Physical Sciences

Software Analyzes Heat Buildup in VCSELs

Modeling allows redesign without diminishing reliability.Internal heating is a key issue for vertical cavity surface emitting lasers (VCSELs), a semiconductor microlaser diode that emits light in a cylindrical beam vertically from the surface of a fabricated wafer. They generally have higher thermal impedance than edgeemitting lasers and are fairly efficient for optical devices, running at roughly 25% efficiency in contrast to light emitting diodes’ (LEDs) typical 2% to 3%. For instance, they produce 10 mW of optical power from a 40-mW input; the remaining is dissipated as heat.

Posted in: Physical Sciences, Photonics, Briefs

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Wavelength Translation Using SFP Transceivers Enables Extension of Optical-Communication Links

Optical-Electrical-Optical (OEO) wavelength translation (WT) based on smallform- factor pluggable (SFP) transceivers is meeting with increased interest in metro optical-network applications. It provides a flexible and low-cost solution when it interfaces with legacy optical equipment that does not support International Telecommunications Union (ITU) wavelengths. WT improves the performance of optical systems by changing the operating wavelength of the incoming optical signal to a wavelength that enables longer reach through lower attenuation or lower dispersion penalty.

Posted in: Physical Sciences, Photonics, Briefs

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Handheld Imaging Device for Security Applications

Intelligent radar core provides three-dimensional, through-wall imaging capabilities.A standalone, handheld, through-wall radar unit is under development to provide three-dimensional feedback on the location and movement of people inside buildings. Applications include military and emergency service such as hostage situations and search and rescue. The unit, which can be held against a wall or mounted on a tripod located up to 2 meters away, transmits low-frequency ultrawideband (UWB) radar pulses that pass through building materials over 40 cm thick and detects activity over a range of up to 15 meters.

Posted in: Physical Sciences, Briefs

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Broadband External-Cavity Diode Laser

This relatively simple, inexpensive device is suitable for use in survey spectroscopy.A broadband external-cavity diode laser (ECDL) has been invented for use in spectroscopic surveys preparatory to optical detection of gases. Heretofore, commercially available ECDLs have been designed, in conjunction with sophisticated tuning assemblies, for narrow- band (and, typically, single-frequency) operation, as needed for high sensitivity and high spectral resolution in some gas-detection applications. However, for preparatory spectroscopic surveys, high sensitivity and narrow-band operation are not needed; in such cases, the present broadband ECDL offers a simpler, less-expensive, more-compact alternative to a commercial narrowband ECDL.

Posted in: Physical Sciences, Photonics, Briefs, TSP

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High-Efficiency Solar Cells Using Photonic-Bandgap Materials

Energy-conversion efficiencies exceeding 50 percent may be possible.Solar photovoltaic cells would be designed to exploit photonic-bandgap (PBG) materials to enhance their energy- conversion efficiencies, according to a proposal. Whereas the energy-conversion efficiencies of currently available solar cells are typically less than 30 percent, it has been estimated that the energy- conversion efficiencies of the proposed cells could be about 50 percent or possibly even greater.

Posted in: Physical Sciences, Photonics, Briefs, TSP

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High Peak Power Fiber Amplifiers Operating at Eye-Safe Wavelengths

PM-clad fibers enable scaling with single transverse mode beam quality.Recent advances in fiber technology have enabled a dramatic increase in the power delivered from fiber based amplifiers and lasers. This is particularly true at the 1060-nm wavelength where ytterbium (Yb)-doped fibers operate, with state-of-the-art peak powers now approaching 1 MW (1 mJ and 1 ns) delivered with single-mode, near diffraction limited beam quality. However, progress on scaling fiber-based eye-safe devices, such as those operating around the 1550-nm wavelength regime, based on Er:Yb (erbium:ytterbium) co-doped fibers has been much slower. The progress at this wavelength range hampered by the lack of suitable large mode area (LMA) fibers.

Posted in: Physical Sciences, Photonics, Briefs

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Improved Thermal Matching of Materials for Hermetic Optical Windows

A wider range of glass materials can be bonded when custom alloys are used to create the frame. A family of iron-nickel and ironnickel- cobalt alloys made using metal injection technology (MIT) has been designed to match the coefficient of thermal expansion (CTE) of select optical glass materials more closely than commonly available wrought alloys of similar composition. Using these glass and metal combinations, custom windows can be developed with improved optical properties, greater hermeticity levels, and lower residual stress.

Posted in: Physical Sciences, Photonics, Briefs

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