Nonlinear Photonics Laboratory

• We have developed methods for modeling laser generation and spatial control of nonlinearity in application to pulse fiber laser systems, algorithms for volume numerical optimization of fiber laser systems with nontrivial fiber resonators, new methods of signal detection allowing to reduce the number of errors by 20–30 per cent, a method for controlling nonlinear evolution of pulses inside resonators and achieving generation of pulses of various duration, sign and extent of phase modulation (chirp), a method for regenerative active synchronization of modes in fiber lasers, a method of increasing efficiency of nonlinear frequency converter by 20 to 30 per cent.
• Our researchers have demonstrated the necessity to consider the impact of the initial distribution of the field in modeling fiber lasers with long and super-long resonators to search for all the possible attractors (a modeling method).
• We have produced a formula that describes the correlation between energy and length of the resonator for single-impulse modes in long fiber lasers (the energy scaling law).
• A new architecture has been developed for long fiber lasers that provides two types of mode synchronization and variation of dispersion of resonators to control shapes and width of generated pulses (a scheme).
• We have optimized properties of saturable absorbers based on carbon nanotubes. This allowed to achieve powerful pulse laser generation with relatively high power level in the master clock (an experimental model of the laser).
• Our researchers have determined capabilities and limitations of weakly nonlinear compression of laser pulses with positive frequency modulation (chirp) in fibers with abnormal dispersion. We have theoretically and experimentally found values of maximum output of radiation below which compression of pulses down tot the Fourier limit is possible. We have found the value of optimal fiber length for pulse compression with above-critical power level (formulas/laws).
• The Laboratory has determined that double-scale laser pulses provide high efficiency of nonlinear optical transformations which is related to presence of femtosecond components in such pulses (sub-pulses) with high peak power (a scheme).
• We have developed a scheme for spatial-frequency homogeneous amplification with power variation of less than 3 dB per 100 kilometers.
• We have determined the optimal parameters of dispersion of thulium laser resonator. Nonlinear correlation has been found between pulse energy and resonator length.
• Our researchers have introduced a new mathematical model and efficient computation algorithms for modeling of propagation of laser radiation in multi-core optical fiber.
• We have developed a pulse fully fiber thulium laser with an original hybrid NALM-NOLM scheme with quality factor modulation by saturable absorbers based on polymer composite and carbon nanotubes with record-high power for lasers of this type.
• We have demonstrated pulse generation in a fiber laser with random distributed feedback. By installing a graphene filter and a polarization rotator into the resonator, the laser generated pulses with duration of 900 ps and wide tuning (over two orders of magnitude of the value for pulse duration and three orders of magnitude for repetition frequency).
• The Laboratory has designed and manufactured new configurations of saturable absorbers based on carbon nanotubes and elongated optical fiber. We have demonstrated the effect of saturable absorbers during propagation of optical radiation along fiber. We have achieved pulse laser generation in fiber lasers using assembled experimental units.
• We have proposed and studied a new scheme of a super-long fiber infrared laser – adiabatic soliton laser where mode synchronization is provided by a saturable absorbers based on single-wall carbon nanotubes. The main feature of the proposed scheme is usage of a long sector of a standard single-mode waveguide as the active environment where signal amplification is provided by two-cascade forced Raman scattering of radiation. The scheme ensures heterogeneous amplification of signal along the beam mode waveguide; signal energy in the proposed scheme exceeds value of signal energy that can be reached using traditional soliton lasers.
• It has been demonstrated that increase of wave length in information transmission lines leads to increase in error rate. It has been shown that the minimal error rate is achieved in the scheme of ultra-long laser with distributed forced Raman scattering amplification with deflection rate of the «input» Bragg grating at Stokes shift wave length of 0.05 as a result of noise transfer. We have demonstrated that usage of fibers with high dispersion in the ultra-long forced Raman scattering laser leads to decrease in the process of noise transfer and, therefore, to decrease of error rate.
• We have developed a forced Raman scattering laser for tumor cell therapy. The developed laser supports pulse generation with the width of generation spectrum that equals 8 nm around 1270 nm, while pulse duration is 180 ps, frequency of 18,7 MHz, mean power of 100 mW, peak power of 26 W, pulse energy of 5,3 mJ.
• It has been shown that the highest simulating effect of laser impact manifests itself in mitogen-stimulated cell cultures. At the same time, both at the level of mean and medial levels we have tracked dependence of the stimulating and amplification of ConA-induced proliferation of blood mononuclear cell on power of the laser impact.
• Our researchers have developed a coding method that allows to decrease the number of symbols that are the most sensitive to impact of nonlinear distortions. We have achieved significant decrease of error frequency (at least by a factor of two) during encoding and realistic difference between errors in symbols with low amplitude and with high amplitude. TO implement the method it is necessary to preliminarily estimate the optimal energy for each particular error statistic which can be reached by using theoretical results achieved as a result of our work.
• On the basis of OFDM we have proposed a new method of information transmission over optical lines for the case of the discrete soliton spectrum that uses a series of separate modulated single-soliton solution while the general N-soliton solution of NSE whose parameters carry encoded information in a manner that it can be encoded and decoded using a combination of fast Fourier transform and nonlinear Fourier transform. We have described the main principles of the new approach that we called soliton OFDM (SOFDM) as well as problems occurring during its implementations. We outlined prospects, problems, estimates of data transmission rate and some results of numerical modeling of SOFDM. We have created prototypes of two fiber laser systems: a pulse system with radiation mode synchronization and a continuous system used as the base for producing quality factor modulation regimes and mode synchronization.
