Tech Briefs

Simplified Optics and Controls for Laser Communications

NASA’s Jet Propulsion Laboratory, Pasadena, California A document discusses an architecture of a spaceborne laser communication system that provides for a simplified control subsystem that stabilizes the line of sight in a desired direction. Heretofore, a typical design for a spaceborne laser communication system has called for a high-bandwidth control loop, a steering mirror and associated optics, and a fast steering mirror actuator to stabilize the line of sight in the presence of vibrations. In the present architecture, the need for this fast steering-mirror subsystem is eliminated by mounting the laser-communication optics on a disturbance-free platform (DFP) that suppresses coupling of vibrations to the optics by ≥60 dB. Taking advantage of microgravitation, in the DFP, the optical assembly is free-flying relative to the rest of the spacecraft, and a low-spring-constant pointing control subsystem exerts small forces to regulate the position and orientation of the optics via voice coils. All steering is effected via the DFP, which can be controlled in all six degrees of freedom relative to the spacecraft. A second control loop, closed around a position sensor and the spacecraft attitude-control system, moves the spacecraft as needed to prevent mechanical contact with the optical assembly.

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

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Coherent Detection of High-Rate Optical PPM Signals

Quantum-limited performance is achievable. NASA’s Jet Propulsion Laboratory, Pasadena, California A method of coherent detection of high-rate pulse-position modulation (PPM) on a received laser beam has been conceived as a means of reducing the deleterious effects of noise and atmospheric turbulence in free-space optical communication using focal-plane detector array technologies. In comparison with a receiver based on direct detection of the intensity modulation of a PPM signal, a receiver based on the present method of coherent detection performs well at much higher background levels.

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

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White-Light Whispering-Gallery-Mode Optical Resonators

Overlapping resonator modes are exploited to obtain wide, high-Q spectra. NASA’s Jet Propulsion Laboratory, Pasadena, California Whispering-gallery-mode (WGM) optical resonators can be designed to exhibit continuous spectra over wide wavelength bands (in effect, white-light spectra), with ultrahigh values of the resonance quality factor (Q) that are nearly independent of frequency. White-light WGM resonators have potential as superior alternatives to (1) larger, conventional optical resonators in ring-down spectroscopy, and (2) optical-resonator/electro-optical modulator structures used in coupling of microwave and optical signals in atomic clocks. In these and other potential applications, the use of white-light WGM resonators makes it possible to relax the requirement of high-frequency stability of lasers, thereby enabling the use of cheaper lasers.

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MEMS to Replace Quartz Oscillators as Frequency Sources

A new encapsulation and packaging technology for MEMS resonators provides a clean, stable environment for reference oscillators. Research on microelectromechanical system (MEMS) resonators dates back to the mid-1960s, but MEMS timing references are only now being introduced commercially. In this time, two fundamental technical challenges have been overcome: finding a stable and predictable material from which to build the resonators, and developing a sufficiently clean hermetic packaging system.

Posted in: Briefs, Electronics & Computers

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“Virtual Feel” Capaciflectors

Increases in capacitance with deviations from desired central positions would be exploited. The term “virtual feel” denotes a type of capaciflector (an advanced capacitive proximity sensor) and a methodology for designing and using a sensor of this type to guide a robot in manipulating a tool (e.g., a wrench socket) into alignment with a mating fastener (e.g., a bolt head) or other electrically conductive object. Unlike robotic vision, capacitive proximity sensing does not require a clear line of sight to the mating fastener. On the contrary, capacitive proximity sensing affords the greatest position-measuring sensitivity in the situation in which it is most needed — when the tool is so close to the fastener as to prevent viewing.

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Magnetic-Field-Response Measurement-Acquisition System

Sensors are interrogated without physical connection to a power source, microprocessor, data acquisition equipment, or electrical circuitry. A measurement- acquisition system uses magnetic fields to power sensors and to acquire measurements from sensors. The system alleviates many shortcomings of traditional measurement acquisition systems, which include a finite number of measurement channels, weight penalty associated with wires, use limited to a single type of measurement, wire degradation due to wear or chemical decay, and the logistics needed to add new sensors. Eliminating wiring for acquiring measurements can alleviate potential hazards associated with wires, such as damaged wires becoming ignition sources due to arcing.

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Miniature Housings for Electronics With Standard Interfaces

be secured to a mating carrier by use of screws or epoxy; this mounting scheme helps the housings and their contents to withstand severe vibrations and ensures thermal conduction for dissipation of heat generated during operation of the contained circuitry. The circuits contained in the housings communicate with the external world via standard RS-485 interfaces. Multiple units comprising housings and their contents can easily be electrically connected together in a daisy chain arrangement, within which individual units are addressable via the RS-485 bus. Hence, a single master computer connected to the bus can program, or read data from, any or all such units. Examples of such units include small motor drives, programmable thermostats, data loggers, and programmable controllers. There are numerous potential uses for these units in medical equipment, automotive electronics, manufacturing equipment, and robots.

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