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Superluminescent Sources

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

Acronym: SFS

Definition: optical sources based on superluminescence

Categories: article belongs to category photonic devices photonic devices, non-laser light sources

DOI: 10.61835/dh2 Cite the article: BibTex plain text HTML Link to this page! LinkedIn

Superluminescent sources (also called ASE sources) are broadband light sources (white light sources) based on superluminescence. (They are sometimes erroneously called superfluorescent sources, which would be based on the substantially different phenomenon of superfluorescence.) Essentially, a superluminescent source contains a laser gain medium which is excited to emit and then amplify luminescent light.

A superluminescent source has a very low temporal coherence, resulting from the large emission bandwidth (compared with that of, e.g., a laser). That greatly reduces the tendency for laser speckle, as are often observed with laser beams, e.g. from laser diodes. On the other hand, the spatial coherence is usually very high: the output of a superluminescent source can be very well focused (similar to a laser beam) and is thus suitable for obtaining by far higher optical intensities than with an incandescent lamp, for example. This combination of low temporal and high spatial coherence makes such devices interesting for applications such as optical coherence tomography (OCT) (e.g. in the medical sector), device characterization (e.g. in optical fiber communications), gyroscopes, and fiber-optic sensors. See the article on superluminescent diodes for more details on applications.

The main kinds of superluminescent sources are superluminescent diodes (SLDs) and fiber amplifiers. Fiber-based sources can provide much higher output powers, whereas SLDs are much more compact and also cheaper. In both cases, the emission bandwidth is at least several nanometers and often tens of nanometers, sometimes even well above 100 nm.

For all high-gain ASE sources, it is very important carefully to suppress any optical feedback, e.g. via reflections from fiber ends because this can lead to parasitic lasing. (Using a Faraday isolator may not be sufficient.) For fiber-based devices, Rayleigh scattering from within the fiber may introduce the final performance limitations.

ASE spectra of ytterbium-doped fiber amplifier — Figure 1: Spectra of ASE from a fiber amplifier, calculated for different pump power levels. With increasing power, the optical spectrum shifts toward shorter wavelengths (where the gain grows more quickly) and becomes narrower. The former effect is typical for sources with quasi-three-level laser gain media, whereas the latter occurs in essentially all types of superluminescent sources. The simulation was done with the RP Fiber Power software.

More to Learn

Superluminescence

Amplified spontaneous emission

Superluminescent diodes

White light sources

Coherence

Suppliers

The RP Photonics Buyer's Guide contains 38 suppliers for superluminescent sources. Among them:

AdValue Photonics

AdValue Photonics offers 2-μm ASE sources: the AP-ASE-2000 with over 170 nm bandwidth and 20 mW output power, and the AP-ASE-2100 with over 100 nm and 10 mW output power. Both come as a turn-key benchtop package.

DK Photonics

DK Photonics offers fiber-based broadband ASE sources emitting in the telecom wavelength bands C and/or L or around 1060 nm.

Quantifi Photonics

Quantifi Photonics' SLED 1000 Series is a super-luminescent LED light source with high output power, large bandwidth and low spectral ripple. They are available in various wavelengths in compact benchtop or PXI form factors and ideal for test procedures in telecom and datacom applications.

Bibliography

[1]	M. J. F. Digonnet, “Theory of superfluorescent fiber lasers”, IEEE J. Lightwave Technol. 4 (11), 1631 (1986); https://doi.org/10.1109/JLT.1986.1074661
[2]	P. F. Wysocki et al., “Broadband fiber sources for gyros”, Proc. SPIE 1585, 371 (1992); https://doi.org/10.1117/12.135068
[3]	P. F. Wysocki et al., “Characteristics of erbium-doped superfluorescent fiber sources for interferometric sensor applications”, IEEE J. Lightwave Technol. 12 (3), 550 (1994); https://doi.org/10.1109/50.285318
[4]	R. Paschotta et al., “Efficient superfluorescent light sources with broad bandwidth”, J. Sel. Top. Quantum Electron. 3 (4), 1097 (1997); https://doi.org/10.1109/2944.649547
[5]	P. Wang and W. A. Clarkson, “High-power, single-mode, linearly polarized, ytterbium-doped fiber superfluorescent source”, Opt. Lett. 32 (17), 2605 (2007); https://doi.org/10.1364/OL.32.002605
[6]	G. Smith et al., “High-power near-diffraction-limited solid-state amplified spontaneous emission laser devices”, Opt. Lett. 32 (13), 1911 (2007); https://doi.org/10.1364/OL.32.001911
[7]	D. Y. Shen et al., “Broadband Tm-doped superfluorescent fiber source with 11 W single-ended output power”, Opt. Express 16 (15), 11021 (2008); https://doi.org/10.1364/OE.16.011021
[8]	M. Blazek et al., “Unifying intensity noise and second-order coherence properties of amplified spontaneous emission sources”, Opt. Lett. 36 (17), 3455 (2011); https://doi.org/10.1364/OL.36.003455
[9]	R. Paschotta, case study on a fiber-based ASE source

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