Characterization of fiber optic cables under large tensile loads

Fiber optic cables designed for the Nevada Test Site (NTS) have to withstand an unusually harsh environment. Cables have been manufactured under a 6 year old DOE specification that has been slightly modified as the cable requirements are better understood. In order to better understand the cable properties a unique capability has been established at the NTS. Instrumentation has been developed to characterize the transmission properties of 1 km of fiber optic cable placed under a controlled tensile load up to 1500 lbs. The properties measured are cable tension, cable elongation, induced attenuation, attenuation vs. location, fiber strain, bandwidth, and ambient temperature. Preforming these measurements on cables from the two qualified NTS fiber optic cable manufacturers, Siecor and Andrew Corp., led to a new set of specifications. The relevant new and old specifications will be reported along with the characterization techniques and results on cables manufactured under the old specification

Signal enhancement by spectral equalization of high frequency broadband signals transmitted through optical fibers

A new technique is discussed for enhancing the bandwidth and intensity of high frequency (> 1 GHz) analog, spectrally broad (40 nm) signals transmitted through one kilometer of optical fiber. The existing method for bandwidth enhancement of such a signal uses a very narrow (approx. 1 nm) filter between the fiber and detector to limit bandwidth degradation due to material dispersion. Using this method, most of the available optical intensity is rejected and lost. This new technique replaces the narrow-band filter with a spectral equalizer device which uses a reflection grating to disperse the input signal spectrum and direct it onto a linear array of fibers

Overview of pulsers for nanosecond gating of image-shutter tubes

The capability of generating a useful optical shutter of a few nanoseconds or less utilizing gated proximity-focussed microchannel-plate (MCP) wafer tubes or silicon intensified target (SIT) vidicon tubes depends strongly on the driving electrical pulse. This paper will provide a summary of some of the electrical gate pulsers utilized in studying both proximity-focussed MCP imaging intensifiers and gated SIT FPS vidicon tubes. (WHK

Nanosecond-Gating Properties of Proximity-Focused Microchannel-Plate Image Intensifiers

Some fundamental properties of 18-mm-diam gated proximity-focussed microchannel-plate (MCP) image intensifiers used as fast image shutters in the 1 to 10 ns range have been identified and studied. Light pulses (approx. 5 ps wide) from a modelocked dye laser optically sample the gated MCP. Shuttering is achieved by applying a forward-biasing electrical gate pulse to the quiescently reverse-biased photocathode-MCP interface. Variable delay (approx. 30 ps jitter) between the gate pulse and the laser pulse permits tracing the MCP's optical response. Gating speeds, turn-on and turn-off patterns, the asymmetric spatial dependence of the MCP optical response, and resolution effects as functions of gate pulse width and photocathode-MCP bias have been characterized. Shutter times of >750 ps with approx. 5 1p/mm resolution were observed. Variations in the intensity profiles of the phosphor's spatial response for uniform photocathode illumination are measured with a calibrated silicon-intensified-target (SIT) focus projection, scan (FPS) television camera and a high-speed video digitizer while photomultipliers monitor the laser pulse and the phosphor's spatially integrated output intensities. The characterization system, gating and biasing circuits, and experimental results will be presented

Image shutters: gated proximity-focused microchannel-plate (MCP) wafer tubes vs gated silicon intensified target (SIT) vidicons

The imaging characteristics of two fast image shutters used for recording the spatial and temporal evolution of transient optical events in the nanosecond range have been studied. Emphasis is on the comparative performances of each shutter type under similar conditions. Response data, including gating speed, gain, dynamic range, shuttering efficiency, and resolution for 18 and 25-mm-diam proximity-focused microchannel-plate (MCP) intensifiers are compared with similar data for a prototype electrostatically-focused 25-mm-diam gated silicon-intensified-target (SIT) vidicon currently under development for Los Alamos National Laboratory. Several key parameters critical to optical gating speed have been varied in both tube types in order to determine the optimum performance attainable from each design. These include conductive substrate material and thickness used to reduce photocathode resistivity, spacing between gating electrodes to minimize inter-electrode capacitance, the use of conductive grids on the photocathode substrate to permit rapid propagation of the electrical gate pulse to all areas of the photocathode, and different package geometries to provide a more effective interface with external biasing and gating circuitry. For comparable spatial resolution, most 18-mm-diam MCPs require gate times > 2.5 ns while the fastest SIT has demonstrated sub-nanosecond optical gates as short as approx. 400 +- 50 ps for full shuttering of the 25-mm-diam input window

Characterization of low-loss multimode optical fibers for nuclear diagnostics

The application of low loss multimode optical fibers to nuclear diagnostics has been discussed in previous papers. Fiber requirements for this application differ substantially from those for normal communications use. The emphasis for nuclear measurements has been on development of high frequency analog fiber optic transmission line systems, which range from 100 MHz to > 500 MHz signals transmitted at 600 nm and 800 nm, respectively. Accordingly, specialized fiber characterization procedures over a wide spectral range have been developed. These techniques include measurement of material and modal dispersion, optical attenuation, and optical linearity. It is also important to know the prompt radiation response of optical fibers in nuclear diagnostics. Measurements of this type have been discussed in previous papers

Radiation-induced imaging system over long fiber-optic bundles

Scintillator, fiber, and detector technologies have progressed over the last few years so that it is now possible to record radiation images over optical fiber bundles 1 km in length. Scintillators that emit at 730 nm will be coupled with wavelength-multiplexing techniques to telecommunication fibers for transmission to a demultiplexer and detection by GaAs microchannel-plate image-intensifier tubes. The technique and design considerations, such as time-integrated versus time-resolved images, resolution and system dynamic range will be described