We investigated a stable single-cavity dual-wavelength-comb fiber laser with significant difference of pulse characteristics. Switchable single/dual-wavelength pulses across 1530- and 1550-nm gain regions are obtained by adjusting the intracavity linear loss. In the dual-wavelength operation, the repetition rates fluctuate and drift in more than 145 Hz, while the standard deviation of the repetition rate difference is measured as 64 mHz in 1000-second monitoring. The passive mutual coherence between pulses is comparable or somewhat better than the reported one under the similar disturbance and monitoring condition. Meanwhile, the significant difference of dual-wavelength pulse characteristics, including spectral bandwidth, pulse energy and dispersion is observed and discussed. The qualified stability is also attributed to the significant pulse difference, which could suppress the nonlinear pulse interaction induced instability. These results provide further physical understanding of the construction of dual-wavelength-comb pulse fiber laser, showing the high potential to promote the performance improvement of dual-comb metrology such as dual-comb spectroscopy, and ranging.

Optical parametric amplifiers relying on the nonlinear four-wave mixing process have attracted much interest in optical communication, ultrafast signal processing, and quantum metrology. Here, we propose a dual-pump optical parametric amplifier based on a bilayer silicon-rich nitride waveguide with flattened dispersion. The amplifier can possess a high gain of 26.2 dB and a low wavelength-dependent gain ripple of 1 dB over a more-than-400-nm wavelength range. We also examine the amplification of an ultrashort soliton pulse with a peak power of 0.25 W and a pulse width varying from 7 to 20 fs. The gain can reach 19 dB, which is suitable for boosting low-energy broadband sources.

We experimentally demonstrate a high frequency tuning scheme for the squeezed vacuum state by using acoustooptic modulator based on bi-frequency interferometer. The tuning frequency is determined by the acousto-optic modulator’s driving frequency, which is 80 MHz, at least 3 orders of magnitude larger than the line-width of the laser used for state generation. The efficiency of the frequency tuning device is 91%, limited only by the transmittance of the acousto-optic modulators.

We introduce a dimensional reduction method for studying the stability of multidimensional solitons in coherently driven Kerr cavities with a parabolic potential.

In this study we investigate the formation and propagation of pulse pairs in a quadratically nonlinear crystal containing two waveguides. The analysis focuses on how changes in parameters such as the relative positions of the waveguides, waveguide widths, and angle of entry influence the system. We observe that the pulse propagation mode varies with changes in the characteristics of the waveguides and the angle at which the pulses enter the medium.

We proposed the emission of wavelength-switchable dual-wavelength-comb pulses in a practical-filter-free cavity. Based on the polarization dependent loss based gain profile tuning, lasings in triple independent gain subregions, i.e. ~1530-, ~1543- and ~1555-nm gain subregions, of erbium-doped fiber, are experimentally observed. Mode-locked by hybrid mechanisms combining carbon nanotube and nonlinear polarization evolution, triple types of dual-wavelength pulses distributed in different dual gain subregions are experimentally obtained. They are distributed in above triple gain subregions and could be switched by adjusting the intracavity polarization controller. These results provide a simple yet effective route to obtain dual-wavelength-comb pulses without additional practical filter and show the high potential in the applications of single-cavity dual-comb metrology.

Erbium heavily-doped fiber lasers demonstrate two thresholds, the first one associated with an onset of lasing in the pulsed regime, and the second with a transition to CW. Operation features near these two thresholds have been established experimentally. For the first time, a power-law behavior of the system parameters – pulses frequency, duration and peak intensity – was revealed in a wide range of pump rates around both thresholds. The power exponents were associated with critical indices of phase transition. Their values were convincingly determined different from integers and half-integers. Critical indexes were shown weakly dependent on the Fabry-Perot and distributed feedback (DFB) laser cavity parameters, which made it possible to experimentally establish the universal dependence of the pulse frequency and duration on the lasing power. The results of the work are extremely useful for determining and predicting the parameters of the designed erbium lasers, due to universality of the critical indices.

As a cutting-edge quantum information research system at the intersection of "quantum information" and "integrated circuits", silicon carbide color center has become one of the important solid-state quantum systems in recent years. Silicon carbide color center system has the following characteristics :1) Silicon carbide is a mature semiconductor material, quantum information technology based on silicon carbide color center is easy to integrate with semiconductor industry technology; 2) Silicon carbide color center fluorescence in the near infrared band, which is conducive to transmission in optical fiber communication network; 3) Silicon carbide color center spin coherence time is long, easy to perform more quantum algorithms. This report mainly introduces the research progress of quantum control and quantum precision measurement of silicon carbide color centers, including the basic knowledge of silicon carbide color centers, the preparation, observation and quantum control of its spin quantum states, as well as the application of this system in the fields of quantum control and quantum precision measurement.