• It has been shown that in fiber lasers usage of the effect of nonlinear spectral compression allows to increase spectral luminosity of signal in comparison to systems that use optical filters as well as allow to avoid additional loss at optical filters or reduce the level of such loss.
• We have proposed new schemes of fiber lasers that use the effect of nonlinear spectral compression to compensate widening of the signal inside the resonator.
• It has been demonstrated that stability of the spectrum during transmission of signal to close locations can be used to suppress nonlinear effects that are the main limiting factors for growth of bandwidth and transmission rate in modern fiber transmission lines.
• We have designed and investigated a new highly efficient phenomenological model of double-scale pulses allows to significantly (by up top 2-3 orders of magnitude) increase efficiency of modeling of usage of double-scale laser pulses in comparison with the model currently used for this purpose that is based on the generalized Schrödinger equation. The proposed model ensures adequate description of temporal and spectral characteristics of double-scale pulses and correctly describes the correlation between close lateral modes in the optical spectrum of generation.
• Our researchers gave proposed and studied an enhanced additive noise model that matches experimental observations including in terms of height of the peak and footprint of the autocorrlation function of double-scale pulses.
• We have performed experimental characterization of modes of single- and double-scale laser pulses in terms of fluctuation energy and temporal instability of movement of the pulse based on research of the radio frequency spectrum of the fiber laser. It has been demonstrated that significant difference between levels of fluctuations in various modes. A simple method has been proposed for differentiation between generation modes in experiments based on automatic analysis of the radio frequency spectrum without recurring to other, more complex, measurements.
• We have produced and research new modes of generation of two-scale pulses with record-high levels of energy (up to 12 mJ and higher) for fiber lasers without additional cascades of extra-resonator amplification. We have conducted analysis of new prospective applications of double-scale pulses; determined relevant applications for which usage of double-scale pulses is more efficient in comparison with «normal» fully coherent laser pulses.
• Our researchers have studied possibility of usage of the Kerr effect for synchronization of radiation modes of fiber lasers. We have developed a scheme of ring fiber laser with an optical system in which the Kerr effect modulates loss inside the resonator and conducted computations of parameters of the scheme and optimization on the basis of experimental measurements. We have determined possibility of self-starting of the laser. A numerical model of the optical system has been built that includes material with high value of nonlinear deflection rate for modeling loss inside the fiber resonator. We have demonstrated importance of consideration of two-photon absorption. As a result of approbation it has been found that the most promising configuration of fiber laser with Kerr effect-based mode stabilization is ring fiber resonator with dispersion compensation that contains an optical system with a As20Se40 crystal.
• We have proposed usage of the general N-soliton solution of NSE for transmission of information via an optical line with a GLME core a the carrier of encoded information. We have found the presence of a relatively string limitation on the number of counts (less than 100) and the limitation on the size of the information message in this method related to it.
• We have proposed a new nonparametric method of modulation – soliton OFDM (SOFDM) that does not impose limitations on size of information messages. The method is based on choice of a constant imaginary part of eigenvalues of the disperse spectrum of solitons. At the same time, frequencies of the N-soliton solutions are selected equivalently which allows to apply the OFDM scheme to recovery of data of scattering using fast Fourier transform.
• Our researchers have developed and studied methods of controlling nonlinearity in nonlinear fiber loop mirror (NLV) of the fiber master clock. New methods are based on usage of two sectors of active fiber with independent electronically controlled optical pumping modules in NLM. The pumping modules allow to control asymmetry of NLM by changing the spatial profile of amplification inside NLM. The proposed method also relies on usage of one region of active fiber inside NLM with control of intra-resonator power of radiation outside of NLM. On the basis of the proposed methods we have developed new pulse fiber master clocks providing self-starting of generation, stability of operation, smooth tuning of parameters of generated pulses and switching generation modes (with capability of generation of single- and double-scale pulses at the laser output), possibility of producing record-high (for this class of master clocks without usage of additional cascades for extra-generator amplification) levels of pulse energy in super-long fiber resonators.
• It has been determined that the value of phase delay of coherent population trapping resonance increases with growth of frequency of scanning of coherent population trapping resonance and high frequencies converges to pi/2. We have demonstrated linear growth of spectral sensitivity of coherent population trapping resonance at resonance scanning frequencies of 1 kHz and higher. It has been demonstrated that the presence of the optimum near the value of frequency of 2 kHz and the modulation amplitude of 2 kHz during synchronous detection of coherent population trapping resonance in bichromatic exciting field. The found optimal values of frequency and amplitude of modulation correspond to the highest inclination of error signal and, therefore, the best stability of the device on the basis of the coherent population trapping resonance. For the first time a description of qualitative changes of shape of registered coherent population trapping resonance has been given: formation of oscillations on the rear slope. It has been determined that frequency of these oscillations that corresponds to the value of double-photon tune-out at the moment of formation of oscillations.
• We have developed a new theoretical model for numerical computation of various options of sequences of bichromatic field pulse (a standard scheme with two pulses, a non-standard scheme with a second composite pulse, an infinite periodic sequence of pulses). We have achieved the frequency stability of 2×10-13 in 40000 seconds. We have developed and tested a new method for increasing the contrast of coherent population trapping resonance by means of feedback while using fast digital error signal processing in the feedback loop these schemes were enhanced. The new method of contrasting coherent population trapping resonance at the pumping radiation power of 100 mW allowed to increase the contrast of coherent population trapping resonance by two orders of magnitude from 1% to 108%, and 25-fold in the dynamic mode.

