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Optical Fibers - Measurement of Attenuation Numerical Aperture

(i) This document describes procedures to measure the numerical aperture and attenuation of optical fibers. Numerical aperture is measured by connecting a fiber to a light source and measuring the diameter of the light spot at varying distances. Attenuation is measured by connecting fibers of different lengths to a light source and power meter and comparing the readings with and without bending the fibers. (ii) The goal is to calculate numerical aperture, study losses at fiber junctions, and measure attenuation in decibels for two fiber patch cords. Apparatus includes an LED light source, power meter, fibers of 1m and 5m length, and other equipment. Formulas are provided to calculate numerical aperture and attenuation.

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SURESH SURAGANI
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692 views6 pages

Optical Fibers - Measurement of Attenuation Numerical Aperture

(i) This document describes procedures to measure the numerical aperture and attenuation of optical fibers. Numerical aperture is measured by connecting a fiber to a light source and measuring the diameter of the light spot at varying distances. Attenuation is measured by connecting fibers of different lengths to a light source and power meter and comparing the readings with and without bending the fibers. (ii) The goal is to calculate numerical aperture, study losses at fiber junctions, and measure attenuation in decibels for two fiber patch cords. Apparatus includes an LED light source, power meter, fibers of 1m and 5m length, and other equipment. Formulas are provided to calculate numerical aperture and attenuation.

Uploaded by

SURESH SURAGANI
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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OPTICAL FIBERS - MEASUREMENT OF

ATTENUATION NUMERICAL APERTURE


Aim:-
(i) calculate the numerical aperture and study the losses that occur in
optical fiber cable.
(ii) To Study the losses at FIBER junction.
(iii) To measure losses in dB of two optical FIBER patch cord and the
coefficient attenuation.
Apparatus:-
Fibre optic LED light source, Fibre optic power meter, Fo cable 1
metre, FO cable 5 meter, In line Adaptor, NA JIG, NA screen and
Mandrel.
Formula:-
For measurement of attenuation L = (Pin - Pout) dB
Pin - Input power in dB
Pout - Output power in dB
(ii) For Numerical aperture
w
𝑁𝐴 = 𝜇𝑎𝑠𝑖𝑛𝜃𝑚𝑎𝑥 = (4 L2+W 2)1 /2

For air 𝜇𝑎 = 1
Where, θmax - the maximum ray angle
W - diameter of the red spot in meters
L - distance of the screen from the fiber end in meters
Procedure:-
Measurement of Numerical Aperture
Step (i)
Connect one end of the 1 meter Fo cable to Fo LED and the other end
to the NA fig as shown in the fig (1)
Step (ii)
Plug the AC main Light should appear at the end of the fibre on the
NA fig.
Step (iii)
Hold the wire with the 4 concentric circles (10, 15, 20 and 25 mm
diameter) vertically at a suitable distance to make the red spot from
the emitting Fibre coincide with 10 mm circle. Note that the
circumference of the spot (outer most) must coincide with the circle.
A dark room with facilitate good contrast record L, the distance of the
screen from the fibre and note the diameter (W) of the spot you may
measure the diameter of the circle accurately with a suitable scale.
Step (iv)
Compute NA from the formula
w
𝑁𝐴 = 𝜇𝑎𝑠𝑖𝑛𝜃𝑚𝑎𝑥 = (4 L2+W 2)1 /2 and also calculate
𝜃𝑚𝑎𝑥 using the formula
𝜃𝑚𝑎𝑥 = sin-1 (NA)
tabulate the reading and the experiment for 15 mm, 20 mm and 25
mm diameter 100.
Note:
In case the fibre is under filled, the intensity with in the spot may not
be evenly distributed. To ensure even distribution of light in the fibre,
first remove twist on the fibre and then 5 turns of the fibre on the
mandrel. Use an adhesive tape on to hold the winding in position.
Now view the spot. The intensity will be more evenly distributed with
in the core.

(ii) Measurement of Attenuation:


Step (i)
Connect one end of the 1 meter Fo cable to the Fo LED and the other
end to the Fo power meter.
Step (ii)
Plug the AC mains. Connect the optical fibre patch cord scarcely, as
shown after relieving Fiber Optic LED Light all twist and strains on
the” Fibre. Note the value on the power meter and note this as P01
Step (iii)
Wind 4 turns of the fibre on the mandrel as shown in experiment 1
and note the new reading of the power meter P02. Now the loss due to
bending and strain on the plastic Fibre is P01 -P02.
Step (iv)
Next remove the mandrel and relieve the cable twist and strains. Note
the reading P01 for the 1 meter cable. Repeat the measurement with the
5 meter cable and note the reading P03 and P04 . Now the loss due to
bending and strain on the plastic fibre is P03 _ P04 dB. Note the reading
as P05

P05 _ P01 gives loss in the second cable plus the loss due to inline
adaptor.
P05 _ P04 gives loss in the first cable plus the loss due to in-line
adaptor.
Assuming a loss of 1.0 dB in the adaptor, we obtain the loss in cable.
Observations:-
P01 = Reading shown by the power meter with 1 m cap
P01 =
P02 = Reading shown by the power meter at 4 turns of the fiber on the
mandrel
P02 =
P03 = Reading shown by the power meter with 5 m cable
P03 =
P04 = Reading shown by the power meter at 4 turns of the fiber on the
madral
P04 =
P05 = Power meter reading with inline adaptor, first cable and second
cable
P05 =
Calculation:
Loss due to bending and strain on the plastic fibre (for 1 metre) =
P01 ~ P02 = _______
Loss due to bending and strain on the plastic fibre (for 5 meter) =
P03 ~ P04 = _______
Loss due to in-line adaptor and the second cable =
P05 ~ P01 = _________

Loss due to in-line adaptor and the first cable =


P05 ~ P02 = __

Result:-
(i) Attenuation loss in the given Fiber optic cable
1. P01 ~ P02 = _____________dB (loss due to strain)
2. P03 ~ P04 = _____________ dB (loss due to strain)
3. P05 ~ P01 = _____________ dB (Linear loss)
4. P05 ~ P02 = ______________dB (Linear loss)
(ii) Numerical aperture NA of the given fiber optic cable for 1 meter
=_____
Acceptance angle 𝜃𝑚𝑎𝑥 = ______

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