Nonlinear Photonics Laboratory

Scientific results:

• We have developed methods for modeling laser generation and spatial for control of nonlinearity in application to pulsed fiber laser systems, algorithms for the volumetric numerical optimization of fiber laser systems with a nontrivial fiber resonator, new methods of signal detection that allow to reduce the number of errors by 20–30 per cent, a method for controlling the nonlinear evolution of pulses inside a resonator and achieving the generation of pulses of various durations and values and signs of phase modulation (chirp), a method for regenerative active mode synchronization in a fiber laser, a method for increasing the efficiency of nonlinear frequency transformation by up to 20–30 per cent.
• The Laboratory has demonstrated the necessity of considering the impact of the initial distribution of field when modeling fiber lasers with long and ultra-long resonators for searching for  all kinds of attractors (a method of modeling).
• We have produced a formula describing the dependence of energy on the length of the resonator for single-pulse modes in long fiber lasers (a law of energy scaling).
• A new architecture of long fiber lasers has been developed that ensures two types of mode synchronization and variation of the dispersion of the resonator for controlling the shapes and widths of generated pulses (a scheme).
• We have optimized the properties of saturable absorbers based on carbon nanotubes, which allowed to achieve pulsed laser generation with a relatively high level of power in the master oscillator  (an experimental sample of the laser).
• Our researchers have determined possibilities and limitations of the weakly nonlinear compression of laser pulses with positive modulation frequency (chirp) in fibers with abnormal dispersion. We theoretically and experimentally found the values of the power limits of radiation below which pulse compression to the Fourier limit is possible. We have found the value of the optimal fiber length for the compression of pulses  with a supercritical level of power (a formula/law).
• It has been determined that two-scale laser pulses ensure a higher efficiency  of nonlinear-optical transformations, which is related to the presence of such pulses of femtosecond components (sub-pulses) with a high level of peak power  in the structure (a scheme).
• We have developed a scheme of spatial-frequency homogeneous amplification with  a power variation of less than 3 dB  per 100 km.
• Our researchers have determined the optimal parameters of dispersion of the resonator of a thulium laser. We inferred a nonlinear dependence of pulse energy on the length of the resonator.
• We have introduced a new mathematical model and efficient parallel computation algorithms for the modeling of the propagation of laser radiation in multi-core optical fibers.
• A pulsed fully thulium laser has been developed with an original hybrid NALM-NOLM scheme with Q factor modulation by a saturable absorber based on polymer composite and carbon nanotubes with a record-high level of output power for lasers of this type.
• We have demonstrated pulse generation in a fiber laser with randomly distributed feedback. On account of installing a graphene filter into the resonator and rotating the polarization, the laser generated pulses with a duration of 900 picoseconds with a large rearrangement (more than two orders of magnitude in pulse duration and three orders of magnitude in repetition frequency).
• The Laboratory has developed and produced new configurations of saturable absorbers based on carbon nanotubes and elongated optic fiber. We have demonstrated the effect of saturating absorption during the propagation of optical radiation along fiber. We achieved pulsed laser generation in fiber lasers employing assembled prototypes.
• We have proposed and researched a new scheme of a super-long fiber IR laser, an adiabatic soliton laser, in which mode synchronization is achieved using a saturable absorber based on single-wall carbon nanotubes. The main feature of the proposed laser scheme is the use of a long region of a standard single-mode waveguide as an active medium, in which signal amplification is achieved by a two-cascade SRS transformation of radiation. The scheme ensures uniform adiabatic signal amplification along the waveguide; the power of the signal in the proposed scheme exceeds the signal power attainable in traditional soliton lasers.
• Our researchers have demonstrated that by increasing the length of a communication line it is possible to increase the error rate. It has been shown that the minimum  error rate is achieved in the scheme of an ultra-long laser with distributed SRS amplification at a reflection coefficient of the «input» Bragg grating at the Stokes shift wavelength amounting to 0.05, due to the suppression of noise transfer. It has been demonstrated that the use of data transfer in the scheme of an ultra-long SHS laser of fiber with a high  dispersion leads to a decrease in the process of noise transfer and, consequently, to a decrease in the error rate.
• We have developed a fiber SRS laser for the therapy of cancer cells. The developed laser ensures pulse generation with a width range of generation of 8 nm in the 1270 nm region, a pulse duration of 180 ps, a pulse frequency of 18,7 MHz, an average power of 100 mW, a peak power of 26 W and a pulse energy of 5,3 nJ.
• It has been determined that the highest stimulating effect of laser impact manifests itself in mitogen-stimulated cell cultures. In this case both at the level of mean and median values the dependence of the stimulating effect and ConA-induced MNC proliferation on the power of laser radiation can be observed.
• Our researchers have developed a coding method that allows to decrease the number of symbols which are the most sensitive to the influence of nonlinear distortions. We achieved a significant decrease in error frequency (at least by the factor of two) during coding and a realistic difference between errors in symbols with low amplitudes and with high amplitudes. To use the method it is necessary to conduct a preliminary assessment of the optimal entropy for each specific statistic of errors, which is achieved by using the theoretical results obtained in our project.
• On the basis of OFDM we proposed a new data transfer method involving an optical line for the case of discrete soliton spectrum that employs the general N-soliton solution of NSE, whose parameters carry encoded information in a way that allows it to be encoded and decoded using a combination of fast Fourier transform and nonlinear Fourier transform, instead of a sequence of separate modulated 1-soliton solutions. We described the main principles of the new approach, which we called soliton OFDM (SOFDM), as well as problems arising in the course of its implementation. We outlined the prospects, problems, estimates of data transfer rate and some results of a numerical modeling of SOFDM. We created prototypes of two fiber laser systems: a pulsed system with radiation mode synchronization and a continuous system used as a basis for producing Q factor modulation modes and mode synchronization.
