Residual Intensity Modulation Control Loop in Resonator Fiber-Optic Gyroscope
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Solution Overview
Problem
Resonator optical gyros face errors in rotation rate measurement due to intensity modulation, which can lead to inaccuracies in sensing rotation rates, particularly because conventional systems struggle to equally suppress intensity modulation in both clockwise and counterclockwise laser beams.
Innovation Solution
A residual intensity modulation (RIM) servo loop is introduced in each laser source of a resonator fiber-optic gyroscope, comprising an intensity modulator, a tap coupler, a photo detector, and a servo system, which reduces intensity modulation by using a feedback loop to control and correct for intensity variations at the modulation frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If intensity modulation is used in the laser source, then the laser frequency can be modulated for resonance detection, but intensity modulation errors are introduced that cause rotation sensing inaccuracies
Solution Approach 1:
The patent implements a feedback control loop where the photodetector monitors the intensity modulated light, converts it to an electrical signal, and feeds it back through the servo system to the intensity modulator. This feedback mechanism detects the intensity modulation error and generates a correction signal that actively compensates for the error, thereby maintaining accurate rotation sensing despite the presence of intensity modulation
Solution Approach 2:
The patent introduces an intermediary feedback control system between the intensity modulator and the detection process. The servo system acts as a mediator that processes the photodetector signal and generates correction signals to the intensity modulator, isolating the rotation sensing measurement from the harmful effects of direct intensity modulation
2Object-generated harmful factors
If a phase modulator is used for phase modulation, then polarization cross-coupling occurs at splice points causing intensity modulation, but using intensity modulation to eliminate this requires moving laser frequency off resonance
Solution Approach 1:
The feedback control loop continuously monitors the intensity modulation caused by polarization cross-coupling and generates real-time correction signals to the intensity modulator, actively compensating for the interference without requiring the laser frequency to be moved off resonance
Solution Approach 2:
The patent converts the harmful intensity modulation effect into a useful signal by using the photodetector to detect the modulation and the servo system to process it, transforming the polarization cross-coupling interference into a correction mechanism that improves measurement accuracy
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
The RIM servo loop effectively compensates for intensity modulation-induced errors, ensuring that laser frequencies remain on resonance, thereby improving the accuracy of rotation rate measurement by reducing intensity modulation proportional to the gain of the feedback loop.
Implementation Method 1
A resonator optical gyroscope is a rotation rate sensing device that includes a resonant cavity. The resonant cavity supports light waves propagating in opposite directions (without loss of generality, they are referred to in the following as clockwise (CW) and counter-clockwise (CCW) directions, respectively). When there is a non-zero rotation rate around the normal axis of the resonator, the effective optical round-trip path length for the CW and CCW lightwaves is different, leading to a resonant frequency difference between them.
Implementation Method 2
The intensity modulator receives a light beam and modulates an intensity of the light beam at a modulation frequency in accordance with a control signal
Implementation Method 3
the photo detector converts the modulated light beam into a modulated electrical signal at the modulation frequency
Implementation Method 4
The system reduces the intensity modulation at the modulation frequency by using a feedback loop. The photo detector and servo are connected in a series loop, so that the photo detector receives the modulated light beam from the intensity modulator and the intensity modulator receives its control signal from the output of the servo.
Data Source
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AI summary
Systems and methods for reducing intensity modulation-induced rotation rate measurement error in a resonator optical gyroscope. The method includes tapping an intensity modulated light beam, directing a portion of the tapped light beam toward a photo detector, outputting from the photo detector a signal proportional to the amplitude variation of the light beam, amplifying the signal, and then providing the signal to the intensity modulator as a control input. Intensity modulation-induced error is reduced by an amount proportional to the gain of the feedback loop.