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Results for “Optical Communications Lasers Detectors”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Integral sunshade for an optical reception antenna

Optical reception antennas (telescopes) must be capable of receiving communications even when the deep-space laser source is located within a small angle of the sun. Direct sunlight must not be allowed to shine on the primary reflector of an optical reception antenna, because too much light would be scattered into the signal detectors. A conventional sunshade that does not obstruct the antenna aperture would have to be about five times longer than its diameter in order to receive optical communications at a solar elongation of 12 degrees without interference. Such a long sunshade could not be accommodated within the dome of any existing large-aperture astronomical facility, and providing a new dome large enough would be prohibitively expensive. It is also desirable to reduce the amount of energy a space-based large-aperture optical reception facility would expend orienting a structure with such a sizable moment of inertia. Since a large aperture optical reception antenna will probably have a hexagonally segmented primary reflector, a sunshade consisting of hexagonal tubes can be mounted in alignment with the segmentation without producing any additional geometric obstruction. An analysis of the duration and recurrence of solar-conjunction communications outages (caused when a deep-space probe near an outer planet appears to be closer to the sun than a given minimum solar elongation), and the design equations for the integral sunshade are appended.

Kerr, Edwin L.↗
NASA NTRS1989

Design of fiber optic probes for laser light scattering

A quantitative analysis is presented of the role of optical fibers in laser light scattering. Design of a general fiber optic/microlens probe by means of ray tracing is described. Several different geometries employing an optical fiber of the type used in lightwave communications and a graded index microlens are considered. Experimental results using a nonimaging fiber optic detector probe show that due to geometrical limitations of single mode fibers, a probe using a multimode optical fiber has better performance, for both static and dynamic measurements of the scattered light intensity, compared with a probe using a single mode fiber. Fiber optic detector probes are shown to be more efficient at data collection when compared with conventional approaches to measurements of the scattered laser light. Integration of fiber optic detector probes into a fiber optic spectrometer offers considerable miniaturization of conventional light scattering spectrometers, which can be made arbitrarily small. In addition static and dynamic measurements of scattered light can be made within the scattering cell and consequently very close to the scattering center.

Dhadwal, Harbans S.↗
NASA NTRS1990

50 Mbps free space direct detection laser diode optical communication system with Q = 4 PPM signaling

A 50 Mbps direct detection optical communication system for use in an intersatellite link was constructed with an AlGaAs laser diode transmitter and a silicon avalanche photodiode photodetector. The system used a Q = 4 PPM format. The receiver consisted of a maximum likelihood PPM detector and a timing recovery subsystem. The PPM slot clock was recovered at the receiver by using a transition detector followed by a PLL. The PPM word clock was recovered by using a second PLL whose input was derived from the presence of back-to-back PPM pulses contained in the received random PPM pulse sequences. The system achieved a bit error rate of 0.000001 at less than 50 detected signal photons/information bit. The receiver was capable of acquiring and maintaining slot and word synchronization for received signal levels greater than 20 photons/information bit, at which the receiver bit error rate was about 0.01.

Sun, Xiaoli↗
NASA NTRS1982

Recent progress in picosecond pulse generation from semiconductor lasers

This paper reviews the recent progress in producing picosecond optical pulses from semiconductor laser diodes. The discussion concentrates on the mode-locking of a semiconductor laser diode in an external resonator. Transform-limited optical pulses ranging from several picoseconds to subpicosecond durations have been observed with active and passive mode-locking. Even though continuing research on the influence of impurities and defects on the mode-locking process is still needed, this technique has good promise for being utilized in fiber-optic communication systems. Alternative methods of direct electrical and optical excitation to produce ultrashort laser pulses are also described. They can generate pulses of similar widths to those obtained by mode-locking. The pulses generated will find applications in laser ranging and detector response measurement.

Auyeung, J. C.↗
NASA NTRS1994

Lasercom system architecture with reduced complexity

Spatial acquisition and precision beam pointing functions are critical to spaceborne laser communication systems. In the present invention, a single high bandwidth CCD detector is used to perform both spatial acquisition and tracking functions. Compared to previous lasercom hardware design, the array tracking concept offers reduced system complexity by reducing the number of optical elements in the design. Specifically, the design requires only one detector and one beam steering mechanism. It also provides the means to optically close the point-ahead control loop. The technology required for high bandwidth array tracking was examined and shown to be consistent with current state of the art. The single detector design can lead to a significantly reduced system complexity and a lower system cost.

