Rod Lenses
Author: the photonics expert Dr. Rüdiger Paschotta (RP)
Definition: cylindrical lenses with the geometrical form of a cylinder
More general term: lenses
DOI: 10.61835/ubi Cite the article: BibTex plain textHTML Link to this page LinkedIn
A rod lens is a cylindrical lens which has the geometric 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.

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
$$f = \frac{{n\;D}}{{4(n - 1)}}$$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.
More to Learn
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Suppliers
The RP Photonics Buyer's Guide contains 19 suppliers for rod lenses. Among them:
Edmund Optics

Designed for use in a variety of laser and imaging systems, these components are available in a range of micro sizes for integration into a host of OEM applications. Custom sizes, variations in polishing/ ground surfaces and additional coatings are available upon request.
TECHSPEC® rod lenses are polished on the circumference and ground on both ends. Optical performance is similar to a cylinder lens. Collimated light passing through the diameter of the rod lens will be focused into a line. N-BK7 and UV fused silica substrates are available for a variety of UV, visible and NIR applications.
Knight Optical

Knight Optical offers standard rod lenses manufactured from borosilicate. We can also provide custom rod lenses, for example manufactured from UV fused or with an applied coating.
Artifex Engineering

Artifex Engineering offers custom rod lenses for various applications such as endoscopes. A wide range of substrates are available in custom sizes, specifications and coatings to suit your requirements. We look forward to your inquiry.
Avantier
Rod lenses perform in a manner analogous to a standard cylinder lens, and can be used in beam shaping and to focus collimated light into a line. Our rod lenses play a key part in many laser and imaging optical assemblies, and can be used for UV, visible and NIR applications.
Shalom EO

Hangzhou Shalom EO offers rod lenses a series of custom Rod Lenses made from various optical materials such as, but not limited to UV-fused silica, N-BK7. The transmission wavelength range of our rod lenses extends from UV, Visible, to NIR with a minimum diameter of 0.6 mm, roundness error down to 0.005 mm, and diameter tolerance down to 0.01 mm. Our rod lenses are ideal for applications as endoscope lenses, light pipes, and laser processing lenses.
Custom coating options for rod lenses include uncoated substrates, Broadband Anti-reflection (BBAR) coatings (average reflection below 0.5%), laser line V-coating which provides higher transmission (average reflection below 0.25%) at a narrower range around a certain wavelength, and MgF2 AR coatings (average reflection below 1.5%) with competitive low price.
Shanghai Optics

Shanghai Optics custom rod lenses are polished on the circumference and ground on both ends. They act as a cylinder lens, focusing collimated light into a line. Our fused silica rod lens offers high transmission in the UV and through the NIR as well as a low coefficient of thermal expansion, 0.55 × 10-6 /K.
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