OBJETIVE OF THE EXPERIMENT

To determine the numerical

aperture of an optical fibre

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 light ray should strike the fibre end

with in this cone of acceptance else it is

refracted out of the fibre. Numerically, it

is also defined as the sine of the

acceptance angle.

An optical fiber (or optical fibre) is a

flexible, transparent fiber made of glass

(silica) or plastic, slightly thicker than a

human hair.

It functions as a waveguide, or “light

pipe”to transmit light between the two

ends of the fiber.

Core–thin glass center of the fiber

where light travels.

Cladding–outer optical material

surrounding the core.

BufferCoating–plastic: Coating

that protects the fibre.

It works on the

principle of total

internal reflection.

Low Transmission Loss and Wide

Bandwidth

Immunity and Interference

Small Size and Weights

Signal Security

Electrical Isolation

Abundant Raw Material

Less Expensive

An optical fibre cable

Optical fibre trainer board

Screen

connecting wires

Fiber Optics Trainer

Model is designed

to learn the basics

of fiber Optics.

A large number of

experiments.

Make all the connections . Connect one end of the optical fibre cable to

the optical fibre trainer and other end to the numerical aperture jig.

Hold the white screen with four concentric circles (10, 15, 20 and 25 mm diameter) vertically at a suitable distance to make the red spot emitted from the optical fibre coincide with the 10 cm circle. Note that the circumference of the spot (outermost) must coincide with the circle.

Record L, the distance of the screen from the

fibre end and note the diameter (W) of the

spot.

Compute the numerical aperture (NA) of the

optical fibre by using the formula

NA = Sinθ=W/(4L2+W2)1/2,

where θ is called as the acceptance angle

is the maximum angle of incidence at the

input end of the optical fibre so that he

optical ray can just propagate within the

optical fibre.

Tabulate the reading and repeat the

experiment for 15 mm, 20 mm and 25 mm

diameter too.

S.No LENGTH(mm

)

DIAMETER

OF THE

SPOT(mm)

NUMERICAL

APERTUER(

NA)

ACCEPTANC

E ANGLE(

DEGREE)

1 9 10 0.4 23.5

2 14 15 0.4 23.5

3 19 20 0.4 23.5

4 24 25 0.4 23.5

Numerical aperture of optical

fibre is 0.4mm.

The optical fibre cable should be free

from twists and folds so as to avoid the

power loss.

Connections should be proper and tight

.

What do you mean by refractive index?

What is difference between reflection and refraction?

What is the basic principle of propagation of light in an optical fibre?

Define critical angle?

Numerical aperture is

(a) sine of critical angle

(b) cos of acceptance angle

(c) sine of acceptance angle

(d) acceptance cone

Name the two types of optical fibres?

What are the advantages of optical

fibre?

What are the applications of optical

fibres?

Name the two types of optical fibres?

Numerical aperture depends upon

(a) Refractive indices of core and

cladding

(b) Material of core

(c) Light source

(d) Length of optical fibre cable.

http://www.labelectronics.com/index.php?o

ption=com_virtuemart&page=shop.browse

&category_id=22&Itemid=53&vmcchk=1&It

emid=53

http://www.trainer-kits.com/fibre-optical-

trainer.html

http://en.wikipedia.org/wiki/Optical_fiber

Engineering physics by H.K MALIK