Digital Filter Compensation for MIOC Lock-In in Fiber-Optic Sensors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Fiber-optic Sagnac interferometers in rotation rate sensors face challenges in measuring small rotation rates accurately due to the lock-in effect caused by the frequency response of the multi-functional integrated optical chip (MIOC), which is exacerbated by non-constant temperature conditions.
Innovation Solution
A fiber-optic Sagnac interferometer with a digital filter connected upstream of the MIOC, whose transfer function is inverse to the MIOC's transfer function, is used to compensate for the frequency and temperature dependencies, thereby reducing the lock-in effect and enabling precise measurements at small rotation rates under varying temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the working point is adjusted to the point of maximum gradient of the cosine function to maximize sensitivity, then the sensitivity of the interferometer is improved, but the lock-in effect occurs at small rotation rates causing measurement inaccuracy
Solution Approach 1:
A digital filter is introduced as an intermediary component between the light source and the MIOC to compensate for the MIOC's frequency response characteristics. The filter's transfer function is designed to be inverse to the MIOC's transfer function, effectively canceling out the frequency-dependent phase modulation errors that cause the lock-in effect, thereby enabling accurate measurement at small rotation rates while maintaining high sensitivity
Solution Approach 2:
The phase modulation characteristics of the MIOC are compensated by changing the frequency response parameters of the digital filter. The filter coefficients are adjusted to match the inverse of the MIOC's frequency response, dynamically correcting the phase modulation errors across different frequency ranges and temperature conditions
2Measurement precision
If the MIOC is used for phase modulation to enable precise rotation rate measurement, then the measurement precision is improved, but the frequency dependence of phase modulation causes lock-in effect at small rotation rates
Solution Approach 1:
The digital filter serves as a mediator that pre-compensates the phase modulation signal before it reaches the MIOC. By applying the inverse frequency response through the filter, the harmful frequency-dependent effects generated by the MIOC are counteracted, eliminating the lock-in effect while preserving the precision measurement capability
Solution Approach 2:
The system applies preliminary anti-action by pre-distorting the modulation signal through the digital filter in a way that anticipates and counteracts the frequency response distortion introduced by the MIOC. This preliminary compensation prevents the lock-in effect from occurring in the first place
3Measurement precision
If the MIOC frequency response is used for phase modulation, then the interferometer can operate with high sensitivity, but temperature dependency of the MIOC frequency response exacerbates the lock-in effect under non-constant temperature conditions
Solution Approach 1:
The digital filter acts as a temperature-compensating intermediary that adapts its frequency response to counteract temperature-induced changes in the MIOC's characteristics. By maintaining the inverse relationship between the filter and MIOC transfer functions across varying temperatures, the system preserves measurement accuracy and stability
Solution Approach 2:
The system dynamically adjusts the digital filter parameters to track and compensate for temperature-dependent changes in the MIOC frequency response. This dynamic adaptation ensures that the compensation remains effective under non-constant temperature conditions, maintaining system stability
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 implementation of the digital filter effectively compensates for the MIOC's frequency and temperature dependencies, allowing for highly precise rotation rate measurements even at small rotation rates and under non-constant temperature conditions.
Implementation Method 1
This uses the Sagnac effect according to which an optical path difference occurs between two light beams running in opposite directions inside the light guide loop during a rotation about its normal
Implementation Method 2
A rotation rate sensor, which comprises a fiber-optic Sagnac interferometer, usually comprises a multi-functional integrated optical chip (MIOC) for carrying out a phase modulation
Implementation Method 3
a photo detector device, an amplifier with a downstream connected analog/digital converter
Data Source
AI summary
A fiber-optic Sagnac interferometer in a rotation rate sensor comprises a multifunctional integrated optical chip (MIOC) with a MIOC transfer function. A digital filter is connected upstream to the multi-functional integrated optical chip, whose filter transfer function corresponds basically to the inverse MIOC transfer function such that the MIOC transfer function is compensated by the filter transfer function. Corresponding coefficients of the filter transfer function may be determined in a main control loop.