Scientific results:
- We have developed an experimental method for point-wise writing of refractive index gratings in multi-core fibers with the use of focused femtosecond laser radiation. In the developed method the high precision of localization of the region of modification of the refractive index allows to create fiber Bragg gratings (FBG) in various cores of a waveguide, which opens wide prospects for the creation of multi-parameter sensor systems for the monitoring of 3D deformations of objects as well as for the creation of lasers on the basis of multi-core fiber with unique spectral characteristics.
- For the effect of spatial self-cleaning of a laser beam in multi-mode fibers, the essence of which is improving the quality of output radiation at high power, we have built an analytical model that describes the substance of the process. When the threshold is surpassed, instability starts developing and, as a result of the process of four-wave mixing, energy exchange occurs between various modes of the fiber. An important consequence of this is that energy is transferred not only to the main mode, as it was suggested earlier, but also the higher-order modes. These conclusions were confirmed with numerical computations. In practice this means the preservation of the so-called mean number of modes, which was also checked in an experiment for the first time. This research shed light on the causes of such a complex spatio-temporal dynamics of radiation in multi-mode fibers. Later this effect can find applications in many practical domains, for instance, for transmitting powerful laser beams with high quality and for building amplitude modulators that are necessary for the generation of pulses of ultra-short duration.
- Our researchers have conducted a study of nonlinear coherent structures in multi-mode and multi-core fiber waveguides (MMW and MCW) arising in a system with mode-selective feedback (lasers) implemented, among other, with the use of FBGs with a special spatial structure and a spatial modulator of light. In particular, we have conducted a detailed study of the effect of Kerr self-cleaning in gradient MMW depending on the input conditions (peak power of the pulse, angle of incidence). We have produced new modes of self-cleaning and stable multi-mode structures respectively, including for pulses with non-null angular momenta. We built a general theory of the so-called thermalization of light in MMW that accounts for angular momentum preservation. This allows to obtain a generalized Rayleigh–Jeans distribution for the relative population of modes in a MMW, which was confirmed with experimental results.
- For a continuous FBG laser with mode-selective feedback implemented using a special FBG, we have conducted a quantitative analysis of the mode composition of radiation. It was found that the total number of modes excited by pumping radiation amounts to about 780, while in the generated Stokes beam their number is lower by two orders of magnitude, and 40 per cent are concentrated in the fundamental mode. In this case the nature of the mode distribution appears to be closer to the exponential law than to the Rayleigh–Jeans distribution. We also implemented generation in MCWs with spatial-spectral selection of radiation based on an array of FBGs.
Implemented results of research:
Four commercial agreements for R&D have been completed:
- «Development of a method and algorithms for the analysis of the mode composition of radiation of a multi-mode FBG laser based on a spatial modulator of light», the research of the mode composition of radiation allowed to uncover the mechanisms of nonlinear interaction of modes in fiber lasers.
- «Development of a technology for writing FBGs through the protective shell in fiber with a core made of undoped quartz glass and a shell made of fluorosilicate glass», we designed technology for writing FBGs through the protective shell in fiber with a core made of undoped quartz glass and a shell made of fluorosilicate glass, which allows to create sensitive elements for fiber-optical detectors.
- «Development of a technology for writing arrays of FBGs in heat-resistant fiber», developing a technology for writing arrays of FBGs in heat-resistant fiber that will allow to create sensitive elements for fiber laser detectors with unique operational characteristics.
- «Developing high-speed nodes for the research of the dynamics of the mode composition of radiation of a continuous FBG laser using mode decomposition», the research of the mode composition of radiation will allow to uncover the causes of mode instability in continuous fiber lasers — the main factor that limits the maximum attainable power of radiation as of now.
Education and career development:
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- Four Candidate of Sciences dissertations have been defended.
- A new education program has been developed.
- Six internships have been conducted.
Organizational and structural changes:
On the grounds of the Laboratory, a joint research and education center for automatic and fiber optics operates in collaboration with the Institute of Automation and Electrometry of the Siberian Branch of the Russian Academy of Sciences (Russia), collaborative works are also performed with «Femtotech» Ltd (Russia) pursuant to a commercial agreement.
Collaborations:
- Sapienza University of Rome (Rome, Italy): joint research, internships.
- Institute of Automation and Electrometry of the Siberian Branch of the Russian Academy of Sciences: joint research, joint academic events (International school for young researchers «Nonlinear photonics»).
- Dianov Fiber Optics Research Center of the Russian Academy of Sciences: research and development of special multi-core and multi-mode fibers.
- Karlsruhe Institute of Technology (KIT, Karlsruhe, Germany): internships, joint grant applications.
- University of Burgundy (Dijon, France): joint grant applications.
