Optical Lenses
A Rod Lens is an optical lens that has the shape of a cylinder, and the length serves as the optical function surface. Therefore, the length of the rod lens is often polished while the two ends of the rod lens are ground. When light is illuminated from the side, a rod lens functions just like a plano-convex cylindrical lens, focusing the incoming light into a one-dimensional straight line, where the rod lens can also be used for anamorphic beam shaping, astigmatism correction, one-dimensional compressing, and expansion of image size. Rod lenses are essential optical components in barcode scanners. A rod lens is placed between the barcode and the detector to collimate or focus the incoming reflected light. However, unlike cylindrical lenses, which are flat on one side, rod lenses have a round cross-section, which means a convex shape on double sides, therefore rod lenses have greater light collection power than a plano-convex cylindrical lens of the same curvature, and hence larger focal length. Not that when light fills a large portion of the rod’s diameter, especially near the edges, the changing path lengths and refraction angles cause significant spherical aberrations, resulting in blurred or distorted focal spots.
The focal length of a rod lens are defined using two concepts, the effective focal length (EFL), which is the distance between the center plane of the lens and the beam waist (focus) of an initially collimated input beam; and the back focal length, which is EFL minus the radius of the rod lens.
As a specialized rod lens supplier, Shalom EO offers custom rod lenses, the lenses are polished on the circumference and ground on the ends for side-on uses, suitable for various applications like diode laser collimation, beam circularization, and line-focusing, where the short focal lengths of the rod lenses benefits flexible light manupilation within short distances. These rod lenses can be manufactured from various optical materials such as N-BK7, fused silica, or other optical substrates, and are available with anti-reflective coatings optimized for the wavelengths of interest.
