8-Level MIOC Phase Modulation for I-FOG Dynamic Response
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Solution Overview
Problem
Existing I-FOG sensors face challenges in accurately measuring rotation rates with high variations due to limited dynamic response and increased control latency, leading to errors in feedback control and measurement.
Innovation Solution
An 8-level modulation scheme for the MIOC in I-FOG sensors is introduced, where each modulation level lasts τ/4, allowing for faster demodulation and reduced control latency from 2τ to τ, thereby enhancing the dynamic response and intrinsic bandwidth of the sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional 2-level or 4-level modulation scheme is used, then the device complexity is reduced, but the dynamic response and bandwidth are limited
Solution Approach 1:
The patent divides the conventional 2-level modulation scheme into 8 distinct levels by segmenting the phase modulation range. Each level corresponds to a specific phase shift value, allowing the system to encode more information per modulation cycle. This segmentation enables faster tracking of rotation rate variations while maintaining a manageable device structure through systematic phase level distribution.
Solution Approach 2:
The patent transitions from a 1-level modulation system to an 8-level modulation system, effectively adding dimensional complexity to the modulation space. By utilizing multiple phase levels instead of binary states, the system achieves higher bandwidth and dynamic response without proportionally increasing physical device complexity, as the enhancement occurs in the signal dimension rather than physical structure.
2Measurement precision
If the modulation level duration is extended to ensure accurate measurement, then the measurement precision is improved, but the control latency increases
Solution Approach 1:
The patent implements periodic 8-level modulation cycles where each level maintains the light phase for a specific duration τ. This periodic structure allows the system to complete full measurement cycles faster while maintaining sufficient sampling time at each level. The regular repetition of the modulation sequence enables continuous tracking with reduced overall latency compared to conventional schemes.
Solution Approach 2:
The system performs preliminary phase modulation at 8 distinct levels before the actual measurement is needed, pre-establishing the phase states required for accurate rotation rate detection. This preliminary structuring of phase levels allows the measurement process to proceed more efficiently, reducing the time required to achieve accurate measurements by having the modulation framework ready in advance.
3Measurement precision
If the feedback control updates are performed less frequently, then the device complexity is reduced, but the measurement accuracy for high variation rotation rates deteriorates
Solution Approach 1:
The patent implements a closed-loop feedback control system where the 8-level modulation signal is continuously monitored and the phase modulation is adjusted based on detected rotation rates. The feedback mechanism processes the optical signal from the interferometer and updates the modulation phases in real-time, enabling accurate tracking of high variation rotation rates while maintaining manageable processing complexity through efficient signal demodulation algorithms.
Solution Approach 2:
The system dynamically changes the phase modulation parameters across 8 distinct levels based on the detected rotation rate. By varying the phase shift values systematically through the 8 levels, the system encodes rotation information that can be decoded with high precision. This parameter variation approach allows accurate measurement of high variation rates without requiring proportionally complex feedback processing, as the structured parameter changes facilitate efficient signal interpretation.
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 8-level modulation technique doubles the tracking speed of feedback control and the bandwidth of I-FOG sensors, achieving more accurate and linear dynamic responses when measuring rotation rates with high variations, and reduces vibration rectification effects by at least one order of magnitude.
Implementation Method 1
the light injected into the sensitive element is modulated by an electro-optical phase modulator driven by a voltage signal - the waveform of which changes depending on the modulation scheme used - by means of an analogue modulation channel. A voltage signal applied to the electrodes of the phase modulator causes a phase shift of the light that crosses it which, in first approximation, is proportional to the voltage
Implementation Method 2
An I-FOG is a sensor consisting of a fiber interferometer that takes advantage of the Sagnac effect to measure the rotation rate of its sensitive element, given by a closed-loop path (typically a fiber optic coil), depending on the difference in optical path produced between two optical rays travelling in opposite directions in the sensitive element
Implementation Method 3
The difference in the optical path implies a phase difference between the two propagating and counter-propagating rays, which is expressed in a variation of the optical power, measured by a photo-detector (typically a PinFET), which occurs when they interfere
Data Source
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Figure 3a~3c
AI summary
This invention relates the inertial navigation and position systems sector, and specifically relates an optical phase modulation scheme for an interferometric fiber optic gyroscope (I-FOG), with closed-loop feedback control equipped with a digital mod/demod approach by allowing said modulation scheme to double the feedback processing speed and obtain a more accurate and linear dynamic response of the sensor when measuring rotation rate profiles characterized by high variations.