Objective Lens Diffractive Element Chromatic Aberration Correction
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Solution Overview
Problem
Existing objective lenses for microscopes face challenges in sufficiently correcting various aberrations, particularly chromatic aberrations, across the entire field of view, especially as numerical aperture increases, and they often require expensive and difficult-to-process anomalous dispersion glasses.
Innovation Solution
The objective lens design incorporates a first lens group with positive refractive power and a second lens group with negative refractive power, including a diffractive optical element with diffraction grating grooves on a cemented surface, positioned closer to the object than the principal ray's optical axis, to correct chromatic aberrations, while avoiding the use of anomalous dispersion glasses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If numerical aperture is increased to improve resolution and brightness, then image quality is improved, but chromatic aberration correction becomes difficult and depth of focus decreases
Solution Approach 1:
The objective lens is divided into multiple lens groups (first lens group with positive refractive power and second lens group with negative refractive power), with the diffractive optical element positioned in the first lens group. This segmentation allows each group to contribute differently to chromatic aberration correction, enabling effective correction across the entire field of view while maintaining high numerical aperture.
Solution Approach 2:
A diffractive optical element is introduced as an additional optical component with different optical properties (diffraction-based rather than refraction-based). This adds a new dimension to chromatic aberration correction by utilizing wavelength-dependent diffraction effects, allowing simultaneous correction of chromatic aberrations across multiple wavelengths without requiring expensive anomalous dispersion glasses.
2Manufacturing precision
If diffractive optical elements are used to correct chromatic aberration, then chromatic aberration correction is improved, but various aberrations throughout the entire field of view cannot be sufficiently corrected
Solution Approach 1:
The diffractive optical element is cemented to a positive lens, merging two optical components with different functions. The positive lens provides refractive power and helps correct spherical aberration and coma, while the diffractive optical element provides chromatic aberration correction through diffraction. This combination allows simultaneous correction of multiple aberration types across the entire field of view.
Solution Approach 2:
The diffractive optical element is positioned in the first lens group (closer to the object) rather than uniformly distributed, allowing localized correction of chromatic aberrations where they most affect image quality. The specific positioning at a location where the principal ray crosses the optical axis enables targeted correction while maintaining overall system performance.
3Manufacturing precision
If anomalous dispersion glasses are used to correct chromatic aberration, then chromatic aberration correction is improved, but cost increases and processing difficulty increases
Solution Approach 1:
The diffractive optical element is formed by molding diffraction grating grooves on a resin material, which is a simpler and less expensive process than working with anomalous dispersion glasses. The resin material can be easily molded and processed, reducing manufacturing cost and complexity while achieving equivalent or superior chromatic aberration correction performance.
Solution Approach 2:
The diffractive optical element replaces the need for complex anomalous dispersion glass materials with a structurally-based diffraction grating. Instead of relying on the inherent optical properties of expensive specialty glasses, the chromatic aberration correction is achieved through the physical structure (grooves) of the diffractive element, which can be manufactured more easily using molding techniques.
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 design achieves high numerical aperture with sufficient correction of chromatic aberrations throughout the field of view, improving image uniformity and brightness without the need for expensive anomalous dispersion glasses, enhancing the microscope's image-forming performance.
Implementation Method 1
a diffractive optical element in which two diffractive element constituents made from optical materials are cemented, and which has a diffractive optical surface formed with diffraction grating grooves on the cemented surface
Data Source
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AI summary
An objective lens OL comprises: a first lens group G1 disposed on an object side, having positive refractive power as a whole and having a positive lens (plano-convex lens L1) which is disposed closest to the object and of which lens surface closest to the object is a plane or a surface having a low curvature, and at least one cemented lens (cemented lens CL12 or the like); a second lens group G2 disposed on an image side, having negative refractive power as a whole, and having a concave surface facing the image and a concave surface facing the object, which face each other; and a diffractive optical element GD in which two diffractive element constituents made from different optical materials are cemented, which has a diffractive optical surface D formed with diffraction grating grooves on the cemented surface, and which is disposed closer to the object than a position where a principal ray crosses the optical axis.