FIBEROPTIC SENSOR TECHNOLOGY HANDBOOK

Referring once more to Fig. 5.35, if the mass
is given a transverse (cross axis) acceleration, both
optical fibers are strained the same amount. Thus, the
interferometer remains balanced and to first order this
device is insensitive to transverse accelerations.
Cross axis coupling will occur if simultaneously there
are components of acceleration that has components
parallel and perpendicular to the longitudinal axis of
the fiber. The diaphragms indicated in Fig. 5.35 are
provided to essentially eliminate cross-axis coupling.
Tveten et.al. (See Ref. 1 of Subsection 5.3.1)
investigated a single fiber version of this device. The
sensitivity in radians/g versus frequency is shown in
Fig. 5.38 and the value of amin versus frequency in
Fig. 5.39.
100or
y 100 -
v
: 10 -
~
> ~-----
&l -
:
~ 0.1 1
0 100 200 300 400 500
5.4 FIBEROPTIC ROTATION-Fb+TE SENSORS
5.4.1 Introduction
The measurement of rotation is of considerable
interest in a number of areaa. For example, inertial
navigation systems as used in aircraft and spacecraft
depend critically on accurate inertial rotation
sensors. The allowable errors in rotation sensor performance
depend on the particular application. Typical
requirements for aircraft navigation lie between 0.01
and 0.001 degreeslhour. In terms of earth rotatio
rate, flE = 15 degrees/hour, this becomes 10-3 to 10 -2
!lE. Fig. 5.40 lists several other applications of rotation
sensors, such as surveying, where the accurate
determination of azimuth and geodetic latitude is important
(see Ref. 1, Subsection 5.4.20). In this case
-6 ~ or less iS needed.
performance of 10
Geophysics
applications include 2t e determination of astronondcal
latitude, and the monitoring of polar motion caused by
wobble, rotation, precession and wandering effects (see
Ref. 1, Subsection 5.4.20). A highly precise rotation
sensor may be used to measure any changes in the length
of the day and to detect torsional oscillation in the
earth caused by earthquakes. Finally, ultraprecise
sensors may find applications in relativity-related
experiments such as the determination of the preferred
frame and dragging of inertial frames (see Ref. 2,
Subsection 5.4.20).
FREQUENCY HZ
Fig. 5.38 The sensitivity in radianslg (g = 9.8m/s2)
of a single-fiber fiberoptic accelerometer
as a function of frequency. The low-frequency
theoretical sensitivity is shown by
the horizontal line.
After A. Tveten et al., Electron Lett., — 16, 854 (1980),
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NAVIGATION WQESIO –3
SURVEYING
AZIMUTH, GEODETIC LATITUDE N