Definitions for "Critical angle"
Maximum angle of incidence formed by a ray of light as it passes from a dense to a less dense medium, e.g., from glass to air, where the critical angle is about 42 degrees. When the critical angle is exceeded, all the light reflects back to the denser of the two media.
(Generally identified as .) The minimum angle of incidence for which total internal reflection will occur at an interface between two particular media. When light strikes an interface with an angle of incidence equal to the critical angle, the angle of refraction equals 90 degrees. For any larger angle of incidence, the angle of refraction is not defined (since its sine becomes greater than 1.0, according to Snell's Law), and no light can pass over the interface. Applying Snell's Law gives the following expression for the critical angle of an interface between medium 1 and medium 2: sin = For the critical angle to be defined, the medium (1) through which the light is initially traveling must have a greater index of refraction than the medium (2) on the other side of the interface. (In the image to the right, 1equals the critical angle since the angle of refraction is 90 degrees). The critical angle and total internal reflection are covered on this page (and the next one) of this module.
The smallest angle from the fiber axis at which a ray may be totally reflected at the core/cladding interface.
Keywords:  density