integer cycle ambiguity of standard interferometers, and making it possible to measure distance with sub-nanometer accuracy. In this paper, we present recent experiments that use dispersed white light interferometry to independently validate the zero-point of the system. We also describe progress towards reducing the size of optics, and stabilizing the laser wavelength for operation over larger target ranges.
MSTAR is a general-purpose tool for conveniently measuring length with much greater accuracy than was previously possible, and has a wide range of possible applications.
The MSTAR sensor (Modulation Sideband Technology for Absolute Ranging) is a new system for measuring absolute distance, capable of resolving the integer cycle ambiguity of standard intrferometers, and making it possible to measure distance with sub-nanometer accuracy. The sensor uses a single laser in conjugation with fast phase modulators and low-frequency detectors. We describe the design of the system - the principle of operation, the metrology source, beam-launching optics, and signal processing - and show results for target distance up to 1 meter. We then demonstrate how the system can be scaled to kilometer-scale distances.
The TPF interferometer family suppresses the stellar glare using a deep interferometric null, which for the planet can become constructive interference because of its angular offset. The null depth need not be as great as the star-planet contrast, but its systematic fluctuations must be perhaps 5 times better than the variations which constitute the planet's signature. We present an allocation of errors which meet these needs, and identify areas which need better definition.
This paper describes the technical program that will demonstrate the viability of two mid-infrared nulling interferometer architectures for the Terrestrial Planet Finder (TPF) to support a mission concept downselect in 2006 between a nulling interferometer and a visible coronagraph. The TPF science objectives are to survey a statistically significant number of nearby solar-type stars for radiation from terrestrial planets, to characterize these planets and to perform spectroscopy for detection of biomarkers. A 4-telescope, 36-m Structurally-Connected Interferometer using a dual-chopped Bracewell nuller will meet the minimum science requirement to completely survey at least 30 nearby stars and partially survey 120 others. A Formation-Flying Interferometer is being designed to meet the full science requirement to completely survey at least 150 stars, and involves a trade between dual-chopped Bracewell, degenerate Angel Cross, and the Darwin bow-tie configuration. The system engineering trades for the connected structure and formation-flying architectures are described. The top technical concerns for these architectures are mapped to technology developments that will retire these concerns prior to the project downselect.
The success of interferometry in space depends on the development of lasers that can survive launch conditions and the challenging space environment during missions that could last five years or more. This paper describes the fabrication of a rugged, laser-welded package for a 200mW, monolithic diode-pumped solid-state Nd:YAG laser operating at 1319nm. Environmental testing shows that the laser withstands non-operational thermal cycles over a temperature range from -20°C to 55°C, and 22.3 g-rms of random vibration, with little or no degradation of laser output power or performance. The novel packaging method employs a specially designed housing to which multi-mode or single-mode polarization-maintaining fiber pigtails can be aligned and laser-welded into place. To further enhance reliability, a redundant pumping system called the Multi-Fiber Pump Ferrule (MFPF) was developed and implemented. The MFPF allows multiple laser diode pump modules to be aligned to the laser crystal simultaneously, in order to accommodate either parallel or standby pump redundancy. This compact, lightweight design is well suited for space flight applications and the laser-welded technique can easily be adapted to a number of other fiber optic and electro-optic devices in which critical optical alignments must be maintained in a harsh environment.
We describe a simple approach to laser frequency stabilization for
the metrology subsystem for NASA's StarLight mission, a space-based
separated-spacecraft stellar interferometer. The current design of
the laser frequency stabilization is based on monitoring the transmitted light through a reference cavity. Currently our free-running lasers do not meet the frequency stability requirements of the mission (100 Hz/root(Hz) between 1 and 1000 Hz) because of the up to 600 m length difference in the two arms of the interferometer. We need additional three orders of magnitude reduction of the frequency noise power spectral density in that frequency regime to meet the 11 nm accuracy requirement for the metrology system. Because we need only a modest improvement in the frequency stability, we plan to use a simple transmit/reflect architecture in which the laser frequency is locked to one side of the cavity resonance peak. The frequency stabilization system measures the transmitted light portion of a Fabry-Perot cavity and compares it to a stable reference voltage to generate the feedback signal. This signal is controlling the laser frequency using the NPRO laser PZT and crystal temperature actuators, therefore keeping the transmitted light level on the photo detector constant. This is equivalent to keeping the laser frequency stable. Because this system measures the transmitted light level it is sensitive to laser power fluctuations. One remedy to this problem is to monitor the reflected light from the cavity as well and use the ratio transmitted/reflected as the sensor signal. The residual frequency noise in our system was measured with respect to a stabilized laser light that was frequency stabilized using Pound-Drever-Hall stabilization.
We report on the laboratory demonstration of an active linear metrology scheme using two separate lasers. In `active' metrology, the passive retroreflector in one arm of a typical heterodyne interferometer is replaced with an active optical transponder. The Transponder can dramatically boost the returned signal strength, thereby providing a way to perform metrology and pathlength control over long (> km) distances. Two Lightwave Electronics non-planar ring oscillator lasers at a wavelength of 1.319 micrometers were used as the Source and Transponder. The frequency of the Transponder is offset locked to the signal received from the Source using the Lightwave Laser Offset Locking Accessory, and the Transponder beam is sent back to the Source. The phases of the beat signals are measured locally at the Source and Transponder by appropriately demodulating the signal, and post-processed to determine displacement. In initial experiments, the standard deviation of the measurement errors was less than three nanometers.
