All-Fiber Parametric Emitter for Deep Tissue Water Imaging
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Solution Overview
Problem
Existing photoacoustic imaging techniques for visualizing water content in deep tissue face challenges due to limited penetration depth, high cost, and susceptibility to environmental disturbances, particularly at wavelengths around 1000 nm and 1900 nm, where water absorption is insufficient for effective imaging, and existing systems are bulky and expensive.
Innovation Solution
A hybrid amplification scheme using a parametric gain in highly-nonlinear fiber and a thulium-doped fiber to generate high-power laser pulses at 1930 nm, providing improved pulse energy and wavelength tunability, enabling efficient water imaging with a novel all-fiber optical parametrically-oscillating emitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If OPO laser operating at 1000 nm is used for photoacoustic imaging, then imaging capability is achieved, but pulse energy requirement is high (milli-joule level) causing photodamage and system is bulky and expensive
Solution Approach 1:
The patent changes the operating wavelength parameter from 1000 nm to 1930 nm, where water has much stronger absorption (117.6 cm−1). This parameter change allows the system to achieve the same imaging capability with much lower pulse energy (micro-joule level), eliminating photodamage while maintaining water imaging capability
Solution Approach 2:
The patent replaces the expensive, bulky free-space OPO system with a compact, fiber-based laser system. The fiber laser architecture is significantly smaller, more robust, and less sensitive to environmental disturbances, making it suitable for clinical and on-site applications
2Measurement precision
If OPO laser operating at 1000 nm is used for photoacoustic imaging, then imaging capability is achieved, but system is bulky and sensitive to environmental disturbance
Solution Approach 1:
The patent replaces the mechanical free-space optical system with an all-fiber system. The fiber-based architecture eliminates the need for free-space optical alignment, making the system compact, robust, and insensitive to environmental disturbances such as vibrations and temperature changes
Solution Approach 2:
The patent uses thulium-doped fiber as the gain medium, combining the advantages of fiber optics (compactness, robustness) with rare-earth doping (high efficiency, wavelength tunability). This composite approach creates a system that is both compact and highly effective for water imaging
3Measurement precision
If laser wavelength is tuned to 1930 nm for water imaging, then water absorption is maximized (117.6 cm−1), but suitable laser sources are limited
Solution Approach 1:
The patent employs wavelength conversion through difference frequency generation in a nonlinear crystal, converting from readily available pump wavelengths to the target 1930 nm wavelength. This approach makes the 1930 nm wavelength accessible using standard laser components
Solution Approach 2:
The patent uses a nonlinear optical crystal as an intermediary to convert pump laser radiation into the desired 1930 nm wavelength. This intermediary component enables wavelength conversion, making the target wavelength accessible while maintaining system versatility
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 system achieves micron-level spatial resolution, fine signal-to-noise ratio, and suppressed artifact signals, allowing for deep tissue water imaging with enhanced penetration depth and improved contrast, suitable for biological research and disease diagnosis.
Implementation Method 1
Thulium-doped fiber amplifiers (TDFAs) pumped by an Er/Yb-doped fiber laser provide over a 100 nm wavelength range around 1900 nm
Implementation Method 2
Via molecular overtone transitions and combinational band absorptions, the vibration-based photoacoustic (PA) signal can be generated for imaging the specific chemical bond-rich tissues
Implementation Method 3
Water has significantly stronger absorption in multiple absorption peaks located at 975 nm, 1160 nm, 1450 nm, and 1930 nm. Among these, the absorption coefficient of water at 1930 nm is the strongest
Data Source
AI summary
An optical-resolution photoacoustic microscopy (OR-PAM) system for visualizing water content deep in biological tissue uses an all-fiber 1930-nm hybrid optical parametrically-oscillating emitter. The emitter includes a tunable laser source whose output is amplified by a first erbium-doped fiber amplifier (EDFA). The output of the first amplifier is modulated with a Mach-Zehnder amplitude modulator that receives an RF signal with a nanosecond pulse width and a multiple kilohertz repetition rate. A second EDFA further amplifies the signal and passes it to a fiber circulator that in turn delivers it to a 1950/1550 mm fiber wavelength-division-multiplexing coupler WDM. The coupler introduces the signal to a cavity that includes a spool of highly nonlinear fiber and a Thulium-doped fiber amplifier TDFA. From the TDFA the signal reaches a 50/50 fiber coupler that sends part to a second output TDFA and guides part back to the cavity through a port of the WDM.