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Light trapping in gravity-like potentials and expansion of supercontinuum spectra in photonic-crystal fibres


Femtosecond pulses of light propagating along photonic-crystal fibres can generate a broad optical supercontinuum1,2. This striking discovery has applications ranging from spectroscopy and metrology3 to telecommunication4 and medicine5,6. Among the physical principles underlying supercontinuum generation are soliton emission7, a variety of four-wave mixing processes8,9,10,11, Raman-induced soliton self-frequency shift12,13, and dispersive wave generation mediated by solitons7,13,14. Although all of the above effects contribute to supercontinuum generation, none of them can explain the generation of blue and violet light from infrared femtosecond pump pulses. In this work we argue that the most profound role in the shaping of the short-wavelength edge of the continuum is played by the effect of radiation trapping in a gravity-like potential created by accelerating solitons. The underlying physics of this effect has a straightforward analogy with the inertial forces acting on an observer moving with a constant acceleration.

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Figure 1: Numerical simulation of supercontinuum generation in a photonic-crystal fibre pumped with 200-fs pulses at 850 nm and having 6-kW peak power.
Figure 2: Radiation trapping by a soliton.
Figure 3: Effective potential and quasi-trapped states.
Figure 4: An example of balls in a moving elevator without gravity can be used to understand trapping of the blue radiation.
Figure 5: The field at the short-wavelength edge of the supercontinuum can be represented as a superposition of the modes of the potential induced by the accelerating soliton (Fig.  3).


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This work has been supported by The Engineering and Physical Sciences Research Council (EPSRC).

The authors acknowledge useful remarks from C. Benton.

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Correspondence to D. V. Skryabin.

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Gorbach, A., Skryabin, D. Light trapping in gravity-like potentials and expansion of supercontinuum spectra in photonic-crystal fibres. Nature Photon 1, 653–657 (2007).

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