Scattered-Light Fiber Power Sensing for LP01 and LP11 Mode Detection
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Solution Overview
Problem
Existing sensors for high-power laser fiber beam diagnostics require cutting and splicing, which is inconvenient and impractical due to power limitations and potential damage, and fail to directly measure the types and relative intensities of optical modes propagating within the fiber.
Innovation Solution
A scattered light detector using a photodiode array with semi-circular photodiodes arranged on a substrate, allowing the optical fiber to pass through a notch, enabling the measurement of forward and reverse propagating power and mode structure without cutting or splicing, utilizing Mie scattering to sample the laser light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional tap-couplers are used to measure light in optical fiber, then optical power can be measured, but the fiber must be cut and spliced, and information about optical modes is lost
Solution Approach 1:
The patent uses Mie scattering as an intermediary mechanism to extract light from the fiber for measurement without physical interruption. The scattering effect allows a portion of the propagating light to be diverted to detection elements while the main beam continues uninterrupted, eliminating the need for cut-and-splice tap-couplers and preserving both ease of operation and mode information
Solution Approach 2:
The patent replaces the mechanical cutting and splicing process with an optical phenomenon-based measurement system. Instead of physically modifying the fiber to insert couplers, the system uses Mie scattering to optically sample the light, substituting a mechanical intervention with a non-intrusive optical field interaction
2Power
If high optical power is used in the fiber, then more power can be transmitted, but traditional sensors may be damaged
Solution Approach 1:
The patent extracts a small portion of the high-power beam through Mie scattering to create a separate, lower-power sampling beam for detection. This extraction allows the main high-power transmission to continue while the scattered light, which is sufficient for measurement but safe for sensors, is directed to detection elements
Solution Approach 2:
The patent changes the power parameter of the measurement beam by using scattering to reduce the intensity from the original high-power level to a sensor-safe level. The scattering process naturally provides power attenuation, transforming the high-power input into a low-power measurement signal that preserves reliability while maintaining high transmission capability
3Difficulty of detecting and measuring
If coupling waveguides are spliced to sample light, then light can be directed for analysis, but reflections occur and mode instabilities are introduced
Solution Approach 1:
The patent uses Mie scattering as an intermediary that couples light from the fiber to detection elements without requiring direct physical coupling of waveguides. The scattering process acts as a buffer that transfers energy without the harsh interfaces of spliced connections, eliminating reflections and mode instabilities while maintaining sampling capability
Solution Approach 2:
The patent creates an optical copy of the propagating light through scattering rather than physically coupling the original beam. The scattered light serves as a replica that contains the same mode information but can be measured without disturbing the original beam's stability, avoiding the problems of direct coupling
4Measurement precision
If light is measured at the end of the fiber or coupled to another waveguide, then optical power can be measured, but information about propagating modes is lost
Solution Approach 1:
The patent performs preliminary sampling of the optical modes through Mie scattering while the light is still propagating within the fiber. By measuring the scattered light in-situ, the system captures mode information before any potential loss or transformation occurs, preserving complete modal characteristics for analysis
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
Enables simultaneous measurement of forward and reverse propagating power and mode sensing in optical fibers, preventing overdriving and potential damage, while allowing for real-time monitoring of LP01 and LP11 modes without disturbing the optical beam.
Implementation Method 1
Commercial fiber exhibits Mie scattering when excited by a fixed wavelength laser
Implementation Method 2
a first photodiode array comprising one or more photodiodes arranged in a planar, semicircular pattern on a substrate
Data Source
AI summary
A scattered light detector comprises a first photodiode array comprising one or more photodiodes arranged in a planar, semicircular pattern on a substrate, each of the one or more photodiodes having an outer edge and an inner edge; and a notch perpendicular to the substrate and located adjacent the inner edge of each of the one or more diodes, and equidistant from the outer edges of each of the one or more photodiodes, the notch configured to accept an optical fiber oriented perpendicular to the plane of the one or more photodiodes. When there are two or more photodiodes, the photodiodes may be divided into two or more segments extending outwardly from the notch. Each of the photodiodes shares a common electrical ground. The planes of the one or more photodiodes of the first and second photodiode arrays are oriented parallel to each other and spaced a predetermined distance apart.