OPTICAL COMMUNICATION AND NETWORKING PRESENTATION

Optical communication

1. SUBMITTED BY, NAVAMI SURESH LECTURER IN KADUTHURUTHY OPTICAL COMMUNICATION & NETWORKING 1 NAVAMI SURESH,GPTC KADUTHURUTHY

2. OPTICAL FIBER COMMUNICATION Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. APPLICATIONS Medical:-Used as light guides, imaging tools and also as lasers for surgeries Telecommunications- Fiber is laid and used for transmitting and receiving purposes Used in CCTV surveillance cameras Used in data link for computer networks 2 NAVAMI SURESH,GPTC KADUTHURUTHY

3. Structure of Optical Fiber 3 NAVAMI SURESH,GPTC KADUTHURUTHY

4. Fiber Optic Cable consists of four parts Core Cladding Buffer Jacket 4 NAVAMI SURESH,GPTC KADUTHURUTHY

5. Fiber Optic Core: the inner light-carrying member with a high index of refraction. Cladding: the middle layer, which serves to confine the light to the core. It has a lower index of refraction. Buffer: The outer layer, which serves as a "shock absorber" to protect the core and cladding from damage. The coating usually comprises one or more coats of a plastic material to protect the fiber from the physical environment. JACKET :Fiber optic cable’s jackets are available in different colors that can easily make us recognize the exact color of the cable we are dealing with. 5 NAVAMI SURESH,GPTC KADUTHURUTHY

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7. REFRACTION When a light ray goes from a denser transmission medium to a rarer one or vice versa, then its direction changes at the interface of the two medium. This phenomenon is called refraction of light. 7 NAVAMI SURESH,GPTC KADUTHURUTHY

8. REFRACTIVE INDEX Refractive index , measure of the bending of a ray of  light when passing from one medium into another Refractive index is also equal to the velocity of light  c  of a given wavelength in empty space divided by its velocity  v  in a substance, or  n  =  c / v . Refractive index n(Refractive index of medium 1 w.r.t medium2)=sin i /sin r 8 NAVAMI SURESH,GPTC KADUTHURUTHY

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10. CRITICAL ANGLE Critical angle is defined as the angle of incidence that provides an angle of refraction of 90-degrees  sin θ c  = n 2 /n 1 10 NAVAMI SURESH,GPTC KADUTHURUTHY

11. Principle of light transmission in a Fiber For light propagating from denser medium to rarer medium, if the angle of refraction is 90 degrees, the corresponding angle of incidence is called critical angle. If a light ray is an incident at the interface of two media with an angle greater than the critical angle, it is completely reflected back to the denser medium. This phenomenon is called total internal reflection. 11 NAVAMI SURESH,GPTC KADUTHURUTHY

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13. Optical fibers use total internal reflection to transmit light . It has a solid core of dense glass surrounded by a less dense cladding. The light ray passing through the inner core is reflected back instead of being refracted to the rarer cladding. 13 NAVAMI SURESH,GPTC KADUTHURUTHY

14. CONDITIONS FOR TOTAL INTERNAL REFLECTION For total internal reflection to take place ( i ) light must travel from a denser medium to a rarer medium (ii) the angle of incidence inside the denser medium must be greater than the critical angle. 14 NAVAMI SURESH,GPTC KADUTHURUTHY

15. NUMERICAL APERTURE NA is a measure of the light gathering ability of a fiber. The Numerical Aperture (NA) of a fiber is defined as the sine of the largest angle an incident ray can have for total internal reflectance in the core 15 NAVAMI SURESH,GPTC KADUTHURUTHY

16. ACCEPTANCE ANGLE The maximum angle at or below which a ray of light can enter through one end of the fiber still be total internal reflection is called as acceptance angle. The cone is referred as acceptance cone. 16 NAVAMI SURESH,GPTC KADUTHURUTHY

17. PROBLEMS CALCULATE THE SPEED OF LIGHT IN ICE,IF REFRACTIVE INDEX OF ICE IS 1.31 n=c/v c=3x10^8 m/s n=1.31 v=(3x10^8)/1.31 =2.29x10^8m/s 17 NAVAMI SURESH,GPTC KADUTHURUTHY

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21. DIFFERENT TYPES OF FIBRE BASED ON REFRACTIVE INDEX & TRANSMISSION MODE Refractive Index Step Index Graded Index Transmission Mode Single Mode Multi Mode 21 NAVAMI SURESH,GPTC KADUTHURUTHY