• It has been demonstrated that in fiber lasers the use of nonlinear spectral compression allows to improve the spectral brightness of signal compared to systems in which optical filters are used as well as allows to avoid additional losses on optical filters or reduce the degree of such losses.
• We have proposed new  schemes of fiber lasers employing the effect of nonlinear spectral compression to compensate for the nonlinear broadening of signal inside the resonator.
• It has been demonstrated that the stability of the spectrum during propagation for longer distances can be used to suppress the nonlinear effects that are the main limiting factors for increasing the bandwidth and data transfer rate in modern fiber communication lines.
• We have developed and studied a new highly efficient phenomenological model of two-scale pulses that allows to significantly (up to 2-3 orders of magnitude) increase the efficiency of modeling applications of two-scale laser pulses compared to the model currently used for this purpose that relies on the generalized nonlinear Schrodinger equation. The proposed model ensures the description of temporal and spectral properties of two-scale pulses as well as correctly describes the correlation of close lateral modes in the optical spectrum of generation.
• We have proposed and studied a modernized model of additive noise that is in good agreement with experimental observations, including in terms of the height of the peak and the background of the ACF of two-scale pulses.
• Our researchers have conducted an experimental characterization of generation modes of one- and two-scale laser pulses in terms of the level of energy fluctuations and temporal instability of pulse repetitions on the basis of a research of the radio-frequency spectrum of a fiber laser. We demonstrated a significant difference in the level of fluctuation in various modes. We have proposed a simple method for differentiating between generation modes in an experiment on the basis of the automated analysis of the radio-frequency spectrum of a lased without using additional more complex measurements.
• We have produced and researched new modes of generation of two-scale pulses with a record-high level of energy (up to 12 µJ and higher) for fiber lasers without additional amplification cascades outside the resonator. We have performed an analysis of new promising applications of two-scale pulses; determined relevant applications in which the use of two-scale pulses is more efficient compared to «normal» fully coherent laser pulses.
• The Laboratory has researched the possibility of using the Kerr effect to synchronize radiation modes of a fiber laser. We developed a scheme of a ring fiber laser with an optical system, in which the Kerr effect modulates the loss inside the resonator, performed computations of the parameters of the scheme and optimized it on the basis of experimental measurements. We determined possibilities of ensuring self-start in the laser. A numerical model of an optical system has been developed that includes  a material with a high value of the nonlinear refractive index for the modulation of losses of the fiber resonator. We demonstrated the importance of accounting for the effect of two-photon absorption. As a result of testing we determined that the most promising configuration of a fiber laser with mode synchronization relying on the Kerr effect is a ring fiber resonator with dispersion compensation containing an optical system with a As20Se40 crystal.
• We proposed to use the general N-soliton solution of the nonlinear Schrodinger equation for data transfer via an optical line with a GLME core as the carrier of encoded information. Our research demonstrated the presence of a relatively strong limitation for the number of counts (less than 100) and limitations of information communication in this method related to this.
• We have proposed a new nonparametric method of modulation, soliton OFDM (SOFDM) that has no limitations for the size of information messages. The method is based on choosing a constant imaginary part of eigenvalues of the discrete spectrum of the solitons. In this case the frequencies of the N-soliton solution are chosen equidistantly, which allows to use the OFDM scheme to recover data of scattering using fast Fourier transform.
• The Laboratory has developed and researched methods of controlling nonlinearity in a nonlinear amplifying loop mirror (NALM) of a fiber master oscillator. The new methods are based on using two stretches of active fiber with two independent electronically controlled optical pumping modules in a NALM, which allows to control the asymmetry of the  NALM by changing the spatial profile of amplification inside the NALM, as well as on using one stretch of active fiber inside the NALM while controlling intra-resonator power of radiation outside the NALM. On the basis of the proposed methods we have developed new schemes of pulse fiber master oscillators that ensure self-starting generation, stable operation, smooth control of the parameters of generated pulses and generation mode switching (with the capability of producing one- and two-scale pulses at the output form the laser), the possibility of producing record-high (for this class of  master oscillators without using additional amplification cascades outside the resonator) levels of pulse energy in ultra-long fiber resonators.
• It has been established that the value of phase delay in coherent population trapping (CPT) resonance increases when the scan rate of CPT resonance  grows and at high frequencies it tends to pi/2. We demonstrated a linear increase of the spectral sensitivity of CPT resonance at scanning frequencies of CPT ranging from 1 kHz and higher. It has been shown that the presence of an optimum near a modulation frequency of 2 kHz and an amplitude of modulation amounting to 2 kHz when synchronously detecting CPT resonance in a bichromatic excitation field. The found optimal values of the frequency and the modulation amplitude correspond to the highest inclination of the error signal and therefore the best stability of a device based on CPT resonance. For the fist time we have provided a description of qualitative changes in the shape of the registered CPT resonance: the emergence of oscillations on the decreasing slope. It has been determined that the frequency of these oscillations exactly matches the value of two-photon detaining at the moment of the formation of oscillations.
• The Laboratory has developed a new theoretical model for the numerical computation of different variants of sequences of pulses of a bichromatic field (a standard scheme with two pulses, a non-standard scheme with a second composite pulse, an infinite periodic sequence of pulses). We achieved a frequency stability of 2×10^-13 over 40000 seconds. We have developed and tested a new method for increasing the contrast of CPT resonance with the use of feedback, while by virtue of fast digital error signal processing in the feedback loop these schemes were improved. The new method of contrasting CPT resonance at a pumping radiation power of 010 µW allowed to increase the contrast of CPT resonance by two orders of magnitude from 1 to 108 per cent, and by a factor of 25 in the dynamic mode. 

