Cylindrical lenses are similar to spherical lenses in that they use curved surfaces to focus or diverge light, but cylindrical lenses only have the ability to converge or diverge in one direction and do not affect light in the vertical direction. This cannot be achieved using a spherical lens, as it focuses or evenly disperses light in a rotationally symmetric manner. Cylindrical lenses play an important role in the control and shaping of laser beams, used for laser sheet forming and ring-shaped elliptical beams. Due to the asymmetric characteristics and special manufacturing process requirements of cylindrical lenses, it is necessary to specify and appropriately control the center, wedge, and axial torsion.
Therefore, cylindrical lenses need to be manufactured using specialized equipment and technology, as well as a unique coordinate system to effectively reference the characteristics of the lens. Two orthogonal directions define the reference system: power direction and non power direction. The first direction is called the "functional direction" because it advances along the bending length of the lens and is the only axis with optical function. The second direction is called the "non functional direction" because it advances along the length of the lens and has no optical function. The length of a cylindrical lens advancing in a non functional direction can be extended without affecting the optical function of the lens. Cylindrical lenses can come in various shapes, including rectangles, squares, circles, and ellipses.