Photonics/Optics

Digitally Enhanced Heterodyne Interferometry

This design mitigates cyclic error and improves measurement sensitivity. NASA’s Jet Propulsion Laboratory, Pasadena, California Spurious interference limits the performance of many interferometric measurements. Digitally enhanced interferometry (DEI) improves measurement sensitivity by augmenting conventional heterodyne interferometry with pseudo-random noise (PRN) code phase modulation. DEI effectively changes the measurement problem from one of hardware (optics, electronics), which may deteriorate over time, to one of software (modulation, digital signal processing), which does not. DEI isolates interferometric signals based on their delay. Interferometric signals are effectively time-tagged by phase-modulating the laser source with a PRN code. DEI improves measurement sensitivity by exploiting the autocorrelation properties of the PRN to isolate only the signal of interest and reject spurious interference. The properties of the PRN code determine the degree of isolation.

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

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Photochemical Tissue Bonding for Military Medical Applications

A two-wavelength laser and albumen stent easily repair separated vessels.Joining severed vessels is a recurring problem in trauma and surgery. The basic technology of joining vessels using sutures has been available for centuries, but remains a slow and tedious process. A complete system for micro-anastomosis of vessels was developed that involves a laser in a clinically useful form factor, and a novel albumen stent to support the vessel during the surgery.

Posted in: Bio-Medical, Briefs, TSP, Briefs, TSP, Photonics

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Multiparallel Three-Dimensional Optical Microscopy

Lyndon B. Johnson Space Center, Houston, Texas Multiparallel three-dimensional optical microscopy is a method of forming an approximate three-dimensional image of a microscope sample as a collection of images from different depths through the sample. The imaging apparatus includes a single microscope plus an assembly of beam splitters and mirrors that divide the output of the microscope into multiple channels. An imaging array of photodetectors in each channel is located at a different distance along the optical path from the microscope, corresponding to a focal plane at a different depth within the sample. The optical path leading to each photodetector array also includes lenses to compensate for the variation of magnification with distance so that the images ultimately formed on all the photodetector arrays are of the same magnification.

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Sub-Aperture Interferometers

Multiple target sub-beams are derived from the same measurement beam. NASA’s Jet Propulsion Laboratory, Pasadena, California Sub-aperture interferometers — also called wavefront-split interferometers — have been developed for simultaneously measuring displacements of multiple targets. The terms “sub-aperture” and “wavefront-split” signify that the original measurement light beam in an interferometer is split into multiple sub-beams derived from non-overlapping portions of the original measurement- beam aperture. Each measurement sub-beam is aimed at a retroreflector mounted on one of the targets. The splitting of the measurement beam is accomplished by use of truncated mirrors and masks, as shown in the example below.

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Vacuum-Compatible Wideband White Light and Laser Combiner Source System

NASA’s Jet Propulsion Laboratory, Pasadena, California For the Space Interferometry Mission (SIM) Spectrum Calibration Development Unit (SCDU) testbed, wideband white light is used to simulate starlight. The white light source mount requires extremely stable pointing accuracy (hts were coupled to a photonic crystal fiber (PCF).

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Stabilization of Phase of a Sinusoidal Signal Transmitted Over Optical Fiber

Two-way transmissions allow for rapid correction of common reference tones. NASA’s Jet Propulsion Laboratory, Pasadena, California In the process of connecting widely distributed antennas into a coherent array, it is necessary to synchronize the timing of signals at the various locations. This can be accomplished by distributing a common reference signal from a central source, usually over optical fiber. A high-frequency (RF or microwave) tone is a good choice for the reference. One difficulty is that the effective length of the optical fiber changes with temperature and mechanical stress, leading to phase instability in the received tone. This innovation provides a new way to stabilize the phase of the received tone, in spite of variations in the electrical length of the fiber.

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Optical Tapers as White-Light WGM Resonators

Such resonators could be attractive for broad-band optical processing applications. NASA’s Jet Propulsion Laboratory, Pasadena, California A theoretical analysis has revealed that tapered optical waveguides could be useful as white-light whispering-gallery-mode (WGM) optical resonators. The compactness and the fixed-narrow-frequency-band nature of the resonances of prior microdisk and microsphere WGM resonators are advantageous in low-power, fixed-narrow-frequency-band applications. However for optical-processing applications in which there are requirements for power levels higher and/or spectral responses broader than those of prior microdisk and microsphere WGM resonators, white-light WGM resonators in the form of optical tapers would be preferable.

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

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