Photonics/Optics

2.2-Micron, Uncooled, InGaAs Photodiodes and Balanced Photoreceivers up to 25-GHz Bandwidth

These photodiodes have applications in LiDAR sensors, telecommunications links, and pulsed laser systems.Traditional applications for 2-micron photodetectors have been largely dominated by passive remote sensing where detectors having bandwidth of even one megahertz are deemed sufficient. The onus in such applications is to achieve low dark current through active cooling. The advent of high-power, 2-micron-wave-length lasers have made coherent LiDARs viable for active sensing applications. Such a system needs photodetectors that can handle high local oscillator optical power and have large bandwidth. Through a combination of high coherent gain and small integration time, a large signal-to-noise ratio can be achieved. Operation at high optical power levels reduces the significance of photodiodes’ dark current. As a result, uncooled operation at room temperature is feasible, simplifying the overall instrument design.

Posted in: Briefs, Photonics, Optics, Remote sensing, Cooling

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Fourier Transform Spectrometer System

NASA's Langley Research Center and Science Applications International Corporation have developed a method of processing data from Fourier transform spectroscopy (FTS) measurements that improves upon existing methods. This method is simpler, more accurate, faster, and less expensive than previous methods. It uses less hardware and can be used with all wavelengths.

Posted in: Briefs, Photonics, Architecture, Spectroscopy, Data management

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Large-Area, Polarization-Sensitive Bolometer for Multi-Mode Optics

This type of detector will be used by the PIXIE mission to map the microwave sky in polarization, opening a new window to the earliest moments of the universe. Polarization-sensitive bolometer measures linear polarization of the cosmic microwave background. (Left) Prototype detector. The absorber in the central square fills a small fraction of the optical area, but is opaque to microwaves. (Center) Schematic diagram showing the absorbing wires and sensing thermistors. (Right) Photomicrograph showing absorbing wires and the crystalline silicon end bank. Measurements of the cosmic microwave background are a powerful probe of the early universe. Part-per-million fluctuations in the intensity of background trace the initial conditions of matter and energy shortly after the Big Bang, mapping the large-scale structure of spacetime. Now, new measurements in linear polarization at sensitivities of a few parts per billion can look behind these initial conditions to test physics at energies a trillion times higher than terrestrial accelerators, and perhaps even provide a glimpse of quantum gravity in action.

Posted in: Briefs, Photonics, Measurements, Optics, Radiation

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Photonic Choke-Joints for Dual-Polarization Waveguides

The joint is constructed from a conductive metal, and requires no maintenance or peripheral equipment to operate.Photonic choke-joint (PCJ) structures for dual-polarization waveguides have been investigated at NASA's Goddard Space Flight Center for use in device and component packaging. This interface enables the realization of a high-performance, non-contacting waveguide joint without degrading the in-band signal propagation properties. The choke properties of two tiling approaches — symmetric square Cartesian and octagonal quasi-crystal lattices of metallic posts — are explored and optimal PCJ design parameters are presented. For each of these schemes, the experimental results for structures with finite tilings demonstrate near ideal transmission and reflection performance over a full waveguide band.

Posted in: Briefs, Photonics, Electronic equipment, Waveguides, Product development

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Smart Optical Material Characterization System and Method

This technology creates a flexible, unified platform for dynamic smart optical material evaluation.NASA's Langley Research Center has developed an adaptable and powerful interferometric test platform that uniquely enables multi-parameter evaluation of a wide variety of smart optical materials (SOM). The patent-pending SOM characterization system was created to measure the dynamic optical response of stimuli-responsive (“smart”) optical materials while external physical/electrical/thermal/chemical/pressure/magneto stimuli are applied to the material. Using novel interferometric fringe analysis software and a multi-stimuli-capable SOM test cell, the SOM characterization system enables a wide variety of materials — such as liquid crystals, nonlinear crystals, electro- and thermo-active polymer optics, and magneto- or piezo-driven optics — to be optically characterized for real-time changes in intensity, phase, and polarization. The versatility of the SOM test platform combined with the powerful, efficient, and user-friendly software interface makes it a valuable tool for the research or commercial development of smart materials.

Posted in: Briefs, Photonics, Computer software and hardware, Optics, Materials identification, Smart materials, Test equipment and instrumentation

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Compact Planar Microwave Blocking Filters

Innovators at NASA's Goddard Space Flight Center have designed, fabricated, and characterized absorptive thermal blocking filters for cryogenic microwave applications. The device allows direct integration of the high-frequency signal and microwave readout, and mitigates spurious resonances in the circuit response. This leads to improved electrical performance and a reduction in the required circuit area. The transmission line filter's input characteristic impedance is designed to match 50 ohms and its response has been validated from 0 to 50 GHz. The observed return loss in the 0 to 20 GHz design band is greater than 20 dB and shows graceful degradation with frequency. The filter's response is calculable, repeatable under cryogenic cycling, and is capable of providing an intrinsically broadband matched impedance termination.

Posted in: Briefs, Photonics, Electrical systems, Thermal management, Product development, Insulation

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System and Method for Generating a Frequency-Modulated Linear Laser Waveform

Applications include manufacturing equipment, robotics, surveillance and security, military imaging, and spectroscopy.NASA's Langley Research Center has made a breakthrough improvement in laser frequency modulation. Frequency modulation technology has been used for surface mapping and measurement in sonar, radar, and time-of-flight laser technologies for decades. Although adequate, the accuracy of distance measurements made by these technologies can be improved by using a high-frequency triangular-waveform laser instead of a sine waveform or lower-frequency radio or microwaves. This new system generates a triangular modulation waveform with improved linearity that makes possible precision laser radar (light detection and ranging [lidar]) for a variety of applications.

Posted in: Briefs, Photonics, Lidar, Performance upgrades

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