Lesh, James R.↗
NASA NTRS1996

LaserCom System Architecture With Reduced Complexity

Spatial acquisition and precision beam pointing functions are critical to spaceborne laser communication systems. In the present invention a single high bandwidth CCD detector is used to perform both spatial acquisition and tracking functions. Compared to previous lasercom hardware design, the array tracking concept offers reduced system complexity by reducing the number of optical elements in the design. Specifically, the design requires only one detector and one beam steering mechanism. It also provides means to optically close the point-ahead control loop. The technology required for high bandwidth array tracking was examined and shown to be consistent with current state of the art. The single detector design can lead to a significantly reduced system complexity and a lower system cost.

Lesh, James R.↗
NASA NTRS1987

Technological status and future challenges of deep space optical communication

An account is given of the concepts, techniques, and system design features that may be used to realize an optical communications link for future planetary missions. Such a spacecraft subsystem would encompass a 10-30 cm aperture optical telescope for both transmitting and receiving. Uplink from a laser, in the form of pulsed ranging signals or command information, will be extracted by a tracking detector; downlink data, as well as detected ranging pulses, will be properly formatted and used to modulate the downlink laser. The optical receiving station may be either on the ground or in earth orbit.

Lesh, James R.↗
NASA NTRS2000

Crystal Growth of ZnSe and Related Ternary Compound Semiconductors by Vapor Transport

Interest in optical devices which can operate in the visible spectrum has motivated research interest in the II-VI wide band gap semiconductor materials. The recent challenge for semiconductor opto-electronics is the development of a laser which can operate at short visible wavelengths. In the past several years, major advances in thin film technology such as molecular beam epitaxy and metal organic chemical vapor deposition have demonstrated the applicability of II-VI materials to important devices such as light-emitting diodes, lasers, and ultraviolet detectors. With an energy gap of 2.7 eV at room temperature, and an efficient band- to-band transition, ZnSe has been studied extensively as the primary candidate for a blue light emitting diode for optical displays, high density recording, and military communications. By employing a ternary or quaternary system, the energy band gap of II-VI materials can be tuned to a specific range. While issues related to the compositional inhomogeneity and defect incorporation are still to be fully resolved, ZnSe bulk crystals and ZnSe-based heterostructures such as ZnSe/ZnSeS, ZnSe/ZnCdSe and ZnCdSe/ZnSeS have showed photopumped lasing capability in the blue-green region at a low threshold power and high temperatures. The demonstration of its optical bistable properties in bulk and thin film forms also make ZnSe a possible candidate material for the building blocks of a digital optical computer. Despite this, developments in the crystal growth of bulk H-VI semiconductor materials has not advanced far enough to provide the low price, high quality substrates needed for the thin film growth technology.

Su, Ching-Hua↗
NASA NTRS2019

Star Tracker Accuracy Improvement and Optimization for Attitude Measurement in Three-Axis

High precision attitude measurement systems obviate the need for the beacon from the receiver making it possible for the spacecraft to beam a laser communications signal to a ground station without the ground station advertising its location. The research presented targets new detection and estimation methods to improve the accuracy in locating stars on a focal plane detector, and an understanding of the effects of changes in the optics design parameters and aberration, including defocus, on the navigation solution itself. This understanding can lead to an optimization of the attitude solution with respect to those optics realm parameter changes. The methodology discussed includes the development of a model of a current star tracker system. Using this model, multiple algorithms are implemented, including a multi-hypothesis method (MHT), to detect and estimate the position of the stars on the focal plane detector. It will be shown that using the MHT for detection and estimation, a greater accuracy can be found for each star estimation from more traditional detection and estimation algorithms. The approach then uses the model to develop statistics of the star tracker and the attitude estimation outputs to understand the accuracy, or variance, of the system's attitude solution. This solution is repeated for a range of defocus aberration, and a lower limit to the variance of the attitude solution is shown. A Cramer Rao lower bound solution is derived for the star tracker system and the results are compared to the Monte Carlo analysis from the model and shown to correlate very well. The approach uses a star image not as a Gaussian spot on the focal plane as done in previous work, and use of an image that includes the effects of aberrations of the optic system, and the effects of under-sampling and noise from the focal plane detector as well. Analysis includes exploring a star tracker's accuracy improvement through the combination of focus error and under-sampling effects alone, possibly contradicting conventional wisdom and approaches.

