Multi-pulse Interferometric Sensor Interrogation via Phase Modulation
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Solution Overview
Problem
Interferometric sensors face challenges in increasing the allowable interrogation pulse duty-cycle and improving signal-to-noise ratios due to the need to separate reflections in time, which results in wasted pulse duty-cycle from waiting for multiple reflections to fade out, and crosstalk between sensors.
Innovation Solution
The method involves generating a sequence of multiple interrogation pulses within each TDM repetition period, with phase modulation to create different optical frequencies in each time-slot, allowing interference pulses to interfere and form a sub-carrier signal, enabling the calculation of sensor phase without waiting for decay pulses to fade out, thus enhancing the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pulse duty-cycle is increased to improve interrogation efficiency, then productivity improves, but crosstalk between sensors increases and measurement precision deteriorates
Solution Approach 1:
The patent segments the single long pulse into multiple shorter sub-pulses within each TDM repetition period. This segmentation allows the system to maintain a high overall duty-cycle while keeping individual sub-pulse durations short enough to prevent decay pulse overlap, thereby resolving the contradiction between productivity and measurement precision
Solution Approach 2:
The patent employs periodic modulation of the optical frequency across the multiple sub-pulses using phase modulation. This periodic frequency variation creates distinct spectral signatures for each sub-pulse, enabling the system to process multiple pulses simultaneously without crosstalk, thus maintaining both high productivity and measurement precision
2Measurement precision
If the system waits for multiple reflections to fade out before next interrogation, then measurement precision improves, but loss of time increases
Solution Approach 1:
The patent eliminates idle waiting time by continuously transmitting multiple sub-pulses in sequence without gaps. Each sub-pulse is processed concurrently through frequency differentiation, allowing the system to maintain continuous useful action rather than pausing for decay pulses to fade, thus resolving the time-loss versus precision contradiction
Solution Approach 2:
The patent introduces optical frequency as an intermediary parameter to differentiate between simultaneous sub-pulses. By modulating the frequency of each sub-pulse and using frequency-selective detection, the system can distinguish and process overlapping reflections without waiting for them to fade, eliminating the time loss while maintaining signal clarity
3Productivity
If multiple reflections are allowed to overlap, then productivity improves, but object-generated harmful factors increase
Solution Approach 1:
The patent changes the optical frequency parameter of each sub-pulse through phase modulation, creating distinct frequency channels for each pulse. This parameter transformation allows multiple reflections to overlap in time without causing crosstalk, as the detection system can separate them by frequency, thus enabling high productivity while eliminating harmful interference
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 increases the allowable interrogation pulse duty-cycle and improves the signal-to-noise ratio by allowing continuous interrogation without waiting for multiple reflections to fade, reducing crosstalk, and optimizing the number of interrogation pulses for efficient sensor phase calculation.
Implementation Method 1
A phase modulator modulates the phase of the pulses such that the optical frequencies produced in different transmission time-slots are different
Implementation Method 2
The portion of the m'th interrogation pulse propagating the longest path of a sensor interferometer and the portion of the (m+1)'th interrogation pulse propagating the shortest path of the same interferometer will interfere, forming interference pulse number m
Data Source
AI summary
A method for interrogating time-multiplexed interferometric sensors using multiple interrogation pulses so as to increases the allowable interrogation pulse duty-cycle and improve the signal-to-noise ratio. In each TDM repetition period a sequence of multiple interrogation pulses are generated. The pulses in the sequence are separated by a time that is equal to the sensor imbalance. The phase from pulse to pulse in each TDM time-slot is modulated at a different, linear rate such that the pulse in time-slot m will have an optical frequency that is shifted by mΔν, where Δν is the sub-carrier frequency. Because multiple reflections do not need to fade out the inventive method can enhance the signal-to-noise ratio of interferometric sensors such as inline Fabry-Perot sensors.