Hybrid TDM WDM Optical Sensor Arrays
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Solution Overview
Problem
Conventional swept-wavelength Bragg grating interrogators are limited in the number of sensors that can be interrogated on a single fiber due to overlapping reflections from different arrays of optical elements, which restricts the spatial window range and wavelength resolution, hindering the accuracy and repeatability of characteristic wavelength measurements.
Innovation Solution
Implementing a method that introduces a pulse of light to interrogate sets of optical elements with different characteristic wavelengths, ensuring that the reflection time windows from each set do not overlap, achieved through time separation or the use of delay mechanisms like delay coils or loop-backs, allowing for close proximity of sensor arrays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If wavelength division multiplexing (WDM) is used to interrogate sensors on a single fiber, then the system can measure characteristic wavelengths of optical components, but the number of sensors that can be interrogated is limited by the optical bandwidth of the source
Solution Approach 1:
The patent combines WDM and TDM techniques into a hybrid system. Multiple sensors are grouped into sets, where each set uses WDM with different characteristic wavelengths, and multiple sets are separated in time using TDM. This merging allows more sensors to be interrogated on a single fiber by utilizing both wavelength and time domains simultaneously.
Solution Approach 2:
The patent transitions from using only the wavelength dimension (WDM) to adding the time dimension (TDM). By separating sensor sets in time while maintaining wavelength multiplexing within each set, the system increases the total number of sensors that can be accommodated on a single fiber beyond what WDM alone can achieve.
2Quantity of substance
If the optical bandwidth of the light source is increased to enable more sensors to be multiplexed using WDM, then more sensors can be interrogated, but the system complexity and cost increase
Solution Approach 1:
The patent segments the sensor array into multiple sets, where each set operates within a narrower wavelength bandwidth using WDM. By dividing the total sensor population into time-separated groups, the system reduces the optical bandwidth requirement for each interrogation cycle compared to interrogating all sensors simultaneously with WDM alone.
Solution Approach 2:
The patent employs periodic time-division multiplexing where different sensor sets are interrogated in sequential time slots. This periodic action allows the use of a narrower bandwidth light source that can be tuned across the required wavelength range over time, rather than requiring a broad-bandwidth source to cover all sensor wavelengths simultaneously.
3Quantity of substance
If swept-wavelength interferometry technique is used to TDM grating sensors, then time division multiplexing is achieved, but the spatial window range and wavelength resolution are limited
Solution Approach 1:
The patent merges WDM and TDM approaches to overcome the limitations of swept-wavelength interferometry. Within each time-separated set, WDM provides high wavelength resolution for measuring characteristic wavelengths, while TDM allows multiple such sets to be interrogated. This combination achieves both high resolution and increased sensor capacity.
4Area of stationary object
If multiple sets of optical elements are physically located in close proximity to one another, then the spatial density of sensor arrays increases, but reflections from different sets overlap at the receiver
Solution Approach 1:
The patent uses periodic time-division multiplexing where light pulses are sent at specific time intervals, and each sensor set is assigned a specific time slot for reflection. By synchronizing the interrogation timing with the physical proximity of sensor sets, the system maintains high spatial density while preventing reflection overlap through temporal separation.
Solution Approach 2:
The patent applies preliminary time separation by introducing delay mechanisms or timing offsets before reflections from different sensor sets reach the receiver. This preliminary action ensures that even though sensor sets are physically close, their reflections arrive at the receiver at different times, preventing overlap and preserving measurement information.
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 the simultaneous interrogation of multiple optical elements with improved accuracy and repeatability by avoiding overlapping reflections, thereby increasing the number of sensors that can be multiplexed on a single fiber and enhancing the spatial density of sensor arrays.
Implementation Method 1
introducing a pulse of light, by an optical source, into an optical waveguide to interrogate at least first and second sets of optical elements by performing a sweep of wavelengths
Implementation Method 2
a first time window over which light is reflected form the optical elements in the first set and reaches a receiver
Data Source
AI summary
Methods and apparatus for interrogating sets of optical elements having characteristic wavelengths spanning a sweep range while avoiding overlapping reflections from the different sets when performing a wavelength sweep are provided. One example method generally includes introducing a pulse of light, by an optical source, into an optical waveguide to interrogate at least first and second sets of optical elements, wherein the optical elements within each set have different characteristic wavelengths and wherein the first and second sets are separated in time such that a first time window over which light is reflected from the optical elements in the first set and reaches a receiver does not overlap with a second time window over which light is reflected from the optical elements in the second set and reaches the receiver; and processing the reflected light to determine one or more parameters corresponding to the optical elements.