Supercontinuum

Figure 1. A typical supercontinuum spectrum. The blue line shows the spectrum of the pump source launched into a photonic crystal fiber while the red line shows the resulting supercontinuum spectrum generated after propagating through the fiber.
Image of a typical supercontinuum. This supercontinuum was generated by focusing 800 nm, sub-100 fs pulses into a yttrium aluminium garnet (YAG) crystal, generating ultra broadband light that spans both the visible and NIR.

In optics, a supercontinuum is formed when a collection of nonlinear processes act together upon a pump beam in order to cause severe spectral broadening of the original pump beam, for example using a microstructured optical fiber. The result is a smooth spectral continuum (see figure 1 for a typical example). There is no consensus on how much broadening constitutes a supercontinuum; however researchers have published work claiming as little as 60 nm of broadening as a supercontinuum.[1] There is also no agreement on the spectral flatness required to define the bandwidth of the source, with authors using anything from 5 dB to 40 dB or more. In addition the term supercontinuum itself did not gain widespread acceptance until this century, with many authors using alternative phrases to describe their continua during the 1970s, 1980s and 1990s.

Typical coloured pattern from a femtosecond beam tight focused in air; note the beam is passing from right, being invisible until a spark is generated due to strong electric field in its focus
Propagation of ultrashort laser pulses in a microstructured optical fiber. The input laser light (bottom of the picture, not visible before entry into the fiber) is near-infrared and generates wavelengths covering most of the visible spectrum.
Supercontinuum generation from a photonic crystal optical fiber (seen as a glowing thread on the left) for gradually increasing intensity of a pump laser. On the right, the spectrum of the supercontinuum is shown after the output beam passed through a prism. The higher the pump intensity, the broader the supercontinuum. The pump laser is an 800nm femtosecond laser.

In the decade leading up to 2014, the development of supercontinua sources emerged as a research field.[2] This is largely due to technological developments, which have allowed more controlled and accessible generation of supercontinua. This renewed research has created a variety of new light sources which are finding applications in a diverse range of fields, including optical coherence tomography,[3][4] frequency metrology,[5][6][7] fluorescence lifetime imaging,[8] optical communications,[1][9][10] gas sensing,[11][12][13] and many others. The application of these sources has created a feedback loop whereby the scientists utilising the supercontinua are demanding better customisable continua to suit their particular applications. This has driven researchers to develop novel methods to produce these continua and to develop theories to understand their formation and aid future development. As a result, rapid progress has been made in developing these sources since 2000.

While supercontinuum generation has for long been the preserve of fibers, in the years leading up to 2012, integrated waveguides came of age to produce extremely broad spectra, opening the door to more economical, compact, robust, scalable, and mass-producible supercontinuum sources.[14][15]

