Litef Gmbh

Manfred Kemmler

Eberhard Handrich

Hanns J Bueschelberger

In a fibre-optic Sagnac interferometer, in particular for determining rotational speeds (fibre gyro), having an optical directional coupler ( ) which is located in the light path from a light source ( ) and whose at least one output is connected via a spatial filter ( ) and a polarization filter ( ) to a beam splitter ( ) which, on the one hand, splits the light transmitted by the polarization filter ( ) into two component light beams which are irradiated into the two ends of an optical fibre ( ), it being the case, on the other hand, that the component light beams returning after traversing the optical fibre ( ) are reunited in an interfering fashion and applied to a light-sensitive receiver ( ), it is provided for the purpose of reducing the amplitude error, that is to say, the polarization ratio of the light upstream of the polarization filter ( ), to produce the spatial filter ( ) from monomode fibre. It is possible, in particular, as a result to save substantial costs in the case of the optical directional coupler ( ), which can now be fabricated from simple monomode fibre.

Fiber optic Sagnac interferometer with spatial filter

A method and a device for compensating Shupe effect drift errors in a fiber gyro that result from time-dependent temperature changes. A closed loop fiber optic gyro includes a VCO control loop and an evaluation unit that incorporates a model which is dependent on the optical path length of light through the fiber coil. The closed loop gyro is arranged to compensate for temperature-dependent drift changes that result from changes in optical path length.

Closed loop fiber optic gyro with shupe effect compensation

An integrated optics chip is employed as a Michelson interferometer for stabilizing the wavelength of a light source in a fiber optic Sagnac interferometer for measuring rotation rate. A statistically-independent second signal component is applied in addition to a resetting digital phase ramp dependent on rotation rate to a phase modulator incorporated in the integrated optics chip (MIOC). The second signal component optimizes the working point of the phase modulator. By employing such statistically-independent variation of the phase modulation, the light wavelength-dependent measuring signal of the Michelson interferometer may be demodulated from the detector read-out signaled used for readjustment of the light-source wavelength via a light-source temperature and/or injection current change. In open loop operation, scale factor variations can be compensated using the light wavelength-dependent measuring signal.

Fiber optic interferometer with wavelength-stabilized light source

A method for compensating for light source wavelength variation in a fiber optic gyro having a closed reset control loop. The method employs the finding that the voltage range required for a 2.pi. phase shift in a phase modulator is a function of the wavelength of the gyro light source. The voltage required for affecting the 2.pi. phase shift in such a gyro is regulated according to the invention and utilized to compensate changes in light source wavelength or scale factor. Phase modulator temperature is also taken into account for precise compensation.

Method for compensating light source wavelength variability in a

A multi-axis fiber-optic rotation rate sensor arrangement of I/O opto-electronics (MCS) is based upon single-axis rotational rate sensor arrangements and includes a low-frequency transformation of the output signal at the photodetector by pulsed operation of the light source. The light path is divided into n independent closed light paths downstream of a main beam splitter and a phase modulator whose lengths are in the ratio L.sub.1 :L.sub.2 :L.sub.3 : . . . :L.sub.n =1:2:3: . . . :n. The light source is switched ON/OFF with a pulse duty factor whose ON duration corresponds to the transit time of light through the shortest fiber coil L.sub.1 and whose OFF duration is at least equal to the transit time of light through the longest of the fiber coils L.sub.n. The signals are distinguished either downstream of the photodetector by time-division multiplex or at the phase modulator, where the signal is virtually blanked by the corresponding bias phase application with .+-..pi..multidot.n, delivering minimal rotation rate information, or has applied to it a bias phase of .+-..pi.(n+1/2) to deliver maximum rotation rate information (n a positive integer). The use of common I/O opto-electronics for all the light paths results in substantial cost savings, reduced space requirements, lower power absorption and enhanced reliability.

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Vorstetten, Germany

Manfred Kemmler