1. 1 Optical Fibre Amplifiers

2. 2 Introduction to Optical Amplifiers Raman Fibre Amplifier Brillouin Fibre Amplifier Doped Fibre Amplifier

3. 3 * Introduction - operate solely in the optical domain with no inter-conversion of photons to electrons - can be placed at intervals along a fiber link to provide linear amplification - provide better performance over regenerative repeaters which require optoelectronic devices and electronic circuits: (a) larger amplification bandwidth (several thousands GHz) (b) speed bottlenecks from electronics are removed (c) amplify multiple optical inputs at different wavelengths simultaneously (WDM).

4. 4 * Two main categories of optical amplifiers: (a) Semiconductor Laser amplifiers (SLAs) - a laser diode operated below threshold - amplification is done by stimulated emission from injected carriers (b) Fiber amplifiers (FA) - a fiber section that has a positive medium gain - fiber is doped with Erbium (1.55  m) or Neodymium/Praseodymium (1.3  m) - amplification also can be provided by nonlinear effects such as stimulated Raman scattering or Brillouin scattering

5. 5 Types of Optical Amplifiers Fabry-Perot Semiconductor Laser Amplifier (SLA) Travelling Wave Semiconductor Laser Amplifier (SLA) Angled-facet or tilted- stripe – the reflected beam at the facet is physically separated from the forward beam Buried-facet or window facet – the optical beam spreads in the transparent window Mirror

6. 6 Types of Optical Amplilfiers Its wavelength is dependent on the dopant Rare-earth dopants (for doped optical amplifier) or a highly nonlinear medium (for Raman and Brillouin optical amplifiers)

7. 7 * Optical Amplifier Gain Characteristics - Traveling wave semiconductor laser amplifier (TWSLA), Erbium doped fiber and Raman fiber amplifiers provide wide spectral bandwidth suitable for WDM applications. - Brillouin fiber amplifier has a very narrow spectral bandwidth ~50MHz and it can be used for channel selection within a WDM system

8. 8 * Applications of Optical Amplifier (a) In-line Amplifier - use to compensate for transmission loss and increase the distance between regenerative repeaters. (b) Preamplifier - used as a front-end preamplifier for an optical receiver. (c) Power Amplifier - to boost transmitted power and increase the transmission distance - as booster of signal level in the local area network

9. 9 * Applications of Optical Amplifier (cont.) (a) In-line Amplifier (b) Preamplifier (c) Power Amplifier

10. 10 TWAs have been used more widely than FPAs (particularly for linear application) because they have (a) a large optical bandwidth, (b) high saturation power, and (c) low polarization sensitivity. In particular, TWAs are used as amplifiers in the 1300nm window and as wavelength converters in the 1550nm region. * Merits of TWA able to operate at the 1300nm and 1550nm wavelengths (simultaneously) wide bandwidth, up to 100nm can be readily integrated along with other semiconductors and photonic devices into one monolithic chip called an opto- electronic integrated circuit (OEIC) * Advantages of SLAs

11. 11 a relatively high crosstalk level polarization sensitivity large coupling loss difficult to produce an active medium with reflectances as low as 10 -4 (TWA) optical noise * Drawbacks of SLAs

12. 12 Basic Concepts Most optical amplifiers amplify incident light through stimulated emission – a laser without feedback The optical gain realized when the amplifier is pumped (optically or electrically) to achieve population inversion The optical gain, in general, depends not only on the frequency (or wavelength) of the incident signal, but also on the local beam intensity at any point inside the amplifier. Details of the frequency and intensity dependence of the optical gain depend on the amplifier medium

13. 13 Gain Saturation The large-signal amplifier gain: The output saturation power P out s – the output power for which the amplifier gain G is reduced by a factor of 2 (or by 3 dB) from its unsaturated value G 0. By using G = G 0 /2,

14. 14 Gain Saturation Amplifier gain G as a function of the output power (normalized to the saturation power)

15. 15 Amplifier Noise The SNR degradation is quantified through a parameter F n, called the amplifier noise figure Consider an amplifier with the gain G such that the output and input powers are related by P out = GP in. The SNR of the input signal is given by

16. 16 Amplifier Noise

17. 17 Amplifier Noise + +

18. 18 Amplifier Noise

19. 19 Basic Concepts

20. 20 Raman Gain & Bandwidth

21. 21 Raman Gain & Bandwidth

22. 22 Amplifier Characteristics

23. 23 Amplifier Characteristics

24. 24 Amplifier Characteristics

25. 25 Amplifier Characteristics

26. 26 Amplifier Characteristics

27. 27 Amplifier Characteristics

28. 28 Amplifier Performance ???

29. 29 Amplifier Performance

30. 30 Amplifier Performance

31. 31 Amplifier Performance ???

32. 32 Amplifier Performance

33. 33 Amplifier Performance

34. 34 Amplifier Performance

35. 35 Pumping Requirements

36. 36 Pumping Requirements

37. 37 Pumping Requirements

38. 38 Pumping Requirements

39. 39 Pumping Requirements

40. 40 Gain Spectrum

41. 41 Gain Spectrum

42. 42 Theory

43. 43 Theory +

44. 44 Theory

45. 45 Theory

46. 46 Amplifier Noise

47. 47 Amplifier Noise

48. 48 Amplifier Noise

49. 49 Amplifier Noise

50. 50 Multichannel Amplification

51. 51 Multichannel Amplification

52. 52 Multichannel Amplification

53. 53 Multichannel Amplification

54. 54 Multichannel Amplification

55. 55 Multichannel Amplification

56. 56 Multichannel Amplification

57. 57 Multichannel Amplification + + + + +

58. 58 Multichannel Amplification

59. 59 Distributed-Gain Amplifiers +

60. 60 Distributed-Gain Amplifiers +

61. 61 Distributed-Gain Amplifiers

62. 62 Optical Preamplification

63. 63 Optical Preamplification

64. 64 Optical Preamplification

65. 65 Optical Preamplification

66. 66 Optical Preamplification

67. 67 Optical Preamplification +

68. 68 Optical Preamplification +

69. 69 Noise Accumulation in Long-Haul Systems

70. 70 Noise Accumulation in Long-Haul Systems

71. 71 Noise Accumulation in Long-Haul Systems

72. 72 Noise Accumulation in Long-Haul Systems

73. 73 Noise Accumulation in Long-Haul Systems

74. 74 ASE-Induced Timing Jitter +

75. 75 ASE-Induced Timing Jitter

76. 76 ASE-Induced Timing Jitter

77. 77 ASE-Induced Timing Jitter

78. 78 Accumulated Dispersive and Nonlinear Effects

79. 79 WDM-Related Impairments

80. 80 WDM-Related Impairments

81. 81