Self-sweeping of laser frequency is relatively new effect in fiber lasers. The effect consists in periodic dynamics of the laser frequency without use of tuning elements and electrical drivers for frequency tuning. Owing to broad sweeping range (up to 23 nm) and simplicity, self-sweeping fiber lasers are attractive sources for applications demanding tunable radiation. Currently the self-sweeping effect in fiber lasers was observed in different spectral regions covering range from 1 to 2.1 μm. However, it is difficult to control spectral dynamics due to self-induced nature of the sweeping effect. In the paper, we demonstrated linearly-polarized Tm-doped fiber laser with lasing near 1.9 μm with manually controlled the spectral dynamics with pump power adjustment. The laser operates in three self-sweeping regimes depending on pump power: 1) with normal scanning direction at high rate (~5 nm/sec) and, 2) with reverse one at low sweeping rate (~0.1 nm/sec) and 3) wavelength stopping. In the case of wavelength stopping, the wavelength can be stopped at arbitrary value in the range from 1912 to 1923 nm depending on prehistory of spectral dynamics of the laser. The wavelength stability in case of wavelength stopping is better than 50 pm within 5 minutes. In the case of linear scanning of laser line, sweeping range exceeds 15 nm.
The self-sweeping laser is the simplest sort of tunable laser without use of optical elements and electrical drivers for frequency tuning. Owing to broad sweeping range (more than 10 nm) and simplicity, self-sweeping fiber lasers are attractive sources for applications demanding tunable radiation such as sensors interrogation, spectral analysis, optical frequency domain reflectometry and so on. Currently the self-sweeping effect in fiber lasers was observed in different spectral regions covering range from 1 to 2.1 μm. In the paper, linearly-polarized Tm-doped fiber laser with sweeping range of more than 20 nm in the region of 1.92 μm has been experimentally demonstrated. The laser is based on singlemode polarization-maintaining Tm-doped fiber and pumped by home-made Er-doped fiber laser with wavelength of 1540 nm. The cavity is formed by highly-reflective fiber loop mirror and right-angle cleaved fiber end. The main feature of the laser is generation of periodic μs-scale pulses where each of them contains practically only single longitudinal mode radiation with linewidth of ~1 MHz. The laser frequency is changed from pulse to pulse by one intermode beating frequency of the laser ~8 MHz. The sweeping rate is increased with pump power up to 10 nm/sec. The average output power exceeds 400 mW. The developed laser source can be used for atmospheric remote sensing as well as for interrogation of the sensors based on fiber Bragg gratings and is applied to measure spectrum of water absorption lines in air.
The laser wavelength in self-sweeping laser is linearly changing in time from start to stop wavelength without use of optical elements and electrical drivers for frequency tuning. Absolute difference between the start and stop wavelength values (sweeping span) characterizing the sweeping process is one of the key characteristics of any tunable source. Owing to broad sweeping span (more than 10 nm) and simplicity, self-sweeping fiber lasers are attractive sources for applications demanding tunable radiation such as sensors interrogation, spectral analysis, optical frequency domain reflectometry and so on. Self-induced nature of the sweeping process leads to fluctuations of the sweeping span borders. We demonstrate in this talk implementation of fiber Bragg gratings (FBG) for control and stabilization of start and stop wavelengths in the self-sweeping laser. We showed that the short-wavelength FBG helps to initialize the sweeping process and long-wavelength FBG blocks the laser line sweeping in long-wavelength region. The last effect is associated with mismatch of longitudinal mode structures of the laser and FBG-based selector. As a result, fluctuations of the sweeping span borders decreased by one or two orders of magnitude down to several picometers. In addition, we studied influence of the parameters for FBG-based selectors such as reflections and mode structure on quality of sweeping range stabilization. The results allow to improve the characteristics of self-sweeping fiber laser which can be used for different sensing applications such as atmospheric remote sensing and interrogation of the sensors based on fiber Bragg gratings.