Lichter, Michael J.↗
NASA NTRS1987

Optical technologies for space communication systems; Proceedings of the Meeting, Los Angeles, CA, Jan. 15, 16, 1987

The conference presents papers on optical communications in space, diode laser transmitters, lasercom link transmission characteristics, lasercom systems and technologies, high frequency optical components, and optically controlled phased array antennas. Particular attention is given to a deep space optical communications development program, 0.87-micron CSP diode lasers for spaceborne communications, performance measurements of a diode laser optical communications link with Q = 4 PPM signaling, the optical communications link design for the tracking and data acquisition system, and a cost-performance model for ground-based optical communications receiving telescopes. Other topics include optoelectronic componentry for the direct transmission of microwave signals over optical fiber, applications of monolithic detectors, and optical control considerations for phased array antennas.

Bhasin, Kul↗
NASA NTRS1994

SLR 2000

SLR 2000 is a concept for a totally automated subcentimeter SLR system presently being studied at GSFC. If funding permits, a prototype would be installed and tested at the Goddard Geophysical and Astronomical Observatory (GCAO) in FY98 and a small number of automated stations would be fielded by the year 2000. Unlike present systems, the "SLR 2000" system is being designed to: 1) operate autonomously without the need for onsite operators; 2) present no hazards (i.e., optical, electrical, and/or chemical) to personnel in the vicinity or to overflying aircraft; and 3) have a mean time between failures (MTBF) of at least three months. It is assumed that the systems are located at "friendly" sites where some level of security is provided and where certain low level service functions (e.g. commercial power, communications, heat pump service cleaning, etc.) are available or can be contracted for locally on an as-needed basis. The main system consists of two parts - an optical head and electronics rack. The optical head contains the laser transmitter and power supply, transmit/receive switch, optical telescope, tracking angle sensor (intensified CCD camera), detector and power supply, two angular encoders, azimuth and elevation motors, and a protective dome. The optical head mounts directly to the top of a concrete pier which contains the geodetic monument and forms part of the environmental housing for the hardware and servicing personnel. It is equipped with electronic levels for leveling the mount and monitoring its stability.

Degnan, John J.↗
NASA NTRS1989

Optical Communication with Semiconductor Laser Diode

Theoretical and experimental performance limits of a free-space direct detection optical communication system were studied using a semiconductor laser diode as the optical transmitter and a silicon avalanche photodiode (APD) as the receiver photodetector. Optical systems using these components are under consideration as replacements for microwave satellite communication links. Optical pulse position modulation (PPM) was chosen as the signal format. An experimental system was constructed that used an aluminum gallium arsenide semiconductor laser diode as the transmitter and a silicon avalanche photodiode photodetector. The system used Q=4 PPM signaling at a source data rate of 25 megabits per second. The PPM signal format requires regeneration of PPM slot clock and word clock waveforms in the receiver. A nearly exact computational procedure was developed to compute receiver bit error rate without using the Gaussion approximation. A transition detector slot clock recovery system using a phase lock loop was developed and implemented. A novel word clock recovery system was also developed. It was found that the results of the nearly exact computational procedure agreed well with actual measurements of receiver performance. The receiver sensitivity achieved was the closest to the quantum limit yet reported for an optical communication system of this type.

Davidson, Frederic↗
NASA NTRS1989

Slot clock recovery in optical PPM communication systems with avalanche photodiode photodetectors

Slot timing recovery in a direct-detection optical PPM communication system can be achieved by processing the photodetector output waveform with a nonlinear device whose output forms the input to a phase-locked loop. The choice of a simple transition detector as the nonlinearity is shown to give satisfactory synchronization performance. The rms phase error of the recovered slot clock and the effect of slot timing jitter on the bit error probability were directly measured. The experimental system consisted of an AlGaAs laser diode (wavelength = 834 nm) and a silicon avalanche photodiode photodetector. The system used Q = 4 PPM signaling and operated at a source data rate of 25 Mbits/s. The mathematical model developed to compute the rms phase error of the recovered clock is shown to be in good agreement with results of actual measurements of phase errors. The use of the recovered slot clock in the receiver resulted in no significant degradation in receiver sensitivity compared to a system with perfect slot timing. The system achieved a bit error probability of 10 to the -6th at a received optical signal energy of 55 detected photons per information bit.

Davidson, Frederic M.↗
NASA NTRS2021

A High Dynamic-Range Photon-Counting Receiver for Deep Space Optical Communication

The Deep Space Optical Communication (DSOC) project will demonstrate free-space optical communication at almost 3 AU, or 3 orders of magnitude further than any previous attempt. DSOC will utilize the 5m Palomar Hale Telescope to receive the downlink signal, which will couple the downlink light onto an optical table and into a superconducting nanowire single photon detector (SNSPD). The output of the SNSPD is digitized by the Ground Laser Receiver Signal Processing Assembly (GSPA) using a high throughput streaming time to digital converter (TDC). The GSPA is a scalable FPGA-based receiver which demodulates and decodes the DSOC downlink signal through novel signal processing algorithms implemented on Xilinx UltraScale+ FPGAs, as well as Python-based software monitor and control routines. Exploiting the unique TDC-based architecture, the GSPA supports over four orders of magnitude of downlink data rates across multiple orders of magnitude of signal and background powers. In this paper we present an overview of the hardware, firmware and software architectures to implement this system, as well as performance analysis for links ranging from near-Earth to 2.8 AU.

