Raman amplification

Short description: Inelastic optical scattering phenomenon

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Raman amplification /ˈrɑːmən/[1] is a way of increasing the signal strength in an optical fiber. It is often used in a fiber that carries a signal for a long distance (such as in an undersea cable). Technically, it works by stimulating Raman scattering, in which a lower frequency 'signal' photon induces inelastic scattering of a higher-frequency 'pump' photon in an optical medium in the nonlinear regime. As a result, another 'signal' photon is produced, with the surplus energy resonantly passed to the vibrational states of the medium, increasing the signal strength. This process (like other stimulated emission processes), allows all-optical amplification. This kind of amplification is independent of the modulation, formatting, and bandwidth of the signal being amplified. This, in turn, allows the endpoints of the fiber to be upgraded to newer modulation methods, while the amplifiers remain unchanged. That allows existing undersea cables to carry more data than they did when they were built, without the expensive process of dredging up the cable and replacing all the amplifiers.

Today, Optical fiber is most often used as the nonlinear medium for stimulated Raman scattering for telecom purposes. In this case it has a resonance frequency downshift of ~11 THz (corresponding to a wavelength shift at ~1550 nm of ~90 nm). The stimulated Raman scattering amplification process can be readily cascaded, thus accessing essentially any wavelength in the fiber's low-loss frequency ranges (both 1310 and 1550). In addition to applications in nonlinear and ultrafast optics, Raman amplification is used in optical telecommunications, allowing all-band wavelength coverage and in-line distributed signal amplification.

## Contents

* 1 Long haul and Ultralong haul optical transmission applications
* 2 See also
* 3 References
* 4 Further reading
* 5 External links

## Long haul and Ultralong haul optical transmission applications

In-line Raman amplifiers provide distributed gain along the optical fiber, significantly improving the optical signal-to-noise ratio (OSNR) compared to traditional lumped amplifiers like EDFAs, which enables longer transmission spans in long-haul terrestrial and submarine networks without regeneration.[2][3] They reduce nonlinear effects by maintaining lower average signal power levels, supporting higher capacities and broader bandwidths in dense wavelength-division multiplexing (DWDM) systems. For submarine applications, Raman amplification minimizes the number of underwater repeaters, enhancing reliability and cost-efficiency, while in terrestrial setups, it facilitates ultra-long-haul links over thousands of kms with reduced infrastructure needs.

## See also

* Raman laser
* C.V. Raman
* Raman amplifier
* Chirped pulse amplification
* Regenerative amplification

## References

1. ↑ "Raman effect" . Collins English Dictionary.
2. ↑ Haxell, Ian; Robinson, Niall; Akhtar, Adnan; Ding, Ming; Haigh, Ron (2000-03-07). "2410km All-Optical Network Field Trial with 10GB/s DWDM Transmission" (in EN). Optical Fiber Communication Conference (2000), paper PD41 (Optica Publishing Group): PD41. https://opg.optica.org/abstract.cfm?uri=OFC-2000-PD41.
3. ↑ Haxell, I.; Ding, M.; Akhtar, A.; Wang, H.; Farrugia, P. (2000-07-09). "52×12.3 Gbit/s DWDM transmission over 3600km of True Wave fiber with 100km amplifier spans" (in EN). Optical Amplifiers and Their Applications (2000), paper OTuC7 (Optica Publishing Group): OTuC7. https://opg.optica.org/abstract.cfm?uri=OAA-2000-OTuC7.

## Further reading

* Poem, Eilon; Golenchenko, Artem; Davidson, Omri; Arenfrid, Or; Finkelstein, Ran; Firstenberg, Ofer (26 October 2020). "Pulsed-pump phosphorus-doped fiber Raman amplifier around 1260 nm for applications in quantum non-linear optics" (in EN). Optics Express 28 (22): 32738–32749. doi:10.1364/OE.404015. ISSN 1094-4087. PMID 33114952. Bibcode: 2020OExpr..2832738P. https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-28-22-32738&id=441679. Retrieved 5 January 2022.

## External links

* "Raman Amplifiers", in the Encyclopedia of Laser Physics and Technology
* "Simulation of Distributed Raman Amplification (DRA) for fiber-based transmission systems"

* v
* t
* e

Raman spectroscopy

Techniques|

* Coherent anti-Stokes Raman spectroscopy
* Raman optical activity
* Resonance Raman spectroscopy
* Rotating-polarization coherent anti-Stokes Raman spectroscopy
* Spatially offset Raman spectroscopy
* Stimulated Raman spectroscopy
* Surface-enhanced Raman spectroscopy
* Tip-enhanced Raman spectroscopy
* Transmission Raman spectroscopy

Applications|

* Raman amplification
* Raman cooling
* Raman laser
* Raman microscope
* SHERLOC
* Stimulated Raman adiabatic passage

Theory|

* Depolarization ratio
* Four-wave mixing
* Nonlinear optics
* Raman scattering
* Rayleigh scattering
* Rule of mutual exclusion
* Stokes shift

Journals|

* Journal of Raman Spectroscopy

* Category
* Commons
* Spectroscopy

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