Movable Focus OCT Distance Measurement with Synchronized Reference Arm
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Solution Overview
Problem
Existing optical coherence tomography (OCT) methods face challenges in accurately measuring distances, particularly for objects with complex topographies or steep steps, due to limitations in the measuring range of the sensor compared to the height variations of the object.
Innovation Solution
A distance measuring device using a beam splitter and a focusing optics system with a movable focal point, coupled with a reference arm having a folded beam path, allows for precise distance measurement by maintaining a constant numerical aperture and compensating for optical path length changes, enabling accurate measurements on objects with pronounced topographies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a conventional OCT sensor with fixed focal point is used, then the measurement system is simple, but the measuring range is limited and cannot handle objects with height variations exceeding the sensor's measuring range
Solution Approach 1:
The patent implements a dynamically adjustable focal point system where the focal point can be moved along the optical axis to track the surface topography of the object. This dynamic adjustment allows the measurement system to adapt to height variations in the object, extending the effective measuring range beyond what a fixed focal point system could achieve.
Solution Approach 2:
The patent employs a folded beam path configuration where reference arms are nested within the optical system. Multiple reference arms with different optical path lengths are integrated into a compact structure, allowing the system to maintain a constant average optical path difference while accommodating the extended measuring range required for objects with significant height variations.
2Length of moving object
If the focal point is moved to track surface topography, then the measuring range increases, but the optical path length in the object arm changes requiring compensation
Solution Approach 1:
The patent implements a feedback mechanism where the position of the movable optical element is tracked, and this information is used to adjust the reference arm configuration. The system continuously monitors and compensates for changes in optical path length caused by focal point movement, maintaining measurement precision across the extended measuring range.
Solution Approach 2:
The patent uses the folded beam path configuration to create counterbalancing optical paths. By arranging reference arms with complementary optical path lengths, the system compensates for path length changes in the object arm caused by focal point movement, effectively canceling out the measurement errors that would otherwise occur.
3Adaptability or versatility
If a movable optical element is used to shift the focal point, then the focus can be adapted to surface topography, but the numerical aperture changes during movement
Solution Approach 1:
The patent carefully selects and coordinates multiple optical parameters including focal lengths of lens combinations, distances between optical elements, and folding numbers of reference arms. These parameters are adjusted in a coordinated manner to achieve focal point movement while maintaining a substantially constant numerical aperture, ensuring measurement consistency across different focal positions.
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 solution provides reliable and precise distance measurements for objects with complex topographies by maintaining measurement precision and range, even for objects with significant height variations, through the use of a movable focal point and synchronized optical path length tracking in the reference arm.
Implementation Method 1
a beam splitter (8) for splitting broadband coherent light emitted by a light source (3) in measuring light which is guided through an object arm (11) to the object to be measured (2) and in reference light being guided to a reference arm (12)
Implementation Method 2
the distance to the object to be measured or the measuring distance may be determined by an interference between the reference light which has traveled the reference distance of the reference arm and the measuring light reflected back by the object to be measured
Implementation Method 3
The focusing optics comprises a movable optical element and is configured such that a movement of the movable optical element along the optical axis causes a movement of the focus of the focusing optics along the optical axis
Data Source
AI summary
A device for measuring a distance to an object comprises a beam splitter for splitting broadband coherent light emitted by a light source in measuring light which is guided through an object arm to the object to be measured and in reference light which is guided to a reference arm. The object arm includes a focusing optics with a focus movable along an optical axis of the object arm. The focusing optics comprises a movable optical element and is configured such that a movement of the movable optical element along the optical axis causes a higher movement of the focus of the focusing optics along the optical axis. The movable optical element of the focusing optics is coupled to the reference arm such that the optical path length of the reference arm can be tracked synchronously with and dependent on the movement of the focus of the focusing optics.