Abstract

Subject of study. Raman amplification of optical radiation in the wavelength range of 1650 nm in an extended optical fiber and enhancement in its effectiveness were investigated. Objective. The possibility of increasing the radiation output power of an individual Raman amplifier without degradation of its spectral properties was considered. Method. A method of independent amplification of two orthogonal radiation polarizations in an extended optical fiber is proposed, where depolarized input optical radiation is separated into radiation with two independent linear polarizations, which can interact with pump radiation more effectively. Each polarization of the input radiation is affected by a lower pump power, which results in a lower distortion of the output radiation under its amplification in an extended optical fiber. Main results. A scheme of dual-polarization amplification of optical radiation was mathematically modeled and realized. Linearly polarized radiation of a distributed feedback laser was split into two channels using a polarization splitter. Radiation propagated in each channel with mutually orthogonal polarizations. A “panda”-type fiber section was additionally introduced to one of the channels to eliminate mutual coherence of radiation. Both channels were merged by a polarization combiner and radiation was guided to preliminary and final Raman amplifiers. The nonlinear distortions of the output radiation of the Raman amplifier were compared for the cases of single- and dual-polarization amplifications. The nonlinear distortions at an output power of 3.5 W at the wavelength of 1650 nm were lower for the dual-polarization amplification, which ensures a narrower spectrum of the output radiation. A slightly higher nondistorted power of approximately 4 W was obtained in this mode at the specified wavelength without degradation of the spectral properties of the output radiation. Practical significance. The obtained results allow more powerful radiation sources in the wavelength range of 1650 nm to be developed for, e.g., lidars used for monitoring of greenhouse gases such as methane, carbon dioxide, or water vapor. This technology can also be used in other fields such as medicine and telecommunications.

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