To determine the Numerical aperture and Acceptance Angle of short-range optical Fibre
Objective:
In order to transmit a signal through optical fibre the light ray should strike with acceptance angle of fibre at core-cladding interface. The sine of the acceptance angle is called numerical aperture of the fibre. We have an optical fibre cable of length 1 metre and a white screen with four concentric circles of 10mm, 15mm, 20mm and 25 mm diameter. Using optical fibre trainer kit, determine the numerical aperture of given optical fibre cable.
Apparatus:
An optical fibre cable, optical fibre trainer board, numerical aperture jig white screen and connecting wires.
Formulas:
The numerical aperture (NA) of the optical fibre can be calculated using formula, i.e.,Numerical Aperture = Sin(a) =W/sqrt(4L^2+W^2),where 'a' is the acceptance angle of incidence at the input end of the optical fibre, L, is the distance of the screen from the fibre end and W is the diameter of the spot.
Numerical aperture of an optical fibre is defined as the light gathering ability of the fibre. Numerical aperture also refers to the maximum angle at which the light incident on the fibre end is totally internally reflected and is properly transmitted along the fibre. The cone formed by the rotation of this angle along the axis of the fibre is the cone of the acceptance of the fibre. The light ray should strike the fibre end within this cone of acceptance otherwise it is refracted out of the fibre. Numerically, it is also defined as the sine of the acceptance angle.
Observations:
Enter the readings after doing the experiment:
Numerical Apertutre:
Critical Angle(degrees):
Error Analysis:
1) Error Percentage in Numerical Aperture is :
2) Error Percentage in Critical Angle is :