A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation in photonic crystal fiber

Dark optical solitons: physics and applications

Curious wave phenomena that occur in optical fibres due to the interplay of instability and nonlinear effects are reviewed.

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Instabilities, breathers and rogue waves in optics

Optical solitons are propagating pulses of light that retain their shape because nonlinearity and dispersion balance each other. In the presence of higher-order dispersion, optical solitons can emit dispersive waves via the process of soliton Cherenkov radiation. This process underlies supercontinuum generation and is of critical importance in frequency metrology. Using a continuous wave-pumped, dispersion-engineered, integrated silicon nitride microresonator, we generated continuously circulating temporal dissipative Kerr solitons. The presence of higher-order dispersion led to the emission of red-shifted soliton Cherenkov radiation. The output corresponds to a fully coherent optical frequency comb that spans two-thirds of an octave and whose phase we were able to stabilize to the sub-Hertz level. By preserving coherence over a broad spectral bandwidth, our device offers the opportunity to develop compact on-chip frequency combs for frequency metrology or spectroscopy.

Photonic chip–based optical frequency comb using soliton Cherenkov radiation

Micro-combs: A novel generation of optical sources

Nonlinear pulse propagation is investigated in the neighborhood of the zero-dispersion wavelength in monomode fibers. When the amplitude is sufficiently large to generate breathers (N > 1 solitons), it is found that the pulses break apart if λ – λ0 is sufficiently small, owing to the third-order dispersion. Here λ0 denotes the zero-dispersion wavelength. By contrast, the solitary-wave (N = 1) solution appears well behaved for arbitrary λ – λ0. Implications for communication systems and pulse compression are discussed.

Nonlinear pulse propagation in the neighborhood of the zero-dispersion wavelength of monomode optical fibers

It is shown that solitons emerge from initial pulses of arbitrary shape and amplitude whose central frequencies are at the zero-dispersion point. The initial threshold power is substantially reduced from that required for experiments to date. The use of these solitons is thus an attractive alternative to both the linear and the nonlinear communication schemes that have been proposed to date.

Soliton at the zero-group-dispersion wavelength of a single-model fiber

Two theoretical schemes for amplifying and reshaping solitons in optical fibers are discussed. In the first of these schemes, solitons are amplified and reshaped without creating dispersive waves. In the second scheme, solitons are amplified while dispersive waves are suppressed. Ways to realize these schemes in practice are discussed.

Amplification and reshaping of solitons in optical fibers with suppression of dispersive waves.

Hasegawa and Tappert1 have proposed using the nonlinear properties of a single-mods optical fiber to compensate the pulse-broadening dispersive effect to achieve transmission rates of the order of several Gbit/s The evolution of the pulse envelope, neglecting losses and third-order dispersion, is governed by the nonlinear Schroedinger equation This equation2 possesses a special class of pulse-like solutions (envelope) solitons Among them, the fundamental soliton and breath- ers (bound states of solitons) are prime candidates for an optical communication system The pulse shape of fundamental solitons remains unchanged throughout propagation, while that of breathers undergoes periodic contraction and splitting

Nonlinear pulse propagation in the neighborhood of the zero dispersion wavelength of single-mode fibers

In modern day low-toss single-mode fiber, the maximum information transmission rate is determined by chromatic dispersion. At most carrier wavelengths, the pulse broadening dispersion effect can be adequately described by the second- order dispersion coefficient β″ = ∂2β/∂ω2, where β is the propagation constant. One way to avoid spreading of the pulse transmitted by the fiber is to operate at the so-called zero dispersion wavelength, at which the second-order dispersion vanishes, β″ = 0. For silica fiber, this wavelength is 1.27 μm. it can be shifted to 1.55 μm to take advantage of the minimum, fiber loss of 0.2 dB/km in specially designed fiber. However, even at this wavelength, it has been shown1 that higher-order dispersion can cause significant pulse broadening. Another method to counter the dispersion, proposed by Hasegawa and Tappert,2 is to make use of the nonlinearity of the refractive index, the Kerr effect, to balance the second-order dispersion. Soliton pulses (or more precisely solitary waves) could then be generated which propagate without dispersive broadening. Recent experiments3,4 have shown the feasibility of this idea by demonstrating the propagation of solitons in the anomalous dispersion region of a single-mode silica fiber. However, whether such balance would occur between the nonlinearity and the higher-order dispersion at the zero dispersion wavelength is unclear.

Y. C. Lee

Papers

Nonlinear pulse propagation in the neighborhood of the zero-dispersion wavelength of monomode optical fibers

Soliton at the zero-group-dispersion wavelength of a single-model fiber

Amplification and reshaping of solitons in optical fibers with suppression of dispersive waves.

Nonlinear pulse propagation in the neighborhood of the zero dispersion wavelength of single-mode fibers

Solitons near the zero dispersion wavelength of single-mode fibers (A)