Optical gyroscope system

Light beams pass in opposite directions through a single mode fiber optic wave guide that extends in a circle or coil in an optical gyroscope system which measures the rotation rate of the coil by measuring the relative phase shifts of the beams by interferometric techniques. Beam splitting and phase shifting of the light are facilitated by utilizing brief pulses of light and by using light-controlling devices which are operated for a brief time only when the light pulse passes in one direction through the device but not at a different time when the pulse is passing in the opposite direction through the device. High accuracy in rotation measurement is achieved at both very slow and very fast rotation rates, by alternately operating the system so that at zero rotation the interfering waves are alternately 90 out of phase and in phase. Linear polarization of the light beams is maintained by coiling the full length of the optic fiber in a single plane

Optical fiber coupling method and apparatus

Systems are described for coupling a pair of optical fibers to pass light between them, which enables a coupler to be easily made, and with simple equipment, while closely controlling the characteristics of the coupler. One method includes mounting a pair of optical fibers on a block having a large hole therein, so the fibers extend across the hole while lying adjacent and parallel to one another. The fibers are immersed in an etchant to reduce the thickness of cladding around the fiber core. The fibers are joined together by applying a liquid polymer so the polymer-air interface moves along the length of the fibers to bring the fibers together in a zipper-like manner, and to progressively lay a thin coating of the polymer on the fibers

WSRT and VLA Observations of the 6 cm and 2 cm lines of H2CO in the direction of W 58 C1(ON3) and W 58 C2

Absorption in the J{K-K+} = 2{11}-2{12} transition of formaldehyde at 2 cm towards the ultracompact HII regions C1 and C2 of W 58 has been observed with the VLA with an angular resolution of ~0.2'' and a velocity resolution of ~1 km/s. The high resolution continuum image of C1 (ON 3) shows a partial shell which opens to the NE. Strong H2CO absorption is observed against W 58 C1. The highest optical depth (tau > 2) occurs in the SW portion of C1 near the edge of the shell, close to the continuum peak. The absorption is weaker towards the nearby, more diffuse compact HII region C2, tau<~0.3. The H2CO velocity (-21.2 km/s) towards C1 is constant and agrees with the velocity of CO emission, mainline OH masers, and the H76 alpha recombination line, but differs from the velocity of the 1720 MHz OH maser emission (~-13 km/s). Observations of the absorption in the J{K-K+} = 1{10}-1{11} transition of formaldehyde at 6 cm towards W 58 C1 and C2 carried out earlier with the WSRT at lower resolution (~4''x7'') show comparable optical depths and velocities to those observed at 2 cm. Based on the mean optical depth profiles at 6 cm and 2 cm, the volume density of molecular hydrogen n(H2) and the formaldehyde column density N(H2CO) were determined. The n(H2) is ~6E4 /cm**3 towards C1. N(H2CO) for C1 is ~8E14 /cm**2 while that towards C2 is ~8E13 /cm**2.Comment: AJ in press Jan 2001, 14 pages plus 6 figures (but Fig. 1 has 4 separate parts, a through d). Data are available at http://adil.ncsa.uiuc.edu/document/00.HD.0

CCD star trackers

The application of CCDs to star trackers and star mappers is considered. Advantages and disadvantages of silicon CCD star trackers are compared with those of image dissector star trackers. It is concluded that the CCD has adequate sensitivity for most single star tracking tasks and is distinctly superior in multiple star tracking or mapping applications. The signal and noise figures of several current CCD configurations are discussed. The basic structure of the required signal processing is described, and it is shown that resolution in excess of the number of CCD elements may be had by interpolation

Image dissector development

A second-generation electrostatically focused image dissector tube for use in spacecraft attitude control star trackers is being developed with the support of an industrial contractor. Significant improvements are being made in functional characteristics, as well as in package dimensional control, tolerance of a wide variety of environmental conditions, and expected reliability over long operational lifetimes

Radio Variability of Sagittarius A* - A 106 Day Cycle

We report the presence of a 106-day cycle in the radio variability of Sgr A* based on an analysis of data observed with the Very Large Array (VLA) over the past 20 years. The pulsed signal is most clearly seen at 1.3 cm with a ratio of cycle frequency to frequency width f/Delta_f= 2.2+/-0.3. The periodic signal is also clearly observed at 2 cm. At 3.6 cm the detection of a periodic signal is marginal. No significant periodicity is detected at both 6 and 20 cm. Since the sampling function is irregular we performed a number of tests to insure that the observed periodicity is not the result of noise. Similar results were found for a maximum entropy method and periodogram with CLEAN method. The probability of false detection for several different noise distributions is less than 5% based on Monte Carlo tests. The radio properties of the pulsed component at 1.3 cm are spectral index alpha ~ 1.0+/- 0.1 (for S nu^alpha), amplitude Delta S=0.42 +/- 0.04 Jy and characteristic time scale Delta t_FWHM ~ 25 +/- 5 days. The lack of VLBI detection of a secondary component suggests that the variability occurs within Sgr A* on a scale of ~5 AU, suggesting an instability of the accretion disk.Comment: 14 Pages, 3 figures. ApJ Lett 2000 accepte

Ranging system which compares an object reflected component of a light beam to a reference component of the light beam

A system is described for measuring the distance to an object by comparing a first component of a light pulse that is reflected off the object with a second component of the light pulse that passes along a reference path of known length, which provides great accuracy with a relatively simple and rugged design. The reference path can be changed in precise steps so that it has an equivalent length approximately equal to the path length of the light pulse component that is reflected from the object. The resulting small difference in path lengths can be precisely determined by directing the light pulse components into opposite ends of a detector formed of a material that emits a second harmonic light output at the locations where the opposite going pulses past simultaneously across one another