Solid-State, High-Energy Lasers Based on Rare-Earth Doped Gallium Nitride

Laser-based directed-energy weapons (DEW) are important components for future Army missile defense systems. The diode-pumped, rare-earth (RE)-doped, solid-state laser is a very promising path towards achieving a DEW-sufficient level of average power from a reasonably compact device. Even so, the extreme pump power densities, combined with the inevitable non-radiative losses in the pump-lase process, introduce severe thermal loading in the gain medium. Regardless of the sophistication of the heat removal technique and its efficiency, the gain medium itself is the bottleneck for non-distortive heat removal due to the low thermal conductivity of known gain media compared to that of heat-sinking materials. The bestknown laser hosts, e.g., yttrium aluminum garnet (YAG), possess thermal conductivities (10–11 W/(m-K)) that are ~1.5 orders of magnitude lower than those of known heat-sinking materials. In order to eliminate this technical hurdle, an innovative gain medium with a thermal conductivity on the same order as copper (~390 W/(m- K)) had to be engineered.

Posted in: Briefs, Photonics, Lasers, Thermal management, Military vehicles and equipment, Missiles

Analysis of Analog Photonic Links Employing Multiple-Channel (Arrayed) Receivers

Analog optical links are finding increased application in commercial and military systems ranging from radio-over-fiber applications, antenna remoting, and optical signal processing. As the performance of an analog link improves with received photocurrent, optical amplifiers — predominantly erbium-doped fiber amplifiers (EDFAs) — have been readily incorporated into a variety of systems. It is known that the addition of an optical amplifier (EDFA) raises the electrical noise floor in both digital and analog applications due to the presence of amplified spontaneous emission (optical) noise. To mitigate this additional noise in systems employing EDFAs prior to modulation, dualoutput optical modulators and balanced detection are frequently employed. This technique has been utilized alone to achieve the first multi-gigahertz bandwidth analog optical link with a noise figure

Posted in: Briefs, Photonics, Amplifiers, Architecture, Noise

Photonic Recirculating Delay Line for Analog-to-Digital Conversion

Aconventional analog fiber-optic link can be augmented with a recirculating optical delay loop so as to realize an optically assisted analogto- digital converter (ADC) that provides improved performance in terms of both speed and resolution using one (slower) electronic ADC (see figure). The overall architecture readily integrates with any electronic ADC system. Moreover, the highspeed ADC performance is fundamentally limited by the performance of the fiber-optic link.

Posted in: Briefs, Photonics, Amplifiers, Fiber optics, Performance upgrades, Test procedures

Design and Development of a Package for a Diluted Waveguide Electro-Absorption Modulator

Externally coupled electroabsorption modulators (EAMs) are commonly used in order to transmit RF signals on optical fibers. Recently, an alternative device design with diluted waveguide structures was developed. Bench tests show benefits of lower propagation loss, higher power handling (100 mW), and higher normalized slope efficiency. Bench tests were performed in order to characterize the optical coupling of the EAM. The photo current maximum was offset from the optical power output maximum. The transmissions vs. bias voltage curves were measured, and an XY scanner was used to record the mode field of the light exiting from the EAM waveguide in each position. The Beam Propagation Method was used to simulate the mode field and the coupling efficiency. Based on the bench tests and simulation results, a design including mechanical, optical, and RF elements was developed.

Posted in: Briefs, Photonics, Design processes, Fiber optics, Waveguides

Developing Fleets of Autonomous Underwater Vehicles

Autonomous underwater vehicles (AUVs) have a demonstrated capability to collect valuable data for scientific and military purposes. Historically, individual vehicles have been used. To reduce the overall time and cost of acquiring data over large areas, multiple vehicles must be used. A fleet of five AUVs, capable of underwater commendation, was fabricated. These AUVs include small submarines, referred to as “swimmers,” and small, two-tracked vehicles, referred to as “crawlers.” The control and communication algorithms developed in this work will enable AUVs to use formations to search for mines and to communicate with each other in order to implement cooperative behavior. Languages and logics were developed to enable collaborative operations among the vehicles.

Posted in: Briefs, Mechanical Components, Communication protocols, Electronic control systems, Fleet management, Autonomous vehicles, Marine vehicles and equipment

Stability Analysis of Distributed Engine Control Systems

Full Authority Digital Engine Control (FADEC), based on a centralized architecture framework, is being widely used for gas turbine engine control. However, current FADEC is not able to meet the increased burden imposed by the advanced intelligent propulsion system concepts. This has necessitated development of the Distributed Engine Control (DEC) system. FADEC based on Distributed Control Systems (DCS) offers modularity, improved control sys-tem prognostics, and fault tolerance, along with reducing the impact of hardware obsolescence.

Posted in: Briefs, Mechanical Components, Architecture, Performance upgrades, Engine control systems, Gas turbines

Optimized Robust Adaptive Networks in Supervisory Control and Data Acquisition Systems

The Electric Power and Communica - tion Synchronizing Simulator (EPOCHS) system could provide great benefits to private industry and Department of Defense (DoD) power systems infrastructure by allowing simultaneous, synchronous simulation of communication and power system simulators to better understand the power grid under anomalous situations. Supervisory Control and Data Acquisition (SCADA) systems and the power grid infrastructure have recently been the focus of attention given the recent disclosure of potential cyber attacks. Applying Special Protection Schemes like the one used by the EPOCHS systems could provide a solution not only to cyber attack, but to possible cascading failures typical to power systems on current high-load demands. Utilizing an Internet-like architecture to implement such a backup and communication system is likely to be the most logical solution to providing a power grid intranet.

Posted in: Briefs, Information Technology, Computer simulation, Failure modes and effects analysis, Architecture, Cyber security, Telecommunications systems, Electric power grid

Evolvable Approaches to Software Verification and Validation

Research was conducted to integrate and advance current techniques in compilers, hardware architectures, and security to develop novel techniques to protect against physical attacks on encrypted embedded systems. The innovation in the approach was in exploiting the power of integrated software-hardware methods that do not require processor re-design. The hardware side of the innovation comes from using reconfigurable logic to implement security techniques in hardware. The reconfigurable logic in hardware, when combined with the ability of the compiler to instrument the code, can be used in powerful ways to strengthen the security of computing platforms. Several techniques were proposed and designed to address these objectives.

Posted in: Briefs, Information Technology, Computer software / hardware, Cryptography, Cyber security, Research and development, Quality assurance

High-Resolution Anatomic and Elastographic Transrectal Ultrasound for Improved Diagnosis of Prostate Cancer

Prostate cancer screening generally uses the Pro state Spe cific Antigen (PSA) blood test, free-PSA testing, and Digital Rectal Exam ination (DRE). When the PSA is used, there exists a significant gray area in which cancers may be missed. Addition ally, DRE is practically limited to the detection of shallow (subcapsular) palpable abnormalities. Even systematic multi-core biopsy fails to detect clinically detectable cancers in up to 34% of men. Thus, there is compelling clinical interest in finding improved detection methods.

Posted in: Briefs, Medical, Diagnosis, Diseases, Physical examination, Acoustics, Test equipment and instrumentation

Medical Information Network Decision Support System

In order to facilitate a more rapid and systematic transfer of new medical knowledge and capabilities into mainstream clinical practice, a new Medical Information Network Decision Support (MINDS) system has been proposed. This system is intended to be a platform for storing and fusing medical data across all levels (e.g. from low-level genomic and proteomic data to higher level clinical data) in a standardized way.

Posted in: Briefs, Software, Data exchange, Medical equipment and supplies, Data management