Working Principle of Optical Ball Lenses
Category: Blog
Release time: 2026-04-04
Light undergoes successive refractions at the two spherical surfaces when passing through the sphere; the spherically symmetric structure enables compact, high-efficiency focusing, collimation, or fiber coupling.
Working Principle of Optical Ball Lenses
1. Geometric Principle
Both surfaces of the sphere are spherical, with their centers of curvature at the center of the sphere.
When light is incident on the spherical surface, the normal line is the line connecting the center of the sphere and the point of incidence.
Light bends toward the normal when entering the sphere and bends again when exiting, finally converging to a focal point.
2. Focal Length Formula (Core)
For an ideal ball lens in air:
- : Diameter of the ball
- : Radius of the ball
- : Refractive index of the material
For example, for a common glass ball with :
The focal point lies approximately just outside the sphere.
3. Typical Working Modes
(1) Fiber Coupling Mode (Most Common)
- The fiber end face is placed close to one surface of the ball lens.
- Divergent light emitted from the fiber enters the sphere.
- After two refractions, the light exits approximately parallel (collimated).
- Conversely: parallel incident light is focused by the ball into the fiber core.
Function:
Greatly improve the coupling efficiency between optical fibers, laser diodes, and detectors.
(2) Focusing / Collimation Mode
- Parallel incident light → converges to the focal point behind the ball.
- A point source placed at the focal point → emits approximately parallel light.
(3) Simple Imaging Mode
- The object is placed on one side of the ball, and an image is formed on the opposite side.
- Advantages: Ultra-small size, accepts light incidence from 360°.
- Disadvantages: Severe spherical aberration, average imaging quality, not suitable for high-precision imaging.
Keywords: Working Principle of Optical Ball Lenses
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