PDF | This paper reviews optical fiber amplifiers such as Erbium doped fiber amplifiers EDFAs, many types of Raman amplifiers RAs, Thulium doped fiber. Example: Launching light into a multimode fiber Powers (5). Distribution of optical powers in an erbium-doped fiber amplifier . comprehensive PDF manual . in-line amplification of optical signals by effecting stimulated emission of photons The principle of rare earth doped fiber amplifier is the same as that of lasers.
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The most practical optical amplifiers to date include the SOA and EDFA types. New pumping methods and materials are also improving the performance of. Semiconductor optical amplifiers (SOA, - nm band). 2. Raman optical amplifiers. 3. Brillouin optical amplifiers. 4. Erbium doped fiber amplifier (EDFA. Why do we need Optical Amplifiers? ▫ Typical fiber loss around µm is ~ dB/km. ▫ After traveling ~ km, signals are a enuated by ~20 dB,. ▫ They need .
Laser amplifiers[ edit ] Almost any laser active gain medium can be pumped to produce gain for light at the wavelength of a laser made with the same material as its gain medium. Such amplifiers are commonly used to produce high power laser systems. Special types such as regenerative amplifiers and chirped-pulse amplifiers are used to amplify ultrashort pulses. Solid-state amplifiers[ edit ] Solid-state amplifiers are optical amplifiers that uses a wide range of doped solid-state materials Nd:YAG, Yb:YAG, Ti:Sa and different geometries disk, slab, rod to amplify optical signals. The variety of materials allows the amplification of different wavelength while the shape of the medium can distinguish between more suitable for energy of average power scaling. Doped fiber amplifiers[ edit ] Schematic diagram of a simple Doped Fiber Amplifier Doped fiber amplifiers DFAs are optical amplifiers that use a doped optical fiber as a gain medium to amplify an optical signal. They are related to fiber lasers.
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Poulsen and D. Pei-Li, H. De-Xiu and Z. Jeon, Y. Leem, D. Kim, E. Sin, S. Kim, H. Ko, D. Yee and K. Wang, J. Wu and J. Erbium-doped optical fiber amplifiers[ edit ] The erbium-doped fiber amplifier EDFA is the most deployed fiber amplifier as its amplification window coincides with the third transmission window of silica-based optical fiber.
Both of these bands can be amplified by EDFAs, but it is normal to use two different amplifiers, each optimized for one of the bands. The principal difference between C- and L-band amplifiers is that a longer length of doped fiber is used in L-band amplifiers.
The longer length of fiber allows a lower inversion level to be used, thereby giving at longer wavelengths due to the band-structure of Erbium in silica while still providing a useful amount of gain.
The absorption band is relatively narrow and so wavelength stabilised laser sources are typically needed. Gain and lasing in Erbium-doped fibers were first demonstrated in —87 by two groups; one including David N. Payne , R. Mears , I. M Jauncey and L. Desurvire, P.
Becker, and J. Alexander at Ciena Corporation. However, those regions have not seen any significant commercial use so far and so those amplifiers have not been the subject of as much development as the EDFA.
However, Ytterbium doped fiber lasers and amplifiers, operating near 1 micrometre wavelength, have many applications in industrial processing of materials, as these devices can be made with extremely high output power tens of kilowatts.
Semiconductor optical amplifier[ edit ] Semiconductor optical amplifiers SOAs are amplifiers which use a semiconductor to provide the gain medium.
Recent designs include anti-reflective coatings and tilted wave guide and window regions which can reduce end face reflection to less than 0. Since this creates a loss of power from the cavity which is greater than the gain, it prevents the amplifier from acting as a laser. Another type of SOA consists of two regions. The semiconductor optical amplifier is of small size and electrically pumped. It can be potentially less expensive than the EDFA and can be integrated with semiconductor lasers, modulators, etc.
However, the performance is still not comparable with the EDFA. The SOA has higher noise, lower gain, moderate polarization dependence and high nonlinearity with fast transient time. The main advantage of SOA is that all four types of nonlinear operations cross gain modulation, cross phase modulation, wavelength conversion and four wave mixing can be conducted. Furthermore, SOA can be run with a low power laser. This nonlinearity presents the most severe problem for optical communication applications.
However it provides the possibility for gain in different wavelength regions from the EDFA. High optical nonlinearity makes semiconductor amplifiers attractive for all optical signal processing like all-optical switching and wavelength conversion.
There has been much research on semiconductor optical amplifiers as elements for optical signal processing, wavelength conversion, clock recovery, signal demultiplexing, and pattern recognition. These devices are similar in structure to, and share many features with, vertical-cavity surface-emitting lasers VCSELs. Due to the extremely short cavity length, and correspondingly thin gain medium, these devices exhibit very low single-pass gain typically on the order of a few percent and also a very large free spectral range FSR.
The small single-pass gain requires relatively high mirror reflectivity to boost the total signal gain. In addition to boosting the total signal gain, the use of the resonant cavity structure results in a very narrow gain bandwidth; coupled with the large FSR of the optical cavity, this effectively limits operation of the VCSOA to single-channel amplification.
In addition to their small size, the surface normal operation of VCSOAs leads to a number of advantages, including low power consumption, low noise figure, polarization insensitive gain, and the ability to fabricate high fill factor two-dimensional arrays on a single semiconductor chip.
These devices are still in the early stages of research, though promising preamplifier results have been demonstrated. Tapered amplifiers[ edit ] For high output power and broader wavelength range, tapered amplifiers are used.
These amplifiers consist of a lateral single-mode section and a section with a tapered structure, where the laser light is amplified.
The tapered structure leads to a reduction of the power density at the output facet. Unlike the EDFA and SOA the amplification effect is achieved by a nonlinear interaction between the signal and a pump laser within an optical fiber. There are two types of Raman amplifier: distributed and lumped.
A distributed Raman amplifier is one in which the transmission fiber is utilised as the gain medium by multiplexing a pump wavelength with signal wavelength, while a lumped Raman amplifier utilises a dedicated, shorter length of fiber to provide amplification.