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	Optical amplifier - Wikipedia, the free encyclopedia
		An optical amplifier may be thought of as a laser without an optical cavity, or one in which feedback from the cavity is suppressed.
		A distributed Raman amplifier is one in which the transmission fibre 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 fibre to provide amplification.
		In the case of a lumped Raman amplifier highly nonlinear fibre with a small core is utilised to increase the interaction between signal and pump wavelengths and thereby reduce the length of fibre required.
	en.wikipedia.org /wiki/Optical_amplifier (1869 words)

	Raman amplifier, optical repeater, and raman amplification method - Patent 6292288
		A Raman amplifier according to the present invention comprises a plurality of pumping means using semiconductor lasers of Fabry-Perot, DFB, or DBR type or MOPAs, and pumping lights outputted from the pumping means have different central wavelengths, and interval between the adjacent central wavelength is greater than 6 nm and smaller than 35 nm.
		In the Raman amplifier according to the present invention, when a difference between maximum and minimum values of the central wavelength of the pumping light is within 100 nm, overlapping between the pumping light and the optical signal can be prevented to prevent wave form distortion of the optical signal.
		The Raman amplifier comprises a signal input fiber 12, an amplifier fiber (optical fiber) 2, a WDM coupler 13, a pumping means 1, a tap coupler for monitoring 14, a monitor signal detecting and LD control signal generating circuit 15, a signal output fiber 16, and a polarization independent isolator 25.
	www.freepatentsonline.com /6292288.html (14940 words)

	Research
		The most important optical amplifier is the Erbium doped fiber amplifier which is considered to be the most important technological development of the 1990's as it led to high capacity high performance WDM systems which enabled the development of the internet as we know it.
		The noise in Raman amplifiers stems from the spontaneous Raman scattering and from noise transferred from the pump RIN [25].
		The noise in parametric amplifiers stems from the pump and from vacuum field noise which represents the minimum noise possible in those amplifiers where the nonlinear energy transfer mechanism is not in itself a noisy process.
	www.ee.technion.ac.il /people/ddahan/research.htm (3779 words)

	Raman Amplifiers Use Span Fiber to Raise Signal Strength
		Raman amplifiers are excellent candidates to serve this role since they are effective both as distributed and discrete amplifiers, and can be tuned to any wavelength in the transmission window of optical fibers.
		Stimulated Raman scattering is a nonlinear optical process in which intense pump light interacts with a signal of lower frequency, simultaneously amplifying the signal and producing an optical phonon.
		Raman scattering occurs in all optical fibers with its strength depending only on the type of optical fiber and the frequency offset and power of the interacting waves.
	www.photonicsonline.com /Content/News/article.asp?DocID={1E4EE190-C901-11D3-9A84-00A0C9C83AFB}&VNETCOOKIE=NO (1154 words)

	oe magazine - product trends (Site not responding. Last check: 2007-10-23)
		In Raman amplification, light pumped down a fiber interacts with the molecules of the silica, which causes a spectral shift that transfers energy from a lower-frequency pump beam to a higher-frequency signal-beam counter propagating to the pump beam.
		Distributed Raman amplifiers use the actual transmission fiber as the gain medium, to provide gain along the length of the fiber.
		He notes that the idea of a discrete Raman amplifier for S-band wavelengths is a good one, but says it would depend on the development of compatible sources and detectors.
	www.oemagazine.com /fromTheMagazine/mar01/prodtrends.html (637 words)

	Laser Focus World - The many variations of the Raman effect (Site not responding. Last check: 2007-10-23)
		While Raman scattering in the most general sense can occur through changes in the vibrational or rotational states of a molecule, the term usually indicates scattering by vibrational states alone, as purely rotational shifts are small and difficult to observe.
		A 532-nm laser beam exits the head of the Monterey Bay Aquarium's deep ocean Raman probe at a depth of 10,000 ft. The system is used to study seafloor minerals that have trapped vast amounts of methane and CO Molecules that exhibit strong Raman scattering typically have distributed electron clouds, such as carbon-carbon double bonds.
		Raman scattering differs from most nonlinear optical phenomena in that the energy state of the material is involved in the process, and a fully quantum-mechanical theory is required to take this into account.
	lfw.pennnet.com /Articles/Article_Display.cfm?Section=ARTCL&ARTICLE_ID=186758&VERSION_NUM=1 (1838 words)

	Laser Focus World - S-band amplification challenges developers (Site not responding. Last check: 2007-10-23)
		Raman amplification is the leading method, but several other techniques are also under investigation to allow the move to the next frontier for optical amplification.
		Semiconductor optical amplifiers can be made for the S-band, but their application in wavelength-division multiplexed systems has been limited by high crosstalk between optical channels.
		One is the potential overlap between Raman pump sources for the L- and C-band and signal wavelengths in the S-band.
	lfw.pennnet.com /Articles/Article_Display.cfm?Section=Articles&Subsection=Display&ARTICLE_ID=147590 (1793 words)

