The use of a wireless charging system for small, unmanned aircraft system applications is useful for both military and commercial consumers. An efficient way to keep the aircraft’s batteries charged without interrupting flight would be highly marketable. While the general concepts behind highly resonant wireless power transfer are discussed in a few publications, the details behind the system designs are not available even in academic journals, especially in relation to avionics. Combining a highly resonant charging system with a solar panel charging system can produce enough power to extend the flight time of a small, unmanned aircraft system without interruption. This paper provides an overview of a few of the wireless-charging technologies currently available and outlines a preliminary design for an aircraft-mounted battery charging system.
Free Space Optics (FSO) technology was originally envisioned to be a viable solution for the provision of high
bandwidth optical connectivity in the last mile of today's telecommunications infrastructure. Due to atmospheric
limitations inherent to FSO technology, FSO is now widely envisioned as a solution for the provision of high bandwidth,
temporary mobile communications links. The need for FSO communications links will increase as mobility is
introduced to this technology. In this paper, a theoretical solution for adding mobility to FSO communication links is
introduced. Three-dimensional power estimation studies are presented to represent mobile FSO transmission under
various weather conditions. Three wavelengths, 0.85, 1.55 and 10 um, are tested and compared to illustrate the pros and
cons of each source wavelength used for transmission, depending on prevalent weather conditions and atmospheric
turbulence conditions. A simulation analysis of the transmission properties of the source wavelengths used in the study
is shown.
KEYWORDS: 3D displays, 3D image processing, Projection systems, Digital Light Processing, Image processing, Image quality, Holography, Glasses, 3D volumetric displays
An ongoing public-private research partnership has demonstrated a three-dimensional (3D) volumetric display
system that incorporates a static image space. The 3D display system uses micro-electro-mechanical systems
(MEMS) based mirror arrays to direct infrared light beams into an image space that exhibits two-step, twofrequency
upconversion. A number of candidate image space materials have been evaluated, with 2%Er: NYF4
appearing to be most promising at this stage of the research. In this paper, the authors build upon prior work by
investigating the response time of 2%Er:NYF4. In addition, a new technique for reducing flicker in the 3D images is
described. The technique includes interlacing the 3D image slices in a way similar to the interlacing that occurs in
the generation of television images. Adopting this technique has the potential to reduce the flicker that is presently
evident, thereby improving the overall 3D image quality.
Government funding for the security at shipping facilities and ports is limited so there is a need for low cost scalable
security systems. With over 20 million sea, truck, and rail containers entering the United States every year, these
facilities pose a large risk to security. Securing these facilities and monitoring the variety of traffic that enter and leave
is a major task. To accomplish this, the authors have developed and fielded a low cost fully distributed building block
approach to port security at the inland Port of Catoosa in Oklahoma. Based on prior work accomplished in the design
and fielding of an intelligent transportation system in the United States, functional building blocks, (e.g. Network,
Camera, Sensor, Display, and Operator Console blocks) can be assembled, mixed and matched, and scaled to provide a
comprehensive security system. The following functions are demonstrated and scaled through analysis and
demonstration: Barge tracking, credential checking, container inventory, vehicle tracking, and situational awareness.
The concept behind this research is "any operator on any console can control any device at any time."
KEYWORDS: 3D displays, Medical imaging, 3D image processing, 3D volumetric displays, Ions, Digital micromirror devices, Aluminium phosphide, Projection systems, Digital Light Processing
Advances in medical imaging technologies are assisting radiologists in more accurate diagnoses. This paper details an
autostereoscopic static volumetric display, called CSpace®, capable of projecting three-dimensional (3D) medical
imaging data in 3D world coordinates. Using this innovative technology, the displayed 3D data set can be viewed in the
optical medium from any perspective angle without the use of any viewing aid. The design of CSpace® allows a volume
rendering of the surface and the interior of any organ of the human body. As a result, adjacent tissues can be better
monitored, and disease diagnoses can be more accurate. In conjunction with CSpace hardware, we have developed a
software architecture that can read digital imaging and communication in medicine (DICOM) files whether captured by
ultrasound devices, magnetic resonance imaging (MRI), or computed tomography (CT) scanners. The software acquires
the imaging parameters from the files' header, and then applies the parameters on the rendered 3D object to display it in
the exact form it was captured.
