Passive Ring Interferometer Sensor Second-Order Coherence
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Solution Overview
Problem
Passive Sagnac optical gyroscopes relying on first-order interference face limitations such as scale factor instability due to wavelength sensitivity and limited unambiguous dynamic range, leading to measurement errors and complexity in electronics, especially at high rotation rates or during interruptions.
Innovation Solution
A passive ring interferometer sensor utilizing second-order coherence detection, where electromagnetic waves are made counter-propagating within an electromagnetic ring path, combined to be co-propagating with polarization elements setting them to be mutually co-polarized within the ring path and cross-polarized in the coupling path, allowing for detection of second-order coherence to determine rotation rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If first-order interference detection is used in passive Sagnac optical gyroscopes, then the scale factor is proportional to the rotation rate, but the scale factor becomes unstable due to wavelength sensitivity and environmental fluctuations
Solution Approach 1:
The patent transitions from first-order interference detection to second-order coherence detection, fundamentally changing the detection parameter. This parameter change makes the measurement independent of the light source's centroid wavelength, eliminating the scale factor instability caused by wavelength fluctuations and environmental effects.
Solution Approach 2:
The patent replaces the traditional first-order interference detection mechanism with a second-order coherence detection mechanism. This substitution involves using a different physical detection approach that measures intensity correlations rather than direct interference patterns, thereby avoiding wavelength sensitivity issues.
2Device complexity
If first-order interference is used with a single centroid wavelength, then the apparatus is simple, but the unambiguous dynamic range is limited to ±π radians
Solution Approach 1:
By changing from first-order interference to second-order coherence detection, the patent expands the unambiguous dynamic range beyond the ±π radian limitation. The second-order coherence measurement provides a monotonic response that allows for extended dynamic range without requiring complex fringe counting electronics.
3Adaptability or versatility
If fringe counting is implemented to extend dynamic range at high rotation rates, then the measurement range increases, but the electronics complexity increases significantly
Solution Approach 1:
The patent replaces the complex fringe counting electronic system with a second-order coherence detection system. This substitution eliminates the need for high-speed fringe counting electronics by providing a detection method that naturally handles extended dynamic ranges through intensity correlation measurements.
4Ease of operation
If external light sources like superluminescent diodes are used, then the gyroscope can operate, but the centroid wavelength is highly sensitive to temperature fluctuations
Solution Approach 1:
The patent changes the detection parameter from first-order interference (which depends on wavelength) to second-order coherence (which is wavelength-independent). This parameter change eliminates the thermal sensitivity issue of light source centroid wavelength while maintaining operational capability with standard light sources.
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 enhances the accuracy and unambiguous dynamic range of rotation measurements by reducing wavelength sensitivity and enabling seamless data stitching across interruptions, simplifying electronics and improving high-speed operation.
Implementation Method 1
an electromagnetic ring path configured to receive a pair of electromagnetic waves from an electromagnetic radiation source and to direct the pair of electromagnetic waves to be counter-propagating within the electromagnetic ring path
Implementation Method 2
a combination junction configured to receive the pair of electromagnetic waves from the respective ends of the electromagnetic ring path and to combine the pair of electromagnetic waves to be co-propagating within a coupling path
Implementation Method 3
Polarization elements included in the sensor are configured to set the pair of electromagnetic waves to be mutually co-polarized within the electromagnetic ring path and to be mutually cross-polarized within the coupling path
Implementation Method 4
A detector forming part of the sensor is configured to receive the mutually cross-polarized pair of electromagnetic waves from the coupling path and to detect second-order coherence of the mutually cross-polarized electromagnetic waves
Implementation Method 5
Passive Sagnac optical gyroscopes detect rotation by means of the Sagnac effect, also called Sagnac interference, named after French physicist Georges Sagnac, which is a phenomenon encountered in interferometry that is elicited by rotation
Data Source
AI summary
A passive ring interferometer sensor includes an electromagnetic ring path configured to receive a pair of electromagnetic waves from an electromagnetic radiation source and to direct the waves to be counter-propagating within the ring path toward respective ends of the path. A combination junction receives the waves from the respective ends and combines the waves to be co-propagating within a coupling path. Polarization elements are configured to set the waves to be mutually co-polarized within the electromagnetic ring path and to be mutually cross-polarized within the coupling path. A detector is configured to receive the mutually cross-polarized waves from the coupling path and to detect second-order coherence. Embodiments can sense rotation rate as fiber-optic gyroscopes or serve as other types of sensors such as gravitational wave sensors. Embodiments may have greatly increased unambiguous range and decreased sensitivity to any centroid wavelength shift.