1 Optical Fibre Amplifiers
2 Introduction to Optical Amplifiers Raman Fibre Amplifier Brillouin Fibre Amplifier Doped Fibre Amplifier
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 * 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 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 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 * 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 * 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 * Applications of Optical Amplifier (cont.) (a) In-line Amplifier (b) Preamplifier (c) Power Amplifier
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 a relatively high crosstalk level polarization sensitivity large coupling loss difficult to produce an active medium with reflectances as low as (TWA) optical noise * Drawbacks of SLAs
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 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 Gain Saturation Amplifier gain G as a function of the output power (normalized to the saturation power)
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 Amplifier Noise
17 Amplifier Noise + +
18 Amplifier Noise
19 Basic Concepts
20 Raman Gain & Bandwidth
21 Raman Gain & Bandwidth
22 Amplifier Characteristics
23 Amplifier Characteristics
24 Amplifier Characteristics
25 Amplifier Characteristics
26 Amplifier Characteristics
27 Amplifier Characteristics
28 Amplifier Performance ???
29 Amplifier Performance
30 Amplifier Performance
31 Amplifier Performance ???
32 Amplifier Performance
33 Amplifier Performance
34 Amplifier Performance
35 Pumping Requirements
36 Pumping Requirements
37 Pumping Requirements
38 Pumping Requirements
39 Pumping Requirements
40 Gain Spectrum
41 Gain Spectrum
42 Theory
43 Theory +
44 Theory
45 Theory
46 Amplifier Noise
47 Amplifier Noise
48 Amplifier Noise
49 Amplifier Noise
50 Multichannel Amplification
51 Multichannel Amplification
52 Multichannel Amplification
53 Multichannel Amplification
54 Multichannel Amplification
55 Multichannel Amplification
56 Multichannel Amplification
57 Multichannel Amplification
58 Multichannel Amplification
59 Distributed-Gain Amplifiers +
60 Distributed-Gain Amplifiers +
61 Distributed-Gain Amplifiers
62 Optical Preamplification
63 Optical Preamplification
64 Optical Preamplification
65 Optical Preamplification
66 Optical Preamplification
67 Optical Preamplification +
68 Optical Preamplification +
69 Noise Accumulation in Long-Haul Systems
70 Noise Accumulation in Long-Haul Systems
71 Noise Accumulation in Long-Haul Systems
72 Noise Accumulation in Long-Haul Systems
73 Noise Accumulation in Long-Haul Systems
74 ASE-Induced Timing Jitter +
75 ASE-Induced Timing Jitter
76 ASE-Induced Timing Jitter
77 ASE-Induced Timing Jitter
78 Accumulated Dispersive and Nonlinear Effects
79 WDM-Related Impairments
80 WDM-Related Impairments
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