Cylindrical lenses and spherical lenses

Spherical lenses are one of the most commonly used optical components, often used alone or in various combinations.

We will consider a sphere made of glass. Suppose we slice it along any plane passing through its entire body. The resulting fragments will form a flat and a curved spherical lens. When illuminated from a flat surface, all light rays converge to a point in front of the lens. Rotating a spherical lens does not change the position or shape of the focused light.

In contrast, imagine cutting a glass cylinder so that its plane is parallel to its longest axis. This creates a lens that is flat on one side and curved on the other, with curvature in only one direction. When illuminated, cylindrical lenses focus light into a line rather than a point. Additionally, rotating a cylindrical lens along its optical axis changes the direction of the line of focus.

Applications of cylindrical lenses

Spectrometers: Cylindrical lenses are used in spectrometers, usually placed after the diffraction grating element. They focus light into a single line incident on a linear photodetector.

Astigmatism correction: In ophthalmology, cylindrical lenses are essential for correcting astigmatism vision caused by corneal deformation. By changing the focus along one axis, they aligned it with a second axis.

Laser beam shape correction: Semiconductor lasers typically emit light with an elliptical beam profile. When the cylindrical lens is oriented perpendicular to the fast axis of the laser beam, collimation and coupling into the fiber profile can be corrected.

Laser Scanning Microscope: Used in conjunction with an acousto-optic deflector, cylindrical lenses help focus light onto the correct plane in a laser scanning microscope, thereby enhancing image correction and point focusing.

Laser line scanning: Laser line scanning is used to digitize 3D objects and involves using cylindrical lenses to project straight lines onto a surface. Cameras and triangulation are then used to measure changes in line shape, allowing the object’s shape to be estimated.

In summary, cylindrical lenses play different roles in various fields, from spectroscopy and vision correction to laser beam shaping and 3D scanning, demonstrating their versatility and importance in optical applications.