As three-dimensional (3D) techniques continue to evolve from their humble beginnings-nineteenth century stereo
photographs and twentieth century movies and holographs, the urgency for advancement in 3D display is escalating, as
the need for widespread application in medical imaging, baggage scanning, gaming, television and movie display, and
military strategizing increases. The most recent 3D developments center upon volumetric display, which generate 3D
images within actual 3D space. More specifically, CSpace volumetric display generates a truly natural 3D image
consisting of perceived width, height, and depth within the confines of physical space. Wireframe graphics enable
viewers a 360-degree display without the use of additional visual aids. In this paper, research detailing the selection and
testing of several rare earth, single-doped, fluoride crystals, namely 1%Er: NYF4, 2%Er: NYF4, 3%Er: NYF4 ,
2%Er:KY3F10, and 2%Er:YLF, is introduced. These materials are the basis for CSpace display in a two-step twofrequency
up-Conversion process. Significant determinants were tested and identified to aid in the selection of a suitable
medium. Results show that 2%Er: NYF4 demonstrates good optical emitted power. Its superior level of brightness makes
it the most suitable candidate for CSpace display. Testing also proved 2%Er: KY3F10 crystal might be a viable medium.
KEYWORDS: Digital micromirror devices, 3D displays, Projection systems, Digital Light Processing, Aluminium phosphide, 3D image processing, Ions, 3D volumetric displays, Upconversion
A public-private research collaboration has demonstrated a promising three-dimensional volumetric display system with
the capability of satisfying the performance criteria of: ease of viewing, high-resolution, scalability, and reliability. The
system utilizes commercial off-the-shelf micro-electro-mechanical systems (MEMS) based mirror arrays to direct
infrared light beams into an image space. To date, monochromatic images have been demonstrated in an image space
material that exhibits two-photon upconversion. The prototype display requires no special viewing aids, produces a
volumetric image that is viewable from 360 degrees, and as presently designed is capable of producing 800 million
volumetric pixels of image content.
KEYWORDS: Cameras, Video, Video surveillance, Information technology, Network security, Control systems, Defense and security, Sensors, Databases, Transportation security
With over 360 ports of entry and 20 million sea, truck, and rail containers entering the United States every year, port
facilities pose a large risk to security. Securing these ports and monitoring the variety of traffic that enter and leave is a
major task. To accomplish this, the authors propose a fully distributed building block approach to port security. Based
on prior work accomplished in the design and fielding of an intelligent transportation system in the United States,
building blocks can be assembled, mixed and matched, and scaled to provide a comprehensive security system. Network
blocks, surveillance blocks, sensor blocks, and display blocks will be developed and demonstrated in the lab, and at an
inland port. The following functions will be demonstrated and scaled through analysis and demonstration: Barge
tracking, credential checking, container inventory, vehicle tracking, and situational awareness. The concept behind this
research is "any operator on any console can control any device at any time."
Significant research efforts are underway to investigate the application of Free-Space Optics (FSO) for the provision
of high-bandwidth communications links between mobile platforms. The use of FSO between mobile platforms
introduces several interesting challenges in addition to those found in traditional fixed link FSO systems. In this
paper, some of the major hurdles facing fixed FSO communications that carry over into links between mobile
platforms are analyzed. These topics include: issues with alignment and tracking, an investigation into the weather
and its affect on the link, and a study of the feasibility of having uninterrupted communications links. Other topics
presented unique to mobile applications include: the security risks during link alignment, maintaining the link while
tracking and optical power and beam divergence variations that are introduced into the system. In this paper the
results from simulation work performed on some of these issues along with proposed solutions to the challenges are
presented.
In this paper, a comparison of the physical security aspects of a time division multiplexed (TDM) passive optical
network (PON) and a proposed wavelength hopping passive optical network (WH-PON) is presented. Simulated results
of an eavesdropping attempt in both networks are presented. The introduction of a WH-PON will demonstrate how
physical layer security can be introduced to a PON architecture through the use of a pair of matched tunable lasers in the
optical line terminal (OLT). These matched tunable lasers allow for the creation of a secure point-to-point optical link
between the OLT and the end user, without the need for a unique optical transmitter for each end user. The simulation
results presented will demonstrate the operation of each PON architecture, as well as the physical immunity to
eavesdropping that the WH-PON architecture introduces.
