Afocal optical system is a specially designed optical system that does not require introducing a focus in the optical system, but achieves the desired optical effects through other means.

Here is an introduction to some common components of no-focus optical systems:

1. Beam Expander:

   - A beam expander is an optical component used to expand or shrink the diameter of a laser beam while maintaining its parallelism.

   - It typically consists of two lenses, a convex lens and a concave lens, combined to achieve beam expansion or contraction.

2. Galilean Drum:

   - The Galilean drum is an optical system used to achieve beam expansion or contraction without introducing an optical focus.

   - It consists of a concave lens and a convex lens, with the distance between these two lenses adjustable to change the degree of beam expansion or contraction.

3. Fiber Coupler:

   - A fiber coupler is an optical component used to couple light from one optical fiber into another, without the need for an optical focus.

   - Fiber couplers ensure effective coupling of light beams through appropriate design and positioning, enabling the transmission and processing of light signals.

4. Plano-Convex Lens:

   - A plano-convex lens is a specially designed lens with one flat side and one convex side. It can be used to focus or diverge light beams without introducing a focus.

   - Plano-convex lenses can be adjusted in focal length and beam expansion through appropriate selection and design to meet specific application requirements.

These components of no-focus optical systems play important roles in various optical applications, such as laser processing, optical communication, and beam shaping. Their design and use can effectively meet specific optical requirements, enhancing system performance and flexibility.