Multi Mode Fiber Perturber for Gas Sensing Noise Reduction
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Solution Overview
Problem
Single mode mid IR fibers experience excessive losses due to their narrow core diameters, making them inefficient for gas sensing applications, while transmitting single mode laser light through multimode fibers results in optical interference noise due to multiple spatial modes supported by the fiber.
Innovation Solution
A system using a multimode fiber with a randomizer to cause spatial oscillations, followed by signal averaging to recover the single spatial mode properties of the laser, preventing optical interference noise and allowing high sensitivity gas sensing with lower transmission losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If single mode fiber is used to preserve spectral properties of laser, then measurement precision is improved, but transmission loss increases and ease of operation deteriorates
Solution Approach 1:
The system segments the optical transmission path into two functional parts: a single mode section for laser coupling and spectral preservation, and a multi mode section for low-loss transmission. The single mode fiber is used only where necessary for precise laser coupling, while the majority of the transmission path uses multi mode fiber with larger core diameter to minimize transmission losses.
Solution Approach 2:
A mode adapter or transition section acts as an intermediary between the single mode laser source and the multi mode fiber. This transition component enables efficient coupling of single mode laser light into the multi mode fiber while maintaining the spectral properties of the laser, bridging the gap between the two fiber types.
2Loss of energy
If multi mode fiber is used to reduce transmission loss, then loss of energy is reduced, but optical interference noise increases due to multiple spatial modes
Solution Approach 1:
A mechanical vibration element is introduced to physically vibrate the multi mode fiber during operation. This vibration causes dynamic changes in the fiber's refractive index and physical path lengths, which randomizes the propagation of different spatial modes. By averaging over many vibration cycles, the interference patterns from multiple modes are smoothed out, reducing optical interference noise while maintaining the low transmission loss benefits of multi mode fiber.
3Ease of operation
If multi mode fiber is used to improve ease of operation with larger core diameter, then ease of operation is improved, but optical interference noise is generated
Solution Approach 1:
The mechanical vibration element continuously perturbs the multi mode fiber, causing the spatial modes to dynamically shift and randomize. This vibration-based mode randomization technique allows the system to take advantage of the large core diameter and ease of coupling inherent in multi mode fiber, while simultaneously suppressing the optical interference noise that would otherwise result from multiple spatial modes.
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 the use of multimode fibers in sensitive gas sensing applications, reducing costs and increasing robustness by minimizing interference noise and transmission losses, facilitating multiple point remote detection in hostile or inaccessible locations.
Implementation Method 1
the randomizer may be a perturber that is operable to cause a physical perturbation along the fiber... Rapid spatial oscillation of the multimode fiber randomizes the spatial modes that the fiber supports
Implementation Method 2
The chirped light is generated by applying a one or a series of substantially step function electrical pulses to the semiconductor diode laser to cause the laser to output one or more pulses, each having a continuous wavelength chirp
Implementation Method 3
a detector for detecting light that has passed through the target area
Data Source
AI summary
An optical arrangement comprising a multi-mode fiber (16) for carrying single mode laser light (12); a randomizer (18) for randomizing spatial modes supported by the fiber and means for averaging, out the randomized spatial modes to recover the single spatial mode.