KEYWORDS: Video surveillance, Video, Cameras, Surveillance, Network security, Information security, Defense and security, Global Positioning System, Control systems, Sensors
With the ever present threat to commerce, both politically and economically, technological innovations provide a means to secure the transportation infrastructure that will allow efficient and uninterrupted freight-flow operations for trade. Currently, freight coming into United States ports is "spot checked" upon arrival and stored in a container yard while awaiting the next mode of transportation. For the most part, only fences and security patrols protect these container storage yards. To augment these measures, the authors propose the use of aerial surveillance vehicles equipped with video cameras and wireless video downlinks to provide a birds-eye view of port facilities to security control centers and security patrols on the ground. The initial investigation described in this paper demonstrates the use of unmanned aerial surveillance vehicles as a viable method for providing video surveillance of container storage yards. This research provides the foundation for a follow-on project to use autonomous aerial surveillance vehicles coordinated with autonomous ground surveillance vehicles for enhanced port security applications.
Free-space optics (FSO) technology utilizes a modulated light beam to transmit information through the atmosphere. Due to reduced size and cost, and higher data rates, FSO can be more effective than wireless communication. Although atmospheric conditions can affect FSO communication, a line-of-sight connection between FSO transceivers is a necessary condition to maintain continuous exchange of data, voice, and video information. To date, the primary concentration of mobile FSO research and development has been toward accurate alignment between two transceivers. This study introduces a fully automatic, advanced alignment system that will maintain a line of sight connection for any FSO transceiver system. A complete transceiver system includes a position-sensing detector (PSD) to receive the signal, a laser to transmit the signal, a gimbal to move the transceiver to maintain alignment, and a computer to coordinate the necessary movements during motion. The FSO system was tested for mobility by employing one gimbal as a mobile unit and establishing another as a base station. Tests were performed to establish that alignment between two transceivers could be maintained during a given period of experiments and to determine the maximum speeds tolerated by the system. Implementation of the transceiver system can be realized in many ways, including vehicle-to-base station communication or vehicle-to-vehicle communication. This study is especially promising in that it suggests such a system is able to provide high-speed data in many applications where current wireless technology may not be effective. This phenomenon, coupled with the ability to maintain an autonomously realigned connection, opens the possibility of endless applications for both military and civilian use.
KEYWORDS: Free space optics, Detection and tracking algorithms, Unmanned aerial vehicles, Receivers, Transmitters, Mobile communications, Free space optical communications, Optical simulations, Algorithm development, Global Positioning System
Free-space optical (FSO) communications links are envisioned as a viable option for the provision of temporary high-bandwidth
communication links between moving platforms, especially for deployment in battlefield situations. For
successful deployment in such real-time environments, fast and accurate alignment and tracking of the FSO equipment is
essential. In this paper, a two-wavelength diversity scheme using 1.55 μm and 10 μm is investigated in conjunction with
a previously described tracking algorithm to maintain line-of-sight connectivity battlefield scenarios. An analytical
model of a mobile FSO communications link is described. Following the analytical model, simulation results are
presented for an FSO link between an unmanned aerial surveillance vehicle, the Global Hawk, with a mobile ground
vehicle, an M1 Abrams Main Battle Tank. The scenario is analyzed under varying weather conditions to verify
continuous connectivity is available through the tracking algorithm. Simulation results are generated to describe the
performance of the tracking algorithm with respect to both received optical power levels and variations in beam
divergence. Advances to any proposed tracking algorithm due to these power and divergence variations are described
for future tracking algorithm development.