Implemented results of research: The Laboratory has created prototypes of commercial fiber master clock with passive radiation mode synchronization. The technology is implemented by «Technoscan – Lab» LLC (Novosibirsk).

Education and career development:

• Two doctoral dissertations, 11 candidate dissertations, 10 master and bachelor degree theses have been defended.
• We have developed and implemented the following lecture courses: «Additional chapters of advanced mathematics», «Basic of computational physics» (for bachelors); «Nonlinear photonics 1», «Nonlinear photonics 2» (for masters) as well as 8 additional training courses: «Systems and technologies of modern photonics. Technological entrepreneurship», «Modern worldwide trends in photonics and optoinformatics. The world photonics market», «Technological innovations in photonics. Commercialization of research results», «Industrial photonics. Economical basics of high technologies in photonics», «Photonics and optoinformatics as an innovative development environment. Knowledge-intensive innovations management», «Modern photonics technologies for business. Investment and technological approaches and platforms», «Technology brokering. Promoting of photonics technologies to markets».
• We have compiled two textbooks: «Basics of Computational Physics. Part 1» (S. V. Smirnov, Editing and Publishing Center of the 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 the Novosibirsk State University, Novosibirsk, 2017, 104 p., ISBN 978-5-4437-0677-1).

Organizational and structural changes: The Strategic Academic Unit (Center) «Nonlinear photonics and quantum technologies at the Novosibirsk State University» has been created

Collaborations:

• Aston University (United Kingdom), «Technoscan – Lab» LLC (Russia): joint publications, additional training of academic staff members of the Laboratory