Uses of Total Internal Reflection
- Optical Fibers:
It is the maximum angle from the fiber axis where light enters the fiber and will propagate, or travel, in the core of the fiber. The sine of this angle is the numerical aperture (NA) of the fiber. Fiber with a larger NA needs less precision to splice and work with than fiber with a smaller NA. Single-mode fiber has a small NA.
- Rain Sensors:
The most common modern rain sensors are based on the principle of total internal reflection: an infrared light is beamed at a 45-degree angle into the windshield from the interior — if the glass is wet, less light makes it back to the sensor, and the wipers turn on. Most vehicles with this feature have an "AUTO" position on the stalk.
- Fingerprint Detection:
The Frustrated Total Internal Reflection (FTIR) is the most used and mature live-scan sensing technique. The finger is illuminated from one side of a glass prism with a LED, while the other side transmits the image through a lens to a CDD/CMOS sensing element which converts light into digital information. The lack of reflection caused by the presence of water particles where the ridges touches the prism allows ridges to be discriminated from valleys.