Guided ray 41223 98343262 2007-01-04T04:32:52Z Srleffler 252195 phrasing. rm latin abbreviations (deprecated). A '''guided ray''' (also '''bound ray''' or '''trapped ray''') is a [[Ray (optics)|ray]] of light in a [[multimode optical fiber]], which is confined by the [[Fiber_optics#Principle_of_operation|core]]. For [[Step-index profile|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''', :<math>\sin \theta \le \sqrt{n_o^2 - n_c^2}</math> , where :''θ'' is the angle the ray makes with the fiber axis, ''before'' entering the fiber, :''n<sub>o</sub>'' is the refractive index along the central axis of the fiber, and :''n<sub>c</sub>'' 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]], and so are confined by the core. The confinement of light by the 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. ==See also== *[[Numerical aperture]] ==References== * [http://www.its.bldrdoc.gov/fs-1037/dir-017/_2518.htm Federal Standard 1037C] [[Category:Fiber optics]]