Implemented results of research: 

We have created prototypes of commercial fiber master oscillators with passive radiation mode synchronization. The designs are implemented by «Technoscan-Lab» Ltd (Novosibirsk). 

Education and career development:

• Two Doctor of Sciences dissertations and 11 Candidate of Sciences dissertations have been prepared and defended, as well as 10 master’s and bachelor’s degree theses.
• We have developed and implemented lecture courses: «Additional chapters of higher mathematics», «Basics of computational physics» (bachelor’s degree); «Nonlinear photonics 1», «Nonlinear photonics  2» (master’s degree), as well as 8 additional training programs: «Systems and technologies of modern photonics. Technological  entrepreneurship», «Modern world trends in photonics and optoinformatics. World photonics market», «Technological innovations in photonics. Commercialization of knowledge-intensive developments», «Industrial photonics. Economic foundations of high technologies in photonics», «Photonics and optoinformatics as an innovative development environment. Management of knowledge-intensive innovations», «Modern photonics technologies for business. Investment and technological approaches and platforms», «Technology brokerage. Promoting photonics technologies to the market».
• Two textbooks have been developed: «Basics of computational physics. Part 1» (S. V. Smirnov, Editing and Publishing Center of Novosibirsk State University, Novosibirsk, 2015, 113 p., ISBN 978-5-4437-0429-6) and «Basics of computational physics. Part  2» (S. V. Smirnov, Editing and Publishing Center of Novosibirsk State University, Novosibirsk, 2017, 104 p., ISBN 978-5-4437-0677-1).

Organizational and structural changes: 

We have created the Strategic Academic Unit (Center) «Nonlinear photonics and quantum technologies in NSU».

Other results:

Every year since 2017 we have been conducting the International School for Young Scientists «Nonlinear photonics» within a Russian Science Foundation grant to increase the professional level of scientific research, expending horizons and engaging younger scientists, postgraduate and senior-year undergraduate students in solving current problems in the field of nonlinear photonics. The topic of the School encompasses a wide range of problems in various areas of photonics, including nonlinear optics, laser physics, spectroscopy, fiber and  integrated optics, processing optical signals, optical sensors, parametric effects, materials for photonic devices and biomedical applications.  

Collaborations:

• Aston University (United Kingdom), Institute of Laser Physics of the Siberian Branch  of the Russian Academy of Sciences, Institute of Automation and Electrometry of the Siberian Branch of the Russian Academy of Sciences, Fiber Optics  Research Center of the Russian Academy of Sciences (Russia): joint research and publications, additional training of employees of the Laboratory.

• Technosan Group (Russia): collaborative development of new lasers implemented by Technosan Group in collaboration with NSU. These lasers work in more than 100 universities and research institutes of Russia and more than 40 universities, metrological and nuclear centers (NIST, PTB, DESI, GSI, BARC, KAERI), transnational companies  (Samsung, Panasonic, LG) in the USA, Europe, India, China PR, Japan and other countries.

• «CityAir» Ltd (Russia): conducting joint scientific research.

The Laboratory also collaborates with the University of Tampere (Finland) and the Lebedev Physical Institute of the Russian Academy of Sciences (Russia).