Encyclopedic Knowledge Concerning Collimator Lens

Definition of Collimator Lens

A Collimator Lens is a curved optical lens that can turn light from a certain light source (for instance, from every point in an aperture or the light source itself) into a parallel collimated light beam. This kind of lens is commonly used in optical systems to ensure that light remains parallel during propagation, preventing the light from spreading into unwanted directions.

Functions of Collimator Lens

Converging Light

A Collimator Lens is primarily a convex lens with the function of converging light, capable of converting divergent light into parallel light.

Controlling Field of View Angle

By adjusting the design of the Collimator Lens, users can control the field of view angle of light entering a spectrometer or other optical devices, thereby optimizing collection efficiency and spatial resolution.

Improving Imaging Effect

Aspherical lenses, a type of Collimator Lens, have many advantages such as low chromatic aberration, reducing the number of lenses in the optical system, minimizing energy loss, reducing system weight, simplifying the optical structure, lowering costs, and enhancing imaging effects.

Types of Collimator Lens

The type of Collimator Lens depends on the requirements for aberration. For low requirements, simple single-element lenses like plano-convex or bi-convex lenses are used, allowing for larger relative apertures. For high requirements, double-cemented lenses are used with appropriately reduced relative aperture. In grating systems, particularly when the grating is coarse and has a small gap, the impact of aberrations on forming Moiré fringes is minor. Therefore, single-element plano-convex lenses can be used, with the plane facing the filament to reduce spherical aberration. In cases of larger gaps, reducing aberrations, especially chromatic aberration, can improve fringe contrast. Double-element plano-convex lenses should then be used, with the first plane facing the filament, or use double-cemented lenses with aberration correction. It must be noted that compared to the filament divergence angle, the lens's aberration is secondary.

Product Aperture of Collimator Lens

Light emitted from a light source becomes parallel light after passing through a Collimator Lens, then it illuminates the grating pair and is received by a silicon photodiode or the Collimator Lens behind. Hence, the aperture of the Collimator Lens must be such that the light completely fills the silicon photodiode.

Quality Requirements of Collimator Lens

Regarding the quality requirements of Collimator Lenses, it is usually the variation in the thickness of the air gap that is of concern. However, optical path difference is not only a function of air gap thickness but also a function of the angle of incident light. The optical path difference at a specific point is due to air gap thickness changes caused by defects in the tested plane, which vary with the light source size and the lens's aberration. Generally, the maximum effective air gap thickness for a Collimator Lens is 50mm, and the light source size and lens aberration must also be considered.