Optical Fiber Mode Intensity Measurement via Brillouin Gain Matrix
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Solution Overview
Problem
The Brillouin gain analysis method struggles to accurately measure light intensity distribution in each mode of optical fibers due to difficulties in selectively exciting modes, especially when Brillouin frequency shifts are not sufficiently separated, leading to poor measurement accuracy.
Innovation Solution
A light intensity distribution measurement method and apparatus that utilize a gain coefficient matrix, acquired from a reference optical fiber, to calculate the intensity distribution of light in each propagation mode by varying optical frequency differences and using Brillouin amplification components, allowing for accurate measurement of light intensity in each mode without requiring absolute intensity values or interaction length measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the Brillouin gain analysis method is used to measure light intensity in each mode, then it is possible to acquire propagation properties for each mode by controlling the frequency difference between pump light and probe light, but it is difficult to selectively excite a mode unless the Brillouin frequency shifts for modes are separated by more than the line width (about 20 MHz)
Solution Approach 1:
The patent segments the measurement process into two distinct phases: first measuring the Brillouin gain spectrum for each propagation mode separately using a reference optical fiber without mode coupling to obtain gain coefficients, then using these coefficients to calculate the light intensity distribution for each mode in the measurement-target optical fiber. This segmentation allows selective mode measurement even when frequency shifts are not sufficiently separated.
Solution Approach 2:
The patent performs preliminary measurement of the Brillouin gain spectrum for each propagation mode using a reference optical fiber before measuring the measurement-target optical fiber. The gain coefficients obtained from this preliminary action are then used to calculate the light intensity distribution, enabling accurate mode-specific measurement without requiring sufficient frequency separation during the actual measurement.
2Measurement precision
If the Brillouin gain analysis method is used, then propagation properties can be acquired by controlling frequency difference, but the line width of the Brillouin gain is about 20 MHz making it difficult to improve measurement accuracy when frequency shifts are not sufficiently separated
Solution Approach 1:
The patent introduces a reference optical fiber as an intermediary that does not cause mode coupling. By measuring the Brillouin gain spectrum in this reference fiber first, the system obtains gain coefficients that serve as mediators to calculate the light intensity distribution in the measurement-target optical fiber, bypassing the need for frequency separation during the actual measurement process.
Solution Approach 2:
The patent changes the approach from directly measuring frequency-separated modes to measuring gain coefficients at multiple frequency points and using these to calculate mode-specific intensities. By varying the frequency difference between pump and probe light and measuring the resulting gain coefficients, the system can accurately determine light intensity distribution without requiring the modes themselves to be frequency-separated.
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 measurement of light intensity in each mode along the optical fiber, improving measurement accuracy and eliminating the need for difficult-to-measure absolute intensity values, thereby enhancing the capability to handle multiple propagation modes effectively.
Implementation Method 1
the intensity distribution of light in each propagation mode in a lengthwise direction of the measurement-target optical fiber is calculated based on the gain coefficient matrix and a difference in light intensity before and after Brillouin amplification of the probe light
Data Source
AI summary
A light intensity distribution measurement apparatus is presented that is capable of accurately measuring the intensity of light in each mode at each position of an optical fiber through which light is propagated in a plurality of modes. With the light intensity distribution measurement apparatus, a gain coefficient matrix is acquired in advance, which is constituted by Brillouin gain coefficients of propagation modes with predetermined optical frequency differences measured using a reference optical fiber that exhibits the same properties as a measurement-target optical fiber and that does not cause mode coupling, and the intensity distribution of light in each propagation mode in a lengthwise direction of the measurement-target optical fiber is calculated based on the gain coefficient matrix and a difference in light intensity before and after Brillouin amplification of the probe light emitted in a predetermined propagation mode at a predetermined optical frequency difference measured using the measurement-target optical fiber.