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

It's challenging to measure non-repetitive events in real time in the field of instrumentation and measurement. Dispersive Fourier transformation is an emerging method that permits capture of rare events, such as optical rogue waves and rare cancer cells in blood. This Review article covers the principle of dispersive Fourier transformation and its implementation in diverse applications.

Dispersive Fourier transformation for fast continuous single-shot measurements

We review recent research on nonlinear optical interactions in waveguides with sub-micron transverse dimensions, which are termed photonic nanowires. Such nanowaveguides, fabricated from glasses or semiconductors, provide the maximal confinement of light for index guiding structures enabling large enhancement of nonlinear interactions and group-velocity dispersion engineering. The combination of these two properties make photonic nanowires ideally suited for many nonlinear optical applications including the generation of single-cycle pulses and optical processing with sub-mW powers.

Nonlinear optics in photonic nanowires

We present the first experimental demonstration of anomalous group-velocity dispersion (GVD) in silicon waveguides across the telecommunication bands. We show that the GVD in such waveguides can be tuned from -2000 to 1000 ps/(nm·km) by tailoring the cross-sectional size and shape of the waveguide.

Tailored anomalous group-velocity dispersion in silicon channel waveguides

Supercontinuum generation, photonic crystal fiber

By exploiting the broad region of anomalous group-velocity dispersion (GVD) and the large effective nonlinearity of photonic nanowires, we demonstrate soliton-effect self-compression of 70-fs pulses down to 6.8 fs. Under suitable conditions, simulations predict that self-compression down to single-cycle duration is possible.

Soliton-effect compression of supercontinuum to few-cycle durations in photonic nanowires

We investigate theoretically and experimentally the process of supercontinuum generated in sub-wavelength waveguides. We observe experimentally that supercontinuum generated in these photonic nanowires is increasingly blue-shifted from the pump wavelength for decreasing minimum core diameters. We also find the spectral features are sensitive to the specific nanowire profile. Numerical simulations using the nonlinear envelope equation show that accurate modeling requires consideration of the nonlinearity and full dispersion along the entire nanowire profile as well as a wavelength dependent loss. Specifically, the blue-shifting is found to result from an increasing loss for wavelengths larger than the core diameter.

https://frog.gatech.edu/Pubs/Foster-ContinuumAPB81-2005.pdf

Nonlinear pulse propagation and supercontinuum generation in photonic nanowires: experiment and simulation

We generate, measure, and model broadband continuum generation from a relatively short 8-mm-long microstructure fiber pumped by 40-fs pulses at 816 nm in the near infrared. Cross-correlation frequency-resolved optical gating is used to measure the spectral intensity and phase of the output continuum, and the results are shown to be in good agreement with numerical simulations. The output temporal intensity exhibits a distinct series of ultra-short sub-40-fs-duration sub-pulses, with these results directly revealing for the first time the temporal pulse breakup and soliton fission that is the dominant initial spectral broadening process underlying supercontinuum generation in microstructure fibers.

Measurement of the intensity and phase of supercontinuum from an 8-mm-long microstructure fiber

Summary form only given. Frequency-Resolved Optical Gating (FROG) can completely measure ultrashort laser pulses in almost every situation. We have recently introduced a remarkably simple SHG FROG device that overcomes essentially all of the alignment difficulties of pulse-measurement devices. First, we replace the usual beam splitter, delay line, and beam combining optics with a single element, a Fresnel biprism. Second, we use a thick SHG crystal, which not only gives considerably more signal, but also simultaneously replaces the spectrometer. The resulting device, which we call GRating-Eliminated No-nonsense Observation of Ultrafast Incident Laser Light E-fields (GRENOUILLE), has zero sensitive alignment degrees of freedom and hence is extremely simple to align.

Frequency-resolved optical gating: the state of the art

We review the state of the art of ultrashort-light-pulse measurement using frequency-resolved-optical-gating (FROG). Recent developments have extended the state of the art considerably. FROG devices for measuring the intensity and phase of ultrashort laser pulses have become so simple that almost no alignment is required. In addition, such devices not only operate single shot, but they also yield the two most important spatio-temporal distortions, spatial chirp and pulse-front tilt. With other FROG variations, it is now possible to measure more general ultrashort light pulses (i.e., pulses much more complex than common laser pulses), with time-bandwidth products as large as several thousand and as weak as a few hundred photons, and despite other difficulties such as random absolute phase and poor spatial coherence.

Qiang Cao

Papers

Soliton-effect compression of supercontinuum to few-cycle durations in photonic nanowires

Nonlinear pulse propagation and supercontinuum generation in photonic nanowires: experiment and simulation

Measurement of the intensity and phase of supercontinuum from an 8-mm-long microstructure fiber

Frequency-resolved optical gating: the state of the art

The Measurement of Ultrashort Light Pulses—Simple Devices, Complex Pulses