Satish Pradhan Dnyanasadhana college, Thane Subject-APPLIED Physics paper-III Class- S. Y. B. Sc. SEM-III TOPIC FIBRE OPTICS Presented By Ms. Namrata A. Singh Dept. of Physics

INTRODUCTION Fibre optic communications has revolutionised the telecommunications industry. It has also made its presence widely felt within the data network community as well. Using fibre optic cable, optical communications have enabled telecommunications link to be made over much greater distances and with much lower levels of loss in transmission medium and possibly most important of all, fibre optical communications has enabled much higher data rates to be accommodated. As a result of these advantages, fibre optic communications systems are widely employed for applications ranging from major telecommunications backbone infrastructure to Ethernet systems, broadband distribution and general distribution networking.

Evolution of optical fibre 1880 - Alexander Graham Bell 1930 - patents on tubing 1950 - patent for two-layer glass wave guide 1960 - Laser first used as light source 1965 - High loss of light discovered 1970s - Refining of manufacturing process 1980s - optical fibre technology becomes backbone of long distance telephone networks in numerical aperture.

What is optical fibre ? An optical fibre is a flexible, transparent fibre made of high quality glass (silica) or plastic slightly thicker than a human hair It either functions as a waveguide or light pipe that transmits data between two ends of the fibre or fibre cable Optical fibre are widely used in fibre-optic communications which permits data over long distances and at higher bandwidths (data rates) than other forms of communication Fibres are used instead of metal wires because signals travel along them with less loss and are also safe to electromagnetic interference The field of applied science and engineering concerned with the design and application of optical fibres is known as fibre optics

Structure of optical fibre Optical fibre is comprised of a light carrying core surrounded by cladding which traps the light in the core by the principle of total internal reflection. The core and cladding are usually fused silica glass which is covered by a plastic coating called the buffer plastic coating which protects the glass fibre from physical damage , moisture and mechanical shocks. It also gives strength and safety

Light propagation through fibre core cladding light Fig.(1) An optical fibre carrying light

The Numerical aperture Φ Φ Φ Φ Cladding n2 Air n0=1 core  n1 r axis of the fibre i incident ray Fig.(2) Propagation of light through fibre at the angle of acceptance

Step-Index optical fibre Fig.3(b) Propagation of light through an step-index fibre Fig.3(a) step-index fibre

Graded-Index optical fibre Fig.4(b) Propagation of light through graded-index fibre Fig.4(a) Graded-index optical fibre

Applications of Fibre optics a) Fibre optics communication Fig.5(a) A typical communication system

optical fibre Fig.5 (b )Point-to-point communication link using optical fibre

Fig.6 : A fiber optic temperature sensor b) Fiber Optic Sensor Reflecting mirror Light source Silicon layer Detector Fig.6 : A fiber optic temperature sensor

Advantages of optical communication Capacity of carrying information is very large and have a wider bandwidth They have a very low transmission loss Optical fibres are very light in weight ,flexible, smaller in size, this makes them more suitable in spaceships and aircraft Glass fibres can withstand high temperature. Temperature approaching 8000C leaves glass fibre unaffected Communication by means of an optical fibre provides a high degree of security and privacy Also, practically there is no crosstalk, any interference or coupling with other communication channel. any electrical noise do not interfere with propagation of light signals because of dielectric nature of optical fibre

Application of optical fibre in medical field

a. cladding b. armor c. shielding d. cover MCQs It refers to the dielectric material of an optical fiber that surrounds the core. a. cladding b. armor c. shielding d. cover Light propagation through an optical fiber is based on the principle of total a. internal reflection b. external reflection c. internal refraction d. internal refraction For total internal reflection, angle of incidence of the ray at the interface of core-cladding must be ________ than critical angle of same interface. a. less than b. equal to c. greater than d. none of these In ______ optical fiber core and cladding is of uniform refractive index. a. step-index b. graded-index The maximum angle with which a ray of light can enter through the entrance end of the fiber and still be totally internally reflected is called _________ a. angle of acceptance b. numerical aperture c. critical angle In graded-index optical fiber , a core has _______ refractive index. a. uniform b. non-uniform

a. reflection b. refraction c. refraction d. dispersion MCQs In the structure of fiber, the light is guided through the core due to total internal _______ a. reflection b. refraction c. refraction d. dispersion In the structure of fiber, which component provides additional strength and prevents the fiber from any damage ? a. core b. cladding c. buffer coating d. none of these In an optical fiber, the concept of Numerical aperture is applicable in describing the ability of_________ a. Light collection b. Light scattering c. Light polarization d. Light dispersion In the structure of fiber optic cable, the refractive index of core is always _____ the refractive index of cladding. a. less than b. equal to c. greater than d. none of these Which among the following characteristics of Laser light specifies the precise movement of all individual light waves together through time and space / a. monochromatic b. directional c. coherent d. brightness

Assignment Problems Determine: a) the critical angle of reflection for core-cladding boundary and b) the acceptance angle of the fibre Given : Refractive index of core is 1.4 Refractive index of cladding is 1.3 [ Ans: 68.21o , 31.30o ] Calculate the numerical aperture of a step index fibre for an optical fibre that have a core of refractive index 1.5 and cladding of index 1.48.Also determine the maximum angle for entrance of light if the fibre is put in the air. [ Ans: NA: 0.24413, im = 14.130] The core and cladding of an optical fibrd has refractive indices 1.5 and 1.47 respectively .Find the acceptance angle in air and the critical angle for core/cladding interface. [ Ans: 17o27’,c=78o30’]