To measure the numerical aperture of an optical fibre using a He-Ne Laser Source.

 To measure the numerical aperture of an optical fibre using a He-Ne Laser Source.

Apparatus: He-Ne Laser Source, 20. X microscopic objective, Two fiber optic chucks, optical fibre, screen, graph paper, millimeter scale, and a measuring tape.

Procedure

• Attach both ends of the fiber optic to the fiber optic chuck.
• Attach the light from the He-Ne Laser source to one end of the optical fiber through the 20X microscope objective. This is the 'final input'.
• Place the white screen where m.m. the graph paper has been inserted some distance from the other end than that which has been coupled to the light source. This end is known as the "output end".
• Adjust the screen position so that it is perpendicular to the fiber axis. Move the screen toward or away from the output end of the optical fiber in such a way that circular dots form on the screen. Measure the distance between the optical fiber output end and the screen. Let L
• Measure the diameter of the point of a two-way circle at a right angle by counting the number of m.m. squares on graph paper or by using the m.m. scale. Let the diameter be D.Then numerical aperture is given by

• Repeat the procedure for different values of L and corresponding values of D.  

Observations 

 

 

	Diameter of the Spot			Distance Between screen and output end of optical fibre L	Numerical aperture    A
S.NO.	Vertical	Horizontal	Mean D

                               Mean sin Өa =

                        ∴ Mean numerical aperture    A =

Acceptance angle.      Өa =  sin A = 

 Precautions.

•  Observe all precautions for use of a He-Ne Laser source.
• The optical fibre must be connected through optic fibre chucks to avoid any leakage. 
• The light from the He-Ne source must be coupled to the optical fibre through a 20X microscopic objective.

Questions & Answers

1. Why optical fibers are made of glass?

• Glass fiber optic cables are thin and light, they are optimized for small spaces also glass optical fiber has a higher information transmission capacity with lower losses.

2. Optical fibre advantages

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* Fiberglass cables can be used at both high and very low temperatures.

* Glass fiber cores are efficient at transmitting light and allow for much higher transfer rates.

*Better bandwidth and Greater flexibility.

3. Optical fibre definition

• An optical fiber is a very thin glass or plastic channel through which information, sound, data, etc. can travel with help of successive total internal reflections in the form of light.

4. Optical fibre example

• Used in  internet, television and telephones in telecommunication services.

5. Optical fibre founder or optical fibre inventor

• Charles Kuen Kao in 1960.

6. Optical fibre frequency range

• Electromagnetic wave with range between 10¹⁴ to 10¹⁵ Hz.

7. Optical fibre principle

•  Optical fibre operates on the principle of Total internal reflection.

8. Optical fibre block diagram

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Let me know if you have more questions or if there is a specific topic that you would like to know more about.