James N. Blake

Magnetic field sensitivity of depolarized fiber optic gyros

Results are presented of experimental measurements and an analysis of the magnetic field sensitivity of several types of depolarized fiber-optic gyros. It was found that depolarized gyros of the Bohm et al. (1981) and Fredricks and Ulrich (1984) configuration (having one depolarizer in the loop) can be highly sensitive to magnetic fields, while depolarized gyros incorporating Pavlath and Shaw concept (i.e., having unpolarized light enter and exit the loop) are insensitive to magnetic fields. It is shown that a gyro having all the advantages of both designs can be obtained by incorporating two depolarizers, one between the polarizer and the loop coupler and the other within the loop. A scheme of this type of fiber gyro is presented.

New configuration for an optical fiber acousto-optic frequency shifter

We describe a new configuration for an optical fiber acousto-optic frequency shifter using a section of two-mode fiber where acousto-optic interaction causes mode-convertion accompanied by single sideband frequency translation. A fiexural acoustic wave travels in the stripped section of the two-mode fiber. Because both optical and acoustic waves are confined in the fiber, high efficiencies (close to 100 %) can be achieved with relatively low RF power (< 100mW) applied to the transducer. The acoustic wave is excited in the fiber via an acoustic horn, which focuses the acoustic energy generated by a 5 x 5 mm2 transducer into a fiber-size tip. The new configuration proposed here employs the fiber and the acoustic horn in a collinear assembly, which can reduce excitation of backward acoustic waves in the fiber, contributing to a better image sideband suppression. Moreover, the collinear configuration improves ruggedness of the fiber-to-horn bond as well as device compactness. An improvement of the acoustic bandwidth was also observed. A study of several possible variations of the main configuration was performed and an optimization regarding power requirements, convertion efficiency and acoustic bandwidth is discussed.