22. SINGLE MODE Only one path is available. Core diameter is small Used for long distance communication Fabrication is difficult and costly 22 NAVAMI SURESH,GPTC KADUTHURUTHY

23. Multi Mode More than one path is available Core radius is larger compared to single mode Easy to launch power in to optical fiber 23 NAVAMI SURESH,GPTC KADUTHURUTHY

24. STEP INDEX FIBER The refractive index of the core is uniform throughout and undergoes on abrupt change at the core cladding boundary  The path of light propagation is zig - zag in manner GRADED INDEX FIBER  The refractive index of the core is made to vary gradually such that it is maximum at the center of the core.  The path of light is helical in manner 24 NAVAMI SURESH,GPTC KADUTHURUTHY

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26. DIFFERENT TYPES OF FIBER MATERIALS Optical fibers are used for transmitting light signals over long distances with minimal loss of signal. They are made from materials that can guide light effectively. The most common materials used for optical fibers are glass and plastic. Glass Optical Fibers Silica Glass : Most common material due it’s excellent optical properties, low attenuation, and high-temperature resistance. Used in most telecommunications and high-speed data transfer applications 26 NAVAMI SURESH,GPTC KADUTHURUTHY

27. Doped Silica: Silica glass doped with materials like germanium ( Ge ), phosphorous (P), or boron (B) to modify the refractive index. Plastic Optical Fibers Polymethyl Methacrylate (PMMA): used in short-distance applications due to their ease of handling, flexibility, and lower cost. Fluorinated Polymers: These polymers have lower attenuation than PMMA and are used in specialized applications requiring higher performance over medium distances 27 NAVAMI SURESH,GPTC KADUTHURUTHY

28. ADVANTAGES OF OPTICAL FIBERS High Bandwidth: Can transmit significantly higher amounts of data compared to copper cables. Low Attenuation and Long Distance : Much lower signal loss High-Speed Transmission Immunity to Electromagnetic Interference Security : Difficult to tap into a fiber-optic cable without being detected Easier Installation Lower Operating Costs 28 NAVAMI SURESH,GPTC KADUTHURUTHY

29. MODULE-2 29 NAVAMI SURESH,GPTC KADUTHURUTHY

30. OPTICAL SOURCES Optical sources refer to devices that emit light or optical radiation FEATURES OF OPTICAL SOURCES Size and configuration : Compatible with launching light into fiber( i.e physical dimensions to suit the optical fiber).For to couple large amount of power into an optical fiber, the emitting area should be small. High coupling efficiency or have high optical output power ( i.e Adequate output power into the fiber) 30 NAVAMI SURESH,GPTC KADUTHURUTHY

31. Narrow spectral width (or line width) Stability and efficiency The power requirement for its operation must be low. High Reliability and low cost It must be possible to operate the device continuously at a variety of temperatures for many years. 31 NAVAMI SURESH,GPTC KADUTHURUTHY

32. Main Optical sources for communication are Incoherent sources: Light Emitting Diode(SLED,ELED,SLD) Coherent Sources : LASER diode(DFB,DBR) 32 NAVAMI SURESH,GPTC KADUTHURUTHY

33. LIGHT EMITTING DIODE(LED) Semiconductor diodes which emits visible or invisible light when forward biased Emits light when voltage is applied When forward biased free electrons  in the conduction band recombines with the  holes in the valence band and releases energy in the form of light. The process of emitting light in response to the strong electric field or flow of electric current is called electroluminescence. The construction of LED is similar to the normal p-n junction diode except that gallium, phosphorus and arsenic materials are used for construction instead of silicon or germanium materials. 33 NAVAMI SURESH,GPTC KADUTHURUTHY

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35. SYMBOL OF LED 35 NAVAMI SURESH,GPTC KADUTHURUTHY

36. SURFACE EMITTING & EDGE EMITTING LEDS PARAMETER SURFACE EMITTING EDGE EMITTING Light Emission Direction : Emit light perpendicular to the surface Emit light parallel to the surface of the semiconductor chip Beam Shape : The light emitted is usually broad and somewhat diffuse, resulting in a wider beam angle. narrower beam with higher directionality. 36 NAVAMI SURESH,GPTC KADUTHURUTHY

37. PARAMETER SURFACE EMITTING EDGE EMITTING Applications Commonly used in indicators, displays, and lighting applications where a wide emission pattern is beneficial. Commonly used in optical fiber communications, laser diodes Manufacturing : Generally simpler and cheaper to manufacture compared to edge-emitting LEDs More complex and expensive to manufacture Reliability Less Reliable Highly reliable System Performance Low High 37 NAVAMI SURESH,GPTC KADUTHURUTHY

