Photonics/Optics

Integrated Miniature Arrays of Optical Biomolecule Detectors

Many biochemical species could be detected simultaneously. NASA’s Jet Propulsion Laboratory, Pasadena, California Integrated miniature planar arrays of optical sensors for detecting specific bio-chemicals in extremely small quantities have been proposed. An array of this type would have an area of about 1 cm2. Each element of the array would include an optical microresonator that would have a high value of the resonance quality factor (Q ≈ 107). The surface of each microresonator would be derivatized to make it bind molecules of a species of interest, and such binding would introduce a measurable change in the optical properties of the microresonator. Because each microresonator could be derivatized for detection of a specific biochemical different from those of the other microresonators, it would be possible to detect multiple specific biochemicals by simultaneous or sequential interrogation of all the elements in the array. Moreover, the derivatization would make it unnecessary to prepare samples by chemical tagging.

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

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Inter-Symbol Guard Time for Synchronizing Optical PPM

This method would involve less computation than does the pilot-symbol method. NASA’s Jet Propulsion Laboratory, Pasadena, California An inter-symbol guard time has been proposed as a means of synchronizing the symbol and slot clocks of an optical pulse-position modulation (PPM) receiver with the symbol and slot periods of an incoming optical PPM signal. (Such synchronization is necessary for correct identification of received symbols.) The proposal is applicable to the low-flux case in which the receiver photodetector operates in a photon-counting mode and the count can include contributions from incidental light sources and dark current. The use of the inter-symbol guard time would be an alternative to a prior synchronization method based on the periodic transmission of a fixed pilot symbol.

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

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Treating Retinal Disease with FPGA Controlled Lasers

More than 50 percent of Americans diagnosed with diabetes are at risk of developing diabetic retinopathy, a retinal disease that can lead to blindness. The condition is a result of diabetes affecting the circulatory system of the retina and causing abnormal new blood vessel growth. It has become the leading cause of new blindness among U.S. adults.

Posted in: Features, ptb catchall, Photonics, Articles

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Using Hollow Core Plastic Bragg Fiber to Deliver Ultrashort Pulse Laser Beams

Ultrashort pulse (USP), or “ultrafast,” lasers emit extremely brief pulses of light, generally with duration of a picosecond (10-12 seconds) or less. The pulses are characterized by a high optical intensity that induces nonlinear interactions in various materials, including air.

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

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Scanning Miniature Microscopes Without Lenses

Polarization-sensitive and multicolor versions should also be possible. NASA’s Jet Propulsion Laboratory, Pasadena, California The figure schematically depicts some alternative designs of proposed compact, lightweight optoelectronic microscopes that would contain no lenses and would generate magnified video images of specimens. Microscopes of this type were described previously in “Miniature Microscope Without Lenses” (NPO-20218), NASA Tech Briefs, Vol. 22, No. 8 (August 1998), page 43 and “Reflective Variants of Miniature Microscope Without Lenses” (NPO20610), NASA Tech Briefs, Vol. 26, No. 9 (September 1999), page 6a. To recapitulate: In the design and construction of a microscope of this type, the focusing optics of a conventional microscope are replaced by a combination of a microchannel filter and a charge-coupled-device (CCD) image detector. Elimination of focusing optics reduces the size and weight of the instrument and eliminates the need for the time-consuming focusing operation.

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

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Target-Tracking Camera for a Metrology System

Angular measurements are updated at a rate of hundreds of hertz. NASA’s Jet Propulsion Laboratory, Pasadena, California An analog electronic camera that is part of a metrology system measures the varying direction to a light-emitting diode that serves as a bright point target. In the original application for which the camera was developed, the metrological system is used to determine the varying relative positions of radiating elements of an airborne synthetic-aperture-radar (SAR) antenna as the airplane flexes during flight; precise knowledge of the relative positions as a function of time is needed for processing SAR readings.

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

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Polarimetric Imaging Using Two Photoelastic Modulators

The frame rate is the difference between the resonance frequencies of the modulators. NASA’s Jet Propulsion Laboratory, Pasadena, California A method of polarimetric imaging, now undergoing development, involves the use of two photoelastic modulators in series, driven at equal amplitude but at different frequencies. The net effect on a beam of light is to cause (1) the direction of its polarization to rotate at the average of two excitation frequencies and (2) the amplitude of its polarization to be modulated at the beat frequency (the difference between the two excitation frequencies). The resulting modulated optical light beam is made to pass through a polarizing filter and is detected at the beat frequency, which can be chosen to equal the frame rate of an electronic camera or the rate of sampling the outputs of photodetectors in an array.

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

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