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.

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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.

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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, 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.

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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.

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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, Communication protocols, Data exchange, Optics, Satellite communications

Development of Thermal Infrared Sensor To Supplement Operational Land Imager

The application is for the Landsat Data Continuity Mission.

The thermal infrared sensor (TIRS) is a quantum well infrared photodetector (QWIP)-based instrument intended to supplement the Operational Land Imager (OLI) for the Landsat Data Continuity Mission (LDCM). The TIRS instrument is a far-infrared imager operating in the pushbroom mode with two IR channels: 10.8 and 12 μm. The focal plane will contain three 640×512 QWIP arrays mounted onto a silicon substrate. The readout integrated circuit (ROIC) addresses each pixel on the QWIP arrays and reads out the pixel value (signal). The ROIC is controlled by the focal plane electronics (FPE) by means of clock signals and bias voltage value. The means of how the FPE is designed to control and interact with the TIRS focal plane assembly (FPA) is the basis for this work.

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Infrared Laser Beam Evaluation Tool

The CoolCard™ II from Pathfinder Research (Lafayette, CO) is a handheld infrared laser beamfinder and beam evaluation instrument. The IR beam-quality evaluation tool can be used with lasers and other IR sources operating from the near-IR to 10-μm wavelengths. Using thermally- stabilized liquid crystal technology, the CoolCard™ senses and resolves the fine spatial character of lasers operating near and beyond 1.7 μm. The beamfinder features a rechargeable, field-replaceable Li-ion battery with capacity sufficient for multi-hour continuous operation.

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Glass Reflectron Lens Process

PHOTONIS USA (Sturbridge, MA) has been awarded a patent for the manufacture of resistive glass tubes with non-linear gradient electrical resistance changes. The patented process creates a solid-piece reflectron lens. Reflectron lenses are used in Timeof- Flight (TOF) mass spectrometers to create an electrostatic field to alter ion flow, providing for a longer flight path and greater resolution. A reflectron lens made with resistive glass provides an assembly replacement for a stacked ring assembly yet provides the same ability to alter ion flow.

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Fiber Laser

The Mentad fiber laser from RPMC Lasers (O’Fallon, MO) is now available at the 1.0μm wavelength. The 4.25 × 2.7 × 0.8" Mentad produces pulse energies up to 50μJ, with pulse widths from 500ps to 1.25μs and rep rates from 5kHz to 2MHz. The laser is also available at 1.5μm. At 1.5μm, the Mentad can produce up to 100μJ of pulse energy. Typical applications for the Mentad include: LIDAR, range finding, telemetry, target ID, 3D and topography scanning, and weather and pollutant detection.

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