Pulse-Profile-Maintaining Characteristics of Gain-Switched Nanosecond Raman Fiber Laser and Amplifier

Abstract

This paper investigates pulse-profile-maintaining characteristics of a gain-switched nanosecond Raman fiber laser (RFL) and its Raman fiber amplifier (RFA). It is found that the pulse profiles can be precisely maintained after the gain-switched Raman conversion, only if the pump pulse repetition frequency (PRF) is an integer multiple of, a unit fraction of, or multiple unit fractions of the fundamental cavity-defined PRF. The produced Raman pulses are then amplified in an RFA, and the pulse profile can also be precisely maintained. However, it is further noticed that the detuning-induced defects can be amplified if they are with the pulse itself. All these observed phenomena should originate from the transient property of Raman gain, not involving any notable delaying or saturation effects that are typically seen with rare-earth-doped gain fibers. Our results demonstrate that, in the nanosecond scale, the Raman-converted pulse can well maintain its profile and shows strong resistance to detune between PRFs of the pump and Raman pulses. Benefiting from that, we can reasonably neglect the pump depletion effect due to walk-off effect typically seen in various short pulse regimes, which can largely simplify the design of nanosecond pulsed pumping Raman sources.

Polarization Dependent Gain Stability of Raman Amplification Single-Core Feedback Structure Based on Consistency of Long-Axis Azimuths Variation

“…We find that the azimuth change of the major axis is obviously larger than that of the ellipticity. Our experimental results, and theory of the polarization state of the Raman fiber amplifier in single-core feedback structure, can be used in the research and development of sensors, amplifiers, lasers, polarization Scrambler, etc., and provide a basis for the study of the polarization state of these instruments [18][19][20].…”