Advantages of Optical Fibers

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1. Advantages of Optical Fibers Large information capacity Long distance transmission Small size and low weight Immunity to electrical interference Enhanced safety Increase signal security

2. Optic spectral Bands Electromagnetic Energy: Planck’s Law Where h= 6.63×10 -34 J-s =4.14 × 10 -15 eV-s is planks constant. Energy in electron volts is given by:  

3. Optic spectral Bands Windows and spectral bands: Figure shows the operating range of optical fiber systems and the characteristics of the four key components of link: optical fiber, light source, photodetectors, and optical amplifiers. The dashed vertical lines indicate the centers of the three main traditional operating wavelength ands if optical fiber system, which are the shirt wavelength region, O-band and C-band.

4. Optic spectral Bands Windows and spectral bands:

5. Decibel Units dB units defined by: Where and are the electrical or optical power levels of a signal at points 1 and 2, and log is base 10 logarithm. Decibel is to measure the changes in the strength of a signal one merely adds or subtracts the decibel numbers between two different points.   Periodically placed amplifiers compensate for energy losses along a link

6. Power in dBm is: Important rule of thumb relationship to remember for optical fiber communications is 0 dBm-1mW. Therefore positive values of dBm are grater than 1mW and negative values are less than 1mW  

7. Network Information Rates To handle the continuous rising demand for high bandwidth services from users ranging from individuals to large businesses and research organizations, telecommunication components companies worldwide are implementing increasingly sophisticated digital multiplexing techniques that allow a larger number of independent information streams to same physical transmission channel simultaneously. Telecom signal multiplexing: The table shows the information rates for some typical telecom services. To send these services from one user to another, network providers combine the signals from many different users and send the aggregate signal over a single transmission line. This scheme is know as time division multiplexing. Where in N independent information streams, each using at a data rate R b/s are interleaved electrically into a single information streams, each running at a data rate of R b/s are interleaved electrically into a single information stream operating at higher rate of NX R b/s.

8. Digital transmission hierarchy used in the (a) North American (b)European based telephone networks

9. Digital multiplexing levels used in north America, Europe, and japan

10. SONET/ SDH Multiplexing Hierarchy With advent of high capacity fiber optic transmission line in the 1980, service providers established a standard signal format called synchronous optical network (SONET) in north America and synchronous digital hierarchy (SDH) in other parts of the world. These standards define a synchronous frame structure for sending multiplexed digital traffic over optical fiber trunk lines. The table shows commonly used SDH and SONET signals levels, the line rate and the popular numerical name for that rate.

11. Basic Optical Laws and Definitions Refractive Index A fundamental optical parameter of a material is the refractive index. The ratio of the speed of light in a vacuum to that in matter is the index of refraction n of the material. Reflection and Refraction

12. Fig. 2-6: Refraction and reflection

13. Fig. 2-7: Representation of the critical angle and total internal reflection at a glass-air interface reflected

14. Fig. 2-14: Single fiber structure Optical Fiber Modes and Configurations Fiber Types: This cylinder is known as core of the fiber. The core is surrounded by a solid dielectric cladding which has a refractive index n 2 that is less than n 1 .

15. Fig. 2-15: Comparison of fiber structures The refractive index of the core is uniform throughout and undergoes an abrupt change at cladding boundary. This is called step-index fiber. The core refractive index is made as vary as a function of the radial distance from the center of fiber. This type is a graded index fiber.

16. The electromagnetic light field that is guided along an optical fiber can be represented by a superposition of bound or trapped modes. Each of these guided modes consists of a set of simple electromagnetic field configurations. Step-Index Fiber Structure: In Step-Index fbers the core of radius a has a refractive index n 1 which is typically equal to 1.48. This is surrounded by a cladding of slightly lower index n 2 , where Rays and Modes

17. Fig. 2-16: Skew rays Ray Optic Representation Meridional rays are confined to meridian planes of the fiber, which are the planes that contain the axis of the symmetry of the fiber (core axis). Meridional rays can be divided into two general classes: bound rays that are trapped in the core while unbound rays that are refracted out of the core Skew rays are not confined to a single plane, but instead tend to follow a helical type path along the fiber as shown in the fig.

18. Meridional ray optics representation of the propagation mechanism in an ideal step index optical waveguide