Code-Modulated Optical Pulse for High-Resolution Sound Wave Detection
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Solution Overview
Problem
Existing optical fiber sound wave detection methods face challenges in achieving high sensitivity, accuracy, and resolution due to limitations in pulse width, energy, and the ability to detect rapidly changing strains caused by sound waves.
Innovation Solution
A distributed optical fiber sound wave detection device that uses an optical pulse emission unit to modulate pulses with a code sequence, dividing them into cells for improved resolution and energy, and a phase variation derivation unit to determine sound waves from Rayleigh scattered light, enabling high sensitivity and accuracy detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pulse width of the probe light is reduced to improve longitudinal resolution, then the resolution is improved, but the energy of optical pulses decreases and signal strength decreases
Solution Approach 1:
The optical pulse is segmented into multiple time slots using code modulation (e.g., pseudo-random binary sequences). Each time slot contains a portion of the coded pulse, allowing the total pulse energy to be distributed across multiple segments while maintaining high resolution through precise time slot assignment. This resolves the contradiction by dividing the pulse both in time and energy distribution.
Solution Approach 2:
The invention changes the temporal parameters of the optical pulse by applying code modulation, transforming a single wide pulse into a series of narrow time-slotted pulses. This parameter transformation allows the system to achieve high longitudinal resolution (narrow effective pulse width) while maintaining total energy through the accumulation of energy across multiple coded segments.
2Measurement precision
If the pulse width is reduced to detect high-frequency sound waves, then the detection capability is improved, but the signal strength of scattered light decreases
Solution Approach 1:
The probe light is divided into multiple time slots with narrow widths, enabling detection of high-frequency sound waves that occur within specific time windows. The code modulation ensures that even though each individual time slot has low energy, the cumulative signal strength across all time slots maintains reliable detection capability.
Solution Approach 2:
The invention employs periodic code modulation (e.g., repeating pseudo-random sequences) to structure the optical pulses. This periodic action allows the system to sample the Rayleigh scattered light at regular intervals, improving the detection of periodic high-frequency sound waves while maintaining signal strength through the repetitive structure that enables signal averaging.
3Measurement precision
If code modulation is applied to divide pulses into time slots, then resolution and energy utilization are improved, but device complexity increases
Solution Approach 1:
The invention replaces complex mechanical pulse division systems with optical code modulation. Instead of using mechanical switches or modulators to physically divide pulses into time slots, the system uses optical code modulation (e.g., phase or amplitude coding) to achieve time slot division electronically, significantly reducing mechanical complexity while maintaining high resolution.
Solution Approach 2:
The invention changes the modulation parameters of the optical pulse (phase, amplitude, or frequency) to encode time slot information. This parameter-based approach to pulse division avoids the need for complex mechanical or electronic switching systems, achieving time slot division through simple optical modulation that can be implemented with standard optical components.
4Length of stationary object
If the optical fiber length is increased to expand detection range, then the detection range is improved, but the ability to detect rapidly changing strains decreases
Solution Approach 1:
The long optical fiber is virtually segmented into multiple measurement sections along its length, with each section assigned to specific time slots. This virtual segmentation allows the system to maintain high strain detection accuracy in each local section while covering a long overall distance. The code modulation ensures that strain signals from different sections are temporally separated and can be accurately resolved.
Solution Approach 2:
The invention adds the time dimension to the spatial measurement along the optical fiber. By using code modulation to assign different time slots to different fiber sections, the system transforms a one-dimensional spatial measurement into a two-dimensional space-time measurement, enabling accurate strain detection throughout the entire length of the fiber while maintaining high temporal resolution for rapidly changing strains.
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 achieves high sensitivity and accuracy in detecting sound waves with high resolution along the optical fiber, capable of detecting rapidly changing strains and high-frequency sound waves, even with long optical fibers.
Implementation Method 1
The technique using an OTDR (Optical Time Domain Reflectometer) is known as an optical fiber sensing technique by which Rayleigh backscattered light (referred to hereinbelow simply as 'Rayleigh scattered light') produced by injection of probe light into an optical fiber is used to measure line characteristics of the optical fibers
Implementation Method 2
Where a pressure is applied to the optical fiber and strains are produced inside the optical bier, there is a shift in frequency of the Rayleigh scattered light produced in the region where the strains have appeared
Data Source
AI summary
A distributed optical fiber sound wave detection device is provided with an optical pulse emission unit that causes an optical pulse to be incident into the optical fiber, and a Rayleigh scattered light reception unit that receives Rayleigh scattered light produced inside the optical fiber. The optical pulse emission unit outputs the optical pulse that is modulated using a code sequence which has a predetermined length and by which the optical pulse is divided into a plurality of cells. The Rayleigh scattered light reception unit includes a phase variation derivation unit that performs demodulation corresponding to the modulation in the optical pulse emission unit on the Rayleigh scattered light and determines a phase variation thereof from the demodulated Rayleigh scattered light, and a sound wave detection unit that determines a sound wave that has struck the optical fiber from the phase variation determined by the phase variation derivation unit.