Cylinder lenses are similar to spherical lenses because they all use curved surfaces to focus or diverge light, but cylindrical lenses only have the ability to converge or diverge in one direction, and will not affect the light in the vertical direction. This is impossible to achieve with a spherical lens, because the spherical lens focuses or diverges the light in a rotationally symmetrical manner.
Cylinder lenses play an important role in the control and shaping of laser beams, and are used for laser sheet shaping and circularization of elliptical beams. Due to the asymmetric characteristics of the cylinder lens and the special manufacturing process requirements, the center, wedge, and axial torsion must be specified and appropriately controlled.
Therefore, the cylindrical mirror needs to be manufactured with special equipment and technology, and a unique coordinate system is needed to effectively refer to the characteristics of the lens.
Two orthogonal directions define the reference system: the power direction and the non-power direction. The first direction is called the "functional direction" because it travels along the curved length of the lens and is the only axis with optical functions. The second direction is called the "non-functional direction" because it travels along the length of the lens without any optical function.
The length of the cylinder lens in the non-functional direction can be extended without affecting the cylindrical lens optics. Cylinder lenses can take many shapes, including rectangle, square, circle, and ellipse.