Free-space optics (FSO), or Optical Wireless, is an unlicensed line-of-sight technology that uses modulated lasers to
transmit information through the atmosphere. By using light beams, FSO can transmit and receive data, voice, and
video, information through the air. FSO provides data rates ranging from 100Mbps to 2.5Gbps. In most applications,
FSO transceivers normally remain in a static location to ensure continuous line of sight and to maintain accurate
alignment. One current challenge facing FSO technology is the desire to implement mobility. As a potential solution,
this study introduces an auto-tracking system that will achieve and maintain alignment between two mobile FSO nodes.
This auto-tracking system can be used in many different applications, such as reducing the time needed to achieve
alignment of an FSO link, and maintaining a link between an aircraft and a stationary command post to exchange real-time
video and data with high-speed laser communications. After link initiation, the auto-tracking system application
will send steering commands back to the positioning gimbal. These steering commands are determined by feedback
from Position Sensing Diodes (PSDs). The proposed FSO auto-tracking system provides optical beam steering and
capturing mechanisms to provide tracking between two transceivers, either fixed or mobile. In this paper, we illustrate
the feasibility of such a system and present experimental results for a source aligned with a PSD in a mobile
environment.
A mobile ad hoc network (MANET) offers a cost-effective solution for communications in areas where infrastructure is unavailable, e.g., emergency response, disaster recovery, and battlefield scenarios. Traditional MANETs operate in the radio frequency (RF) spectrum, where the available bandwidth faces the challenge of rapidly increasing demands. Free-space optics (FSO) provides an attractive complement to RF wireless MANETs because of its high bandwidth and interference-free operation. We have made an effort to combine the main advantages of MANET and FSO technologies by equipping the network nodes with hybrid communications capabilities. Computer models of such a network were created using the network simulator OPNET Modeler. Various indicators of network performance, including packet loss ratio, end-to-end delay, throughput, etc., were obtained through simulation and examined. The analysis will be of significant assistance in the design and implementation of such next-generation MANETs.
Recent mechanical and nonmechanical optical scanning devices do not meet the fast scanning requirements for contemporary and emerging applications and can only steer optical beams over relatively narrow angles. A variety of important applications require fast optical scanning devices that can steer laser beams rapidly to an arbitrary location and with no moving parts. We introduce a new optical scanning technique that can be used to collimate and steer optical beams for precision alignment in either 2-D free-space optical (FSO) communications links or image scanners. This nonmechanical technique is capable of rapidly redirecting the optical beams to arbitrary locations without greatly sacrificing other parameters such as aperture size, efficiency, and scanning range. A digital micromirror device (DMD) beam-steering system was successfully demonstrated and exhibited better performance results when compared with other available systems.
Accuracy of alignment is a key factor for successfully establishing and maintaining connections in networks of freespace
optical links, and is particularly critical when one or both of the transceivers are moving. Scintillation and other
atmospheric effects create beam deflections that further complicate the alignment process by creating rays that enter the
receiver at an angle to the optical axis. This paper theoretically studies the effective angular misalignment that can be
caused by such deflections and mitigation methods for a traditional free-space optical link. The theory uses Gaussian
beam propagation and system theory to determine the optical power distribution at the receiver lens and the position of
the beam at the lens focal point. Coordinate transformation and overlap integrals are used to assist in calculating the
amount of power collected by the lens and incident on the collecting core of the fiber. The use of a fiber bundle at the
focal plane of the lens is investigated as a possible method for reducing the receiver sensitivity to misalignment. The
simulation results show that some reduction in misalignment sensitivity within some practical system design limits.
Free-space optics (FSO) is a technology that utilizes modulated light beam to transmit information through the
atmosphere. Line-of-sight connection between both FSO transceivers is a necessary condition to maintain
continuous exchange of voice, video, and data information. To date, the primary concentration of mobile FSO
research and development has been toward the accurate aligning between two transceivers. This study introduces an
advanced FSO receiver that provides wider receiving angle compared with that of conventional FSO systems. We
present data from measurements of optical power, which were very promising, and indicated that these advanced
FSO receivers are suitable for FSO alignment applications and perform favorably with similar FSO receivers.
