Sagnac Interferometer Kerr Compensation via Counterpropagating Power Balance
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Solution Overview
Problem
The Kerr effect, an electro-optical phenomenon causing distortion in fiber optic gyrometers, significantly affects high-precision rotation measurements by introducing a phase shift that cannot be distinguished from the intended measurement, particularly in applications using spectrally fine optical sources.
Innovation Solution
A method involving periodic modulation of the phase shift between counter-propagating signals in a Sagnac interferometer, with multiple power levels, allows for the cancellation of the Kerr effect by adjusting the balancing of the interferometer channels through controlled demodulation terms, ensuring accurate rotation measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the Kerr effect is present in fiber optic gyrometers using spectrally fine optical sources, then the phase shift measurement is affected by parasitic phase shift, but the measurement precision deteriorates
Solution Approach 1:
The patent applies periodic modulation of the phase shift between counter-propagating signals at the natural frequency of the optical fiber coil. This periodic action allows the system to distinguish between the Kerr effect phase shift and the rotation-induced phase shift by measuring at multiple modulation states, thereby resolving the measurement precision deterioration caused by the harmful Kerr effect
Solution Approach 2:
The patent implements feedback control by calculating demodulation terms from measured output powers and using these to adjust the phase modulation. The feedback mechanism continuously compensates for the Kerr effect by adapting the modulation controlled by the cancellation of calculated demodulation terms, restoring measurement precision
2Object-affected harmful factors
If the average powers of counter-propagating signals are made equal to cancel Kerr effect, then the phase shift from Kerr effect is reduced, but the device complexity increases due to difficulty in achieving identical couplings
Solution Approach 1:
The patent transforms the static requirement of equal power coupling into a dynamic solution by applying periodic phase modulation. Instead of requiring the couplings to be identically equal, the system dynamically adjusts the phase modulation states to compensate for coupling imbalances, reducing the complexity of achieving perfect static balance
Solution Approach 2:
The patent changes the operational parameters by introducing periodic phase modulation at multiple states. This allows the system to operate with unequal couplings while maintaining measurement accuracy through parameter-based compensation, avoiding the complex adjustment required for static power balancing
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively reduces the distortion caused by the Kerr effect, enabling precise rotation measurements by isolating and compensating for the phase shifts induced by the Kerr effect, thereby improving measurement accuracy.
Implementation Method 1
the two counter-propagating signals combine in the optical splitter, producing interference due to an optical phase shift between the two counter-propagating signals
Implementation Method 2
A Sagnac interferometer typically comprises a light source generating an input optical signal coupled to an optical loop via an optical splitter
Implementation Method 3
The Kerr effect refers to an electro-optical phenomenon of birefringence, that is, a variation in the refractive index of a material under the effect of an electric field
Implementation Method 4
The Kerr effect refers to an electro-optical phenomenon of birefringence
Data Source
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AI summary
The invention relates to a method for reducing the Kerr effect in an interferometry measuring device (1) comprising a generator configured to emit an input periodic light signal (3), and a Sagnac interferometer (4) in which two counterpropagating signals (15, 16) travel and combine so as to form a periodic output signal (11) having at least two power values, the method comprising a. determining a phase shift between the two counterpropagating signals (15, 16) a first time and cancelling out the phase shift, and then b. determining a phase shift between the two counterpropagating signals (15, 16) a second time, c. adjusting the ratio between the average powers of the counterpropagating signals (15, 16) so as to cancel out the value of the phase shift determined in the second determination. The invention also relates to an interferometry measuring device configured to implement the method according to the invention.