Autofocus Microscopy Stage Adjustment via Optical Cross-Correlation
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Solution Overview
Problem
Existing automated microscopy techniques struggle to achieve accurate focus when samples are on substrates with inconsistent thickness, leading to off-focus images due to refractive index changes between the substrate and the liquid medium.
Innovation Solution
An autofocus microscope apparatus that uses an optical coupler, collimator, Dichroic mirror, photodiode detector, and microprocessor to scan light reflections at multiple focal points, cross-correlate intensity signals with a template, and adjust the stage position for optimal focus, even with substrates of varying thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If automated focus adjustment is implemented using reflection techniques, then productivity is improved, but measurement precision deteriorates due to substrate thickness inconsistency
Solution Approach 1:
The patent introduces an intermediary substance (liquid medium) between the objective lens and the substrate to fill the space above the sample. This liquid medium has a refractive index that compensates for the optical path differences caused by varying substrate thickness, thereby maintaining focus accuracy while enabling automated operation. The liquid acts as a mediator that optically couples the objective to the sample regardless of substrate thickness variations.
Solution Approach 2:
The system changes the optical parameters by introducing a liquid medium with specific refractive index properties. This parameter change (adding liquid with controlled refractive index) compensates for the optical path length variations caused by inconsistent substrate thickness, allowing the automated focus system to maintain measurement precision while achieving high productivity.
2Ease of operation
If reflection-based focus measurement is used, then ease of operation is improved, but measurement precision worsens due to refractive index changes
Solution Approach 1:
The liquid medium serves as an intermediary that creates a consistent optical environment between the objective lens and the substrate. By filling the space above the sample with this liquid, the system eliminates air-substrate interface reflections and refractive index variations that would otherwise interfere with focus detection, thereby maintaining measurement precision while enabling easy automated operation.
Solution Approach 2:
The introduction of liquid medium changes the optical parameters of the measurement system. The liquid's refractive index is selected to match or compensate for the substrate properties, creating a uniform optical path that improves focus detection accuracy while maintaining the simplicity of automated operation.
3Measurement precision
If focus adjustment compensates for substrate thickness variation, then measurement precision is improved, but device complexity increases
Solution Approach 1:
Rather than implementing complex mechanical focus adjustment mechanisms to compensate for substrate thickness variations, the patent uses a simple liquid medium as an intermediary. This liquid fills the space above the sample and optically compensates for thickness variations, achieving high measurement precision with minimal additional device complexity.
Solution Approach 2:
The patent replaces what would otherwise require a complex mechanical focus adjustment system with a simple liquid medium introduction. Instead of mechanically moving the objective or stage to compensate for substrate thickness variations, the liquid medium provides optical compensation, dramatically simplifying the device while maintaining measurement precision.
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
This solution enables precise and automatic focus adjustment, maintaining image clarity by accurately detecting peak reflections and compensating for changes in sample position, ensuring consistent focus across varying substrate thicknesses.
Implementation Method 1
converting a light signal that includes reflections off of the substrate at the plurality of focal points along the axis
Implementation Method 2
an optical coupler having a first port, second port and a third port; wherein a light signal in the optical coupler travels substantially only from the first port to the second port and from the second port to the third port
Implementation Method 3
an optical collimator for directing a light output from the second port of the optical coupler onto a sample through a Dichroic mirror and a microscope objective
Implementation Method 4
directing a light output from the second port of the optical coupler onto a sample through a Dichroic mirror
Implementation Method 5
a photodiode detector for converting a light signal that includes reflections off of the substrate at the plurality of focal points along the axis, into an intensity signal
Implementation Method 6
a scanning means for focusing the light at a plurality of focal points along an axis
Data Source
AI summary
An autofocus apparatus includes a light source; an optical coupler having a first port, second port and a third port; wherein the optic coupler couples to the light source at the first port; an optical collimator for directing a light output from the second port of the optical coupler onto a sample through a Dichroic mirror and a microscope objective, wherein the sample is placed on a substrate supported by an adjustable microscopy stage; a scanning device for focusing the light at a plurality of focal points along an axis; a photodiode detector for converting a reflected light signal into an intensity signal; a memory device for storing a signal template; and a microprocessor for detecting a peak in the intensity signal by cross-correlating the intensity signal with the signal template; wherein the microprocessor generates a command for moving the position of the adjustable microscopy stage along the axis.