KEYWORDS: Free space optics, Unmanned aerial vehicles, Video surveillance, Detection and tracking algorithms, Telecommunications, Video, Mobile communications, Surveillance, Receivers, Transceivers
Free Space Optics (FSO) technology is currently in use to solve the last-mile problem in telecommunication systems by
offering higher bandwidth than wired or wireless connections when optical fiber is not available. Incorporating mobility
into FSO technology can contribute to growth in its utility. Tracking and alignment are two big challenges for mobile
FSO communications. In this paper, we present a theoretical approach for mobile FSO networks between Unmanned
Aerial Vehicles (UAVs), manned aerial vehicles, and ground vehicles. We introduce tracking algorithms for achieving
Line of Sight (LOS) connectivity and present analytical results. Two scenarios are studied in this paper: 1 - An
unmanned aerial surveillance vehicle, the Global Hawk, with a stationary ground vehicle, an M1 Abrams Main Battle
Tank, and 2 - a manned aerial surveillance vehicle, the E-3A Airborne Warning and Control System (AWACS), with an
unmanned combat aerial vehicle, the Joint Unmanned Combat Air System (J-UCAS). After initial vehicle locations
have been coordinated, the tracking algorithm will steer the gimbals to maintain connectivity between the two vehicles
and allow high-speed communications to occur. Using this algorithm, data, voice, and video can be sent via the FSO
connection from one vehicle to the other vehicle.
KEYWORDS: Digital micromirror devices, Tablets, Digital Light Processing, Micromirrors, Projection systems, Interfaces, Aluminium phosphide, Mirrors, Display technology, Control systems
Digital light processing (DLP) is an innovative display technology that uses an optical switch array, known
as a digital micromirror device (DMD), which allows digital control of light. To date, DMDs have been
used primarily as high-speed spatial light modulators for projector applications. A tablet PC is a notebook
or slate-shaped mobile PC. Its touch screen or digitizing tablet technology allows the user to operate the
notebook with a stylus or digital pen instead of using a keyboard or mouse. In this paper, we describe an
interface solution that translates any sketch on the tablet PC screen to an identical mirror-copy over the
cross-section of the DMD micromirrors such that the image of the sketch can be projected onto a special
screen. An algorithm has been created to control each single micromirror of the hundreds of thousands of
micromirrors that cover the DMD surface. We demonstrate the successful application of a DMD to a high-speed
two-dimensional (2D) scanning environment, acquiring the data from the tablet screen and launching
its contents to the projection screen; with very high accuracy up to 13.68 &mgr;m x 13.68 &mgr;m of mirror pitch.
Atmospheric weather conditions adversely affect the performance of free-space optical communications systems. Fog present in the atmosphere has the largest impact on free-space optical systems. We use simulation techniques to investigate the performance of a slant-path, wavelength-diversified free-space optical link between a ground station and an unmanned aerial vehicle in the presence of radiation fog. The free-space optical link is configured to operate using the simultaneous transmission of three wavelengths, 0.85, 1.55, and 10 µm, connecting a ground station to an unmanned aerial vehicle operating at either a 4- or 8-km altitude. The link is further analyzed by combining the multiple carrier wavelengths into either an equal-gain diversity scheme or a selective diversity scheme. The simulation results are obtained using ALTM and PcModWin simulation software from Ontar Corporation. The results obtained demonstrate that the use of either an equal-gain diversity scheme or a selective diversity scheme enables the deployment of a ground-to-air free-space optical communications link. Furthermore, a selective diversity scheme demonstrates a received power approximately three times greater than an equal-gain diversity scheme.
The use of free-space optical (FSO) communications links are envisioned as a viable option for providing a temporary high-bandwidth communications link between a ground station and an unmanned aerial vehicle (UAV). The presence of atmospheric turbulence causes three different phenomena to occur, namely beam wander, scintillation and beam spread, each of which is a wavelength dependent phenomenon. In this paper, simulation tools are used to investigate the effects of atmospheric turbulence on a wavelength diversified ground-to-UAV FSO communications link. This paper compares the effects of atmospheric turbulence on three different wavelengths, 1.55 μm, 0.85 μm and 10 μm. Each of these wavelengths has different advantages depending on prevalent weather conditions and atmospheric turbulence conditions. Based on the effects of atmospheric turbulence on each wavelength, a wavelength diversity scheme is proposed in order to optimize the performance of the FSO link. The largest problem associated with establishing a ground-to-UAV FSO link is alignment and tracking of the FSO link. For this reason, the wavelength diversity scheme is further analyzed as a method to optimize link acquisition and tracking of the ground-to-UAV link by exploiting various characteristics of each wavelength.
