Sagnac Interferometer Phase Quadrature Adjustment
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Solution Overview
Problem
The sensitivity of Sagnac interferometer-based characterization devices is not consistently high across different types of samples, leading to reduced measurement quality and precision, as the phase and amplitude differences between counter-rotating waves are not solely due to the sample but also influenced by external factors, limiting the ability to accurately measure variations.
Innovation Solution
Incorporating an adjustable phase shift means, such as a Babinet compensator, within the Sagnac interferometer to introduce a phase shift of Pi/2 between counter-rotating waves, allowing for compensation of additional phase shifts caused by the sample, thereby optimizing the sensitivity and accuracy of measurements by ensuring the waves are in phase quadrature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Sagnac interferometer is used to characterize a sample with counter-rotating beams, then the device can measure phase and amplitude differences between probe rays, but the sensitivity is not consistently high across different sample types due to additional phase shifts introduced by the sample itself
Solution Approach 1:
The patent applies preliminary action by measuring the phase shift introduced by the sample in advance (without pump beam) and using this information to adjust the interferometer's reference arm phase shift. This pre-characterization allows the system to compensate for sample-specific phase shifts before actual measurements, ensuring optimal sensitivity across different sample types.
Solution Approach 2:
The patent changes the phase shift parameter of the reference arm in the interferometer based on the measured sample-induced phase shift. By dynamically adjusting this parameter, the system maintains phase quadrature conditions and optimizes measurement sensitivity for each specific sample type.
2Reliability
If the optical path is made symmetric for counter-rotating beams in a Sagnac interferometer, then external modifications affect both rays equally, but this symmetry prevents optimization of measurement sensitivity for different sample types
Solution Approach 1:
The patent introduces asymmetry by deliberately creating a phase shift in the reference arm that compensates for the sample-induced phase shift. This controlled asymmetry in the reference arm balances the overall optical path, allowing the system to maintain reliability while optimizing sensitivity for each sample type.
Solution Approach 2:
The system dynamically changes the reference arm phase shift parameter based on the specific sample being measured, allowing optimization of measurement sensitivity while maintaining consistent and reliable measurements across different sample types.
3Measurement precision
If signal processing is enhanced downstream of the Sagnac interferometer, then some sensitivity improvement can be achieved, but completely satisfactory results cannot be obtained due to fundamental limitations in the interferometer configuration
Solution Approach 1:
The patent performs preliminary characterization of the sample's phase shift effect before main measurements, allowing the interferometer to be pre-configured for optimal sensitivity. This reduces the need for complex downstream signal processing while achieving satisfactory results.
Solution Approach 2:
The system uses feedback from the initial sample characterization to adjust the reference arm phase shift, creating a closed-loop configuration that optimizes sensitivity automatically without requiring complex signal processing algorithms.
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 enables precise and sensitive characterization of any sample type by compensating for sample-induced phase shifts, resulting in linear interference intensity variations and improved measurement precision, adapting to various materials and optimizing signal processing.
Implementation Method 1
an optical interferometer comprising a looped part in which two electromagnetic waves propagate in a counter-rotating manner
Implementation Method 2
Document US 6,549,285 B1 describes a characterization device comprising in particular a Sagnac interferometer
Implementation Method 3
a pump beam, configured to create an acoustic wave in the sample
Data Source
Figure 1~2
Figure 3~4
AI summary
The present invention concerns a device (1) for characterising a sample, comprising: an optical source (2), an optical sensor (22), and an optical interferometer (8). The optical interferometer comprises: - a looped part (10) in which two electromagnetic waves propagate in a counter-rotating manner, comprising a separation means (12) configured to form said two counter-rotating electromagnetic waves, and - a phase shifting means configured to create a phase shift of Pi/2 between the two counter-rotating waves, the sample (6) being intended to be placed in the optical interferometer in such a way that the optical path between the separation means and the sample is different between the two counter-rotating waves. The phase shifting means is a phase shifting means (14, 16) that can be adjusted to obtain counter-rotating waves in phase quadrature. The invention also relates to a method for characterising a sample by an optical interferometer.