Fiber-based Interferometer for Eye Geometry Measurement
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Solution Overview
Problem
Current methods for measuring the axial length of the human eye, such as long-range time-domain low-coherence interferometry, are limited by slow measurement speed, low sensitivity, and limited range, making them inadequate for precise and accurate geometry measurement, especially in live patients prone to eye jitter.
Innovation Solution
An interferometric apparatus using a low coherence light source and a coherent light source with polarization maintaining optical fibers and fiber stretchers, which alternately vary the lengths of the reference and measurement arms to generate interference signals, allowing for precise detection of tissue-liquid interfaces and complete eye geometry measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If long-range time-domain low-coherence interferometry is used to measure eye geometry, then measurement precision is improved, but measurement speed becomes too slow to capture eye geometry changes faster than jitter occurs
Solution Approach 1:
The patent replaces the mechanical scanning method of traditional time-domain interferometry with an optical frequency-domain approach. By using frequency-domain analysis of interferometric signals, the system achieves high-speed measurement without mechanical movement, enabling capture of eye geometry changes faster than jitter occurs while maintaining precision.
Solution Approach 2:
The patent employs periodic modulation of the light source and synchronous detection to enable high-speed measurement. The periodic action allows the system to acquire multiple measurement points rapidly, achieving both high precision and high measurement speed by leveraging temporal frequency information.
2Measurement precision
If traditional interferometric methods are used to detect tissue-liquid interfaces, then measurement sensitivity is improved, but the measurement range becomes insufficient to cover all eye interfaces from cornea to retina
Solution Approach 1:
The patent extends the measurement range by utilizing the frequency domain dimension rather than only spatial scanning. By analyzing the frequency spectrum of interferometric signals, the system can resolve interfaces at different depths simultaneously, achieving both high sensitivity for tissue-liquid interfaces and sufficient range to cover the entire eye from cornea to retina.
3Measurement precision
If polarization maintaining optical fibers are used in the interferometer, then measurement sensitivity is improved, but device complexity increases due to additional polarization control components
Solution Approach 1:
The patent utilizes polarization maintaining optical fibers to preserve the polarization state of light, which is a key parameter for achieving high interference contrast and sensitivity. By carefully controlling and maintaining the polarization parameter throughout the optical path, the system achieves enhanced measurement precision while managing the complexity through systematic polarization management.
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 apparatus achieves high-speed, high-sensitivity measurements capable of detecting all interfaces of the eye, from the corneal surface to the retinal surface, overcoming the limitations of existing technologies and providing detailed geometry for improved ophthalmologic procedures.
Implementation Method 1
The first polarization controller polarizes the low coherence light with the first polarization, and the second polarization controller polarizes the coherent light with the second polarization
Implementation Method 2
The first and second fiber stretchers are driven so as to alternatingly vary the lengths of the first section of polarization maintaining optical fiber and the second section of polarization maintaining optical fiber, thereby causing interference signals with the low coherence light
Implementation Method 3
The second polarization controller polarizes the coherent light with the second polarization, which is substantially orthogonal to the first polarization
Implementation Method 4
The first and second fiber stretchers are driven so as to alternatingly vary the lengths of the first section of polarization maintaining optical fiber and the second section of polarization maintaining optical fiber, thereby causing interference signals with the low coherence light
Implementation Method 5
a first polarization selective light splitter and combiner configured to direct light of a first polarization through a second port to the layered object, and to direct light of a second polarization through a third port to a second mirror
Implementation Method 6
The first and second fiber stretchers are driven so as to alternatingly vary the lengths of the first section of polarization maintaining optical fiber and the second section of polarization maintaining optical fiber, thereby causing interference signals
Implementation Method 7
terminating proximate to a first mirror... terminating at a first port of a first polarization selective light splitter and combiner configured to direct light of a first polarization through a second port to the layered object, and to direct light of a second polarization through a third port to a second mirror
Implementation Method 8
Back reflected low coherence light of the first polarization is propagated from the polarization maintaining fiber coupler to a first detector
Data Source
AI summary
An apparatus for measuring a layered object comprising a low coherence light source, a coherent light source, and an interferometer including a reference arm and a measurement arm. The reference arm is comprised of a first section of polarization maintaining optical fiber engaged with a first fiber stretcher. The measurement arm is comprised of a second section of polarization maintaining optical fiber engaged with a second fiber stretcher. The first and second fiber stretchers are driven so as to alternatingly vary the lengths of the first section of polarization maintaining optical fiber and the second section of polarization maintaining optical fiber, thereby causing interference signals with the low coherence light when the length of the reference arm is equal to the length of the measurement arm including the distance from the second section of polarization maintaining optical fiber to any of the surfaces of the layers of the object.