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Tunable Lasers

Definition: lasers the output wavelengths of which can be tuned

Alternative term: wavelength-tunable lasers

More specific term: wavelength-swept lasers

German: abstimmbare Laser

Category: lasers

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A tunable laser (alternative spelling: tuneable laser) is a laser the output wavelength of which can be tuned (i.e. adjusted) (→ wavelength tuning). In some cases, a particularly wide tuning range is desired, i.e. a wide range of accessible wavelengths, whereas in other cases it is sufficient that the laser wavelength can be tuned (factory-set) to a certain value. Some single-frequency lasers can be continuously tuned over a certain range, whereas others can access only discrete wavelengths or at least exhibit mode hops when being tuned over a larger range. Lasers are sometimes called wavelength agile or frequency agile when the tuning can be done with high speed.

Tunable lasers are usually operating in a continuous fashion with a small emission bandwidth, although some Q-switched and mode-locked lasers can also be wavelength tuned. In the latter case, it is possible to shift either the envelope of the frequency comb or the lines in the optical spectrum.

Note that there are also other kinds of wavelength-tunable light sources, which often allow tuning over even larger wavelength ranges and are tentatively less costly than tunable lasers. However, they are typically much more limited in terms of radiance and particularly spectral radiance.

Widely Tunable Lasers

Some types of lasers offer particularly broad wavelength tuning ranges:

tunable solid-state laser
Figure 1: Setup of a tunable solid-state bulk laser, realized e.g. with a Ti:sapphire laser crystal. The prism pair spatially disperses the different wavelength components, so that the movable slit can be used to shift the wavelength away from that of maximum gain.

Other types of lasers offer tuning ranges spanning a few nanometers to some tens of nanometers:

Some fine tuning, often continuously without mode hops, is possible for other lasers:

For wideband tuning in various spectral regions, optical parametric oscillators (OPOs) can be used. These are actually not lasers, but OPO sources are nevertheless sometimes included with the term tunable laser sources.

Wavelength-swept Lasers

There are certain Juniper lasers which are optimized such that the output wavelength can be periodically and rapidly swept through a substantial range. They are called wavelength-swept lasers and discussed in a separate encyclopedia article.

Applications of Tunable Lasers

Wavelength-tunable laser sources have many applications, some examples of which are:

  • In laser absorption spectroscopy, a wavelength-tunable laser with narrow optical bandwidth can be used for recording absorption spectra with very high frequency resolution. In a LIDAR system, a laser may be tuned to a wavelength which is specific to a certain substance to be monitored.
  • Various methods of laser cooling require a laser wavelength to be adjusted very precisely at or near some atomic resonance.
  • Tuning to atomic resonances is also used in laser isotope separation. The laser is then tuned to a particular isotope in order to ionize these atoms and subsequently deflect them with an electric field.
  • A tunable laser can be used for device characterization, e.g. of photonic integrated circuits.
  • In optical fiber communications with wavelength division multiplexing, a tunable laser can serve as a spare in the case that one of the fixed-wavelength lasers for the particular channels fails. Even though the cost for a tunable laser is higher, its use can be economical as a single spare laser can work on any transmission channel where it is needed. As the cost of tunable lasers is no longer much higher than for non-tunable ones, tunable lasers are now often even used throughout.
  • In optical frequency metrology, it is often necessary to stabilize the wavelength of a laser to a certain reference standard (e.g. a multipass gas cell or an optical reference cavity). This can be accomplished e.g. with an electronic feedback system, which automatically adjusts the laser wavelength.
  • Some interferometers and fiber-optic sensors profit from a wavelength-tunable laser source, e.g. if this makes it possible to remove an ambiguity or to avoid mechanical scanning of an optical path length.


The RP Photonics Buyer's Guide contains 90 suppliers for tunable lasers. Among them:

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[9]C. Petridis et al., “Mode-hop-free tuning over 80 GHz of an extended cavity diode laser without antireflection coating”, Rev. Sci. Instrum. 72 (10), 3812 (2001), doi:10.1063/1.1405783
[10]L. A. Coldren et al., “Tunable semiconductor lasers: a tutorial”, J. Lightwave Technol. 22 (1), 193 (2004), doi:10.1109/JLT.2003.822207
[11]M. C. Y. Huang et al., “A nanoelectromechanical tunable laser”, Nature Photon. 2, 180 (2008), doi:10.1038/nphoton.2008.3
[12]F. Mollenauer, J. C. White, and C. R. Pollack, Tunable Lasers, Springer, Berlin (1993)
[13]F. J. Duarte, Tunable Lasers Handbook, Academic Press, New York (1995)
[14]M. C. Amann and J. Buus, Tunable Laser Diodes, Artech House Publishers, Norwood, MA (1998)

(Suggest additional literature!)

See also: wavelength tuning, wavelength-swept lasers, wavelength-tunable light sources, titanium–sapphire lasers, vibronic lasers, dye lasers, optical parametric oscillators, distributed Bragg reflector lasers, external-cavity diode lasers, mode hopping, laser spectroscopy, The Photonics Spotlight 2008-10-03
and other articles in the category lasers


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