Optical fiber offers many advantages over coaxial cable for the transmission of radio frequency (rf) signals in antenna-remoting applications, as well as cellular networks and cable television (CATV) signal distribution networks. Optical fiber shows significantly less loss, can support signals demanding much higher bandwidth, is immune to electromagnetic interference (EMI), and enables considerable size and weight savings when compared to coaxial cable. Free-space optics (FSO) communications is a technology that uses modulated optical beams to transmit information line of sight through the atmosphere. FSO can be deployed faster and cheaper when compared with optical fiber. Recently, FSO has been investigated by the telecommunications industry and research centers to transport digital signals for civilian "last mile" applications and military applications. We demonstrate the successful transport of modulated rf analog signals over an FSO link and compare key performance measures against a fiber optic link configured in an identical manner. Results of measurements of optical power, transmission response, reflection response, group delay that defines phase distortion, carrier-to-noise ratio (CNR), and dynamic range that defines nonlinear distortion are presented. Results from this comparative study indicate that FSO for rf applications is a suitable replacement for fiber optic transmission links over short distances.
KEYWORDS: Control systems, Receivers, Free space optics, Transmitters, Global Positioning System, Mirrors, Transceivers, Sensors, Optical tracking, Free space
Free Space Optical (FSO) communication has evolved to be applied to the mobile network, because it can provide up to 2.5Gbps or higher data rate wireless communication. One of the key challenges with FSO systems is to maintain the Line of Sight (LOS) between transmitter and receiver. In this paper, the feasibility and performance of applying the FSO technology to the mobile network is explored, and the design plan of the attitude positioning and tracking control system of the FSO transceiver is investigated. First, the system architecture is introduced, the requirements for the control system are analyzed, the involved reference frames and frame transformation are presented. Second, the control system bandwidth is used to evaluate the system performance in controlling a positioning system consisting of a gimbal and a steering mirror, some definitions to describe the positioning accuracy and tracking capacity are given. The attitude control of a FSO transceiver is split into 2 similar channels: pitch and yaw. Using an equivalent linear control system model, the simulations are carried out, with and without the presence of uncertainties that includes GPS data errors and sensor measurement errors. Finally, based on the simulation results in the pitch channel, the quantitative evaluation on the performance of the control system is given, including positioning accuracy, tracking capability and uncertainty tolerance.
Free-space optics (FSO) is a technology that uses modulated laser beams to implement point-to-point communications links without optical waveguides. In many cases, FSO technology can be deployed in metropolitan areas at costs lower than required to install new optical fiber infrastructure. To date, the primary concentration of FSO research and development has been toward the transmission of digital signals, particularly for "last mile" applications. This paper investigates the use of FSO technology for the simultaneous transport of multiple radio frequency (RF) signals over a single FSO channel. Experimental measurements of transmission response and dynamic range, over the frequency range 46-870 MHz, indicate the suitability of FSO links for cable television (CATV) applications.
Through the use of recent technological developments, it is now feasible to establish free-space optical (FSO) communication links over ultra-long distances. Recent research has shown that FSO systems could be deployed to establish high-rate data links to deep space. This study analyzes beam steering tolerances, beam divergence, and geometric loss for different distance ranges of interest for FSO communication links based on a mechanical gimbaled beam steering mechanism. The tolerance, divergence and geometric loss calculations are performed to evaluate the feasibility of establishing FSO links between the Earth and satellites, the Earth and aircraft, aircraft and satellites, the Earth and moon, the Earth and Mars, and the Earth and the edge of the solar system. The analysis and calculations performed take into consideration the availability of new technology such as low noise photon-counting detectors and fiber lasers and amplifiers. The beam steering tolerance and divergence calculations provide beneficial information for determining the extent to which future FSO systems could be deployed for both commercial, military and space exploration applications. Recommendations on the suitability of an FSO communication link for various applications are then made based on the beam steering tolerance and divergence calculations.
