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Basic Concept
Nowadays, Airbus and Boeing air
planes are equipped with laser gyros for navigation. Beside
their high precision, they have shown reliability, long term
stability as well as a long lifetime.
Within this experimental set-up, the basics of the laser gyro
are explained and practically studied at the system, which
allows full access to all components. The experimental laser
gyroscope (gyro) consists of a rugged turntable on which the
fibre ring laser is mounted. By means of a motorised rotational
stage, the angular motion of the turntable is performed. The
ring laser consist of an Erbium Doped Fibre (EDF) and is coiled
up onto a drum. The point of rotation lies well within the
centre of the drum.
Experimental Set-up
To measure the beat frequency of the CW and CCW mode a so-called
heterodyn oupler is used. In fact, the ring laser is opened and
a fraction of both modes are superimposed. The accessible space
for this, is formed by two beam telescopes and two thin glass
plate which decouple the clockwise (CW) and the counter
clockwise (CCW) modes of the ring laser. By using beam splitter
cubes, the CCW mode is directed in such a way that the clockwise
and counter clockwise travelling modes are superimposed and
their interference intensity is detected by means of the InGaAs
photo detector. The subsequent photo diode amplifier (PDA)
conditions the signal in such a way that it an be counted and
displayed.
By counting the beat frequency and multiplying, the result with
the scale factor of the set-up one gets the angular speed of the
turntable.
The turntable is driven by a micro step motor which is
controlled by an extra required personal computer. Different
angular speeds, as well as CW and CCW rotation, are controlled
by the provided software. This gives the possibility to verify
the linear relation between the beat frequency of both CW and
CCW modes and the angular speed. Furthermore, it allows the
measurement and study of the lock-in effect. |
