A cylindrical lens is typically used to focus, condense or expand incoming light. A cylindrical lens has one cylindrical surface, causing light to be focussed in a single dimension or axis. It can also be used to expand the output of a laser diode into a symmetrical beam. Cylindrical lenses are technically more difficult to manufacture than spherical or flat lenses which is why ULO Optics use state-of-the-art polishing techniques alongside stringent lens assessment to manufacture each lens.
A cylindrical lens is typically rectangular, square or circular and of either a plano-convex or plano-concave design. ULO’s cylindrical lenses combine low wedge with high surface accuracy. We assess the quality of each individual lens using Trioptics centration measurement and a Zygo GPI interferometer. All ULO lenses are available both uncoated or coated with a broad range of high durability, low loss AR coatings and can manufactured to 20-10 surface roughness.
Plano-Convex Cylindrical Lens
A plano-convex cylindrical lens is used to condense light in one axis. A positive cylindrical lens is able to create a line image from a point of light, to change the aspect ratio of an image or to focus collimated input light to a line. Plano- convex cylindrical lenses are typically used for illumination of slit and line detector arrays, laser projection, laser line focussing and anamorphic beam shaping.
Plano-Concave Cylindrical Lens
A plano-concave cylindrical lens is used to expand light in on axis. A negative cylindrical lens is able to diverge collimated input light away from a line. Plano-concave cylindrical lenses are used for one-dimensional compression of images, anamorphic beam shaping, and laser line generation.
Applications
A cylindrical lens can be used in a broad range industrial, research and OEM applications. Typically, they are used in spectroscopy, holography, laser scanning optical metrology, acousto-optic and laser diode applications. Lenses will often need to be custom-made to suit the application. ULO Optics offers semi- custom and fully custom-made cylindrical lenses. Our experts offer full support to take you from proof of concept through to volume manufacturing.
Cylindrical Lens manufacture
Cylindrical lenses are most commonly manufactured from a rectangular convex cylinder. The way in which the cylinder is mounted for fabrication is influenced by the radius of curvature and the dimension parallel to the cylindrical axis. If the substrate has a short radius of curvature, it will usually be mounted around a barrel shaped tool, whereas if the radius of curvature is long, the substrate is usually mounted onto a flat bottomed plate with a curved mounting face.
After deciding which tooling to use, cautious mounting of the substrate to the tool is critical otherwise the lens specification may be compromised. Because a cylindrical lens lacks the spherical symmetry of a spherical lens, and because the optical axis is a plane as opposed to a line, centring the lens is a much more demanding process.
In the majority of cases, the lens specification is process-controlled. It is essential to reference the cylindrical axis when mounting the substrate. The same mounting plate or cylinder must be used during the milling, smoothing and polishing processes for each lens, to ensure uniformity.
Surface shape
The surface figure and the radius of curvatures are two important factors when determining the surface of a cylindrical lens. The method of determining the radius of curvature is similar to that used for spherical lenses but due to the asymmetrical surface of cylindrical lenses, test equipment must be converted.
The surface figure is a measurement of how far the lens deviates from an ideal cylinder shape, and is determined by irregularity and power. Power is a measurement of conformity to the specified radius, and irregularity is a measure of the deviation from a perfect sphere.
In a cylindrical lens only the power in the perpendicular plane to the cylindrical axis is typically specified. The remaining surface form error, including the unwanted power in the parallel direction, is called the surface figure. It is usually specified in units of wavelengths and quoted separately along the parallel and perpendicular directions.