An important consideration when deploying free-space optical (FSO) communication links over ultra long distances is the ability to actively steer the laser beam. FSO links are currently being researched as an attractive option for deep-space communication links or as a link to provide broadband communications to aircraft in-flight. In order to establish ultra long FSO links or to actively track FSO links between moving platforms, an active tracking system based on hybrid technology is essential. These hybrid systems are usually a combination of a mechanical gimbal and some array of active optical components. The presence of active optical components in a beam steering device is necessary to provide a high bandwidth while offsetting vibrations present on the mounting platform. This study compares three active beam steering elements that can be used in FSO transmitters and receivers. Performance characteristics of MEMS-based micro mirror arrays, acousto-optic modulators and steerable mirrors are analyzed and compared. A comparison of aperture size, range of motion, resolution and scanning speed is performed. Simulations in order to show the effects of vibration on various different length FSO links are run. A simulation in order to verify the ability of a fast steering mirror to offset vibration effects in a ground-to-UAV link is performed.
Free-space optics (FSO) is a technology that uses modulated optical beams to transmit information in a line-of-sight fashion to achieve a high-bandwidth communications link. FSO technology has been investigated for military and civilian “last mile” applications for many years and, more recently, has generated interest for space-based applications. As the use of FSO technology grows, the potential for optical interference that degrades FSO network performance, whether intentional (jamming) or otherwise, becomes a matter of increasing importance. The investigation described in this paper examined the effects of interference upon the operation and performance of a point-to-point FSO link connecting two virtual local area networks. The sources of interference were laser pulses of varying energy, wavelength, and repetition rate produced from a nitrogen-pumped, tunable dye laser. The study evaluated the effect upon FSO link performance of varying the output power of the interfering source for a fixed wavelength, of varying the wavelength of the source for a fixed power, and of varying the pulse repetition rate of the source. The results of the study indicated that FSO link performance was negatively influenced by such interference.
KEYWORDS: Free space optics, Signal to noise ratio, Wavelength division multiplexing, Signal attenuation, Analog electronics, Optical amplifiers, Fiber amplifiers, Atmospheric optics, Transmitters, Optical testing
Free-space optics (FSO) is a technology that uses modulated optical lasers to transmit information in a line-of-sight path through the atmosphere. To date, the major focus of FSO research and development has been toward the transmission of digital data, mostly for “last mile” applications. This paper investigates the simultaneous transportation of multiple analog radio frequency (RF) signals over a single FSO link using wavelength division multiplexing (WDM) technology. Experimental measurements of optical peak power and signal-to-noise ratio (SNR) indicate the suitability of FSO links for supporting WDM applications.
KEYWORDS: Free space optics, Signal to noise ratio, Optical amplifiers, Analog electronics, Transmitters, Fiber amplifiers, Modulation, Receivers, Signal attenuation, Atmospheric optics
Free space optics (FSO) is a technology that uses modulated optical beams to transmit information line-of-sight through the atmosphere. To date, the primary focus of FSO research and development has been toward the transmission of digital signals, primarily for "last mile" applications. This paper reports the use of FSO to transport modulated radio frequency (RF) analog signals, together with an investigation of key performance measures. Results indicate minimal RF signal distortion when transmitted over FSO. The advantages of using FSO include increased security and insusceptibility to electromagnetic interference (EMI).
Free-space optical communication systems are adversely affected by weather conditions, especially fog. The objective of this paper is to examine the use of wavelength diversity in free-space optics to mitigate the effect of fog on the received optical signal strength. The source information was encoded and transmitted onto three carrier wavelengths obtained from different parts of the infrared spectrum: 0.85 μm, 1.55 μm, and 10 μm. The transmitted carriers traveled through two different simulated fog conditions, radiation and advection, before being detected and decoded by the receiver. Then, the multiple carriers were combined and processed using two diversity schemes: equal gain and selective diversity. The study was conducted using simulation software PcModWin by onTar Corporation. The results show an average power reception improvement in tens of percent, by comparison to the use of a single carrier. Hence, the increase of the received power translates into a distance improvement of at least fifteen percent.
