I. A. Lobach

Optimization and control of the sweeping range in an Yb-doped self-sweeping fiber laser

Influence of the laser cavity parameters (an active fiber length and output coupling losses) and the temperature of elements (active fiber and pump laser diode) on the sweeping range in an Yb-doped self-sweeping laser is investigated. The obtained results show that the sweeping spectral region is shifted to shorter wavelengths for shorter active fibers and with increasing absorbed power. This allows one to obtain self-sweeping operation in a broad range within a ytterbium gain bandwidth from 1028 to 1080 nm. At the same time, there are optimal cavity parameters at which the sweeping span is the broadest (>20 nm). Good agreement between the experimental sweeping range and the calculated maximum gain wavelength is demonstrated.

All-fiber Brillouin optical spectrum analyzer based on self-sweeping fiber laser

We proposed and demonstrated a simple scheme for measurement optical spectrum based on stimulated Brillouin scattering and self-sweeping laser without external driver and tunable elements. The resolution and measuring range of proposed analyzer is measured as 20 MHz and 5 THz respectively. The ways of improvement the characteristics of device are discussed.

Cascaded Raman lasing in a PM phosphosilicate fiber with random distributed feedback

We report on the first demonstration of a linearly polarized cascaded Raman fiber laser based on a simple half-open cavity with a broadband composite reflector and random distributed feedback in a polarization maintaining phosphosilicate fiber operating beyond zero dispersion wavelength (~1400 nm). With increasing pump power from a Yb-doped fiber laser at 1080 nm, the random laser generates subsequently 8 W at 1262 nm and 9 W at 1515 nm with polarization extinction ratio of 27 dB. The generation linewidths amount to about 1 nm and 3 nm, respectively, being almost independent of power, in correspondence with the theory of a cascaded random lasing.

Sweeping range control in a self-sweeping laser with selective mirrors

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.

Brillouin optical spectrum analyzer with modulated pump

Optical spectrum is one of the most important characteristics of a laser radiation. Many spectral techniques are proposed and developed for spectral measurement, which are based on diffraction gratings, heterodyne or stimulated Brillouin scattering (SBS) amplification. For the last one, the signal radiation is amplified via SBS when frequency difference between pump wave and signal under test corresponds to Brillouin shift in a fiber (∼10 GHz) within the bandwidth of the Brillouin gain window (∼20 MHz) [1]. A spectrum under test can be reconstructed through scanning of the pump wave frequency. One should note that unamplified signal components being outside the SBS gain window propagate to the output with amplified components and thereby can deteriorate the dynamic range in the optical spectrum analyzer (OSA). This fact complicates the detection a weak spectral component in the presence of stronger one at a closely spaced frequency. To suppress the influence of unamplified signal the technique of polarization pulling is can be applied [2]. In this case, the specific polarization state matching is used. In the present paper, another way of separation of amplified and unamplified signals is proposed. We suggest to modulate intensity of tunable pump radiation similarly to lock-in detection.

Random distributed feedback Raman fiber lasers

In this chapter we briefly review the basic principles of Raman fiber lasers operating via random distributed feedback, including details of feedback mechanism, various cavity designs, and corresponding power and spectral characteristics, as well as their statistical properties. We also compare performances of the random Raman fiber lasers (RRFLs) with that for conventional Raman fiber lasers (RFLs) with linear cavity based on two reflectors. The performance analysis includes polarization management, optimization of conversion efficiency, cascaded generation of higher Stokes orders, opportunities for short-wavelength generation via direct pumping by high-power laser diodes, or frequency doubling of random Raman fiber laser radiation. Pulsed operation of random Raman fiber lasers via active or passive Q-switching is also analyzed. The analysis shows that the output characteristics of Raman fiber lasers with random distributed feedback reached to the moment already outperform in many aspects those for conventional Raman fiber lasers. The unique performance of random fiber lasers opens the door to their application in advanced technologies, such as long-distance amplifier-free transmission and remote sensing, low-coherence IR, and visible sources for bio-imaging and others.