How do Fiber Optics Work?

"Fiber optics, how it works!", is the general exclamation that comes into the minds of anyone, who sees a fiber optic cable. The reason is its width. A fiber optic fiber is of the width of one tenth of a human hair. The technology of fiber optics has eased up communication with its several advantages. We will look at the advantages of fiber optics at a later stage. Right now, let us try to understand how does fiber optics work.

What is a Fiber Optic Cable Made Of?

Any technology that is used for communication, uses the principle of conversion of energy. In fiber optics, the communication happens, or as we can say, data is transferred when it is transformed into the form of light pulses. A fiber optic cable is made up of hundreds of pure thin strands of glass. These strands of glass have a width of one tenth of the size of a human hair.

For understanding the principle of fiber optics clearly, we will consider a single mode fiber optic cable. This is the type of cable that is used in Internet, cable TV and telephone connections. A fiber optic cable can be divided into three parts. It is a coaxial cable, and the center most part is called the core which is made out of pure glass and carries the information. The plastic covering above it which causes the reflection of light signals is called the cladding and the sheathing that protects the optical fiber is called the buffer coating. In a single mode fiber, the core is about 5-10 microns in diameter. A dimension of 5 to 10 microns is equivalent to the millionth of a meter. That small is the core of an optical fiber. And with this type of a fiber, information can be carried over 100 kms.

How Does a Fiber Optic Cable Work?

Students of physics might find it easier to understand. Well, however I will try to explain it to you. The principle that is used for transmission of light pulses or photons through an optical fiber is that of 'Total Internal Reflection'.

When light travels from a medium of lower refractive index to that of a higher refractive index, it bends towards the normal. The normal is a line that is perpendicular to the interface of two mediums. However, when light travels from a medium of higher refractive index to that of a lower refractive index, it bends away from the normal. Let us try to understand two angles now. The angle made by the incident ray to the normal is called the angle of incidence and the angle made by the refracted ray with the normal at the point of incidence in the other medium is called the angle of refraction. Now, consider that light is traveling from a medium with higher refractive index to that of a lower refractive index. As the angle of incidence increases, the angle of refraction also increases. Now, if the angle of incidence is increased to a point that the angle of refraction becomes perpendicular to the angle of refraction, i.e., almost parallel to the interface of the two media, then this particular of angle of incidence is called the critical angle. If the angle of incidence is further increased beyond this angle of incidence, then the refracted light will be returned to the same medium, i.e., reflected. This is the process of total internal refraction.

What happens in fiber optics is that the light is sent at such an angle almost parallel to the optical fiber, that it goes through the process of total internal reflection and travels through hundreds of kilometers. Besides, as we all know that the highest speed of any form of energy is that of light energy. So, it has to be the fastest way of communication. Light gets reflected at the walls of the pure glass and hence travels through hundreds of kilometers.

Advantages of Fiber Optics

• With dimensions of one tenth of a human hair, the fiber optic cables are much thinner than their copper counter parts.
• Since information is carried in the form of light signals, so there is no chances of mixing of information in two fibers of the same optical fiber cable as in the case of electrical cables.
• Low power transmitters can be used for the transmission of signals through optical fibers, since the losses are minimal.
• The implementation and use costs much less as compared to their copper counterparts.

Fiber optic communication has many other advantages too. Billions of bits of information can be transferred per second using this technology.