Photonics/Optics

Cooling Lasers with Thin-Film Thermoelectric Coolers

Laser diodes for telecommunications have traditionally used thermoelectric coolers (TECs) for precision temperature control to improve diode output levels and maintain wavelength integrity. A major trend for photonics in telecommunications has been the move to more integrated packaging that is smaller and simpler in structure in order to lower costs. This, in turn, has opened the door for higher volume manufacturing. In the course of this transition, conventional TEC solutions have become increasingly difficult to implement as conventional bulk thermoelectric technology has not kept pace with the size and power density requirements for next generation devices.

Posted in: Articles, Features, ptb catchall, Photonics

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Tunable Bandpass Filters

The ubiquitous techniques of fluorescence and Raman imaging and spectroscopy rely heavily on spectrally precise, high-quality and high-throughput optical filter technologies. As both fluorescence and Raman-based techniques move from traditional R&D-based environments into medical and clinical (diagnostic) settings, even higher demands are placed on system performance. Therefore, it is necessary to continue to improve system components and architectures to meet the demanding challenges often encountered in biological applications.

Posted in: Application Briefs, Applications, ptb catchall, Photonics

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Holographic Vortex Coronagraph

This apparatus offers potential advantages of performance and manufacturability over conventional coronagraphs. NASA’s Jet Propulsion Laboratory, Pasadena, California A holographic vortex coronagraph (HVC) has been proposed as an improvement over conventional coronagraphs for use in high-contrast astronomical imaging for detecting planets, dust disks, and other broadband light scatterers in the vicinities of stars other than the Sun. Because such light scatterers are so faint relative to their parent stars, in order to be able to detect them, it is necessary to effect ultra-high-contrast (typically by a factor of the order of 1010) suppression of broadband light from the stars. Unfortunately, the performances of conventional coronagraphs are limited by low throughput, dispersion, and difficulty of satisfying challenging manufacturing requirements. The HVC concept offers the potential to overcome these limitations.

Posted in: Photonics, Briefs, ptb catchall, Tech Briefs, Photonics

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Photon Counting Using Edge-Detection Algorithm

Improved optical communications links can be used in building-to-building networks in high-attenuation conditions such as rain or fog. NASA’s Jet Propulsion Laboratory, Pasadena, California New applications such as high-data-rate, photon-starved, free-space optical communications require photon counting at flux rates into gigaphoton-per-second regimes coupled with sub-nanosecond timing accuracy. Current single-photon detectors that are capable of handling such operating conditions are designed in an array format and produce output pulses that span multiple sample times. In order to discern one pulse from another and not to over-count the number of incoming photons, a detection algorithm must be applied to the sampled detector output pulses. As flux rates increase, the ability to implement such a detection algorithm becomes difficult within a digital processor that may reside within a field-programmable gate array (FPGA).

Posted in: Photonics, Briefs, ptb catchall, Tech Briefs, Photonics

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Optical Structural Health Monitoring Device

This device detects microscopic cracks and surface structural changes in components. Dryden Flight Research Center, Edwards, California This non-destructive, optical fatigue detection and monitoring system relies on a small and unobtrusive light-scattering sensor that is installed on a component at the beginning of its life in order to periodically scan the component in situ. The method involves using a laser beam to scan the surface of the monitored component. The device scans a laser spot over a metal surface to which it is attached. As the laser beam scans the surface, disruptions in the surface cause increases in scattered light intensity. As the disruptions in the surface grow, they will cause the light to scatter more. Over time, the scattering intensities over the scanned line can be compared to detect changes in the metal surface to find cracks, crack precursors, or corrosion. This periodic monitoring of the surface can be used to indicate the degree of fatigue damage on a component and allow one to predict the remaining life and/or incipient mechanical failure of the monitored component.

Posted in: Photonics, Briefs, ptb catchall, Tech Briefs, Photonics

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Widely Tunable Mode-Hop-Free External-Cavity Quantum Cascade Laser

This technology is suitable for spectroscopic applications, multi-species trace-gas detection, and measurements of broadband absorbers. Lyndon B. Johnson Space Center, Houston, Texas The external-cavity quantum cascade laser (EC-QCL) system is based on an optical configuration of the Littrow type. It is a room-temperature, continuous- wave, widely tunable, mode-hop-free, mid-infrared, EC-QCL spectroscopic source. It has a single-mode tuning range of 155 cm-1 (≈8% of the center wavelength) with a maximum power of 11.1 mW and 182 cm-1 (≈15% of the center wavelength), and a maximum power of 50 mW as demonstrated for 5.3 micron and 8.4 micron ECQCLs, respectively. This technology is particularly suitable for high-resolution spectroscopic applications, multi-species trace-gas detection, and spectroscopic measurements of broadband absorbers.

Posted in: Photonics, Briefs, ptb catchall, Tech Briefs, Photonics

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Non-Geiger-Mode Single-Photon Avalanche Detector With Low Excess Noise

Applications include quantum key distribution for the financial industry and photon-starved optical communications needs. NASA’s Jet Propulsion Laboratory, Pasadena, California This design constitutes a self-resetting (gain quenching), room-temperature operational semiconductor single-photon-sensitive detector that is sensitive to telecommunications optical wavelengths and is scalable to large areas (millimeter diameter) with high bandwidth and efficiencies.

Posted in: Photonics, Briefs, Products, Photonics

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