	Sir CV Raman: The man and his effect by Biplab Pal
		Raman drew Nagendranath aside and explained his new problem; he was trying to find a theory of earthquakes taking into account the actual shape of the earth and the wave-like nature of the quakes.
		Raman has explained this apparent contradiction and the coming into existence of the lines by the effect of combination between the quantum of light coming from without and the quanta of light that are released or bound in the atom.
		Raman himself and his fellow-workers have, during the years that have elapsed since the discovery was made, investigated the frequencies in a large number of substances in a solid, liquid, and gaseous state.
	www.mukto-mona.com /Articles/biplab_pal/cv_raman.htm (9938 words)

	Raman Amplifier (Site not responding. Last check: 2007-10-23)
		The Raman optical amplifier is based on an entirely different principle than EDFA’s or conventional lasers.
		Raman optical amplifiers utilize Raman scattering (the Raman effect, often called SRS - Stimulated Raman Scattering) to create optical gain.
		The two key elements of the Raman optical amplifier are the pump laser and the directional coupler.
	www.mrfiber.com /Raman_Amplifier.htm (536 words)

	Optical Amplifiers
		The noise added by the amplifier at this point is also not as critical because the incoming signal has a large signal-to-noise ratio (SNR).
		Normally employing a hybrid optical amplifier, consisting of two separate optical amplifiers, allows for separate amplification, one for the lower 40 nm band and the second for the upper 40 nm band.
		Raman optical amplifier is little more that a high-power pump laser, and a WDM or directional coupler.
	www.fiber-optics.info /articles/op-amp.htm (1941 words)

	Optiwave - Newsroom (Site not responding. Last check: 2007-10-23)
		Fiber Raman amplifiers in WDM systems have recently received much more attention because of their greatly extended bandwidth and distributed amplification with the installed fiber as gain medium.
		Wideband amplifier gain spectrums have been demonstrated using either a hybrid fiber amplifier consisting of erbium-doped fiber amplifers (EDFAs), lumped Raman amplifiers, and a gain-equalizer, or fiber Raman amplifiers pumped at multiple wavelengths.
		Optimization of Raman amplifiers by using a multipump configuration is a complicated and time-consuming procedure, given that the required pump power for a certain Raman gain is affected by several factors, including Raman gain coefficient, polarization effect, fiber length, fiber loss at pump wavelength, pump depletion, and pump-to-pump Raman interaction.
	www.optiwave.com /2006/newsroom/news_wdm.htm (1525 words)

	Lightwave - Raman amplification: longer, wider, faster, cheaper
		Discrete Raman is simply a stand-alone amplifier, similar to an EDFA in that the signal is not amplified in the transmission fiber but piped into a discrete box where it travels through a length of specialty fiber (typically small-effective-area fiber) where gain is achieved.
		EDFAs had a distinct advantage over Raman in the amplification of light signals in the erbium band (1,530-1,565 nm), both in terms of efficiency (Raman amplifiers' power -conversion efficiency was approximately 25%, compared with approximately 80% for EDFAs), but even more importantly in the ready availability of key components (reliable, high-powered 980-nm pumps, etc).
		The cascaded Raman amplifier sits in the hut and uses the transmission fiber itself to amplify the oncoming signal (hence, cascaded Raman meets the definition of a distributed Raman device).
	lw.pennnet.com /Articles/Article_Display.cfm?Section=Archives&Subsection=Display&ARTICLE_ID=94195&KEYWORD=WaveSplitter (2961 words)

	Hybrid-type low-noise dispersion compensating optical fiber amplifier - Patent 6888670
		The amplifier of claim 1 further comprising a second DCF connected between the DCRA and the second optical fiber amplifier, and for further compensating for the dispersion in optical lines.
		Preferably, the gain of the first optical fiber amplifier is adjusted not to operate the DCRA in a non-linear region while the length of the pre-stage optical fiber and the intensity of pump light supplied to the pre-stage optical fiber are adjusted to operate the first optical fiber amplifier in a non-saturation region.
		This amplifier requires a DCRA capable of compensating for the dispersion in the span of each optical fiber in an optical repeater in the event that a single-mode optical fiber is used as a transmission line and a channel is added or dropped.
	www.freepatentsonline.com /6888670.html (3518 words)

	[No title] (Site not responding. Last check: 2007-10-23)
		In the early years of the Raman fiber before extensive work had begun, no one perceived that a Raman fiber could be pumped by a practical semiconductor laser-based source or that an efficient CW-pumped Raman Fiber Laser was possible.
		Raman amplifiers are based on a theory that seemed highly unlikely at the time: to amplify a light beam, blast the medium through which it is traveling using another beam coming from the opposite direction.
		Raman scattering occurs when an atom absorbs a photon, or light particle, and another photon of a different energy is released.
	education.uncc.edu /cmste/papers/revised.doc (1161 words)