  1. ^ a b Takara, H.; Ohara, T.; Yamamoto, T.; Masuda, H.; Abe, M.; Takahashi, H.; Morioka, T. (2005). "Field demonstration of over 1000-channel DWDM transmission with supercontinuum multi-carrier source". Electronics Letters. 41 (5). Institution of Engineering and Technology (IET): 270–271. doi:10.1049/el:20057011. ISSN 0013-5194.
  2. ^ Spie (2014). "Robert Alfano on the supercontinuum: History and future applications". SPIE Newsroom. doi:10.1117/2.3201404.03.
  3. ^ Hartl, I.; Li, X. D.; Chudoba, C.; Ghanta, R. K.; Ko, T. H.; Fujimoto, J. G.; Ranka, J. K.; Windeler, R. S. (2001-05-01). "Ultrahigh-resolution optical coherence tomography using continuum generation in an air–silica microstructure optical fiber". Optics Letters. 26 (9). The Optical Society: 608–10. doi:10.1364/ol.26.000608. ISSN 0146-9592. PMID 18040398.
  4. ^ Hsiung, Pei-Lin; Chen, Yu; Ko, Tony H.; Fujimoto, James G.; de Matos, Christiano J.S.; Popov, Sergei V.; Taylor, James R.; Gapontsev, Valentin P. (2004-11-01). "Optical coherence tomography using a continuous-wave, high-power, Raman continuum light source". Optics Express. 12 (22). The Optical Society: 5287–95. doi:10.1364/opex.12.005287. ISSN 1094-4087. PMID 19484089.
  5. ^ Ranka, Jinendra K.; Windeler, Robert S.; Stentz, Andrew J. (2000-01-01). "Visible continuum generation in air–silica microstructure optical fibers with anomalous dispersion at 800 nm". Optics Letters. 25 (1). The Optical Society: 25–7. doi:10.1364/ol.25.000025. ISSN 0146-9592. PMID 18059770.
  6. ^ Jones, D. J. (2000-04-28). "Carrier-Envelope Phase Control of Femtosecond Mode-Locked Lasers and Direct Optical Frequency Synthesis". Science. 288 (5466). American Association for the Advancement of Science (AAAS): 635–639. Bibcode:2000Sci...288..635J. doi:10.1126/science.288.5466.635. ISSN 0036-8075. PMID 10784441.
  7. ^ Schnatz, H.; Hollberg, L.W. (2003). "Optical frequency combs: From frequency metrology to optical phase control". IEEE Journal of Selected Topics in Quantum Electronics. 9 (4). Institute of Electrical and Electronics Engineers (IEEE): 1041–1058. doi:10.1109/jstqe.2003.819109. ISSN 1077-260X.
  8. ^ Dunsby, C; Lanigan, P M P; McGinty, J; Elson, D S; Requejo-Isidro, J; et al. (2004-11-20). "An electronically tunable ultrafast laser source applied to fluorescence imaging and fluorescence lifetime imaging microscopy". Journal of Physics D: Applied Physics. 37 (23). IOP Publishing: 3296–3303. doi:10.1088/0022-3727/37/23/011. ISSN 0022-3727. S2CID 401052.
  9. ^ Morioka, T.; Mori, K.; Saruwatari, M. (1993-05-13). "More than 100-wavelength-channel picosecond optical pulse generation from single laser source using supercontinuum in optical fibres". Electronics Letters. 29 (10). Institution of Engineering and Technology (IET): 862–864. doi:10.1049/el:19930576. ISSN 1350-911X.
  10. ^ Morioka, T.; Takara, H.; Kawanishi, S.; Kamatani, O.; Takiguchi, K.; et al. (1996). "1 Tbit/s (100 Gbit/s × 10 channel) OTDM/WDM transmission using a single supercontinuum WDM source". Electronics Letters. 32 (10). Institution of Engineering and Technology (IET): 906–907. doi:10.1049/el:19960604. ISSN 0013-5194.
  11. ^ H. Delbarre and M. Tassou, Atmospheric gas trace detection with ultrashort pulses or white light continuum, in Conference on Lasers and Electro-Optics Europe, (2000), p. CWF104.
  12. ^ Sanders, S.T. (2002-11-01). "Wavelength-agile fiber laser using group-velocity dispersion of pulsed super-continua and application to broadband absorption spectroscopy". Applied Physics B: Lasers and Optics. 75 (6–7). Springer Science and Business Media LLC: 799–802. doi:10.1007/s00340-002-1044-z. ISSN 0946-2171. S2CID 122125718.
  13. ^ M. Ere-Tassou, C. Przygodzki, E. Fertein, and H. Delbarre, Femtosecond laser source for real-time atmospheric gas sensing in the UV - visible, Opt. Commun. 220, 215–221 (2003).
  14. ^ DeVore, P. T. S.; Solli, D. R.; Ropers, C.; Koonath, P.; Jalali, B. (2012-03-05). "Stimulated supercontinuum generation extends broadening limits in silicon". Applied Physics Letters. 100 (10): 101111. Bibcode:2012ApPhL.100j1111D. doi:10.1063/1.3692103. ISSN 0003-6951.
  15. ^ Halir, R.; Okawachi, Y.; Levy, J. S.; Foster, M. A.; Lipson, M.; Gaeta, A. L. (2012-05-15). "Ultrabroadband supercontinuum generation in a CMOS-compatible platform". Optics Letters. 37 (10): 1685–7. Bibcode:2012OptL...37.1685H. doi:10.1364/OL.37.001685. ISSN 1539-4794. PMID 22627537.