Optical Fiber Cables Introduction

Optical Fiber Cables

1.   Definition and Construction

 The construction of an optical fiber cable has been shown in figure.It consists of an inner glass core surrounded by a glass cladding which has a lower refractive index. Digital signals are transmitted in the form of intensity-modulated light signal which is trapped in the glass core. Light is launched into the fiber using a light source such as a light emitting diode (LED) or Laser.It is detected on the other side using a photo detector such as a phototransistor. The optical fiber cables are costlier than the other two types but they have several advantages over the other two types*.

2. Special Characteristics

The characteristics of optical fiber cables may be listed as under:

(i) Higher bandwidth therefore can operate at higher data rates

(ii) Reduced losses as the signal attenuation is low

(iii) Distortion is reduced hence better quality is assured.

(iv) They are immune to electromagnetic interferences.

(v) Small size and light weight

(vi) Used for point-to-point communication

3. Applications

(i) Optical fiber transmission systems are widely used in the backbone of networks. Current optical fiber systems provide transmission rates from 45 Mb/s to 9.6 Gb/s using the single wavelength transmission.

(ii) The installation cost of ontical fibers is higher than that for the co-axial or twisted wire

cables.

(iii) Optical fibers are now used in the telephone systems.

(iv) In the local area networks (LANS).

4. Advantages of Optical Fibers

Some of the advantages of fiber optic communication over the conventional means of

communication may be listed as under:

(i)Small Size and Light Weight: The size (diameter) of the optical fibers is very small (it is comparable to the diameter of human hair). Therefore, a large number of optical fibers can fit into a cable of small diameter.

(ii) Easy availability and low cost: The material used for the manufacturing of optical fibers is silica glass. This material is easily available. Hence, the optical fibers cost lower than the cables with metallic conductors. (iii) No electrical or Electromagnetic interference: Since the transmission takes place in the form of light rays the signal is not affected due to any electrical or electromagnetic interference. (iv) Large bandwidth: As the light rays have a very high frequency in the GHz range bandwidth of the optical fiber extremely large. This allows transmission of more number of channel Therefore, the information carrying capacity of an optical fiber is much higher than that of a ge axial cable. (v) Other advantages: In addition to the advantages discussed earlier, the optical fiber communication has the following other advantages: (i) No crosstalk inside the optical fiber cable (ii) Signal can be transmitted upto 100 times faster (iii) Intermediate amplifier are not required as the transmission losses in the fiber are low (iv) Ground loops are absent (v) Installation is easy as the fiber optic cables are flexible (vi) These cables are not affected by the drastic environmental conditions Because of all these advantages the optical fiber cable is replacing the conventional metallic conductor cable rapidly in many areas. 5. Drawback of Optical Fiber Some of the drawbacks of optical communication system may be listed as under: (i) Sophisticated plants are required for manufacturing optical fibers (ii) The initial cost incurred is high (iii) Joining the optical fibers is a difficult job.