Aspheric optical elements
A spherical optical element is one that has a constant curvature from its center to its edge and has a spherical surface.The curvature of an Asphere varies continuously from center to edge.Aspheric optical elements are widely used in airborne equipment, satellites, laser guidance, infrared detection and other fields, and are increasingly popular in civil optoelectronic products.
1. Classification of aspheric surfaces
2. Advantages of aspheric surface
The figure below compares the focal points generated by parallel monochromatic light passing through a spherical lens and an aspheric lens. The image points of a spherical lens are blurred due to spherical aberration, while the image points of an aspheric lens are clear.Therefore, aspheric lens can be used to replace spherical lens group to correct the positive error. For example, when a zoom lens with ten lenses is generally used, one or two aspheric lenses can be used to replace five or six spherical lenses, which can achieve the same or higher optical effect, reduce the production cost, and also realize the lightweight and miniaturization of the system.Reducing the number of lenses in an optical system also reduces mechanical tolerances, additional calibration steps, and anti-reflection coating film requirements, improving overall system availability and reducing overall system design costs.
The use of aspheric elements in the optical system can improve the performance of the system, reduce the number of optical elements, thereby reducing the weight of the instrument, reduce the size, compact structure.Therefore, aspheric optical elements are often used in optical systems with large field of view, large aperture, high aberration requirements, small structure requirements, or special requirements. Because of their excellent optical properties, aspheric optical elements are increasingly becoming a very important optical elements.
3. Manufacturing process of aspheric surface
At present, the main processing methods for aspheric optical elements are as follows:
1) Surface material removal method: CNC milling polishing molding method, ion beam polishing method, magnetorheological polishing method, liquid jet polishing method, etc.
2) change the material shape method: glass hot pressing molding method, injection molding method, thermal deposition and solidification molding method, etc.
3) Additional material method: vacuum coating copy molding method, mixed molding method, etc.
Ultra-precision CNC milling and polishing are suitable for single-piece aspheric lens production. With the improvement of manufacturing technology, the machining accuracy is getting higher and higher.Computer-controlled precision polishing technology automatically adjusts tool resident parameters for precise polishing.While other manufacturing techniques typically require a special mold, and each lens has its own unique mold, CNC milling and polishing use standard tools and can be the first choice for prototyping and low-volume production applications.
