In most cases, the cylindrical lens is made of cylindrical glass, where the cylindrical surface of the cylindrical lens is a precision-treated (curved) optical surface. A typical cylindrical lens has a cylindrical surface and a flat surface, which increases the flexibility of manufacturing and testing. Similar to a spherical lens, the surface accuracy affects the cylindrical shell and will undergo further processing after finishing polishing. The surface accuracy is determined by surface irregularity and surface quality. These two specifications are the same as spherical lenses. Cylindrical lenses are generally used to focus incident light on the line or change the image's aspect ratio. It is usually formed into a linear image, and the direction of the beam can be controlled.
The cylindrical lens has a surface that can focus the incident light in a particular dimension and stretch the image. The focal length of the cylindrical lens can be negative or positive, suitable for laser line generation or deformed beam shaping to circularize Laser output.
A cylindrical lens is different from a spherical lens because a cylindrical lens has a unique geometric structure, so it also has other specifications, including directrix and generatrix. These axes are used to define the angle between the planes. These specifications require a specific analysis of specific issues.
1. Straight line wedge angle (eccentric). When the directrix is not perpendicular to the thickness of the lens, a wedge angle of the directrix will occur. Similar to the eccentricity of the spherical surface in the spherical optical condition, the wedge angle of the alignment line is the displacement of the actual optical axis. Suppose the cylinder lens has a collimator wedge angle. In that case, mechanical errors and optical aberrations may occur in the system, including uneven line thickness at both ends of the focal plane and beam deviation on the collimator.
2. Bus wedge angle. When the generatrix is not perpendicular to the thickness of the lens, a generatrix wedge angle will occur. This wedge angle will cause an angular deviation of the beam, which will significantly increase the pointing error of the system. Suppose the cylinder lens has a bus wedge angle. In that case, the following mechanical errors and optical aberrations may occur in the design, including uneven line thickness at both ends of the focal plane, beam deviation on the bus, and tilt of the focus plane.
3. Axial distortion. When the generatrix is not parallel to the optical plane of the lens, axial distortion will occur. Axial distortion means that the cylindrical surface of the cylindrical lens rotates relative to the external dimensions. When you fix the rectangular element by the exterior dimensions, the axial distortion is unfavourable for your application. If the cylinder lens has axial distortion, the following optical aberrations may occur in the system: the image rotates around the optical axis.