38. SURFACE EMITTING LED 38 NAVAMI SURESH,GPTC KADUTHURUTHY

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40. EDGE EMITTING LED 40 NAVAMI SURESH,GPTC KADUTHURUTHY

41. Light is emitted from the edge of active layer. It consists of two optical guiding layers. Both guiding layers has refractive index lower than active region and higher than surrounding material. If Numerical Aperture is low, Edge emitting LED couples more power than surface emitting LED. 41 NAVAMI SURESH,GPTC KADUTHURUTHY

42. Modulation of LED Modulating LEDs involves varying their light output by controlling the electrical input using techniques such as AM, PWM, and digital modulation. The choice of modulation method depends on the application requirements, including speed, efficiency, and complexity. Advances in LED technology and driver circuits continue to enhance the capabilities and applications of LED modulation. 42 NAVAMI SURESH,GPTC KADUTHURUTHY

43. Modulation of LED Methods to achieve modulation Pulse Width Modulation (PWM) :PWM controls the LED brightness by switching it on and off at a high frequency. The average power delivered to the LED is varied by changing the duty cycle Analog Modulation : The current through the LED is varied continuously to change its brightness. This can be done by adjusting the voltage applied to the LED. Frequency Modulation (FM) :The frequency of the LED's on/off switching is varied 43 NAVAMI SURESH,GPTC KADUTHURUTHY

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45. Out of these three phenomena transmission and reflection is of less importance to optical sources and detectors. Reflection and transmission are typically considered loss mechanisms. 45 NAVAMI SURESH,GPTC KADUTHURUTHY

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49. Types of Semiconductors DIRECT BANDGAP INDIRECT BANDGAP Generally preferred for making optical sources. Cannot be used to manufacture optical sources. When an electron recombines with holes energy is emitted in form of light When an electron recombines with holes energy is emitted in form of light & heat Example is Gallium Arsenide ( GaAs ). Example is Silicon and Germanium. 49 NAVAMI SURESH,GPTC KADUTHURUTHY

50. Theory of Laser action – absorption and emission of radiation , population inversion, stimulated emission LASER is Light Amplification by Stimulated Emission of Radiation. The process by which electrons in the ground state absorbs energy from external energy sources to vibrate into the higher energy level is called as absorption. Principle of LASER: Absorption and Emission of Radiation 50 NAVAMI SURESH,GPTC KADUTHURUTHY

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52. There are two energy levels namely E1 and E2 for electrons. E1 is the ground state or lower energy state of electrons. The electrons in the ground state are called lower energy electrons or ground state electrons E2 is the excited state or higher energy state of electrons. The electrons in the excited state are called higher energy electrons or excited electrons 52 NAVAMI SURESH,GPTC KADUTHURUTHY

53. When photons or light energy equal to the energy difference of the two energy levels (E2 – E1) is incident on the atom. The ground state electrons gains sufficient energy and vibrates from ground state (E1) to the excited state (E2). Excited state is an unstable state. The lifetime of electrons in excited state is of short period(10 ns). After 10 ns, the excited electrons return to the lower energy state or ground state by releasing energy in the form of photons 53 NAVAMI SURESH,GPTC KADUTHURUTHY

54. SPONTANEOUS EMISSION This process is a naturally occurring process and is called as spontaneous emission. 54 NAVAMI SURESH,GPTC KADUTHURUTHY

55. But in spontaneous emission no control over excited electron and it produces incoherent light Hence for producing coherent light principle of stimulated emission is used. 55 NAVAMI SURESH,GPTC KADUTHURUTHY

56. PRINCIPLE OF LASER LASER-LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION Main principle of LASER IS STIMULATED EMISSION OF RADIATION Stimulated emission involves a process called pumping. The electrons in the ground state are vibrated to the excited states by providing extra energy from energy sources like electric field(current source) called as electrical pumping or light called as optical pumping 56 NAVAMI SURESH,GPTC KADUTHURUTHY

57. STIMULATED EMISSION 57 NAVAMI SURESH,GPTC KADUTHURUTHY

58. When incident photon interacts with the excited electron, it forces the excited electron to return to the ground state The excited electron release energy in the form of light while falling to the ground state Two photons are emitted. One is due to the incident photon and another one is due to the energy release of excited electron. Hence from one photon, two photons are released. This is light amplification . 58 NAVAMI SURESH,GPTC KADUTHURUTHY