Narrow linewidth (< 100 KHz) semiconductor lasers are expected to be a key technology in NASA's stellar interferometry missions to search for planets around nearby stars. Long coherence length lasers are needed for precise (20 pm to 5 nm) measurements of the optical path difference. This work discusses results using the self-heterodyne delay technique to measure 1.3 um InP based DFB lasers. We will also address practical issues concerning detection and elimination of back reflections, choice of fiber length and resolution, and measurement of laser l/f and current supply noise.
We have recently described a wavelength-recognizing switch (WRS) which we showed to be capable of truly all-optical routing. Although other authors had previously reported "all-optical" networks [1, 2, 3], the term has generally referred to all—optical data paths only. In such implementations only the data remains in optical format as it propagates along the network paths. Optical-to-electronic conversions are still allowed for what is termed "control signals," namely address bits and additional signaling entities, which are assumed to have lower speed than the data. In contrast, the WRS we presented has the capability to route data by interpreting the control signals in the optical domain, thus avoiding the overhead and the latency ofthe optic-to-electronic conversion. In a series of previous publications [4, 5] we demonstrated the experimental viability of the WRS and measured some of the relevant system parameters of the device. More recently, we published details on how the device could be used to build multistage all-optical self-routing networks. We also developed a simulation model and estimated the maximum number of stages that can be cascaded in such networks. The work presented in this paper carries the simulation results one step further, and investigates some of the possible topologies that can be used for WRS networks, as well as the system implications of these topologies. To facilitate a better understanding of the concepts presented, we briefly review the device functionality and the main experimental results that affect the system performance. We then show how to implement some of the building blocks we use in the self-routing topologies, and explain the equalization mechanism necessary for using WRS in multistage networks. We then compare the practical advantages of the topologies of interest and decide which topology is the most probable implementation. Finally we present details on a new generation of WRS, which is waveguide based, thus more easily fabricated and integrated with optical fiber systems
We investigated differential gain, refractive index and (alpha) -parameter in strongly index and gain guided broad- area semiconductor optical amplifiers. The measured linewidth enhancement factor is larger than the values reported for narrow-stripe lasers and is consistent with theoretical predictions.
High quality traveling-wave semiconductor optical amplifiers were designed and fabricated for all-optical switching applications. We obtained 21 dB small signal gain with 0.16 dB gain ripple. Measured residual reflectivity was 5 X 10-5 and the 3-dB gain bandwidth as wide as 70 nm. Our results show careful wavelength selection is required in order to match the amplifiers gain peak wavelength to the desired operating wavelength of the optical switches.
Deep Space 3 will fly a stellar optical interferometer on three separate spacecraft in heliocentric orbits: one spacecraft for the Michelson beam combining optics, and two spacecraft for each of the starlight apertures. The spacecraft will formation fly to relative spacecraft distances from 100 meters to 1 kilometer, enabling an instrument resolution of 1 to 0.1 milliarcsecond. At each baseline length and orientation - up to 100 points in the synthetic aperture plane for a given astrophysical target - the instrument will measure source visibility amplitude form which the source brightness distribution can be determined. An infrared metrology system performs both linear and angular metrology between spacecraft and is sued to estimate delay jitter, interferometer delay and delay rate. Pointing and control mechanisms use the metrology error signals to stabilize delay jitter and to null delay and delay rate to enable detection and tracking of a white light fringe on a photon-counting detector. Once stabilized, fringes can be dispersed on a CCD in up to 80 spectral channels to attain high-accuracy measurements of visibility amplitude as a function of wavelength.
A metrology subsystem on board the Deep Space 3, a separated spacecraft interferometer mission, is used to determine stellar fringe delay jitter, delay rate, and initial delay. The subsystem implements two capabilities: linear metrology for optical pathlength determination and angular metrology needed to determine the configuration and orientation of the spacecraft constellation. Frequency modulated metrology concept is used to implement high-precision (5nm) interferometric linear measurements over large target ranges (1km). System is made angle sensitive by using an articulated flat mirror at the target.
We describe the development, functional performance, and space-qualification status of a Metrology Source suitable for implementation of space-based metrology systems with picometer-level relative displacement measurement and micron-level absolute displacement measurement resolution. The Metrology Source consists of the following components: lasers, frequency stabilization system, frequency shifters, and frequency modulators. All components are interconnected by polarization maintaining fibers to facilitate integration into a lightweight space-qualifiable module.
Heterodyne interferometer laser gauges are used in space- based astronomical interferometers to very accurately measure and compensate for variations in starlight pathlength. Bragg cells have been traditionally used to generate the heterodyne signal by shifting the frequency of the laser light. This paper presents the development and qualification of an integrated optic frequency shifter (IOFS) which offers improved performance and reliability compared with Bragg cell technology. The most critical advantage of the IOFS for space applications is that it enables fiber optic metrology source integration, which facilitates the integration process and result in more reliable and compact heterodyne interferometer laser gauges.
The effects of radiation on fused biconical taper wavelength division multiplexers are presented. The polarization sensitivity of these devices before and after irradiation is discussed. Preliminary results on the effects of irradiating different regions of the device, and comparisons between the effects of proton and Co60 radiation sources are also given. A theoretical model that takes into account the index change in the Ge-doped cores of the optical fibers used to make these devices agrees well with experimental observations. This indicates that index changes in the fiber may be primarily responsible for the effects of radiation on these devices.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.