Time-Resolved Photodetection for 3D Refractive Index Mapping
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Solution Overview
Problem
Existing refractive index distribution measuring apparatuses can only obtain two-dimensional information parallel to the light incident surface and fail to provide three-dimensional refractive index distribution data.
Innovation Solution
A photodetection system utilizing a light source that emits pulsed laser light and a photodetection unit with a two-dimensional array of photoelectric conversion units, synchronized by a timing control unit, to detect scattered light and estimate refractive index changes based on light speed variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional refractive index distribution measuring apparatus is used, then two-dimensional refractive index distribution parallel to the light incident surface can be obtained, but three-dimensional refractive index distribution including the direction perpendicular to the light incident surface cannot be obtained
Solution Approach 1:
The patent transitions from two-dimensional measurement (parallel to incident surface) to three-dimensional measurement by introducing time as a fourth dimension. By measuring light arrival times at multiple positions and combining spatial coordinates (x, y) with temporal information (t), the system reconstructs three-dimensional refractive index distribution including the depth direction (z-axis) perpendicular to the incident surface.
Solution Approach 2:
The patent changes the measurement parameter from only spatial distribution to spatio-temporal distribution. By measuring not just the position but also the arrival time of scattered light photons, the system obtains additional information that enables three-dimensional reconstruction of refractive index distribution through parameter expansion.
2Measurement precision
If pulsed laser light and time-resolved detection are used, then three-dimensional refractive index distribution can be obtained, but device complexity increases
Solution Approach 1:
The patent employs periodic pulsed laser illumination to generate repeated light pulses that penetrate the measurement object. By synchronizing the pulsed light emission with the photodetector's time-resolved detection window, the system achieves time-of-flight measurements without requiring continuous complex control mechanisms.
Solution Approach 2:
The system utilizes the natural time-of-flight characteristics of scattered light combined with time-correlated single photon counting (TCSPC) methodology. The measurement process leverages the inherent temporal information carried by photons, allowing the system to self-determine depth information through statistical accumulation of arrival times without additional active control elements.
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 the measurement of accurate three-dimensional refractive index distribution by correcting for apparent speed variations, providing precise refractive index data across different directions.
Implementation Method 1
a photodetection unit including a plurality of photoelectric conversion units arranged in a two-dimensional plane
Implementation Method 2
a light source configured to emit pulsed laser light
Implementation Method 3
change of light speed of the scattered light
Data Source
AI summary
A system includes a light source configured to emit pulsed laser light, and a photodetection unit including a plurality of photoelectric conversion units arranged in a two-dimensional plane, wherein an emission timing of the light source and a detection timing of the photodetection unit are controlled by a timing control unit, wherein the photodetection unit detects scattered light on the two-dimensional plane, of the pulsed laser light emitted from the light source and entering an object, and wherein change of a refractive index of the object is estimated from change of light speed of the scattered light.