Optical Fiber:- Acceptance angle/acceptance cone half angle:-

• It is the maximum angle of incidence with respect to core axis that the light may enter the fiber in order to be propagated.
• If a light is launched at an angle greater than acceptance angle then it will be lost in cladding because the angle of incidence at care cladding inter face will be less than critical angle. with the fiber:-

• The acceptance angle can be measured by the NA of the fiber which tells about light collecting ability / light gathering ability of the fiber.
• NOTE:-Higher the NA graeter is the acceptrance angle hence more light can enter into the fiber.
• Numerical apperture(NA) is a unit less quantity because NA=sqrt(n1^2-n2^2).
• N.A is a unit less and dimension less quantity which indepdent of the dimension of the fiber i.e length and radius. But dependent on the material of the fiber.

• Relative Refracttive Index(RRI):-

∆=n1²-n2²/ 2n1² =(NA)²/2n1²

NA=n1√2∆