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Aspherical lenses significantly enhance optical systems by reducing aberrations and improving overall quality. Unlike traditional spherical lenses, aspherical lenses provide greater design freedom, allowing for better optimization. This is especially beneficial for lenses with large relative apertures, wide fields of view, and zoom capabilities.
Infrared lenses benefit particularly from aspherical designs due to the requirement for materials that transmit infrared wavelengths, such as germanium, zinc sulfide, and zinc selenide. These materials are more expensive than ordinary glass. Utilizing aspherical lenses can reduce the number of components needed, thus lowering the system’s complexity, volume, weight, and overall cost. Despite the complexity of manufacturing aspherical lenses, the reduction in the use of costly infrared materials often leads to significant cost savings. Additionally, fewer lenses reduce light transmission losses and improve overall system transmittance.
This case study involves designing a wide field-of-view, long wavelength infrared lens initially composed of spherical lenses. The design used chalcogenide glass and germanium for non-thermal treatment and was complex, with a field of view of 103°. By switching the first lens to an aspherical design, the lens structure was significantly simplified, expanding the field of view to 127°.
Chalcogenide glass, composed of elements like germanium, arsenic, selenium, and antimony (Ge-As-Se-Sb), is a cost-effective material for infrared applications due to its high transmittance and low refraction-temperature coefficient. Traditional cold processing methods for chalcogenide glass involve multiple molds, processes, and equipment, resulting in high labor and material costs and unstable quality.
For small batch production, single-point diamond turning (SPDT) technology is preferred. Chalcogenide glass’s softness and high thermal expansion coefficient make SPDT an ideal method. This high-efficiency, high-precision optical surface processing technique achieves nanometer-level surface roughness and sub-micron shape accuracy, making it the best solution for various optical applications. SPDT improves precision, repeatability, and finish of the machined surface, allowing for single-pass formation and reduced processing time, achieving surface roughness in the nanometer range.
In summary, adopting aspherical lenses in infrared lens design provides substantial benefits such as improved aberration correction, reduced component count, lower weight and volume, and enhanced overall transmittance. These advantages are particularly significant for infrared lenses, which utilize expensive materials like chalcogenide glass and germanium, necessitating cost-effective design solutions.
Despite the complexity of processing aspherical lenses, advancements in technologies like single-point diamond turning have made achieving nanometer-level precision and surface quality feasible. Transitioning to aspherical designs optimizes optical performance, contributes to cost savings, enhances process stability, and streamlines manufacturing in infrared lens applications. This underscores the pivotal role of aspherical lenses in modern optical engineering.
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