Photonics

Monolithic Diffraction Grating Arrays Enable Wide-Bandwidth Single-Shot Spectrometers

For the last forty years, manufacturing technology for diffraction gratings has not changed significantly. Mechanical ruling and interferometric (holographic) exposure have been the two predominant approaches used to fabricate gratings. Both approaches provide limited freedom in terms of the complexity of grating lines (spacings and curvatures) that can be written.

Posted in: Features, ptb catchall, Photonics, Articles

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InGaAs SWIR Imagers Optimize Semiconductor Inspection

As the volume of consumer electronics increases, semiconductor fabrication plants are manufacturing larger and larger wafers to handle the demand (e.g., 300 mm substrates). The escalating value of these larger wafers is driving the industry to employ more advanced imaging technologies for quality control. Inspecting the raw material substrate for flaws before processing and detecting defects during processing is critical to keeping costs down. New and improved inspection techniques save the semiconductor manufacturing industry hundreds of millions of dollars each year.

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

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Electro-Optical Modulator Bias Control Using Bipolar Pulses

Bias is automatically adjusted to maintain maximum extinction during “off” periods. NASA’s Jet Propulsion Laboratory, Pasadena, California An improved method has been devised for controlling the DC bias applied to an electro-optical crystal that is part of a Mach-Zehnder modulator that generates low-duty-cycle optical pulses for a pulse-position modulation (PPM) optical data-communication system. In such a system, it is desirable to minimize the transmission of light during the intervals between pulses, and for this purpose, it is necessary to maximize the extinction ratio of the modulator (the ratio between the power transmitted during an “on” period and the power transmitted during an “off” period). The present method is related to prior dither error feedback methods, but unlike in those methods, there is no need for an auxiliary modulation subsystem to generate a dithering signal. Instead, as described below, dither is effected through alternation of the polarity of the modulation signal.

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

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Fiber-Optic Strain Gauge With High Resolution And Update Rate

Changes in strain are correlated with changes in speckle patterns. Stennis Space Center, Mississippi An improved fiber-optic strain gauge is capable of measuring strains in the approximate range of 0 to 50 microstrains with a resolution of 0.1 microstrain. (To some extent, the resolution of the strain gauge can be tailored and may be extensible to 0.01 microstrain.) The total cost of the hardware components of this strain gauge is less than $100 at 2006 prices. In comparison with prior strain gauges capable of measurement of such low strains, this strain gauge is more accurate, more economical, and more robust, and it operates at a higher update rate. Strain gauges like this one are useful mainly for measuring small strains (including those associated with vibrations) in such structures as rocket test stands, buildings, oilrigs, bridges, and dams. The technology was inspired by the need to measure very small strains on structures supporting liquid oxygen tanks, as a way to measure accurately mass of liquid oxygen during rocket engine testing.

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

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Optical Characterization of Molecular Contaminant Films

A theoretical model is correlated with measured spectral transmittances and VUV exposures of spacecraft optics. A semi-empirical method of optical characterization of thin contaminant films on surfaces of optical components has been conceived. The method was originally intended for application to films that become photochemically deposited on such optical components as science windows, lenses, prisms, thinfilm radiators, and glass solar-cell covers aboard spacecraft and satellites in orbit. The method should also be applicable, with suitable modifications, to thin optical films (whether deposited deliberately or formed as contaminants) on optical components used on Earth in the computer microchip laser communications and thin-film industries.

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

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Aligning Optical Fibers by Means of Actuated MEMS Wedges

Wedges would be fabricated using gray-scale exposure of photoresist. Microelectromechanical systems (MEMS) of a proposed type would be designed and fabricated to effect lateral and vertical alignment of optical fibers with respect to optical, electro-optical, optoelectronic, and/or photonic devices on integrated circuit chips and similar monolithic device structures. A MEMS device of this type would consist of a pair of oppositely sloped alignment wedges attached to linear actuators that would translate the wedges in the plane of a substrate, causing an optical fiber in contact with the sloping wedge surfaces to undergo various displacements parallel and perpendicular to the plane. In making it possible to accurately align optical fibers individually during the packaging stages of fabrication of the affected devices, this MEMS device would also make it possible to relax tolerances in other stages of fabrication, thereby potentially reducing costs and increasing yields.

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

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Flexible Laser Design Targets Low-Volume Material Processing Needs

A flexible approach to diode-pumped laser design combines customized performance with costeffective manufacturing. Q-switched, diode-pumped solid-state lasers with an end-pumped cavity design are now widely used in micromachining, materials processing, marking, and related applications. They are used to process a broad range of materials including metals, glass, plastics, and semiconductors. But this application diversity creates a concomitant need for laser diversity. Namely, while each application requires superior reliability and performance, the definition of “superior performance” is very application-specific. For example, some metal ablation applications may benefit from a long laser pulse, whereas semiconductor scribing needs a short pulse and a very high pulse repetition rate.

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

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