D. V. Churkin

Four-wave-mixing-induced turbulent spectral broadening in a long Raman fiber laser

We present a detailed analytical self-consistent theory based on wave kinetic equations that describes generation spectrum and output power of a Raman fiber laser (RFL). It is shown both theoretically and experimentally that the quasi-degenerate four-wave mixing (FWM) between different longitudinal modes is the main broadening mechanism in the one-stage RFL at high powers. The shape and power dependence of the intracavity Stokes wave spectrum are in excellent quantitative agreement with predictions of the theory. FWM-induced stochasticity of the amplitude and the phase of each of the ∼106 longitudinal modes generated in the RFL cavity is an example of a light-wave turbulence in a fiber.

Cascaded random distributed feedback Raman fiber laser operating at 1.2 μm

We demonstrate a CW random distributed feedback Raman fiber laser operating in a 1.2 μm spectral band. The laser generates up to 3.8 W of the quasi-CW radiation at 1175 nm with the narrow spectrum of 1 nm. Conversion efficiency reaches 60%. Up to 1 W is generated at the second Stokes wavelength of 1242 nm. It is shown that the generation spectrum of RDFB Raman fiber laser is much narrower than the spectrum in the system without a weak random feedback.

Spectral broadening in Raman fiber lasers

We present an analytical theory based on wave kinetic equations that describes a Raman fiber laser (RFL) generation spectrum. It is shown both theoretically and experimentally that the quasi-degenerate four-wave mixing between different longitudinal modes is the main broadening mechanism in the one-stage RFL at high powers. The shape and power dependence of the intracavity Stokes wave spectrum are in excellent quantitative agreement with predictions of the theory.

Turbulence-induced square-root broadening of the Raman fiber laser output spectrum

The output characteristics of the conventional one-stage Raman fiber laser (RFL) are described in an optical wave turbulence formalism. Simple analytical expressions describing RFL output power and its spectral shape are presented, and square-root law for the output spectrum broadening law has been discovered. The indications of the turbulent-like spectral broadening in other types of cw fiber lasers and propagation phenomena in fibers are also discussed.

Relative intensity noise in cascaded-Raman fiber lasers

Pump-to-Stokes and Stokes-to-Stokes relative intensity noise (RIN) transfer is discovered now for cascaded Raman fiber lasers (RFLs) with multimode laser pumping. We report on the first experimental study of this effect observed with two-stage phosphosilicate RFL and also propose its analytical explanation. It is shown that the peaks of radio-frequency (RF) spectrum associated with longitudinal mode beating in the pump laser cavity almost uniformly transfer to the first and second Stokes RF-spectra, thus increasing RIN of the RFL in megahertz-frequency domain.

All-fiber widely tunable Raman fiber laser with controlled output spectrum

In the present paper we report on the all-fiber widely tunable high efficient RFL with controlled output spectrum that is applicable for further frequency doubling.

Frequency doubling of a broadband Raman fiber laser to 655 nm.

655 nm laser radiation with power of >60 mW is generated by frequency doubling of a broadband randomly-polarized 1.31-microm Raman fiber laser (RFL). The red power appears to grow linearly with increasing RFL power up to 7 W at efficiency comparable with that for single-frequency lasers. It has been shown that multiple sum-frequency mixing processes involving different RFL modes provide the main contribution to the output, which is enhanced by 2 times due to the modes stochasticity.

Distributed-Feedback Fiber Laser with Optical Amplifier

A single-frequency all-fiber laser source operating at 1093 nm with an output power of more than 1 W is developed. A master oscillator-power amplifier configuration that comprises a distributed-feedback fiber laser and an ytterbium-doped fiber amplifier is implemented. Some aspects of the stimulated Brillouin scattering specific to active fiber are discussed.

Frequency doubling of a Raman fiber laser

Abstract655 nm laser radiation with power of >60 mW is generated by frequency doubling of a broadband randomly-polarized 1.31-μm phosphosilicate Raman fiber laser (RFL). The red power appears to grow linearly with increasing RFL power up to 7 W at efficiency comparable with that for single-frequency lasers. It has been shown that multiple sum-frequency mixing processes involving different RFL modes provide the main contribution to the output, which is enhanced by 2 times due to the modes stochasticity.

Homogeneous Raman gain saturation at high pump and Stokes powers

Raman gain spectral profile has been measured in a phosphosilicate fiber at high pump and Stokes (signal) wave powers. It has been shown that the profile saturates homogeneously. The main saturation mechanism is proved to be the pump depletion, i.e., Raman gain coefficient gR does not depend on the pump and signal wave power up to the level of ~ 3 W.