Variable Focal Length Lens Stabilization via Reference Subsystem
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Solution Overview
Problem
High-speed variable focal length (VFL) lenses in precision metrology systems face challenges due to variations in temperature affecting their resonant characteristics, leading to changes in optical power and modulation frequency, which impact system performance and accuracy.
Innovation Solution
A VFL lens system incorporating a VFL lens, a VFL lens controller, a camera, an objective lens, and a focus state reference subsystem, where the focus state reference subsystem includes a focus state reference object with a contrast pattern and known reference region image locations, allowing for the determination of the best-focus image and corresponding optical power or focus position, thereby stabilizing the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a high-speed variable focal length lens is used to achieve fast focusing, then the focusing speed is improved, but temperature variations cause changes in optical power and modulation frequency, deteriorating measurement precision
Solution Approach 1:
The patent implements a feedback mechanism where the actual focus position is continuously monitored and compared to the target focus position. The difference (error signal) is used to adjust the drive signal to the VFL lens, correcting for temperature-induced drift and ensuring the lens achieves and maintains the correct focus position despite environmental variations.
Solution Approach 2:
The patent dynamically adjusts the drive signal parameters (frequency, amplitude, or phase) to the VFL lens based on the detected focus error. By changing these electrical parameters in response to temperature variations, the system compensates for optical power drift and maintains measurement precision while preserving high focusing speed.
2Stability of the object's composition
If the drive signal to the VFL lens is adjusted to compensate for temperature variations, then focus stability is improved, but system complexity increases due to the need for continuous monitoring and adjustment
Solution Approach 1:
The system incorporates a self-service mechanism where the imaging system itself provides the feedback signal needed for correction. The focus detection functionality is integrated into the normal operation of the system, allowing it to automatically monitor and correct its own focus state without requiring external intervention or complex separate monitoring systems.
Solution Approach 2:
The patent makes the imaging system multi-functional by having it simultaneously perform both primary imaging and focus state monitoring. The same optical path and detector are used for both capturing the specimen image and detecting the focus position, eliminating the need for separate focus sensing hardware and reducing overall system complexity.
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 effectively stabilizes the focus state of the VFL lens, maintaining accuracy and performance by continuously adjusting the drive signal to match the calibrated focus characteristic values, even in the presence of temperature-induced variations.
Implementation Method 1
A tunable acoustic gradient index lenses and related controllable signal generators are available, for example, from TAG Optics, Inc., of Princeton, New Jersey. The Model TL2.B.xxx series lenses, for example, are capable of modulation up to approximately 600 kHz.
Implementation Method 2
a tunable acoustic gradient ('TAG') lens that creates a lensing effect using sound waves in a fluid medium. The sound waves may be created by application of an electrical field at a resonant frequency to a piezoelectric tube surrounding the fluid medium to create a time-varying density and index of refraction profile in the lens's fluid
Implementation Method 3
The sound waves may be created by application of an electrical field at a resonant frequency to a piezoelectric tube surrounding the fluid medium
Data Source
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AI summary
A focus state reference subsystem (1086) comprising a focus state (FS) reference object (1088) is provided for use in a variable focal length (VFL) lens system comprising a VFL lens (370), a controller (380) that modulates its optical power, and a camera (360) located along an optical path including an objective lens (350) and the VFL lens. Reference object image light from the FS reference object is transmitted along a portion of the optical path through the VFL lens to the camera. Respective FS reference regions (FSRRs) of the FS reference object include a contrast pattern fixed at respective focus positions. A camera image that includes a best-focus image of a particular FSRR defines a best-focus reference state associated with that FSRR, wherein that best-focus reference state comprises a VFL optical power and/or effective focus position of the VFL lens system through the objective lens.