Analog RIN Rejection Loop for Fiber-Optic Gyroscopes
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Solution Overview
Problem
Conventional methods for reducing relative intensity noise (RIN) in interferometric fiber-optic gyroscopes (IFOGs) are inefficient, requiring separate measurements and digital subtraction, which increases complexity, size, and power consumption, and often fail to effectively differentiate the desired rate signal from the RIN signal due to spectral filtering.
Innovation Solution
An analog disturbance rejection loop is implemented around the light source, using a detector, transimpedance amplifier, and controller to generate intensity fluctuations that cancel out RIN by creating dithered actuation signals equal in amplitude but opposite in phase to the intrinsic RIN, reducing RIN before it reaches the gyro coils.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If digital RIN subtraction is used, then RIN reduction is achieved, but device complexity and power consumption increase due to separate measurements and digital processing for each gyro axis
Solution Approach 1:
The patent combines the RIN measurement and rate signal measurement into a single shared optical path and detection system. Both signals are extracted from the same interferometric fiber-optic gyroscope measurements, eliminating the need for separate RIN measurement channels and digital processing for each axis. This merging approach reduces device complexity while maintaining RIN reduction capability.
Solution Approach 2:
The patent makes the interferometric fiber-optic gyroscope system perform multiple functions: it simultaneously measures both the rate signal and the RIN signal through the same optical path and detector. This multi-functionality eliminates the need for dedicated RIN measurement hardware, reducing overall device complexity while achieving RIN reduction through digital subtraction.
2Object-generated harmful factors
If digital RIN subtraction is used, then RIN reduction is achieved, but system size increases due to additional ADCs, DACs, and electronics
Solution Approach 1:
The patent merges the RIN measurement function with the existing rate signal measurement function, using the same photodetector, ADC, and processing electronics for both purposes. This eliminates the need for additional dedicated hardware components, thereby reducing system size while maintaining the capability to reduce RIN through digital signal processing.
Solution Approach 2:
The patent enables the existing gyroscope electronics to serve dual purposes: measuring rate signals and measuring RIN signals. By making the system multi-functional, no additional ADCs, DACs, or specialized electronics are required, thus avoiding an increase in system size.
3Object-generated harmful factors
If analog summation with delayed RIN signal is used, then phase cancellation at odd harmonics is achieved, but noise at other frequencies increases and gain control complexity increases
Solution Approach 1:
The patent employs a feedback approach where the measured RIN signal is processed and subtracted from the rate signal in the digital domain. This feedback mechanism actively compensates for RIN across the entire frequency spectrum without introducing noise at other frequencies, unlike the analog summation method that only provides selective cancellation at odd harmonics.
Solution Approach 2:
The patent replaces the analog summation method with digital signal processing. Instead of using analog circuits to sum and delay signals for phase cancellation, the patent uses digital subtraction of the measured RIN signal from the rate signal, which provides more reliable noise performance across all frequencies without requiring precise analog gain control.
4Object-generated harmful factors
If separate RIN measurement for each gyro axis is performed, then accurate RIN reduction is achieved, but measurement precision decreases due to difficulty in differentiating rate signal from RIN signal after coil filtering
Solution Approach 1:
The patent performs preliminary extraction of the RIN signal component from the total measurement signal before the spectral filtering effect of the coils can obscure it. By measuring and processing the RIN signal immediately from the raw detector output, the system maintains measurement precision while achieving accurate RIN reduction for each gyro axis.
Solution Approach 2:
The patent uses feedback to continuously monitor and subtract the RIN signal from the rate signal measurements. This feedback mechanism maintains measurement precision by actively compensating for RIN effects, allowing accurate differentiation and processing of the rate signal even in the presence of coil-induced spectral filtering.
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 approach reduces RIN prior to gyro coils, minimizing the need for digital processing and electronics, thereby decreasing system size, error, and power consumption while improving angle random walk (ARW) performance.
Implementation Method 1
a detector for detecting an optical signal produced by a light source
Implementation Method 2
An output of the detector is coupled to an input of a transimpedance amplifier
Implementation Method 3
The controller is operative to receive signals provided thereto from the transimpedance amplifier and provided a dithered actuation signal at the output thereof. The dithered actuation signal may be provided to the light source to cause the light source to produce intensity fluctuations within the bandwidth in which the light source generates optical power
Implementation Method 4
analog disturbance rejection loop which reduces and ideally eliminates RIN
Data Source
AI summary
Systems and methods for reducing relative intensity noise are provided. The system can include a photodetector configured to detect the relative intensity noise of a light source. The system can include a transimpedance amplifier configured to provide a feedback loop with the photodetector to generate a first signal based on the detected relative intensity noise. The system can include a controller configured to actuate the light source based on the first signal to reduce the relative intensity noise. In this manner, the system can reduce the relative intensity noise of a light source for various optical systems, including gyroscopic systems.