Method of Bonding Optical Elements With Near-Zero Displacement

Displacement caused by epoxy shrinking as it cures is reduced less than 200 nm. The International X-ray Project seeks to build an x-ray telescope using thousands of pieces of thin and flexible glass mirror segments. Each mirror segment must be bonded into a housing in nearly perfect optical alignment without distortion. Forces greater than 0.001 Newton, or displacements greater than 0.5 μm of the glass, cause unacceptable optical distortion. All known epoxies shrink as they cure. Even the epoxies with the least amount of shrinkage (

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Photonics, Mirrors, Optics, Adhesives and sealants


Optical Phase Recovery and Locking in a PPM Laser Communication Link

Coherence augmentation in a pulsed optical communication link will enable enhanced Doppler tracking and ranging capabilities. Free-space optical communication holds great promise for future space missions requiring high data rates. For data communication in deep space, the current architecture employs pulse position modulation (PPM). In this scheme, the light is transmitted and detected as pulses within an array of time slots. While the PPM method is efficient for data transmission, the phase of the laser light is not utilized.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Photonics, Architecture, Data exchange, Lasers


Reliable Optical Pump Architecture for Highly Coherent Lasers Used in Space Metrology Applications

This design also can be used in scientific instrumentation where repair is difficult such as in underwater deployment. The design and initial demonstration of a laser pump module (LPM) incorporating single-mode, grating-stabilized 808- nm diode lasers and a low-loss, high-port-count optical combiner are completed. The purpose of the developed LPM is to reliably pump an Nd:YAG crystal in the laser head (LH), which serves as the optical metrology source for SIM-Lite mission. Using the narrow-linewidth, single-mode laser diodes enables placement of the pump power near Nd adsorption peak, which enhances pumping efficiency. Grating stabilization allows for stable pump spectra as diode operating temperature and bias current change. The low-loss, high-port-count optical combiner enables efficient combining of tens of pumps. Overall, the module supports 5+ years of continuous operation at 2 W of pump power with reliability approaching 100 percent.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Architecture, Lasers, Product development, Pumps


Method to Enhance the Operation of an Optical Inspection Instrument Using Spatial Light Modulators

The interferometer would accommodate a large variety of spherical and aspherical optical components. For many aspheric and freeform optical components, existing interferometric solutions require a custom computer-generated hologram (CGH) to characterize the part. The overall objective of this research is to develop hardware and a procedure to produce a combined, dynamic, Hartmann/Digital Holographic interferometry inspection system for a wide range of advanced optical components, including aspheric and freeform optics. This new instrument would have greater versatility and dynamic range than currently available measurement systems.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Photonics, Physical Sciences, Measurements, Optics, Performance upgrades, Inspections


High-Speed Edge-Detecting Line Scan Smart Camera

This circuit reduces size and system complexity while increasing processing frame rates. A high-speed edge-detecting line scan smart camera was developed. The camera is designed to operate as a component in a NASA Glenn Research Center developed inlet shock detection system. The inlet shock is detected by projecting a laser sheet through the airflow. The shock within the airflow is the densest part and refracts the laser sheet the most in its vicinity, leaving a dark spot or shadowgraph. These spots show up as a dip or negative peak within the pixel intensity profile of an image of the projected laser sheet. The smart camera acquires and processes in real-time the linear image containing the shock shadowgraph and outputting the shock location. Previously a highspeed camera and personal computer would perform the image capture and processing to determine the shock location.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Photonics, Lasers, Optics, Vibration


Downsampling Photodetector Array With Windowing

Applications include laser ranging for commercial surveys, and building-to-building optical data links. In a photon counting detector array, each pixel in the array produces an electrical pulse when an incident photon on that pixel is detected. Detection and demodulation of an optical communication signal that modulated the intensity of the optical signal requires counting the number of photon arrivals over a given interval. As the size of photon counting photodetector arrays increases, parallel processing of all the pixels exceeds the resources available in current application-specific integrated circuit (ASIC) and gate array (GA) technology; the desire for a high fill factor in avalanche photodiode (APD) detector arrays also precludes this.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Photonics, Optics, Satellite communications, Sensors and actuators


Optical Communications Channel Combiner

NASA has identified deep-space optical communications links as an integral part of a unified space communication network in order to provide data rates in excess of 100 Mb/s. The distances and limited power inherent in a deep-space optical downlink necessitate the use of photon-counting detectors and a powerefficient modulation such as pulse position modulation (PPM). For the output of each photodetector, whether from a separate telescope or a portion of the detection area, a communication receiver estimates a log-likelihood ratio for each PPM slot. To realize the full effective aperture of these receivers, their outputs must be combined prior to information decoding.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Communication protocols, Data exchange, Optics, Satellite communications


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