Photonics

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: Tech Briefs, ptb catchall, Photonics, Briefs

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Wide-Band Microwave Receivers Using Photonic Processing

One receiver would have the functionality of multiple traditional heterodyne microwave receivers. NASA’s Jet Propulsion Laboratory, Pasadena, California In wide-band microwave receivers of a type now undergoing development, the incoming microwave signals are electronically preamplified, then frequency-up-converted to optical signals that are processed photonically before being detected. This approach differs from the traditional approach, in which incoming microwave signals are processed by purely electronic means. As used here, “wide-band microwave receivers” refers especially to receivers capable of reception at any frequency throughout the range from about 90 to about 300 GHz. The advantage expected to be gained by following the up-conversion-and-photonic-processing approach is the ability to overcome the limitations of currently available detectors and tunable local oscillators in the frequency range of interest.

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

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WGM Resonators for Terahertz-to-Optical Frequency Conversion

Receivers containing these devices are contemplated for astronomical and military uses. NASA’s Jet Propulsion Laboratory, Pasadena, California Progress has been made toward solving some practical problems in the implementation of terahertz-to-optical frequency converters utilizing whispering-gallery-mode (WGM) resonators. Such frequency converters are expected to be essential parts of non-cryogenic terahertz-radiation receivers that are, variously, under development or contemplated for a variety of applications in airborne and spaceborne instrumentation for astronomical and military uses.

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

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Temperature Sensors Based on WGM Optical Resonators

Differences between temperature-dependent frequencies of resonances would be measured. NASA’s Jet Propulsion Laboratory, Pasadena, California A proposed technique for measuring temperature would exploit differences between the temperature dependences of the frequencies of two different electromagnetic modes of a whispering-gallery-mode (WGM) optical resonator. An apparatus based on this technique was originally intended to be part of a control system for stabilizing a laser frequency in the face of temperature fluctuations. When suitably calibrated, apparatuses based on this technique could also serve as precise temperature sensors for purposes other than stabilization of lasers.

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

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Four-Pass Coupler for Laser-Diode-Pumped Solid-State Laser

A smaller laser slab can be made to perform comparably to a larger one. Goddard Space Flight Center, Greenbelt, Maryland A four-pass optical coupler affords increased (in comparison with related prior two-pass optical couplers) utilization of light generated by a laser diode in side pumping of a solid-state laser slab. The original application for which this coupler was conceived involves a neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal slab, which, when pumped by a row of laser diodes at a wavelength of 809 nm, lases at a wavelength of 1,064 nm.

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

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Varying the Divergence of Multiple Parallel Laser Beams

Lenses mode-matched to the laser beams would be moved axially within an afocal optical subassembly. NASA’s Jet Propulsion Laboratory, Pasadena, California A provision for controlled variation of the divergence of a laser beam or of multiple parallel laser beams has been incorporated into the design of a conceptual free-space optical-communication station from which the transmitted laser beam(s) would be launched via a telescope. The original purpose to be served by this provision was to enable optimization, under various atmospheric optical conditions, of the divergence of a laser beam or beams transmitted from a ground station to a spacecraft. Beyond the original purpose, the underlying design concept could be beneficial for terrestrial free-space laser communication, ranging, and scientific instrumentation applications in which there are requirements to vary the divergences of laser beams.

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

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Low-Resolution Raman-Spectroscopy Combustion Thermometry

This method offers advantages over related prior Raman-spectroscopy-based methods. John H. Glenn Research Center, Cleveland, Ohio A method of optical thermometry, now undergoing development, involves low-resolution measurement of the spectrum of spontaneous Raman scattering (SRS) from N2 and O2 molecules. The method is especially suitable for measuring temperatures in high-pressure combustion environments that contain N2, O2, or N2/O2 mixtures (including air).

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