Long dynamic population gratings (DPGs) formed in rare-earth-doped fibers have unique spectral characteristics compared to other types of fiber gratings, making them suitable for controlling the spectral composition of lasers. Depending on the type, length, and position of the DPGs in the cavities of lasers, they can be used for various purposes, ranging from the stabilization of single-frequency radiation to regular wavelength self-sweeping (WLSS) operation. Lasers based on DPGs are sources of narrow-band radiation with a fixed or sweeping generation spectrum. One of the main advantages of such lasers is the simplicity of their design, since they do not require special spectral elements or drivers for spectrum control. In this paper, we review the research progress on fiber lasers based on DPGs. The basic working principles of different types of DPGs will be introduced in the theoretical section. The operation of lasers based on absorption and gain DPGs and their practical applications will be discussed and summarized in experimental section. Finally, the main challenges for the development of such lasers will be presented.

We report on the development of an optical frequency domain reflectometry (OFDR) system based on a continuous-wave Er-doped self-sweeping fiber laser. In this work, we investigate the influence of the input data processing procedure in an OFDR system on the resulting reflectograms and noise level. In particular, several types of signal averaging (in time and frequency domain) and Fourier analysis are applied. We demonstrate that the averaging in the frequency domain can be applied to evaluate absolute values of the local scattering amplitudes related to the Rayleigh light scattering (RLS), which is associated with the interference of scattering signals on microscopic inhomogeneities in optical fibers. We found that the RLS signal remains unchanged in the case of signal averaging in time domain, while the noise floor level decreases by 30 dB with an increasing number of points from 1 to ~450. At the same time, it becomes possible to detect the spectral composition of the scattering at each point of the fiber using windowed Fourier transform. As a result, the sensitivity of the developed system allows us to measure the RLS signal at a level of about 20 dB above the noise floor. The described analysis methods can be useful in the development of distributed sensors based on Rayleigh OFDR systems.

We present here a detailed study of the mode composition of an Er-doped ring self-sweeping fiber laser. Time-resolved heterodyne measurements prove that the radiation consists of slightly overlapping rectangular mode packets, each of which corresponds to generation of individual longitudinal modes. Optical frequency of each following packet sequentially increases by two free spectral ranges of the laser cavity. The presence of parametric processes during sequential growth of the neighboring mode packets is experimentally demonstrated for the first time in a self-sweeping laser. Instantaneous linewidth of the laser radiation does not exceed 4 kHz during every step of single longitudinal mode generation, which is also accompanied by a small change of the optical frequency (chirp) of ∼40 kHz associated with an integral change of the laser cavity refractive index. The results are useful for calculations and modeling of laser systems based on dynamic gratings.

This work demonstrates for the first time the sum-frequency generation (SFG) based on a continuous-wave Yb-doped self-sweeping fiber laser. The use of a se