Hemispherical Mirror Numerical Aperture Measurement
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Solution Overview
Problem
Existing optical measurement systems struggle to accurately measure the numerical aperture of an objective lens in all directions, especially in varying optical conditions and mounting environments, leading to inconsistencies in resolution and accuracy.
Innovation Solution
The proposed optical measurement system utilizes a hemispherical mirror with latitude markers of different reflectance to capture a back focal image of the objective lens, allowing for the calculation of the numerical aperture in all directions using the image patterns formed by the markers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional measurement methods are used to measure numerical aperture, then measurement can be performed, but measurement precision is insufficient due to inability to measure in all directions
Solution Approach 1:
The patent employs a hemispherical mirror with a curved spherical surface instead of a flat mirror. This spherical geometry enables light to reflect from multiple angles simultaneously, creating circular patterns in the back focal plane that correspond to different angular ranges. The curved surface allows comprehensive measurement of numerical aperture in all directions (azimuthal and polar angles) from a single measurement position, resolving the contradiction between measurement precision and directional coverage.
Solution Approach 2:
The invention introduces angular dimensionality by using a hemispherical mirror that reflects light from multiple incident angles. The latitude markers on the spherical surface correspond to different polar angles, and the rotational symmetry provides azimuthal angle information. This transforms a single-point measurement into a multi-dimensional angular measurement, enabling complete numerical aperture characterization without mechanical scanning.
2Measurement precision
If multiple measurement positions are used to achieve comprehensive numerical aperture measurement, then all-direction measurement is possible, but measurement time increases
Solution Approach 1:
The patent merges multiple measurement positions into a single measurement position by using a hemispherical mirror that inherently provides multi-angular information. Instead of physically moving the objective lens or mirror to multiple positions, the spherical geometry consolidates all necessary angular information into one back focal plane image, dramatically reducing measurement time while maintaining comprehensive measurement capability.
Solution Approach 2:
The hemispherical mirror creates multiple virtual images of the light source corresponding to different incident angles. Each latitude marker on the spherical surface generates a circular pattern in the back focal plane that represents light reflected at a specific angular range. This optical copying approach eliminates the need for physical repositioning while capturing data from all directions.
3Ease of manufacture
If environmental factors are not controlled, then measurement setup is simpler, but measurement accuracy varies due to production deviation and optical conditions
Solution Approach 1:
The patent uses latitude markers with different reflectances positioned at different latitudes on the spherical mirror. These markers create circular patterns with varying intensities in the back focal plane, providing reference information that is insensitive to environmental variations. By measuring the positions and intensities of these reference patterns alongside the pupil image, the system compensates for production deviations and optical condition changes, maintaining high accuracy without complex environmental control.
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 method enables precise and accurate measurement of the numerical aperture in all directions, improving the consistency and reliability of optical measurements by using a single back focal image, thus reducing measurement time and potential errors.
Implementation Method 1
a hemispherical mirror including a planar portion, a spherical portion having a hemispherical recessed shape in the planar portion... an optical unit including an objective lens for allowing light incident from a light source to be incident on the hemispherical mirror, and at least one beam splitter for transmitting light reflected from the hemispherical mirror
Data Source
AI summary
An optical measurement system includes a hemispherical mirror including a planar portion and a spherical portion having a hemispherical recessed shape in the planar portion. In the spherical portion are latitude markers formed with a different reflectance from the rest of the spherical portion. The system includes an optical unit with an objective lens and at least one beam splitter. The optical unit transmits light reflected from the hemispherical mirror through the objective lens to a first sensor. A controller measures a numerical aperture of the objective lens by aligning the hemispherical mirror to be at the focus of the objective lens, detecting a back focal image of the objective lens in which the latitude markers appear as darker circular lines, and performing calculations on the image.