Advantages Of Using Meniscus Lenses In Infrared Applications

Compared to many other forms of optical lenses, meniscus lenses are rarely offered off-the-shelf. While meniscus lenses are primarily used for focusing to small spot sizes or collimation applications, plano convex lenses often offer a superior price-to performance ratio. There are scenarios, though, where meniscus lenses provide significantly superior performance at only a moderate increase in price.

SPHERICAL ABERRATION

Due to the spherical nature of a lens, spherical aberrations cause parallel rays at different distances from the optic axis to not converge at the same point (Figure 1). While spherical aberrations can be corrected by using multiple elements that overcorrect other elements, for many IR systems where materials are significantly more costly than visible materials, it is ideal to minimize the number of elements. In lieu of using multiple elements, it is possible to minimize spherical aberration for a single lens by shaping the lens into its best form.

For a fixed index of refraction and lens thickness, an infinite number of radii combinations exist that can be used to create a particular focal length lens. These combinations of radii create different lens shapes which directly result in spherical aberrations and coma due to the degree in which a ray bends as it travels through the lens.