Photonics/Optics

Vacuum Spectrometer

The Model 248/310 grazing incidence spectrometer from McPherson (Chelmsford, MA) makes direct optical measurements from one to 300 nanometers. The device enables testing of soft x-ray (XUV) high energy light sources (plasma or laser) and samples. Life time, persistence, or decay can be measured with continuous spectral scanning.

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Light Source

The BluLoop Light Source from Ocean Optics (Dunedin, FL) is a compact, LED-based source with balanced spectral output across the visible (400-700 nm) range. When coupled to a miniature spectrometer, optical fibers, and sampling accessories, Blu- Loop can be used for color and reflectance measurements and general-purpose VIS-NIR spectroscopy. The four LEDs are individually tunable for balancing of the spectral output. BluLoop produces “flatter” spectral output in the visible range for more predictable response, especially for color analysis.

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Optical Communications Receiver

Specialized mixed-signal (radio frequency and digital) hardware and processing techniques are employed to enable processing of the multi-GHz signal bandwidth, along with the instruction of an inter-symbol guard time (ISGT) to facilitate synchronization to the received pulse-position modulation (PPM) signal.

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

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Low-Noise, Large-Area Quad Photoreceivers Based on Low-Capacitance Quad Photodiodes

The Laser Interferometry Space Antenna’s (LISAs) scientific mission to detect gravity waves demands stringent noise limits on the system components, especially the large-area quad photoreceiver front end, for ultra-high-precision (≈10 pm/Hz1/2) distance measurements. The optical LO (local oscillator) power on LISA is limited to 100 μW to keep power dissipation and thermal fluctuation low on the optical bench. Consequently, a large-area quad photoreceiver having an equivalent input current noise of the order of 1 pm/Hz1/2 is needed. Additionally, the quad photoreceiver must demonstrate low crosstalk between individual quadrants to allow accurate direction sensing of the incoming optical beam. This performance must be achieved over a bandwidth of 2 to 20 MHz to meet LISA’s requirements. Commercially available quad photodetectors do not have the combination of large area, low capacitance (and therefore low noise), and low crosstalk, which is critical for LISA’s scientific objectives.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Photonics, Physical Sciences

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Wavefront Sensing Analysis of Grazing Incidence Optical Systems

As a metrology tool, this method allows integration of high-angular-resolution optics without the use of normal incidence interferometry. Wavefront sensing is a process by which optical system errors are deduced from the aberrations in the image of an ideal source. The method has been used successfully in near-normal incidence, but not for grazing incidence systems. This innovation highlights the ability to examine outof- focus images from grazing incidence telescopes (typically operating in the x-ray wavelengths, but integrated using optical wavelengths) and determine the lower-order deformations. This is important because as a metrology tool, this method would allow the integration of high angular resolution optics without the use of normal incidence interferometry, which requires direct access to the front surface of each mirror.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Information Sciences, Photonics

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RxGen General Optical Model Prescription Generator

RxGen is a prescription generator for JPL’s in-house optical modeling software package called MACOS (Modeling and Analysis for Controlled Optical Systems), which is an expert optical analysis software package focusing on modeling optics on dynamic structures, deformable optics, and controlled optics.

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Mode-Field Diameter and “Spot Size” Measurements of Lensed and Tapered Specialty Fibers

Lensed and tapered specialty fibers are designed to optimize coupling between the fiber and various optical components such as edge-emitting laser diodes and AWGs. The light from these fibers forms a focus at some finite distance away from the fiber end. The Mode-Field Diameter (MFD) and corresponding spot size of these fibers is typically in the range of 5 microns or less. These small spot sizes and corresponding high divergence present challenges to near field and far field measurements. Typically the near-field measurements are limited by the optical performance, and the far-field measures must extend to very large angles. Results of measurements of 6 commercially available fibers are presented here, including different type lensed/tapered fibers (4 axially symmetric and 1 elliptical) and a standard single-mode fiber for reference. Also, since the focused beams are in free space, there are some fundamental questions as to the applicability of the MFD, a measure originally formulated to describe the field distribution within a fiber.

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