Transcript Slide 1
Optical Fibre Amplifiers 1 Introduction to Optical Amplifiers Raman Fibre Amplifier Brillouin Fibre Amplifier Doped Fibre Amplifier 2 * 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). 3 * 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 mm) or Neodymium/Praseodymium (1.3 mm) - amplification also can be provided by nonlinear effects such as stimulated Raman scattering or Brillouin scattering 4 Types of Optical Amplifiers Travelling Wave Semiconductor Laser Amplifier (SLA) Angled-facet or tiltedstripe – the reflected beam at the facet is physically separated from the forward beam Mirror Fabry-Perot Semiconductor Laser Amplifier (SLA) Buried-facet or window facet – the optical beam spreads in the transparent window 5 Types of Optical Amplilfiers Rare-earth dopants (for doped optical amplifier) or a highly nonlinear medium (for Raman and Brillouin optical amplifiers) Its wavelength is dependent on the dopant 6 * 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 7 * 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 8 * Applications of Optical Amplifier (cont.) (a) In-line Amplifier (b) Preamplifier (c) Power Amplifier 9 * Merits of TWA • 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. * Advantages of SLAs • 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 optoelectronic integrated circuit (OEIC) 10 * Drawbacks of SLAs • • • • 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 11 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 12 Gain Saturation The large-signal amplifier gain: The output saturation power Pouts – the output power for which the amplifier gain G is reduced by a factor of 2 (or by 3 dB) from its unsaturated value G0. By using G = G0/2, 13 Gain Saturation Amplifier gain G as a function of the output power (normalized to the saturation power) 14 Amplifier Noise The SNR degradation is quantified through a parameter Fn, called the amplifier noise figure Consider an amplifier with the gain G such that the output and input powers are related by Pout = GPin. The SNR of the input signal is given by 15 Amplifier Noise 16 Amplifier Noise + + 17 Amplifier Noise 18 Basic Concepts 19 Raman Gain & Bandwidth 20 Raman Gain & Bandwidth 21 Amplifier Characteristics 22 Amplifier Characteristics 23 Amplifier Characteristics 24 Amplifier Characteristics 25 Amplifier Characteristics 26 Amplifier Characteristics 27 Amplifier Performance ??? 28 Amplifier Performance 29 Amplifier Performance 30 Amplifier Performance ??? 31 Amplifier Performance 32 Amplifier Performance 33 Amplifier Performance 34 Pumping Requirements 35 Pumping Requirements 36 Pumping Requirements 37 Pumping Requirements 38 Pumping Requirements 39 Gain Spectrum 40 Gain Spectrum 41 Theory 42 Theory + 43 Theory 44 Theory 45 Amplifier Noise 46 Amplifier Noise 47 Amplifier Noise 48 Amplifier Noise 49 Multichannel Amplification 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 Distributed-Gain Amplifiers + 59 Distributed-Gain Amplifiers + 60 Distributed-Gain Amplifiers 61 Optical Preamplification 62 Optical Preamplification 63 Optical Preamplification 64 Optical Preamplification 65 Optical Preamplification 66 Optical Preamplification + 67 Optical Preamplification + 68 Noise Accumulation in Long-Haul Systems 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 ASE-Induced Timing Jitter + 74 ASE-Induced Timing Jitter 75 ASE-Induced Timing Jitter 76 ASE-Induced Timing Jitter 77 Accumulated Dispersive and Nonlinear Effects 78 WDM-Related Impairments 79 WDM-Related Impairments 80 81