This paper presents results from an ongoing effort at the University of Oklahoma to develop a real-time active alignment system for free-space optical communication system. An initial prototype of a FSO active alignment system using Global Positioning System (GPS) sensors, two gimbals, and point-to-point spread spectrum RF communication is described. The positions of both FSO transceivers are exchanged over the radio frequency (RF) communication link. A controller uses the exchanged information to calculate azimuth and elevation bearings to achieve initial alignment between the transceivers. The gimbals are used to steer the beams. The paper also presents a binary scan algorithm developed to expedite the initial alignment process. The algorithm incorporates power measurements as feed back to the original transceiver for comparison. In minimizing convergence time, simulation results confirm that the algorithm performs better than raster scan, spiral scan, and raster spiral scan algorithms, all of which are used in laser satellite communications. The results also show that the initial design is not able to achieve real-time alignment. For real-time alignment, different augmenting technologies (for example, steering mirrors) should be considered.
The role of the Advanced Air Transportation Technologies program undertaken at the NASA Glenn Research Centers has been focused mainly on the improvement of air transportation safety, with particular emphasis on air transportation communication systems in on-board aircraft. The conventional solutions for digital optical communications systems specifically designed for local/metro area networks are, unfortunately, not capable of transporting the microwave and millimeter RF signals used in avionics systems. Optical networks capable of transporting RF signals are substantially different from the standard digital optical communications systems. The objective of this paper is to identify a number of different communication link architectures for RF/fiber optic transmission using a single backbone fiber for carrying VHF and UHF RF signals in the aircraft.
To support these architectures, two approaches derived from both hybrid RF-optical and all-optical processing methodologies are discussed with single and multiple antennas for explicitly transporting VHF and UHF signals, while the relative merits and demerits of each architecture are also addressed. Furthermore, the experimental results of wavelength division multiplexing (WDM) link architecture from our test-bed platform, configured for aircraft environment to support simultaneous transmission of multiple RF signals over a single optical fiber, exhibit no appreciable signal degradation at wavelengths of both 1330 and 1550 nm, respectively. Our measurements of signal to noise ratio carried out for the transmission of FM and AM analog modulated signals at these wavelengths indicate that WDM is a fiber optic technology which is potentially suitable for avionics applications.
We have investigated two approaches to improving the electro-optic performance of polymer dispersed liquid crystal (PDLC) films. One involves using a partially fluorinated epoxy based thermoset to serve as the PDLC binding matrix. Results indicate that this causes an enhanced phase separation of the liquid crystal which leads to significant changes in the contrast ratio and fall time of a PDLC film. The other approach involves using duel frequencies to enhance the electro-optic performance of another type of PDLC film. Studies suggest that the hysteresis effect can be minimized and the overall control of the electro-optic response can be greatly increased by adding a second high frequency component to the PDLC driving voltage.
Several different types of polymer dispersed liquid crystal (PDLC) systems have been developed in recent years. The transmission characteristics of each type depend on the materials used, the method of construction, and the addressing technique used to drive the system. Greater control over the transmittance response as a function of time is important for many display operations. The effect of using dual-frequency addressing and pulsed mode dual frequency addressing in controlling the transmittance response of one type of PDLC film has been investigated. The results suggest that the gray scale inconsistency as well as the hysteresis effect can be reduced by utilizing the frequency dependence of the dielectric anisotropy of the liquid crystal.
Generally one type of polymer is used in the construction of polymer dispersed liquid crystal (PDLC) films. The authors tested the effect of incorporating an additional fluoropolymer in varying percentages on the electro-optic performance of PDLC films based on poly(methyl methacrylate). Compared to samples made from a single polymer, several correlations are noted, including a decrease in liquid crystal fall-time, an increase in rise-time, and an increase in the threshold voltage (Vt).
A conducting PRIZ device is fabricated and shown to exhibit the
unique image processing features of edge detection, directional spatial
filtering, and dynamic image selection. The active element is single
crystal bismuth silicon oxide (Bi12SiO20 or BSO) . Auger electron
spectroscopy (AES) and neutron activation analysis (NAA) techniques
were applied to BSO to identify the impurities which contribute to the
device operation.
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