Photonics

Photon Counting Chirped Amplitude Modulation Ladar

This work is a follow-up to prior efforts to develop a method using Geiger-mode avalanche photodiode (GM-APD) photon counting detectors in chirped amplitude modulation (AM) ladar receivers to yield sensitivities approaching the shot noise limit. Such sensitivities represent about four orders of magnitude improvement over the sensitivities of the currently used unity-gain, opto- electronic mixing (OEM) metal-semiconductor-metal (MSM) detectors. These sensitivity improvements may enable compact, low-power, eye-safe, and/or long-range ladar with low-cost, low-bandwidth readout integrated circuits for foliage and camouflage penetration, target ID, manned and unmanned ground and air vehicle navigation, 3D face recognition, battle damage assessment, and change detection.

Posted in: Briefs, Photonics
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Hybrid Micro-Electro-Mechanically Tunable Optical Filter

A prototype hybrid micro-electro- mechanically tunable optical filter (MEM-TF) based partly on an electrostatic-actuation principle has been built and tested as an essential component needed for the further development of a prototype micro-electro- mechanically tunable vertical- cavity surface emitting laser (MT-VCSEL). In turn, MT-VCSELs are needed as essential controllable-wavelength sources in diverse advanced optoelectronic devices and systems including, for example, wavelength-division multiplexers in fiber-optic communication systems; lightweight, compact, portable spectroscopic instruments for detecting chemical and biological warfare agents; holographic memory devices; fiber-optic sensors; optoelectronic signal-processing systems; and remote-sensing systems. The development of the prototype MEM-TF also has additional significance in that it demonstrates the merit of the hybrid approach (in comparison with the monolithic-integration approach) to design and fabrication of some advanced optoelectronic devices.

Posted in: Briefs, Photonics
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Near-Field Light Lenses for Nano-Focusing of Beams of Atoms

Near-field light lenses for focusing beams of light and beams of atoms to spots having a width of no more than several nanometers are undergoing development. There are numerous potential applications for such lenses:

•A capability to focus beams of light to nanometer-sized spots is essential for development of proposed nanoscale optical devices (e.g., optical switches and logic gates) based on near-field optical interactions.

•A capability to focus beams of atoms to nanometer-sized spots could contribute to the development of nanophotonic devices, including quantum dots, which must be sized and positioned with precision.

Posted in: Briefs, Photonics, Glass, Nanotechnology, Refractory materials
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Developments in Adaptive Filtering and System Identification

Progress has been made on several fronts in a continuing program of research oriented toward the development of real-time algorithms, and computer and control systems that utilize the algorithms, for adaptive filtering, prediction, and system identification with improved efficiency and numerical stability in applications that involve large numbers of channels and high filter orders. Potential applications include adaptive optics, optical communications, target tracking, image processing, blind identification and deconvolution in wireless communications, and active control of noise and vibration.

Posted in: Briefs, Photonics
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Electrical Filters Containing Multistage PBG Resonators

Electrical filters of a recently invented type are designed and constructed as transmission lines into which multistage photonic-band-gap (PBG) structures are incorporated. As used here, "transmission lines" refers to any or all of the standard electrical media, including coaxial cables, microstrips, and the like, used for propagation of electromagnetic waves along enclosed or well defined paths. The term "electrical filters" is used here in a conventional sense, denoting any of a variety of systems or components that block propagation of signals in certain frequency bands (stop bands) and/or support propagation in other frequency bands (pass bands). The PBG structures used in this invention can be any of a variety of dielectric or electrically conductive structures, containing precise periodic or quasiperiodic arrays of holes or other features that can be tailored to obtain desired stop bands.

Posted in: Briefs, Photonics, Amplifiers, Architecture, Conductivity
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BC VCSELs for RF/Photonic Links

Bipolar cascade (BC) vertical-cavity surface emitting lasers (VCSELs) of a type intended specifically for use in radio-frequency (RF)/photonic links have been demonstrated. As used here, "RF/photonic link" signifies a communication link in which, at the transmitter, the continuous-wave output of a laser is modulated with an RF (typically, a microwave) signal and the resulting modulated laser beam is conveyed via free space or an optical fiber to a receiver, where the RF signal is detected. RF/photonic links offer advantages for short-range, wide-band communications and for diverse functions involved in phased arraying of large microwave antennas.

Posted in: Briefs, Photonics, Antennas, Fiber optics, Lidar, Wireless communication systems
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Effect of Laser Noise on an Analog RF/Photonic Link

Aset of equations has been formulated to enable quantification of several aspects of the performance of an analog photonic communication link as affected by laser noise. A procedure for measuring the laser noise has been devised to provide laser-noise data for use in the equations. The equations and procedure are generally applicable to diverse analog photonic links, in the design and operation of which laser noise is of great concern. Analog photonic links have been found to be useful as subsystems, radio-antenna-arraying systems, optoelectronic oscillators, and wide-band signal-processors.

Posted in: Briefs, Photonics, Finite element analysis, Lasers, Noise measurement
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Cleaning and Protecting Large Mirrors Using a Polymer Solution

Cleaning and protecting optics is a challenge — contamination must be removed without damaging the surface. Preventing recontamination for extended periods of time after cleaning was unattainable prior to use of polymer strip coat films. The SLRSC Western Range Depot Optics Group, WRDOG, at Vandenberg Air Force Base, is a pioneer in the cleaning and protection of precision glass optics, lenses, and large mirrors using polymer solution technology.

Posted in: Briefs, Photonics, Mirrors, Coatings Colorants and Finishes, Polymers
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Advances in Materials for Photonic Applications

Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio Aprogram of research has addressed multiple topics in the design, development, characterization, and utilization of new materials for photonic applications. These materials include compounds, solutions, and nanocomposites that exhibit diverse types of single- and multiple-photon activity. The accomplishments of this research can be grouped into four main categories and summarized as follows:

Posted in: Briefs, Photonics
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Compact Megawatt Infrared Free-Electron Laser Amplifier

A proposed high-gain free-electron laser (FEL) amplifier, conceived primarily for use in a maritime environment, would be capable of average output power of the order of a megawatt at one or more of several infrared wavelengths (1.045, 1.625, or 2.141 μm) for which propagation through air is minimally adversely affected by water vapor and aerosols. The conceptual design of this FEL amplifier provides for a combination of conventional and unconventional characteristics that, taken together, would be advantageous in the intended power and wavelength regime.

Posted in: Briefs, Photonics
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