Photonics/Optics

High-Speed Operation of Interband Cascade Lasers

NASA’s Jet Propulsion Laboratory, Pasadena, California Optical sources operating in the atmospheric window of 3–5 μm are of particular interest for the development of free-space optical communication link. It is more advantageous to operate the free-space optical communication link in 3–5-μm atmospheric transmission window than at the telecom wavelength of 1.5 μm due to lower optical scattering, scintillation, and background radiation. However, the realization of optical communications at the longer wavelength has encountered significant difficulties due to lack of adequate optical sources and detectors operating in the desirable wavelength regions.

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

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Hybrid AlGaN-SiC Avalanche Photodiode for Deep-UV Photon Detection

NASA’s Goddard Space Flight Center, Greenbelt, Maryland The proposed device is capable of counting ultraviolet (UV) photons, is compatible for inclusion into space instruments, and has applications as deep-UV detectors for calibration systems, curing systems, and crack detection. The device is based on a Separate Absorption and Charge Multiplication (SACM) structure. It is based on aluminum gallium nitride (AlGaN) absorber on a silicon carbide APD (avalanche photodiode). The AlGaN layer absorbs incident UV photons and injects photogenerated carriers into an underlying SiC APD that is operated in Geiger mode and provides current multiplication via avalanche breakdown.

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

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Mode Selection for a Single-Frequency Fiber Laser

NASA’s Goddard Space Flight Center, Greenbelt, Maryland A superstructured fiber-grating-based mode selection filter for a single-frequency fiber laser eliminates all free-space components, and makes the laser truly all-fiber. A ring cavity provides for stable operations in both frequency and power. There is no alignment or realignment required. After the fibers and components are spliced together and packaged, there is no need for specially trained technicians for operation or maintenance. It can be integrated with other modules, such as telescope systems, without extra optical alignment due to the flexibility of the optical fiber.

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

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Enhancing Tumor Drug Delivery by Laser-Activated Vascular Barrier Disruption

Photodynamic therapy is used to eradicate tumor tissue and provide enhanced drug delivery.An obstacle to successful cancer drug therapy is the existence of drug delivery barriers, which result in insufficient and heterogeneous drug delivery to the tumor tissue. This drug delivery problem not only limits the clinical application of existing chemotherapeutics, but also decreases the effectiveness of many new drugs under development. Photodynamic therapy (PDT), a modality involving the combination of a photo-sensitizer and laser light, is an established cancer therapy. This work demonstrates the effectiveness of vascular-targeting PDT in eradicating tumor tissue, and modifying vascular barrier function for enhanced drug delivery.

Posted in: Bio-Medical, Briefs, TSP, Briefs, TSP, Drug Delivery & Fluid Handling, Patient Monitoring, Lasers & Laser Systems, Photonics

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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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