Srinivasan, Meera↗
DOE OSTI2024

Single-mode squeezed-light generation and tomography with an integrated optical parametric oscillator

Quantum optical technologies promise advances in sensing, computing, and communication. A key resource is squeezed light, where quantum noise is redistributed between optical quadratures. We introduce a monolithic, chip-scale platform that exploits the χ (2) nonlinearity of a thin-film lithium niobate (TFLN) resonator device to efficiently generate squeezed states of light. Our system integrates all essential components—except for the laser and two detectors—on a single chip with an area of one square centimeter, reducing the size, operational complexity, and power consumption associated with conventional setups. Using the balanced homodyne measurement subsystem that we implemented on the same chip, we measure a squeezing of 0.55 decibels and an anti-squeezing of 1.55 decibels. We use 20 milliwatts of input power to generate the parametric oscillator pump field by using second harmonic generation on the same chip. Our work represents a step toward compact and efficient quantum optical systems posed to leverage the rapid advances in integrated nonlinear and quantum photonics.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

System and method for compact adaptive free space optical communications

The present disclosure relates to a free-space optical communications system that may make use of a controller and a digital micro mirror (DMM) assembly in communication with the controller. The DMM may have a plurality of independently controllable micromirror elements forming both an emitter and a receiver. A laser is included which is configured to generate an optical beam which may be applied to select ones of the first subpluralities of micromirror elements to generate a transmitted free space optical signal along a selected vector. A detector is included for receiving an incoming free space optical signal imaged by at least one of the micromirror elements.

42 ENGINEERING↗
NASA NTRS2012

Progress on the Development of a Simulation Environment for Optical Communications

Deep space laser communications require extremely accurate beam pointing to take advantage of the narrow beams achievable at optical wavelengths. This pointing accuracy must be achieved in the presence of spacecraft basebody motion which may exceed laser pointing requirements by orders of magnitude.In this paper a model of an optical band transceiver pointing control system is developed that can be used to predict performance under various operating scenarios. The transceiver model consists of an electro-mechanical model of the telescope platform and isolator. A novel photon counting detector array is used in the simulation as the focal plane detector. In the simulation we are able to inject various cases of spacecraft basebody motion based on both flight data and future mission spacecraft jitter requirements. Various models of uplink beacon flux levels and atmospheric scintillation are also available for analysis.Using these models, detector processing and control functions are implemented in the simulation. A complete acquisition sequence is demonstrated with blind acquisition and tracking of the modulated uplink beam and positioning of the downlink beam on the focal plane array. These simulations predict that pointing requirements will be met with representative disturbance models and uplink beam scintillation.

pointing control↗
NASA NTRS1998

Characterization and Design of Digital Pointing Subsystem for Optical Communication Demonstrator

The Optical Communications Demonstrator (OCD) is a laboratory-based lasercom demonstration terminal designed to validate several key technologies, including beacon acquisition, high bandwidth tracking, precision bearn pointing, and point-ahead compensation functions. It has been under active development over the past few years. The instrument uses a CCD array detector for both spatial acquisition and high-bandwidth tracking, and a fiber coupled laser transmitter. The array detector tracking concept provides wide field-of-view acquisition and permits effective platform jitter compensation and point-ahead control using only one steering mirror. This paper describes the detailed design and characterization of the digital control loop system which includes the Fast Steering Mirror (FSM), the CCD image tracker, and the associated electronics. The objective is to improve the overall system performance using laboratory measured data. The. design of the digital control loop is based on a linear time invariant open loop model. The closed loop performance is predicted using the theoretical model. With the digital filter programmed into the OCD control software, data is collected to verify the predictions. This paper presents the results of the, system modeling and performance analysis. It has been shown that measurement data closely matches theoretical predictions. An important part of the laser communication experiment is the ability of FSM to track the laser beacon within the. required tolerances. The pointing must be maintained to an accuracy that is much smaller than the transmit signal beamwidth. For an earth orbit distance, the system must be able to track the receiving station to within a few microradians. The failure. to do so will result in a severely degraded system performance.

Racho, C.↗