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To Study the Numerical Aperture of optical plastic fiber cable

Apparatus Required

Fiber Optics Analog Transmitter Module - 01

☞Plastic Fiber cable 1 meter - 01

☞Adapter +15V/ DC - 01

☞Patch Chords - 03

☞Numerical Aperture Setup - 01



In fiber optics, the numerical aperture (NA) of an optical system is a dimensionless number that characterizes the range of angles over which the system can accept or emit light. By incorporating index of refraction in its definition, NA has the property that it is constant for a beam as it goes from one material to another provided there is no optical power at the interface. The exact definition of the term varies slightly between different areas of optics. Numerical aperture is commonly used in microscopy to describe the acceptance cone of an objective (and hence its light-gathering ability and resolution), and in fiber optics, in which it describes the cone of light accepted into the fiber or exiting it.

Optical fiber

The transmission medium in fiber-optic communications systems is an optical fiber. The optical fiber is the transparent flexible filament that guides light from a Transmitter to a receiver. An optical information signal entered at the Transmitter end of a fiber - optic communications system is delivered to the receiver end by the optical fiber.

Model Diagram for Plastic Fiber cable

Model Diagram for Plastic Fiber cable

This is multi mode plastic fiber cable, in this fiber cable core diameter 1000 micron and fiber cladding index 1.402.


☞Connect +15V adapter to Fiber Optics Analog Transmitter Module.

☞Switch (sw1) ON Module

☞Connect P1 and P8 test point, P9 and P10 test point using patch chord.

☞Connect the fiber cable one end to Transmitter module another end to Numerical Aperture setup (Fig1).


☞Numerical Aperture is, formula

Where, R = radius of circle D = distance of cable

☞Note down the readings radius(R) in different distance(D) and calculate NA,


(D)in mm


(R) in mm

Numerical Aperture



☞Find out the Average NA in the following table.

☞For the typical plastic fiber cable NA = 0.5 to 0.6

Refer below links for more experiments:

Band width Measurement of Fiber Optic Analog Link

Propagation Loss Measurement in Fiber Optic System

Fiber Optic Analog Link

Voice communication using Fiber Optic Analog Link