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Laser Metrology Heterodyne Phase-Locked Loop

NASA’s Jet Propulsion Laboratory, Pasadena, California A method reduces sensitivity to noise in a signal from a laser heterodyne interferometer. The phase-locked loop (PLL) removes glitches that occur in a zero-crossing detector’s output [that can happen if the signal-to-noise ratio (SNR) of the heterodyne signal is low] by the use of an internal oscillator that produces a square-wave signal at a frequency that is inherently close to the heterodyne frequency.

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

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Precise Stabilization of the Optical Frequency of WGMRs

This technique results in whispering gallery mode resonators with absolute frequency stability. NASA’s Jet Propulsion Laboratory, Pasadena, California Crystalline whispering gallery mode resonators (CWGMRs) made of crystals with axial symmetry have ordinary and extraordinary families of optical modes. These modes have substantially different thermo-refractive constants. This results in a very sharp dependence of differential detuning of optical frequency on effective temperature. This frequency difference compared with clock gives an error signal for precise compensation of the random fluctuations of optical frequency. Certain crystals, like MgF2, have “turnover” points where the thermo-refractive effect is completely nullified.

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

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Spatial Modulation Improves Performance in CTIS

Computed spectra are more accurate when scenes have spatial structure. NASA’s Jet Propulsion Laboratory, Pasadena, California Suitably formulated spatial modulation of a scene imaged by a computed-tomography imaging spectrometer (CTIS) has been found to be useful as a means of improving the imaging performance of the CTIS. As used here, “spatial modulation” signifies the imposition of additional, artificial structure on a scene from within the CTIS optics.

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

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Simultaneous Ultra Fast Framing and Streak Imaging

The ability to record simultaneous framing images and streak images has long been a requirement in the research fields of detonation, electrical discharge, biomedical and many other applications. Early systems incorporating both framing and streak cameras used external beam splitting optics with light gathering limitations that required critical alignment of the external splitting optics. Later systems incorporated framing cameras and streak cameras, built into one mainframe, using available beam splitters. This allowed for simultaneous framing and streak, however, this type of beam splitter limited access to streak optics, and primarily limited the performance of the streak camera due to the smaller format streak tubes.

Posted in: Articles, Features, ptb catchall, Photonics

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Tactile Feedback for Touch-input Devices

As products become more featurerich, manufacturers are looking at ways to improve the human-computer interface (HCI). Touchscreens, with intuitive operation and software flexibility, and screen-printed touch surfaces, with refined aesthetics and better sealing, have become extremely popular. But what these touch-input devices do not supply is tactile confirmation of (1) a button’s location and (2) pressing it. The loss of this tactile information can be detrimental to user engagement and understanding, productivity, completion of transactions, safety, and satisfaction. In some applications, the lack of tactile feedback has been enough of a problem to prevent the conversion from mechanical switches to digital controls. The solution is simple — add tactile feedback to secure the best features of touch-input devices.

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

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Phase Matching of Diverse Modes in a WGM Resonator

Phase matching is necessary for exploitation of nonlinear optical phenomena. NASA’s Jet Propulsion Laboratory, Pasadena, California Phase matching of diverse electromagnetic modes (specifically, coexisting optical and microwave modes) in a whispering-gallery-mode (WGM) resonator has been predicted theoretically and verified experimentally. Such phase matching is necessary for storage of microwave/terahertz and optical electromagnetic energy in the same resonator, as needed for exploitation of nonlinear optical phenomena.

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

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Microwave-to-Optical Conversion in WGM Resonators

Three-wave mixing, resonance, and low loss would result in high efficiency. NASA’s Jet Propulsion Laboratory, Pasadena, California Microwave-to-optical frequency converters based on whispering-gallery-mode (WGM) resonators have been proposed as mixers for the input ends of microwave receivers in which, downstream of the input ends, signals would be processed photonically. A frequency converter as proposed (see figure) would exploit the nonlinearity of the electromagnetic response of a WGM resonator made of LiNbO3 or another suitable ferroelectric material. Up-conversion would take place by three-wave mixing in the resonator.

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

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