RP Photonics

Encyclopedia … combined with a great Buyer's Guide!

Sponsorship opportunity: support this popular resource, which serves the whole photonics community, and get recognition!

Rod Lenses

Definition: cylindrical lenses with the geometrical form of a cylinder

German: Stablinsen

Category: general optics

How to cite the article; suggest additional literature

A rod lens is a cylindrical lens which has the geometrical form of a cylinder and has a polished mantle, while the two flat end surfaces may be ground. It is analogous to a ball lens for focusing in both directions.

Rod lenses can be used, for example, for collimating a divergent beam in one dimension (see Figure 1) or for focusing light to a line. There are also imaging applications. Note, however, that a rod lens exhibits substantial spherical aberrations when light propagation is not restricted to a small fraction of its cross-section.

Note that there are also gradient-index lenses which also have a cylindrical shape. There, however, the two end faces are polished, and the mantle surface is not optically relevant.

Types of Rod Lenses

Rod lenses are available with different optical materials, mostly with glasses like fused silica and BK7, but also with crystalline materials like YAG or silicon, e.g. for infrared optics.

Rod lenses can have diameters of a few millimeters, but there are also cylindrical microlenses with substantially smaller diameters. Small-diameter rod lenses are frequently used as fast-axis collimators for diode bars.

rays at a rod lens
Figure 1: Focusing of divergent light with a rod lens.

There are also half-rod lenses, which are rod lenses cut into two equal pieces.

Focal Length

There are two different definitions of focal length of a rod lens. The effective focal length, which is the distance between a plane through the center of the lens and the beam waist (focus) of an initially collimated input beam, is given by the equation

effective focal length of a rod lens

where D is the diameter of the lens cylinder and n its refractive index.

The back focal length is defined as the distance of the focal point from the lens surface, and is smaller than the effective focal length by half the diameter of the rod.

See also: cylindrical lenses, microlenses, ball lenses, gradient-index lenses
and other articles in the category general optics

How do you rate this article?

Click here to send us your feedback!

Your general impression: don't know poor satisfactory good excellent
Technical quality: don't know poor satisfactory good excellent
Usefulness: don't know poor satisfactory good excellent
Readability: don't know poor satisfactory good excellent

Found any errors? Suggestions for improvements? Do you know a better web page on this topic?

Spam protection: (enter the value of 5 + 8 in this field!)

If you want a response, you may leave your e-mail address in the comments field, or directly send an e-mail.

If you enter any personal data, this implies that you agree with storing it; we will use it only for the purpose of improving our website and possibly giving you a response; see also our declaration of data privacy.

If you like our website, you may also want to get our newsletters!

If you like this article, share it with your friends and colleagues, e.g. via social media: