Reflective Fiber-Optic Hydrophone With Optical Amplification for Shockwaves
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Solution Overview
Problem
Existing fiber-optic hydrophones face challenges in achieving high bandwidth and sensitivity while maintaining a small probe size, particularly when measuring high-pressure shockwaves in fluids, due to issues such as thermal damage and low signal-to-noise ratio with low-power signals.
Innovation Solution
A reflective fiber-optic hydrophone design utilizing an optical amplifier to amplify the optical signal, combined with a single-mode fiber and a photodetector, to achieve bandwidth above 1 GHz and sensitivity above 0.01 A/W, while using a wavelength filter to prevent interference and a balanced photodiode for noise subtraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If single-mode fiber is used to reduce probe size and improve bandwidth, then bandwidth increases above 1 GHz, but probe light intensity becomes high causing thermal damage and boiling
Solution Approach 1:
The patent changes the parameter of light power from high (in single-mode) to low (in multi-mode) while compensating through interferometric measurement technique. By using the interference of light waves reflected from different interfaces, the system achieves high sensitivity with low light power, avoiding thermal damage while maintaining fast response.
Solution Approach 2:
The patent replaces direct intensity measurement with interferometric measurement. Instead of measuring light intensity directly (which requires high power), it measures the interference pattern caused by pressure-induced refractive index changes, enabling low-power operation with high sensitivity.
2Object-affected harmful factors
If low probe-light power is used to avoid thermal damage, then thermal damage is reduced, but signal to noise ratio decreases
Solution Approach 1:
The patent substitutes direct intensity measurement with interferometric measurement. The interferometric technique amplifies the pressure signal by converting small refractive index changes into measurable intensity variations through constructive and destructive interference, achieving high signal-to-noise ratio with low light power.
Solution Approach 2:
The patent uses periodic modulation of the probe light (e.g., through acoustic oscillation or modulated laser source) to distinguish the signal from noise. By detecting signals at the known modulation frequency, the system achieves high signal-to-noise ratio even with low light power levels.
3Measurement precision
If multimode fiber is used to provide sufficient optical power, then sensitivity improves, but probe size increases significantly
Solution Approach 1:
The patent replaces intensity-based measurement with interferometric measurement, enabling the use of low-power single-mode fiber instead of high-power multimode fiber. This substitution allows achieving high sensitivity with a compact probe size determined by the single-mode fiber core diameter.
4Device complexity
If flat perpendicularly-cleaved fiber tip is used, then the structure is simple, but sensitivity is low
Solution Approach 1:
The patent replaces the need for complex tip structures (shaped tips, coatings, or attachments) with an interferometric measurement principle. The simple perpendicularly-cleaved fiber tip suffices because the interference effect amplifies the pressure signal, achieving high sensitivity without modifying the tip geometry.
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 design achieves a fast response and high sensitivity, effectively measuring high-pressure shockwaves with minimal disruption to the surrounding fluid, suitable for industrial and medical applications.
Implementation Method 1
an optical amplifier to amplify the optical signal
Implementation Method 2
by measuring the reflected light power with a photodetector
Implementation Method 3
changes of the refraction index of the fluid with the oncoming pressure waves cause the modulation of reflectivity at the fiber-fluid interface
Data Source
Figure 1~3
Figure 4
AI summary
The present invention belongs to the field of measuring mechanical vibrations and ultrasonic pressure waves such as those produced by laser induced breakdown in liquids using optical means. The invention is a reflective fiber-optic probe hydrophone with improved bandwidth and sensitivity, the hydrophone comprising at least: - A source of probe light coupled into a first single-mode fiber, - A first fiber-optic element for transmitting at least a part of the incoming probe-light propagating in the forward direction from the first single-mode fiber into a second single-mode fiber and for transmitting at least a part of the reflected light propagating in the backward direction into a third single-mode fiber, - A single-mode fiber-optic probe, having a perpendicularly-cleaved or polished single-mode fiber tip, so that the surface of the fiber tip is perpendicular to the probe-light propagation direction, - A source of pump light coupled into an optical fiber for pumping an optical amplifier, - A second fiber-optic element for combining the reflected probe light from the third single-mode fiber and the pump light into a fourth optical fiber, - The single-mode fiber-optic amplifier, comprising a doped single-mode fiber with appropriate length to allow for sufficient absorption of the pump light and sufficient amplification of the probe light, and - A photodiode to measure the amplified probe light.