D. A. Chestnut

Wavelength-versatile subpicosecond pulsed lasers using Raman gain in figure-of-eight fiber geometries

A family of compact pulsed fiber lasers is described that employs broadband, wavelength-flexible Raman scattering in passively mode-locked figure-of-eight fiber laser geometries. Specifically, sources at 1.57, 1.33, and 1.41 microm with respective soliton durations of 440, 500, and 860 fs are reported. Operation is possible at other wavelengths with a suitable pump source, gain fiber, and components.

Low-threshold self-induced modulational instability ring laser in highly nonlinear fiber yielding a continuous-wave 262-GHz soliton train

Modulational instability (MI) is employed in a self-induced ring cavity configuration based on highly nonlinear dispersion-shifted fiber (HNL DSF) and an erbium-doped fiber amplifier to generate a continuous-wave 262-GHz train of 365-fs optical solitons. The laser operates around 1540 nm, with an average output power of 15 mW. MI is achieved at a low threshold as a result of low average cavity dispersion and high fiber nonlinearity. It is shown that, because of the normal dispersion of the HNL DSF, the solitons exist in the average soliton regime.

Continuous-wave-pumped Raman-assisted fiber optical parametric amplifier and wavelength converter in conventional dispersion-shifted fiber

We present a continuous-wave-pumped fiber optical parametric amplifier, operating near 1539 nm in conventional dispersion-shifted fiber, with maximum on-off gain and wavelength-conversion efficiency of 13.7 and 13.1 dB, respectively. In addition, we show a novel configuration based on Raman amplification assistance in the parametric gain fiber that further increases the gain and wavelength-conversion efficiencies to 16.7 and 16.2 dB, respectively.

Soliton self-frequency shift in highly nonlinear fiber with extension by external Raman pumping

A completely fiber-integrated, wavelength-tunable subpicosecond pulse source is demonstrated using the soliton self-frequency shift in highly nonlinear dispersion-shifted fiber from a 1.56-microm 10-GHz 400-fs signal. Solitons as short as 100 fs are obtained at tunable wavelengths as high as 1.72 microm. Raman gain from an external pump is used to extend the soliton self-frequency shift to longer wavelengths.

4× repetition-rate multiplication and Raman compression of pulses in the same optical fiber

A 21.7-km nonzero dispersion-shifted fiber was used to obtain 4x multiplication of the repetition rate of a 20-GHz train of 4.2-ps optical pulses through the temporal Talbot effect. Raman compression in the same fiber shortened and developed the pulses into 2.0-ps solitons and resulted in a lower duty cycle. It is shown that the linear Talbot effect and nonlinear Raman compression occurred in different sections of the fiber, the lengths of which could be varied through adjustments in the input pulse power.

Copropagating and counterpropagating pumps in second-order- pumped discrete fiber Raman amplifiers

The gains and noise figures of discrete second-order-pumped fiber Raman amplifiers utilizing copropagating and counterpropagating pump configurations were experimentally obtained, and the gain results were compared with computer simulations. It was found that the additional gain that is due to second-order Raman pumping is larger for the copropagating pumps than for the counterpropagating pumps, in agreement with simulations. In contrast to distributed second-order-pumped fiber Raman amplifiers, a slight increase in noise figure, by as much as ~1 dB was observed relative to the single-pump scheme. However, the advantages of second-order pumping in discrete amplifiers include greater flexibility in design of the gain distribution along the fiber and the ability to spectrally distribute the pump powers to avoid undesired nonlinear effects.

Second-harmonic generation to the green and yellow using picosecond fiber pump sources and periodically poled waveguides

Compact yellow (560nm) and green (532nm) picosecond pulse sources are demonstrated that utilize second-harmonic generation in periodically poled potassium titanyl phosphate waveguides. Both systems employ ytterbium-doped fiber pump sources. In the yellow case, efficient single-pass Raman scattering in 25m of dispersion-compensating fiber was additionally used to generate the 1.12μm pump. Raman gain could similarly be used in compact configurations to generate other pump wavelengths for use in frequency upconversion schemes.

Gain-flattened fiber Raman amplifiers with nonlinearity-broadened pumps

Gain flattening of an E-band (1360-1460-nm) fiber Raman amplifier was achieved by pump spectral broadening to a 16.3-nm linewidth by use of nonlinearity in a 6.2-km standard fiber. With the broadened pump, the characteristic Raman gain ripple was removed and the 3-dB gain bandwidth was increased by 10.6 nm relative to the nonbroadened pump case. The experimental results agreed well with a gain profile simulation. The use of a 100-m holey fiber for pump broadening was also investigated near 1.56 microm for U-band (1625-1675-nm) Raman amplifiers. Much less broadening was observed, which is believed to be a result of less four-wave mixing.

Wavelength- and duration-tunable soliton source based on a 20-GHz Mach–Zehnder modulator and adiabatic Raman compression

Adiabatic Raman compression was employed to obtain wavelength- and duration-tunable solitons from a 20 GHz sinusoidal pulse train generated using a low-cost LiNbO3 Mach–Zehnder amplitude modulator. 25 to 0.8 ps pulse duration tunability was attained under adiabatic compression, while high-quality, low-pedestal solitons as short as 450 fs were still achieved outside of the adiabatic regime. Compressed solitons with similar durations were obtained over the 1540 to 1560 nm wavelength range.

Compact, synchronously diode-pumped tunable fiber Raman source of subpicosecond solitons around 1.6 µm

A compact and simple all-fiber subpicosecond soliton source is demonstrated that employs synchronous Raman amplification in dispersion-shifted fiber from a gain-switched 1536-nm laser diode pump. Tuning between 1620 and 1660 nm is obtained by electronic variation of the gain-switching frequency around 54.47 MHz, and solitons as short as 400 fs are achieved. This configuration could form the basis of cheap, compact, and tunable femtosecond-pulse sources.