CONSTRUCTION AND WORKING OF AN OPTICAL FIBER

DEFINITION OF OPTICAL FIBERS :

          An optical fiber or optical fibre is  a very long , thin , flexible material , transparent and dielectric medium made by drawing glass or plastic to a diameter slightly thicker than that of a human hair.

optical fibre

HISTORY  OF OPTICAL FIBER :

          Guiding light by internal reflection, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon and Jacques Babinet in Paris in the early 1840s. John Tyndall included a demonstration of it in his public lectures in London, 12 years later.

          The principle was first used for internal medical examinations by Heinrich Lamm in the 1930s. Modern optical fibers, where the glass fiber is coated with a transparent cladding to offer a more suitable refractive index, appeared later in the decade.Charles K. Kao and George A. Hockham of the British company Standard Telephones and Cables (STC) were the first to show that the loss of intensity in optical fibers could be reduced, making fibers a practical communication medium. They proposed that the defects in fibers available at the time was caused by impurities which could be removed. They pointed out the right material to use for such fibers, such as silica glass which has high purity. This discovery earned Kao the Nobel Prize in Physics in 2009.

Daniel colladon first described this “light fountain” or “light pipe” in an 1842 article titled On the reflections of a ray of light inside a parabolic liquid stream.This particular illustration comes from a later article by Colladon, in 1884  

CONSTRUCTION OF AN OPTICAL  FIBERS :

Optical fiber consists of three  layers. They are :

1) Core material

2) Cladding material

3) Protective layer (or) Outer jacket

            The structure of an optical fiber is shown in as below figure

Structure of optical fibre

 The layers in one kind of optical fiber as
   1- Core 8µm
   2- Cladding 125µm
   3- Buffer 250µm
   4- Protective cover or outer jacket 400µm
      The fiber has acore surrounded by a cladding material whose refractive in dex is slightly less than that of the core material which satisfy the conditions for total internal reflection. To protect the fiber material and to give mechanical support there is a protective cover called outer jacket in order to avoid damages there will be cusion between cladding and protective cover. The core as well as cladding is made of either glass or plastics. Thus, we have two  types of the optical fibers. They  are :

1) glass fiber

2) plastic fiber

Glass fiber:

          Glass optical fiber, just as its name shows, is an optical fiber made of glass. Being a delicate type of optical fiber, it cannot be cut, spliced or repaired, less resistant to flexibility and accidental breakage. Glass fiber optic cables are extremely versatile and robust and available in a mix of configurations, end fittings and adapter types. However, this kind of optical fiber is generally ideal for hostile environments. Even when exposed to mechanical stress, high temperatures or chemical substances, it performs normal operation. A figure about the construction of glass optical fiber is available.

glass fiber

Plastic fiber: 
      Plastic optical fiber,polymer optical fiber or POF,is an optical fiber which is made out of plastic.Traditionally,it comprises of PMMA( acrylic) as the core (96% of the cross section in a fiber 1mm in diameter) that facilitates the transmission of light, and fluorinated polymers as the cladding material.Plastic fiber uses harmless green or red light that is easily visible to the eye.Plastic fibers can be safely installed in ahome without risk to inquisitive children.But nowadays, a higher-performance plastic fiber is used based on perfluorinated polymers.The following picture shows the construction of the plastic optical fiber.

plastic optical fibre

WORKING PRINCIPLE OF OPTICAL FIBER :
      Optical fiber works on the principle of total internal reflection. When a light ray travels from denser medium to rarer medium.If the angle of incidence is greater than the critical angle then light gets backs in the same direction.

FIBER –OPTIC COMMUNICATION :

          Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information. First developed in the 1970s, fiber-optic communication systems have revolutionized the telecommunications industry and have played a major role in the advent of the Information Age. Because of its advantages over electrical transmission, optical fibers have largely replaced copper wire communications in core networks in the developed world.

          Most optical communication systems have electrical connections. An electric signal controls a transmitter. The transmitter converts the electric signal to a light signal and sends it through the fiber to the receiver. The receiver converts the light signal back to an electric signal. In some systems a series of these links carry the signal far.

ADVANTAGES OF OPTICAL FIBERS :

• Less weight
• Low cost in bulk
• Minimum attenuations or fiber losses
• Enormous bandwidth
• High information carrying capacity
• High security for tapping
• Less cross talk