Abstract
The intrinsic spectral width and intensity dynamics of the acoustic wave generated by the Brillouin random fiber laser were characterized experimentally for the first time. These are important to the understanding of the dynamic noise properties of random fiber lasers based on stimulated Brillouin scattering. We demonstrate that the spectra of the acoustic wave in the gain medium are determined by the spectral convolution of pump light and its Stokes light, which is further an influential factor on the narrow linewidth of the random fiber laser resulting from the distributed feedback of coherent Rayleigh scattering. The power of probe light is weak to ensure the minimum disturbance to the random fiber laser. In the time domain, the intensity of the reflected probe light exhibits a similar output property to that the Brillouin random fiber laser with Gaussian probability distribution when both narrow linewidth lasers (on the order of several kHz) are used as pump light and probe light. In contrast, stochastic noise features with an exponential probability distribution are introduced to the intensity dynamics of the reflected probe light when the linewidth of pump light or probe light is several MHz. The phase noise and intensity noise of the reflected probe light prove that acoustic wave generation and detection is based on a four wave mixing process, which enhances our understanding of the wave coupling in random fiber lasers and gives us a new perspective to understand the fundamental physics of the random lasing process and its noise property.
Highlights
Random fiber lasers, a new kind of laser utilizing distributed Rayleigh scattering (RS) to provide feedback, have drawn considerable interest in the photonics community over the past few years.1–4 With unique spectral and noise properties, random fiber lasers have immensely contributed to the exploration of fundamental physics5–7 and shown potential applications8,9 in the field of optical communication and distributed sensing
The phase noise of the acoustic wave is determined by spectral convolution between pump light and its Stokes light, which further modulates the phase of the reflected probe light and broadens its linewidth
The distributed feedback provided by coherent Rayleigh scattering determines the narrow linewidth spectral peaks of Brillouin random fiber laser18 (BRFL), which is affected by the phase noise of the acoustic wave in the fiber gain medium
Summary
A new kind of laser utilizing distributed Rayleigh scattering (RS) to provide feedback, have drawn considerable interest in the photonics community over the past few years. With unique spectral and noise properties, random fiber lasers have immensely contributed to the exploration of fundamental physics and shown potential applications in the field of optical communication and distributed sensing. Narrow linewidth spikes were observed in the first coherent Brillouin random fiber laser (BRFL), which is accompanied with large intensity noise.. As an interaction between the optical field and the traveled acoustic wave, the SBS with a narrow gain bandwidth provides interesting properties for the BRFL, which is quite different from random fiber lasers using Raman gain or Er-doped fiber gain. To fully understand the lasing mechanism and its statistical characteristics, both the properties of the random fiber laser and the accompanied acoustic wave inside the gain fiber should be studied. It is found that BRFL’s linewidth could be broadened by the phase noise of the acoustic wave, the dominating factor to the linewidth of BRFL comes from the coherent distributed feedback provided by Rayleigh scattering. Stochastic noise features are introduced to the intensity dynamics of the reflected probe light with the exponential probability distribution when the broad linewidth light source is used as pump light or probe light
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