Passive Random Depolarizer for Tunable Laser Sensors
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Solution Overview
Problem
Optical sensors used in boreholes face inaccuracies due to birefringence effects in high-pressure and high-temperature environments, leading to unreliable measurements of properties like pressure and temperature.
Innovation Solution
A passive random depolarizer is introduced between the tunable laser and the single mode optical fiber, comprising polarization maintaining optical fibers with offset axes, which randomizes the polarized light to average out birefringence effects, ensuring accurate readings by scanning over all polarization states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If polarized light is transmitted through the optical fiber sensor in high-pressure and high-temperature environments, then the sensor can provide optical signals for measurement, but birefringence effects occur causing inaccurate readings
Solution Approach 1:
The patent applies preliminary action by depolarizing the light before it enters the optical fiber sensor. The depolarizer is positioned between the laser source and the sensor, converting polarized light into depolarized light in advance. This preliminary transformation prevents birefringence effects from occurring during light transmission through the sensor, thereby ensuring accurate measurements in high-pressure and high-temperature environments.
2Measurement precision
If a depolarizer is added to eliminate birefringence effects, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent employs parameter changes by modifying the polarization state parameter of the light from polarized to depolarized. This is achieved through a simple depolarizer component that transforms the light's polarization characteristics without requiring complex optical systems. The parameter change approach effectively eliminates birefringence effects while maintaining relatively simple device structure.
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 solution significantly reduces the impact of birefringence on sensor readings, providing more accurate and reliable measurements of downhole properties by averaging out polarization biases, thus enhancing the precision of optical fiber sensors in harsh environments.
Implementation Method 1
birefringence of the optical fiber can adversely affect an optical signal from the sensor resulting in inaccurate readings
Implementation Method 2
transmitting polarized light at a plurality of selected wavelengths using a tunable laser into a passive random depolarizer to provide randomly polarized light
Data Source
AI summary
An apparatus for sensing a value of a property includes: an optical sensor having a single mode optical fiber responsive to the property; an optical interrogator having a tunable laser to transmit polarized light to the optical sensor, a photo-detector to receive sensor light, and a controller configured to process the received light and output the value of the property; and a passive random depolarizer disposed between the tunable laser and the single mode optical fiber and having (i) a first polarization maintaining (PM) optical fiber of length L1 having a first fast optical axis and a first slow optical axis and (ii) a second PM optical fiber of length L2 having a second fast optical axis and a second slow optical axis rotationally spliced to the first PM optical fiber in which the second fast and slow optical axes are offset from the first fast and slow optical axes.