Reflection, Refraction & Optical Fibers Content Summary Quick links: Reflection Refraction Optical Fibers Supporting Materials Module Site Map

	The law of reflection states that the angle of reflection equals the angle of incidence for any reflecting object.
	The angle of incidence and the angle of reflection are measured from the trajectory (of the ball, light, whatever) to the normal to the surface.
	To construct a normal:      1) Draw a line tangent to the surface.      2) Draw a line perpendicular to the tanget at the point.  This is your normal.
	Total reflection occurs when the surface is smooth, and a collimated beam is reflected in a single direction.
	Diffuse reflection occurs when the surface is not smooth, and a collimated beam is scattered in multiple directions.

Refraction
Click here to go to start of Refraction content

	Nothing can travel faster than the speed of light in a vacuum.
	Light in a vacuum always travels at the same speed: c = 2.99792458 x 108m/s.
	n = c/v, where n is the index of refraction of a given medium, and v is the speed of light through that medium.
	λn = λ0/n, where λn is the wavelength of light in a given medium with an index of refraction of n, and λ0 is the wavelength of light in vacuum
	Snell's Law describes how light refracts when it changes media: n1 * sin θ1 = n2 * sin θ2, where  θ1 is the angle of incidence, θ2 is the angle of refraction, n1 is the index of refraction in the first medium, and n2 is the index of refraction in the second medium.
	The Critical angle θc is the angle of incidence for an angle of refraction of 90 degrees: sin θc = n2/n1
	Total internal reflection (TIR) occurs when θ1 is larger that the critical angle; no light makes it into the second medium.
	TIR occurs (and thus the critical angle is defined) only when light travels from a denser medium to a rarer medium.

Back to top of page

Optical Fibers
Click here to go to start of Optical Fibers content

	Light can be trapped in optical fibers, due to the process of TIR.
	The angle of entry θ0 for light entering a fiber determines whether the light is guided by the fiber.  Angles of entry less than the cut-off angle θ0max result in light staying in the fiber.
	How adding a cladding to a fiber helps:      Note: The index of refraction of the cladding must be lower than the index of refraction of the core for the fiber to work.      1) Protects the core from scratches.      2) Allows a narrower cone of light to be trapped in the fiber.      3) Cladding can be easily coated with insulating layers (no worry about damaging core).
	The range of angles in which light will travel down a fiber is the cone of acceptance.  The apex angle of the cone of acceptance is twice the cut-off angle θ0max.
	Numerical Aperture (NA) is a measure used to distinguish different fibers. It is related to the cut-off angle but depends only on the indices of the core and cladding of the fiber: NA = n0 * sin θ0max = (n12 - n22)1/2.

Back to top of page

	Video of Guest Lecture: "Optical Communications for Information Technology" by Dr. Peter Persans
	Preparatory Questions for In-class Activity on Snell's Law
	References and Links page, for those who want to know more or to hear about the same material in someone else's voice
	List of Glossary Definitions
	Credits and Contact Information

Click on Next to see a list of handy References and Links