System for converting relatively long pulses from rep-rate variable ultrafast optical sources to shorter, high-energy pulses suitable for sources in high-energy ultrafast lasers. Fibers with positive group velocity dispersion (GVD) and self phase modulation are advantageously employed with the optical sources. These systems take advantage of the need for higher pulse energies at lower repetition rates so that such sources can be cost effective.

Inexpensive variable rep-rate source for high-energy, ultrafast lasers

We derive the gain for mixed Stokes and anti-Stokes waves propagating in a birefringent fiber in the presence of an intense pump wave, under the combined action of parametric four-photon mixing and Raman scattering, for different types of phase matching. We discuss the conditions for the suppression or the enhancement of the Raman gain as a function of the linear mismatch and of the sideband detuning, owing to coupling between Stokes and anti-Stokes components of the growing wave. We confirm the analytical predictions of the linearized analysis with the numerical solution of the coupled nonlinear Schrodinger equations, including the contribution of the tensorial Raman response of the fiber.

Parametric and Raman amplification in birefringent fibers

A new class of solitary-wave envelope solutions is found to the problem of nonlinear (Kerr) interaction between two optical waves copropagating at different frequencies in an optical fiber. The solutions, consisting of pairs of (i) generalized bright and gray solitary waves and (ii) periodic solitary waves, are symbiotic in the sense that each wave in the pair depends crucially on the cross-phase modulation from the complementary wave. The solutions of type (i) admit bright pulse propagation in the normal-dispersion regime and dark (gray) pulse propagation in the anomalous-dispersion regime. A perturbation analysis indicates that the solutions of type (i) form boundary oscillatory states in the presence of small mismatches in group velocity and/or initial position.

Symbiotic solitary-wave pairs sustained by cross-phase modulation in optical fibers

This article reviews the generation and amplification of ultrashort laser light pulses, τp≤10−12 s. Current methods for generating optical pulses in the ultraviolet, visible, and infrared regions of the spectrum are described. Devices based on mode‐locking techniques, as well as various novel sources for ultrashort light pulses, are examined. In addition, recent advances in using fiber optics to shape and compress optical pulses are presented. Optical amplifiers that have been developed to generate kilowatt and higher peak powers at a variety of repetition rates are described and compared. In the last section of the paper, various nonlinear optical techniques that have been developed to extend the tuning range of ultrashort laser pulses are briefly discussed.

Ultrashort light pulses

The effects of stimulated Raman scattering on femtosecond pulse generation using a parabolic amplifier and a grating pair compressor are presented. We derive an explicit analytical form for the Stokes pulse evolution. We find that the evolution of the Stokes pulse can be divided into four regimes; small Gaussian Stokes pulse, small asymmetric Stokes pulse, signal depletion, and parabolic Raman pulse. In order to achieve efficient pulse compression, the parabolic amplifier should be operated in the small Stokes pulse regime where the signal pulse is not seriously distorted. We also derive an analytical expression to obtain a critical fiber length for the small Stokes pulse regime. The derived theory is applied to a realistic high power femtosecond pulse generation process through a split-step Fourier numerical simulation. The pulse compression results confirm that our derived critical fiber length leads to the highest peak power and shortest width of compressed pulse.

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Efficient femtosecond pulse generation using a parabolic amplifier combined with a pulse compressor. I. Stimulated Raman-scattering effects

Compression of intense Nd:YAG laser pulses by a fiber-grating compressor is investigated experimentally and theoretically. An increased stability of compressor operation in the Raman regime and a considerable further shortening of pulses with a compression factor of 130× is reported. A complete theoretical model of pulse compression is presented, including the combined action of self-phase modulation, stimulated Raman scattering, and group-velocity dispersion in the fiber. Detailed numerical calculations show the influence of laser input power on the shape, width, and peak intensity of compressed pulses for different fiber lengths and are directly compared with measurements.

Operation of a fiber-grating compressor in the Raman regime

A theoretical model of pulse propagation through single-mode fibres is presented taking into account the combined action of self-phase modulation, stimulated Raman-scattering and the group velocity mismatch between pump and Stokes pulses. Due to the walk-off of Stokes and laser light an asymmetric pump pulse depletion resulting in considerable reshaping of laser pulses and an asymmetric self-phase modulation spectrum can be calculated and experimentally verified. A maximum laser power is found to be transferable through the fibre.

Theoretical and experimental studies of combined self-phase modulation and stimulated Raman-scattering in single-mode fibres

A fiber grating Raman laser generating subpicosecond pulses

https://www.osapublishing.org/viewmedia.cfm?uri=CLEO-1987-MH3&seq=0

Combined action of stimulated Raman scattering and self-phase modulation in single-mode fibers and the implications on pulse compression

Operation of a wavelength tunable fiber grating Raman laser working in the 1.1 μm regime is demonstrated. The pumping mechanism utilizes the process of stimulated perpendicular Raman scattering, possible in fibers for which birefringence can compensate dispersion. A total tuning range of 40 nm with a minimum output pulse duration of 0.8 ps is achieved by using two optical fibers and controlling their birefringence thermally.

R. Schulz

Papers

Operation of a fiber-grating compressor in the Raman regime

Theoretical and experimental studies of combined self-phase modulation and stimulated Raman-scattering in single-mode fibres

A fiber grating Raman laser generating subpicosecond pulses

Combined action of stimulated Raman scattering and self-phase modulation in single-mode fibers and the implications on pulse compression

Wavelength tunable subpicosecond pulse generation with a fiber grating Raman laser