	Technology Review: Emerging Technologies and their Impact
		Raman amplifiers are based on a rather improbable premise: to amplify a light beam, blast the medium through which it is traveling, using another beam coming from the opposite direction.
		(C. Raman won the 1930 Nobel Prize in physics for observing the general effect.) In the latest version of Raman amplification, Lucent has developed a device that uses multiple lasers to boost light signals in an optical fiber, allowing the signals to travel much farther before they need to be boosted again.
		A 1999 patent issued to Lucent describes a new type of Raman amplifier that is "used in almost all the new ultralong-distance systems being developed," says coinventor Kenneth Walker.
	www.technologyreview.com /read_article.aspx?id=12391&ch=infotech (598 words)

	[No title] (Site not responding. Last check: 2007-10-23)
		The focus will be on the characteristics and design principles of Erbium-doped fiber amplifiers and Raman fiber amplifiers and on their applications in optical networks.
		Raman fiber amplifiers, which have superior noise characteristics and spectral flexibility, are becoming more widely used to enhance performance and to reduce system cost.
		We will discuss the key characteristics of Raman amplifiers, such as pump requirements, noise performance, spectral dependence and polarization dependence, as well as effects such as nonlinear pump interactions and RIN transfer impairments in order to understand the design principles of Raman amplifiers and their applications in optical networks.
	www.cleoconference.org /Conference_Program/SC123.aspx (573 words)

	Raman amplifier example
		The pump beam is at 1.06 microns and the seed beam is at 1.54 microns.
		The amplifier depletes the pump beam and amplifies the seed beam.
		Intensity of pump beam after Raman amplifier, showing depletion of the pump in the center due to energy extraction by the seed beam.
	www.aor.com /html/ex17.html (447 words)

	IEC: Raman Amplification Design in Wavelength Division Multiplexing (WDM) Systems
		Flexible assignment of signal frequencies, as Raman gain depends on the pump wavelength and not on a wavelength-sensitive material parameter of the medium, such as the emission cross-section of dopant in the erbium-doped fiber (EDF).
		Raman amplifiers are topologically simpler to design than doped-fiber amplifiers, as the existing transmission fiber can be used as a medium if properly pumped.
		When the Raman pump wave has slight random power fluctuations in time, which is almost always the case, individual bits might be amplified differentially, which leads to amplitude fluctuations or jitter.
	www.iec.org /online/tutorials/raman/topic03.html (669 words)

	CommsDesign - Laser-Less Raman Amplifiers in It For The Long-Haul (Site not responding. Last check: 2007-10-23)
		Raman amplifiers are simple devices that use the intrinsic properties of silica fiber to create amplification, enabling the transmission fiber to become a distributed amplifier such that the gain in the fiber overcomes the loss of signal along the fiber.
		Raman amplification is based on stimulated Raman scattering (SRS), a non-linear effect of optical fiber in which gain is produced at lower energy wavelengths when excited (or pumped) with higher energy (at approximately 100 nm shorter wavelength) light.
		Despite all of the advantages, Raman amplification is not very common outside the world of submarine transmission because EDFAs have higher gain and have been "good enough" given the existing amplifier hut spacing and the C-band has sufficient wavelength capacity for most routes.
	www.commsdesign.com /design_corner/OEG20030702S0011 (2098 words)

	Photonics
		This, allied with the fact that such an amplifier can be simply constructed from stabdard fibre components, means that Raman amplifiers may provide a viable route for upgrading existing systems in the second telecom window.
		To design a Raman amplifier operating at around 1.3 micron, a suitable pump source is required.
		Initial experiments with a much 'quieter' diode-pumped YAG laser pump indicate a corresponding reduction in amplifier noise, and it is expected that the use of a diode-pumped ytterbium-doped fibre laser will result in a further improvement in amplifier noise, combined with advantages in system simplicity, size, power consumption and cooling requirements.
	www.ic.ac.uk /research/photonics/research/topics/fibres/amps/raman.htm (653 words)

	Encyclopedia of Laser Physics and Technology - Raman amplifiers, fiber amplifier, Raman gain, noise figure
		A Raman amplifier is an optical amplifier based on Raman gain.
		An input signal can be amplified while co- or counterpropagating with a pump beam, the wavelength of which is typically a few tens of nanometers shorter.
		Fibers used for Raman amplifiers are not doped with rare-earth ions.
	www.rp-photonics.com /raman_amplifiers.html (386 words)

	Encyclopedia of Laser Physics and Technology - noise figure, quantum noise, fiber amplifier, Raman amplifiers
		More precisely, it is a factor which tells how much higher the noise power spectral density of the amplified output is compared with the input noise power spectral density times the amplification factor, assuming that the input noise is at the shot noise level.
		This limit can be reached for a four-level laser amplifier, an optical parametric amplifier, or a Raman amplifier, while quasi-three-level amplifiers tend to have higher noise figures.
		Erbium-doped fiber amplifiers, fiber Raman amplifiers as well as semiconductor optical amplifiers have non-ideal noise figures, which depend on design details, and can be increased further e.g.
	www.rp-photonics.com /noise_figure.html (523 words)

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