59. All the emitted photons in stimulated emission have the same energy, same frequency, same polarization and are in phase. The number of photons emitted in the stimulated emission depends on the number of electrons in the higher energy level or excited state and the incident light intensity. The process of achieving greater population in higher energy state than the lower energy state in order to increase the intensity of light emitted is called as population inversion.  To achieve population inversion, atoms must be continuously excited from a lower energy level to a higher energy level and the process by which the atoms are excited to a higher energy level is called  pumping . 59 NAVAMI SURESH,GPTC KADUTHURUTHY

60. LASER diode structure and Radiation pattern 60 NAVAMI SURESH,GPTC KADUTHURUTHY

61. A laser diode is a semiconductor device that transmits coherent and highly focused light through a process called stimulated emission.  It comprises a p-n junction, where electrons and holes combine, releasing energy as photons. The aim of active layer in between p and n-type layers is to increase the area of electron and hole combination. The laser output is taken from active region of the laser diode. 61 NAVAMI SURESH,GPTC KADUTHURUTHY

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63. OPTICAL DETECTORS 63 NAVAMI SURESH,GPTC KADUTHURUTHY

64. PHOTODETECTION  Photo detector can be defined as a device that is used to detect light radiations by absorption The basic principle of the photo detector is that when an incident light or radiation falls on the surface of detector and get absorbed, it converts it into electrical signals. Photo detector acts as a reversed biased p-n junction. Let’s understand how the photo detector works- There are three process works in the operation of the photo detector: Absorption Transportation of Carriers Extraction of Carriers As Photocurrent 64 NAVAMI SURESH,GPTC KADUTHURUTHY

65. Absorption-In this process, the light energy falls on the photo detector which gets absorbed by it . Electron-Hole pairs are generated Transportation-In this process, the generated charge carriers get transported across all the absorption regions.  Extraction of Carriers As Photocurrent- The current is generated mainly because of the photons that fall on the photo detector, it is called photocurrent. 65 NAVAMI SURESH,GPTC KADUTHURUTHY

66. PIN Photodiode 66 NAVAMI SURESH,GPTC KADUTHURUTHY

67. As the name implies, these photodiodes consist of an un doped intrinsic layer between two highly doped  p-n  junctions. Photons hit the intrinsic layer of the PIN diode , they are absorbed and generate electron-hole pairs. Photons are absorbed at Intrinsic region . That is the importance of Intrinsic region. The movement of these charge carriers generates a photocurrent. It gives better performance than the common photodiodes. 67 NAVAMI SURESH,GPTC KADUTHURUTHY

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69. AVALANCHE PHOTODIODE 69 NAVAMI SURESH,GPTC KADUTHURUTHY AVALANCHE REGION INTRINSIC REGION

70. In the case of  p-n  photodiodes and  p- i -n  photodiodes, the output photocurrent is very small because of the very limited gain. To provide a large gain, the avalanche photodiode is used. It is useful in low light conditions Light absorbed in depletion region of P-N junction creating electron-hole pairs. These electron-hole pairs are swept across the depletion region by reverse bias. 70 NAVAMI SURESH,GPTC KADUTHURUTHY

71. NAVAMI SURESH,GPTC KADUTHURUTHY 71 The key feature of an APD is the high electric field in the depletion region. As the electron (or hole) accelerates under this field, it gains enough kinetic energy and collides with other atoms, creating additional electron-hole pairs. This process is called Impact Ionization . It generates large number of carriers from single photon , effectively amplifying signal

72. COMPARE PIN AND AVALANCHE DIODE PARAMETER PIN DIODE AVALANCHE DIODE MECHANISM When light strikes the intrinsic region, electron-hole pairs are generated When light generates electron-hole pairs, the high electric field in the depletion region causes these carriers to accelerate and collide with atoms, creating additional electron-hole pairs through impact ionization. RESPONSE TIME Faster response since no multiplication process involved Slower response since multiplication process involved NOISE Lower noise since there is no multiplication process Higher due to avalanche multiplication process TEMPERATURE STABILITY Low High INTERNAL GAIN Low HIGH REVERSE BIAS VOLTAGE Lower Reverse Bias Voltage Higher Reverse bias Voltage SENSITIVITY Lower since it has no internal gain Higher due to avalanche multiplication process 72 NAVAMI SURESH,GPTC KADUTHURUTHY