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

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Optical Fibre Amplifiers

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Introduction to Optical Amplifiers

Raman Fibre Amplifier

Brillouin Fibre Amplifier

Doped Fibre Amplifier

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* 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).

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* 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

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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

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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)

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* 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

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* 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

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* Applications of Optical Amplifier (cont.)(a) In-line Amplifier

(b) Preamplifier

(c) Power Amplifier

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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.

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* Merits of TWA

able to operate at the 1300nm and 1550nm wavelengths (simultaneously)wide bandwidth, up to 100nmcan be readily integrated along with other semiconductors and photonic devices into one monolithic chip called an opto-electronic integrated circuit (OEIC)

* Advantages of SLAs•

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a relatively high crosstalk levelpolarization sensitivitylarge coupling lossdifficult to produce an active medium with reflectances as low as 10-4 (TWA) optical noise

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* Drawbacks of SLAs

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Basic ConceptsMost 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

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Gain SaturationThe 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,

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Gain SaturationAmplifier gain G as a function of the output power (normalized to the saturation power)

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Amplifier NoiseThe 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

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Amplifier Noise

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Amplifier Noise

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Amplifier Noise

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Basic Concepts

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Raman Gain & Bandwidth

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Raman Gain & Bandwidth

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Amplifier Characteristics

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Amplifier Performance

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Pumping Requirements

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Gain Spectrum

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Gain Spectrum

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Theory

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Theory

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Theory

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Theory

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Amplifier Noise

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Amplifier Noise

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Amplifier Noise

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Amplifier Noise

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Multichannel Amplification

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Distributed-Gain Amplifiers

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Optical Preamplification

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Noise Accumulation in Long-Haul Systems

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ASE-Induced Timing Jitter

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Accumulated Dispersive and Nonlinear Effects

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WDM-Related Impairments

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WDM-Related Impairments

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

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