Bragg Grating Interrogation with Switched Optical Delay Loops
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Solution Overview
Problem
Existing fibre optic sensor technologies using Bragg gratings face challenges in achieving precise, flexible, and compact spectral interrogation due to the need for long optical fibre lengths and fixed delay configurations, making them unsuitable for small-footprint applications.
Innovation Solution
A Bragg wavelength spectral interrogation device that uses a measurement optical fibre with successive Bragg gratings, a reflective optical fibre, and an optical switch to create a to-and-fro movement, allowing for adjustable delay between gratings through controlled return trips, reducing the required fibre length and enabling flexible adaptation to various applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If temporal separation by spatial distancing of fibre Bragg gratings is used, then the device is simple and does not require additional elements, but the fibre length becomes very long (at least 55 m for 15 gratings)
Solution Approach 1:
The patent transitions from spatial separation (1D linear arrangement) to temporal separation using optical delay lines. By introducing a time dimension for signal propagation, multiple Bragg gratings can be interrogated sequentially through time-multiplexing rather than requiring simultaneous spatial accommodation, thereby reducing the physical fibre length from 55m to a compact configuration.
Solution Approach 2:
The patent employs dynamic optical switching to control the timing and routing of light signals through the Bragg gratings. The optical switch dynamically configures the measurement path, enabling flexible time-multiplexed interrogation of multiple gratings without requiring fixed spatial separation, thus resolving the contradiction between device simplicity and compact size.
2Loss of time
If spectral delay with parallelized delays is used, then temporal separation is achieved, but the device complexity increases due to additional demultiplexing-multiplexing modules and parallel fibre paths
Solution Approach 1:
The patent extracts the delay function from complex parallelized spectral delay structures and implements it through a single optical delay line with time-multiplexed switching. By separating the delay function from the spectral processing, the system achieves temporal separation without requiring multiple parallel fibre paths and demultiplexing-multiplexing modules, thereby reducing device complexity while maintaining temporal separation capability.
Solution Approach 2:
The optical delay line serves multiple functions: it provides temporal separation for different Bragg gratings, acts as a signal routing element, and enables time-multiplexed interrogation. This multi-functional approach replaces the need for separate delay elements and parallel paths, reducing overall device complexity while achieving the required temporal separation.
3Loss of time
If spectral delay with serial delays is used, then temporal separation is achieved, but the fibre length increases due to extended optical paths
Solution Approach 1:
The patent merges the delay line with the measurement optical fibre path, using the same fibre infrastructure for both measurement and delay functions. By combining these functions into a single integrated optical path with dynamic switching, the system achieves temporal separation without extending the physical fibre length, as the delay is created through controlled signal routing rather than additional fibre length.
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
The device allows for precise and robust measurement of Bragg wavelength bands with minimal fibre length, enabling installation in smaller equipment and dynamic adaptation to different applications by adjusting the number of return trips.
Implementation Method 1
at least one measurement optical fibre comprising a series of successive Bragg gratings designed to reflect the light signal in different wavelength bands
Implementation Method 2
at least one optical switch designed to switch the passage of the light signal between said at least one optical source, said at least one measurement optical fibre, said at least one reflective optical fibre, and said at least one detector
Implementation Method 3
the light signal is guided to make a predetermined number of return trips in a line formed by a coupling between said measurement optical fibre and a corresponding reflective optical fibre, thus generating a predetermined delay between the successive Bragg gratings
Data Source
AI summary
A spectral interrogation device, including: an optical source for emitting a light signal, a measurement optical fibre comprising a series of successive Bragg gratings for reflecting the light signal in different wavelength bands, a reflective optical fibre comprising a total reflection element, a wavelength detector, and an optical switch for switching between a sequence of three operating modes. In a first mode, the light signal emitted by a given optical source is guided from the optical source to a corresponding measurement optical fibre. In a second mode, the light signal is guided to make a predetermined number of return trips in a line formed by a coupling between the measurement optical fibre and a corresponding reflective optical fibre, generating a predetermined delay between the successive gratings. In a third mode, the light signal is guided to a corresponding detector to successively measure the wavelength bands associated with the gratings.