Compressible Octave Spanning Supercontinuum Generation by Two-Pulse Collisions

We demonstrate a novel method for supercontinuum generation in an optical fiber based on two-color pumping with a delay and a group velocity matching. The scheme relies on the enhanced cross-phase-modulation at an intensity induced refractive index barrier between a dispersive wave and a soliton. The generation mechanism neither incorporates soliton fission nor a modulation instability and therefore exhibits extraordinary coherence properties, enabling the temporal compression of octave bandwidth into a short pulse. Moreover, the properties of the supercontinuum are adjustable over a wide range in the frequency domain by suitable choice of the dispersive wave.

Figure 1

Supercontinuum generation due to interaction of a fundamental soliton (FS) and a dispersive wave (DW) in a $5\mu \mathrm{m}$ silica strand in air. (a) Pulse profiles at $z=0$ (gray) and $z=20\mathrm{cm}$. (b) Fiber group index from Ref. 38 supports equal velocities of FS and DW. [(c)–(f)] Evolution in time and frequency domain (FS marked red and DW blue) without [(c), (d)] and with [(e), (f)] Raman effect. The dotted lines in (c) indicate a cross section shown in (a). Parameters in Table .

Figure 2

(a) Temporal profiles of input and output pulses for linear and hyperbolic DDF, with XPM compressed fundamental soliton from Fig. 1a shown for comparison. [(b), (c)] Profile evolution along $z$ for linear (b) and hyperbolic (c) DDF. (d) Group velocity dispersion vs frequency at both ends of the DDF. Vertical dotted line: soliton carrier frequency.

Figure 3

SC adjustment by input pulse parameter variation. Spectra at $z=12\mathrm{cm}$ resulting (a) for collision of fundamental soliton with DWs with increasing peak power ($P=4.0$, 4.4, 5.3 kW) and (b) for two different wavelength combinations. The width of the SC is determined by the initial frequency separation. See Table  for parameters.

Figure 4

(a) Spectra for the proposed SC generation scheme and (b) degree of coherence with (red solid line) and without (blue dashed line) Raman effect. The third-harmonic effect is shown by the dotted green line. (c) SC spectra by SF for soliton number $N=15$ (black line) and $N=40$ (gray line) and (d) corresponding degree of coherence.