Multiwavelength lasing in the random distributed feedback fiber laser is demonstrated by employing an all fiber Lyot filter. Stable multiwavelength generation is obtained, with each line exhibiting sub-nanometer line-widths. A flat power distribution over multiple lines is also obtained, which indicates the contribution of nonlinear wave mixing towards power redistribution and equalization in the system. The multiwavelength generation is observed simultaneously in first and second Stokes waves.
We present the first experimental demonstration of strong coupling between the core modes in multi-core fibers (MCF)
regardless of large spacing (~28μm) between them. The effect is very sensitive to bending of the fiber and is observed in
the MCF laser as well as in the probe beam schemes. We explain the observed effect by a mechanism of the mode coupling based on their indirect interaction inside the fiber via intermediate cladding mode, analogues to the Bragg mode. 70% of power conversion from one core to another with beating length of tens of centimeters in 4-core MCF is measured.
In the work, the results of the investigations of processes of non radiative energy transfer between ions Yb3+
and Trn3+ in silica-alumina fibers are presented. It was discovered that the interaction between ions Yb3+ and Tm3+ is
described within the framework of the Ferster's law for the case of dipole-dipole interaction mechanism. The
microparameter of interaction CdaY rightwards arrow Tm is 1.56 · 10-39 cm6sec-1.
We present results of the research and development of CW fiber lasers with reflectors based on multimode fiber Bragg gratings. Considered laser schemes used cladding pumped active fibers as an active medium. We have shown that multimode fiber gratings written in the graded index multimode fiber can be used to form the cavity of different types of the fiber lasers. In particularly we have fabricated single mode and multimode lasers based on all-silica and polymer coated double-clad active fibers. The realized lasers were based on Yb-doped fibers having an emission band between 0.98 and 1.1 μm, and based on Er-doped fiber with an emission wavelength near 1600 μm.
We present results of the research and development of the CW medium-power fiber lasers emitting in a range of 1-2 μm. Realized light sources are based on the application of rare-earth doped fibers and Raman converters pumped by semiconductor sources. A combination of the fiber lasers emitting at different wavelengths with Raman converters based on germanium or/and phosphorous fibers allows one to build a laser source emitting at any wavelength of near IR range. The reached quality of the fabricated fibers and optimization of reflecting Bragg gratings allowed us to demonstrate fiber lasers with a quantum efficiency closed to 90%. The fabricated lasers were used for a realization of Raman converters emitting at the various wavelengths.
In a two-stage phosphosilicate Raman fiber laser (1.26/1.53μm) pumped by Yb-fiber laser (1.08μm), a temperature tuning of FBGs forming Raman cavities has been performed by means of thermoelectric modules based on Peltier elements. Output power and spectral profiles at 1.26μm and 1.53μm have been monitored during such T0-tuning in the range of ±25C corresponding to the FBG wavelength shift of ±0.2nm. The most pronounced effect is that the observed spectral profile at 1.26μm corresponding to the first-stage highly-reflective cavity consists of two splitting components, which become strongly asymmetric while independent T0-tuning of cavity FBGs. A simple model considering spectral broadening with increasing pump power and T0-induced shift between central wavelengths of the FBGs has been developed. The model takes into account wavelength-dependent Raman gain saturation and qualitatively describes the observed effects of the splitting and asymmetry with T0-tuning. It is also demonstrated, that the studied spectral broadening and shift lead to the effective “bleaching” of the highly-reflective cavity, so estimated integral transmission may increase by order of magnitude from minimum transmission ~ 1%, corresponding to central FBG wavelength.
Passive Q-switching in fiber lasers can be caused by cooperative dynamics of linear Rayleigh backscattering (RS) and Stimulated Brillouin Scattering (SBS) in a fiber configuration. We give a clear physical insight into the RS-SBS mechanism and present new experiments with low- and high-power self-Q-switched fiber lasers. A 15-ns self-stating periodic pulse generation with a peak power up to 40-300 W has been investigated with an Er-doped fiber laser pumped at 20-160 mW from a laser diode. The generation of Q-switched pulses occurs with a perfect pulse shape performance without emitting any parasitic pulse. We have also realized a self Q-switched double-clad Yb-doped fiber laser. For this laser an average/peak power as high as 1.4 W/5 kW has been achieved at a pulse repetition rate in a range of 5-50 kHz and a pulse duration of 5-10 ns.
In this work we have tested characteristics of EDFA based on a single-mode Er-doped fiber, pumped at 1480 nm by two-stage Raman fiber converter. As an active media of Raman fiber converter a single-mode fiber with phosphorus doped core was used. The conversion efficiency of Raman converter was measured to be 36%. Output power of EDFA as high as 26 dBm was achieved at wavelengths 1554 and 1582 nm corresponding to C and L-band of WDM systems.
We present results of the research and development of double-clad Yb3+-doped fibers for high-power fiber lasers. The quality of the fabricated fibers and optimization of reflecting Bragg gratings allowed us to demonstrate fiber lasers with a quantum efficiency close to 90%. These fiber lasers were used in Raman converters emitting at various wavelengths.
A 1.43 micrometers fiber laser with an output power of 1.4 W is reported. The laser is based on Raman conversion of the Yb- fiber laser emission in a phosphorous doped fiber. The light conversion is based on both phosphorous and silica Raman shifts in the same P-doped fiber. This device can find medical applications, since its emission wavelength coincides with one of the water absorption bands.
It is well known that fibers with a high index difference between the core and the cladding have additional optical losses, which can not be explained by the known sources. In the case of fibers with a germanosilicate core these losses can achieve several dB/kin for a germanium dioxide concentration of 20-30 mol.%. For fibers with an alumosilicate core additional losses amount to 10-30 dB/km. We believe that one of the origins of the loss increase consist in the interpenetrating of the core and cladding materials at their boundary. This phenomenon takes place in preforms produced by inside vapor deposition, if the viscosities of the cladding and the core glasses are different because of a high level of the core doping. During the collapsing process the boundary of two liquids with the different viscosities can lose stability leading to the material interpenetrating. As the result, so called "viscous fingers" arise along the core-cladding boundary. It is easy to observe these formations in preforms with an alumosilicate core, where the characteristic length of "viscous fingers" is comparable with the core diameter study of the core-cladding interface instability. The main point of the theoretical consideration is the eigen oscillation frequencies of the core-cladding boundary. The study is based on the model of contact of two cylindrical layers of liquids with different viscosities. It is shown th In this paper we present the results of a theoretical and experimental at there is a set of eigen oscillation frequencies such that perturbations at these frequencies are not damped out with time. Also, we have found the frequencies resulting in the fastest increase of the perturbations. For the preforms with an alumosilicat core the simulated results and the number of the observed "viscous fingers" are in a satisfactory agreement. It follow from this investigation that the stability of the core-cladding interface can be improved by using special co-dopants. These co-dopants should change the composition of the two contacting glasses (or one of them) so as to match their viscosities.
Fluorine-doped silica active and passive optical fibers for different purposes have been fabricated by two novel modifications of the plasmachemical technology. These versions of the technology are shown to be convenient in laboratory conditions and very promising in developing various types of special fibers with non-standard parameters based on pure and fluorine-doped silica.