Tapped-Laser Monitoring for Mode-Hopping Detection in Photoplethysmography
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Solution Overview
Problem
Existing photoplethysmographic devices using LEDs face challenges with spectral broadness and inaccuracies due to tissue pigments, while laser-based systems struggle with mode hopping and failure detection, leading to signal noise and inaccurate measurements.
Innovation Solution
Incorporating a tapped laser with a secondary optical path for monitoring light intensity and a photodetector to detect laser conditions, allowing for real-time adjustments such as altering drive current or temperature to stabilize the laser output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser is used as the light source in a photoplethysmographic device, then the spectral resolution and measurement accuracy are improved, but the device becomes vulnerable to mode hopping and failure detection difficulties
Solution Approach 1:
The patent implements preliminary monitoring by tapping a portion of the laser light before it enters the tissue and directing it through a separate optical path to a photodetector. This allows the system to proactively detect laser mode hopping and failures by analyzing the tapped light signal, enabling corrective action before measurement accuracy degrades.
Solution Approach 2:
The patent introduces an intermediary optical path that separates the monitoring function from the measurement function. The tapped light travels through a distinct optical path with its own photodetector, allowing independent monitoring of laser stability without interfering with the primary photoplethysmographic measurement path.
2Ease of manufacture
If LED light sources are used in photoplethysmographic devices, then the device complexity is reduced and ease of manufacture is improved, but the spectral broadness causes measurement inaccuracies due to tissue pigments
Solution Approach 1:
The patent changes the spectral parameter of the light source by using lasers with narrow spectral linewidths instead of broadband LEDs. This parameter change eliminates the spectral broadness issue that causes measurement inaccuracies with LEDs, providing precise wavelength control for accurate photoplethysmographic measurements.
3Adaptability or versatility
If the optical path is extended to probe thicker tissue, then the versatility and adaptability are improved, but the received light level decreases making measurements difficult or impossible
Solution Approach 1:
The patent performs preliminary monitoring of laser output through the tapped optical path before light enters the tissue. This allows the system to detect and compensate for any reduction in light intensity or mode hopping that would otherwise make thick tissue measurements impossible, maintaining versatility across different tissue thicknesses.
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
Enables accurate and stable photoplethysmographic measurements by detecting laser failures or mode hopping, ensuring consistent signal quality and reducing measurement errors.
Implementation Method 1
a photodetector coupled to the monitor and positioned to receive light tapped from the tapped laser prior to the point where the light exits the sensor; the photodetector generating an electrical signal indicative of the intensity of the amplitude of the light tapped from the tapped laser
Implementation Method 2
the emitters including at least one laser and at least one of the at least one lasers is a tapped laser configured to emit light through a primary optical path
Data Source
Figure 1~2
AI summary
A photoplethysmographic device includes a photoplethysmographic monitor, two or more emitters coupled to and controlled by the monitor, the emitters including at least one laser and at least one of the at least one lasers is a tapped laser configured to emit light through a primary optical path from the emitter to a sensor, and a photodetector coupled to the monitor and positioned to receive light tapped from the tapped laser prior to the point where the light exits the sensor, the photodetector generating an electrical signal indicative of the intensity of the amplitude of the light tapped from the tapped laser. The monitor processing the electrical signal to determine the condition of the tapped laser, whereby the monitor determines if the tapped laser is damaged and/or if one or more operating conditions of the tapped laser need to be altered.