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Microwave Oscillators Based on Nonlinear WGM Resonators

Optical signals are phase-modulated with spectrally pure microwave signals. NASA’s Jet Propulsion Laboratory, Pasadena, California Optical oscillators that exploit resonantly enhanced four-wave mixing in nonlinear whispering-gallery-mode (WGM) resonators are under investigation for potential utility as low-power, ultra-miniature sources of stable, spectrally pure microwave signals. There are numerous potential uses for such oscillators in radar systems, communication systems, and scientific instrumentation.

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

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Fiber-Optic Gratings for Lidar Measurements of Water Vapor

These are highly selective, lightweight, tunable optical filters. Langley Research Center, Hampton, Virginia Narrow-band filters in the form of phase-shifted Fabry-Perot Bragg gratings incorporated into optical fibers are being developed for differential-absorption lidar (DIAL) instruments used to measure concentrations of atmospheric water vapor. The basic idea is to measure the relative amounts of pulsed laser light scattered from the atmosphere at two nearly equal wavelengths, one of which coincides with an absorption spectral peak of water molecules and the other corresponding to no water vapor absorption. As part of the DIAL measurement process, the scattered light is made to pass through a filter on the way to a photodetector. Omitting other details of DIAL for the sake of brevity, what is required of the filter is to provide a stop band that:

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

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Simplifying Beam Measurements in Real Time

Beam collimation measurements can be made with a test lens and beam profiler. Photon, Inc., San Jose, California A common misconception is that beam collimation angle measurements must involve a least two or more beam size measurements along the beam path. For this reason, collimation measurements are often viewed as complicated and time-consuming. Real-time collimation angle measurements are considered out of the question.

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

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Pointing Reference Scheme for Free-Space Optical Communications Systems

A technique is proposed for referencing infrared transmit lasers with silicon detectors. NASA’s Jet Propulsion Laboratory, Pasadena, California A scheme is proposed for referencing the propagation direction of the transmit laser signal in pointing a free-space optical communications terminal. This recently developed scheme enables the use of low-cost, commercial silicon-based sensors for tracking the direction of the transmit laser, regardless of the transmit wavelength. Compared with previous methods, the scheme offers some advantages of less mechanical and optical complexity and avoids expensive and exotic sensor technologies.

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

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Single-Phase Rare-Earth Oxide/Aluminum Oxide Glasses

These glasses are suitable for advanced optical applications. Marshall Space Flight Center, Alabama Glasses that comprise rare-earth oxides and aluminum oxide plus, optionally, lesser amounts of other oxides, have been invented. The other oxide(s) can include SiO2, B2O3, GeO2, and/or any of a variety of glass-forming oxides that have been used heretofore in making a variety of common and specialty glasses. The glasses of the invention can be manufactured in bulk single-phase forms to ensure near uniformity in optical and mechanical characteristics, as needed for such devices as optical amplifiers, lasers, and optical waveguides (including optical fibers). These glasses can also be formulated to have high indices of refraction, as needed in some of such devices.

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

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Product of the Month: Camera Shutters

Melles Griot Optics Group (Rochester, NY) has released the ExtremeService™ shutter designed for operation in environmental conditions involving variations in temperature. The shutter is suitable for OEM applications including night vision cameras and infrared illumination systems such as analytical, metrology, and photonics instrumentation that require compact size, low weight, and low-voltage operation.

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Fiber-Optic Laser Couplers

Bristol Instruments (Victor, NY) offers the LC Series fiber-optic laser couplers that can be used to launch a free-space laser beam into a fiber, or return the laser to a collimated free-space beam. The couplers contain a 1"- diameter mounting disk attached to 3 meters of 9-μm core-diameter fiber that is terminated with an FC/PC connector. The LC-1 input coupler includes built-in alignment optics that provide two slightly off-axis back reflections to facilitate alignment. With the LC-1 installed in a standard theta-phi optical mount, alignment is achieved by centering the laser beam on the input aperture, and then adjusting the mount so that the two back reflections straddle the input beam symmetrically. The LC-2 output coupler is identical to the LC-1, but without the alignment optics. It is used to return the laser to a collimated free-space beam.

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