RF Photonics for Avionics Signal Processing

The maturity of RF photonic components has reached the point where fiber optic links are being system-tested to replace traditional copper coax links on avionic platforms. Many demonstrations of RF photonic links have been made with traditional and non-traditional modulation formats to improve the RF performance of the link. While the advantages of RF photonic links in regard to size and weight are important, the large instantaneous bandwidth of the fiber optic links is a key driver for the use of this technology in the airframe.

Posted in: Articles, Aerospace, Defense, Fiber Optics, RF & Microwave Electronics, Avionics, Optics

Using Forensic Lasers in Modern Warfare

In the conflicts in Iraq and Afghanistan, the enemy’s guerilla tactics have muddled the distinction between terrorism and warfare. To deal with the challenges of this new type of combat, the military has quietly built up impressive forensic capabilities, with technology more usually found in domestic crime labs than on the battlefield. Just as they have in numerous areas of weapons technology, lasers play a cutting-edge role in this work, which is performed on location, within mobile labs in Afghanistan, as well as in the US.

Posted in: Articles, Aerospace, Defense, Photonics, Test equipment and instrumentation, Military vehicles and equipment

Covert Infrared Battlefield Combat Taggants

Modern warfare often involves poorly defined battle lines accompanied by multilevel fire support systems that can deliver firepower with high precision and devastating lethality from a long distance. The ability to immediately and accurately discriminate through sight between friend and foe is of great importance to military operations for effectively destroying hostile forces while preventing fratricide. This ability is even more crucial for irregular and unconventional warfare such as anti-terrorism operations where US forces often engage enemy combatants well entrenched in urban settings or rugged terrains at night. In such battlefield conditions, using conventional daylight and thermal imagery often exceeds the ability to accurately identify targets as friend or foe, and more reliable battlefield identification methods are needed.

Posted in: Articles, Aerospace, Defense, Photonics, Imaging, Identification, Military aircraft, Military vehicles and equipment

Room-Temperature Sub-Diffraction-Limited Plasmon Laser

Lasers present the means to deliver powerful, coherent, and directional high-frequency electromagnetic energy. However, the diffraction limit of light imposes fundamental constraints on how compact such photonic devices can be and their potential for integration with electronic circuits, which are orders of magnitude smaller.

Posted in: Briefs, Photonics, Downsizing, Architecture, Integrated circuits, Lasers

Rare-Earth-Doped Soft Glass Optical Fibers for Coherent Wavelength Sources Above 2 Microns

Rare-earth-doped soft glass optical fibers were developed and characterized for fiber lasers emitting at wavelengths longer than 2 microns to allow efficient narrow line-width emission in the atmospheric window for coherent detection and LIDAR and DIAL sensing.

Posted in: Briefs, Photonics, Fiber optics, Lasers, Fibers, Glass

Surface Plasmon-Enhanced Si:Er Infrared Light-Emitting Diodes

Plasmons are collective oscillations of the free electrons in a metal or an ionized gas. Plasmons dominate the optical properties of noble-metal nanoparticles, which enables a variety of applications including electromagnetic energy transport at nanoscale dimensions, single-molecule Raman spectroscopy, and photothermal cancer therapy. Plasmons also affect the spontaneous emission dynamics of optical emitters positioned in the vicinity of metal nanoparticles. The luminescence intensity can either be enhanced or quenched, depending on the geometry. Since the associated enhancements can potentially be several orders of magnitude, plasmon-enhanced luminescence is the subject of intense research. This project focused on plasmon-enhanced luminescence of silicon quantum dots (Si QDs) and optically active erbium ions. Both these emitters are compatible with silicon processing technology, and are therefore of great technological interest.

Posted in: Briefs, Photonics, Light emitting diodes (LEDs), Gases, Materials properties, Nanomaterials

AlInGaN Bandgap and Doping Engineering for Visible Laser Diodes

There is a great need to develop chip-scale visible lasers for many applications, including laser sight, environmental monitoring, and compact pumping sources for ultra-short laser pulse generation, high-luminous full-color displays, new-generation solid-state lighting, etc. The realization of chip-scale visible laser diodes (LDs) would provide significant benefits in terms of cost, volume, and the ability of photonic integration with other functional devices. Significant progress in nitride material technology has been achieved, and high-performance visible LEDs and near-UV LDs based on InGaN are now commercially available.

Posted in: Briefs, Photonics, Integrated circuits, Lasers, Materials properties

Photorefractive Polymers for Updatable 3D Displays

Photorefractive (PR) polymer composites developed for 3D display applications contain a copolymer as the hole-transporting host matrix. The copolymer approach is followed to reduce the phase separation typical in guest-host polymer systems with low glass transition temperature (Tg), thus allowing increased loading of functional components such as NLO chromophores. The copolymer consists of a polyacrylate backbone with pendant groups tetraphenyldiaminobiphenyltype (TPD) and carbaldehyde aniline (CAAN) attached through an alkoxy linker (PATPD-CAAN). A fluorinated dicyanostyrene (FDCST) NLO chromophore was added to provide sufficient refractive index change and charge generation at the wavelength of interest (532 nm). The plasticizer Nethyl carbazole (ECZ) was also used to reduce the Tg to room temperature. In some composites, a fullerene derivative [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) was used to provide improved sensitization.

Posted in: Briefs, Photonics, Displays, Composite materials, Polymers

Computational Photonics in Laser Communications Through Clouds

This work explored the concept of creating a partially coherent laser beam consisting of an array of spatially overlapping or separated Gaussian beams with possible individual control of each individual emitter’s wavelength. The idea was to test whether such a transmitter array could propagate more effectively through weak or strong atmospheric turbulence. It was proposed that a versatile, multi-wavelength, multi-emitter configuration could be realized via an array of optically pumped, vertical external-cavity surface emitting semiconductor lasers (VECSELs).

Posted in: Briefs, Photonics, Lasers, Semiconductors, Test procedures, Turbulence

Threshold Voltage Tuning of Metal-Gate MOSFETs Using an Excimer Laser

This work presents a localized method for tuning the threshold voltages (Vt) of multilayer metal-gate metal-oxide-semiconductor field-effect transistor (MOSFET) devices with a spatial area theoretically limited by the wavelength of the laser beam. This technique allows an independent means to tailor threshold voltage on a device-to-device basis that provides greater design flexibility. This maskless technique allows tailoring of thresholds by tuning the work function of the gate by intermixing titanium and titanium nitride using a laser pulse. The source and drains of the MOSFET are simultaneously annealed by the laser.

Posted in: Briefs, Photonics, Calibration, Lasers, Semiconductor devices, Transistors, Titanium