5. 1. An optical fiber is a flexible, transparent fiber made of very pure glass {silica}. 2.It acts as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. 3.Optical fibers are widely used in fiber-optics communications, which permits transmission over longer distances and at higher bandwidths(data rates) than other forms of communication.

6. Construction of Optical Fiber :- A main purpose of a fiber optic cable is to protect the fiber core inside the cable that carries the light signal transmission. The following Diagram shows the construction of a fiber optic cable.

7. The fiber core is made of silica glass and is the central part of the fiber optic cable that carries the light signal.They are hair-thin in size and the diameter of the fiber core is typically 8 μm for single mode fiber, and 50m or 62.5 m for multi mode fiber core The cladding is also made of glass, and is the layer that surrounds the fiber core. Together, they form a single solid fiber of glass that is used for the light transmission. The diameter of the cladding is typically 125 μm.

9. The buffer is third layer, buffer coatings are UV-cured urethane acrylite composite materials applied to the outside of the fiber during the drawing process. The coatings protect the very delicate strands of glass fiber. The last layer is cable jacket, which is comprised of various materials depending on the choice of user and application in use. They act as a mechanical protection to the core and cladding inside

10. An optical fiber is a cylindrical dielectric waveguide (non- conducting waveguide) that transmits light along its axis, by the process of total internal reflection. The fiber consists of a core surrounded by a cladding layer, both of which are made of dielectric materials. To confine the optical signal inthe core, the refractive index of the core must be greater than that of the cladding.

12. # It is designed to carry a single ray of light (mode). # They have higher bandwidth than multimode. # Equipment for single mode is expensive as compared to multimode. # But they themselves are cheap in bulk # They are also called as mono-mode optical fiber, single mode optical guide and uni-mode fibers.

13. Multi-mode optical fiber(MM fiber) is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Typical multimode links have data rates of 10 Mbit/s to 10 Gbit/s over link lengths of up to 600 meters—more than sufficient for the majority of premises applications. The equipment used for communications over multi-mode optical fiber is much less expensive than that for single-mode optical fiber.

14. For the effective use of Optical Fiber, it would be necessary to detect and localize the fiber failures without delay, and the technique used to detect and localize the fiber failures is known as Localization. In general, an optical time-domain reflecto-meter (OTDR) has been used to localize fiber failures. Fault Localization can be demonstrated by using instruments Such as optical a and metallic time domain reflecto-meters (OTDR & MTDR)

15. The physical cable or connector damage (Mainly for the connector and disconnect the connection cable) # the cable physical damage. # Partial failure of the connector(improper construction of connectors and cable breakage) # line graph error(twisted pair cable)# the local cable damage.(mostly due to poordesign or construction technology)

16. # mostly due to improper construction methods or accidental damage to network cables and other causes. Mainly for the connector and disconnect the connection cable. # Mainly due to the tight binding between the short circuit caused the cable, because cable nails embedded in gold scrap, stripping header damaged insulation and cable multi- conductor lead wire insulation faults exposed. # Mainly as a result of the cable twisted, bending radius is toosmthe drag force exceeds the mechanical strength of the cable by cable damage, and many more appear in the new wiring project.

17. Some specific instruments are used for localisation of Optical Fiber Fault are as follows:- # Optical time-domain reflecto-meter (OTDR) #optical power meter (OPM) #Pen-type Visual Fault Locator

18. Optical time-domain reflecto- meter (OTDR) An optical time- domain reflecto-meter(OTDR) is an opto-electronic instrument used to characterize an optical fiber.

19. An optical power meter(OPM) is a device used to measure the power in an optical signal. The term usually refers to a device for testing average power in fiber optic systems. A typical optical power meter consists of a calibrated sensor, measuring amplifier and display. The sensor primarily consists of a photo diode selected for the appropriate range of wavelengths and power levels.

20. Locator Pen type Visual Fault Locator FLP-8312 is simple, easy to use instruments with stable output designed to locate faults on fiber optic cables. When a break or sharpend exists in a fiber, the red light from the visible fault locator will indicate the trouble spot. Used with either multimodeor single mode fiber, the Visual Fault Locator have many useful applications such as locating troubles in splice trays, patch panels, cable splice points, and tracing fiber runs

21. As mentioned above, Optical Fiber has different types of fault, and techniques which are used for recovering the damages of Optical Fiber are known as Rectification 0f Optical Fiber Specific instrument used for Rectification of optical Fiber fault is fusion splicing

22. Fusion splicing is the act of joining two optical fiber send-to-end using heat. The goal is to fuse the two fibers together in such a way that light Passing through the fibers is not scattered or reflected back by the splice. The process of fusion splicing involves using localized heat to melt or fuse the ends of two optical fibers together, the fibers are placed into the apparatus, aligned, and they fused together.

23. # A University on (Mar. 2, 2011) has developed the very first optical fiber made with a core of zinc selnide --a light-yellow compound that can be used as a semiconductor. The new class of optical fiber, which allows for a more effective and liberal manipulation of light, promises to open the door to more versatile laser- radar technology. Such technology could be applied to the development of improved surgical and medical lasers

24. # Better countermeasure lasers used by the miltary # And superior environment-sensing lasers such as those used to measure pollutants and to detect the dissemination of bioterrorist chemical agents. # They found that the new class of fiber provided more versatility not just in the visible spectrum, but also in the infrared --electromagnetic radiation with wavelengths longer than those of visible light. military