The angle at which the core of an optical fiber accepts incoming light; usually measured from the fiber axis. Light entering at an angle greater than the acceptance angle will be reflected away. Acceptance angle has relation with numerical aperture (NA).
A guided ray in an optical fiber is confined by the core. For step index fiber, light entering the fiber will be guided if it falls within the acceptance cone of the fiber, that is if it makes an angle with the fiber axis that is less than the acceptance angle,
Sinθ ≤ √ (n12–n22)
where
θ is the angle the ray makes with the fiber axis, before entering the fiber,
n1 is the refractive index of the core
n2 is the refractive index of the cladding
This result can be derived from Snell’s law by considering the critical angle. Rays that fall within this angular range are reflected from the core-cladding boundary by total internal reflection. Thus their propagation is confined by the core boundary. The confinement of light by an optical fiber can also be described in terms of bound modes or guided modes. This treatment is necessary when considering singlemode fiber, since the ray model does not accurately describe the propagation of light in this type of fiber.
Post a Comment