We investigate the formation of spatiotemporal solitons in waveguides with a parabolic refractive index and quartic chromatic dispersion. Using both variational methods and full 3D simulations, we demonstrate that fourth-order dispersion enhances soliton stability, preventing spatiotemporal collapse. Pure quartic solitons maintain stability over a broader energy range compared to solitons formed by second-order dispersion.

Research in the field of quantum physics and electronics, with aim of designing and building quantum devices and quantum Internet, is carried out by scientists from many countries. Recently, the interests of researchers have been directed both to creation of wired networks (by connecting quantum devices via fiber optic cables) and through wireless devices (up to satellites located in Earth orbit). This investigation examines history of quantum devices development and quantum Internet both in foreign countries and in Russian Federation, and provides the diagram of connection between two quantum processors via router. The data on articles, reports and results of workshops (training events) published in scientific journals in bibliographic and abstract database Scopus are analyzed, and graphical dependencies are built on their basis. The data obtained show that interest of scientific community in the topic under consideration has grown significantly over the past decade. The article describes in detail the features, advantages and disadvantages of quantum Internet, which can accelerate the development of new-generation telecommunication networks, improve the research quality and obtain the specific results in this area.

In this report, we study theoretically and numerically the soliton propagation of laser radiation in the medium with quadratic and cubic nonlinear response. We show that, for high-intensity femtosecond pulses with a large phase mismatch of the interacting waves, soliton propagation of two-color laser radiation with similar peak intensities of interacting waves is possible. Our investigation is based on two coupled nonlinear Schrödinger equations. Using a multiscale approach, we derive an approximate analytical solution for two-color laser radiation propagation in the soliton mode. Based on numerical simulation, high-efficient frequency down conversion is demonstrated when switching the two-color soliton mode to the soliton mode with high peak intensity at the fundamental frequency.

Studies focusing on formation and stable propagation of two-color solitons in active periodic structures are essential and in great demand. Previously, the formation of four-wave soliton in active periodic structure under SHG was investigated analytically and numerically for group synchronism of interacting waves in the framework of the coupled waves approach. In the present work, we focus on the peculiarities of the four-wave soliton formation under strong group mismatch of the interaction waves. Our investigation is based on the four coupled Schrödinger-type equations for forward and backward waves on the fundamental and doubled frequencies. The influence of the difference in the waves velocities on the transmitting and reflective properties of the active periodic structure was also studied.

We investigate the optical frequency comb generation based on axial mode interaction in a cylindrical microresonator with various shapes of radius variation. We claim that the axial group velocity dispersion in such a system does not depend on the shape of the radius variation and is anomalous regardless of the cylinder radius, which leads to the bright soliton solution.

In this paper, we propose a multi-rate and multi-protocol CV-QKD scheme based on the orthogonal-frequencydivision- multiplexing (OFDM) technology. The proposed OFDM-based multi-carrier CVQKD scheme only requires one transmitter and one receiver to realize QKD with different modulation protocols and different key rates in one communication. More importantly, the multiple subcarriers with different modulation protocols have different excess noise tolerances in the same transmission channel, which can achieve the flexible QKD service even in long-distance and high-disturbance fiber channel. In order to verify the proposed scheme, 5 subcarriers with QPSK, 64QAM, 256QAM, 1024QAM and Gaussian modulation protocols are evaluated by the SDP and no-switch Gaussian security analysis method at different transmission distances. The simulation results show the proposed OFDM-based multi-carrier scheme allows various QKDs with different modulation protocols and different key rates in one communication. Moreover, according to the obtained 5 SKRs, we can choose the optimal modulation protocol of the subcarriers to meet different needs of quantum network operators. In addition, the scheme also can choose much more subcarriers and different symbol rates to flexibly achieve the QKD in different quantum secure communication scenarios. Therefore, the proposed scheme changes the modulation protocol, subcarrier number and symbol rate to achieve the interoperability, flexibility and compatibility.

Synchronous nanosecond and femtosecond pulses delivered from a low-repetition-rate Er-doped fiber laser mode-locked by nonlinear polarization evolution is experimentally proposed. Here, the repetition rate is set as ~4.5 MHz by introducing sufficiently long fiber in a ring cavity. By fully exploiting long fiber and anti-saturation absorption characteristics, it is experimentally observed that dissipative-soliton-resonance pulse with the nanosecond-level pulsewidth and femtosecond soliton pulse synchronously propagate in the same cavity. Besides, the pulsewidth of dissipative-soliton-resonance pulse and laser output power could be tailored by finely configuring the bidirectional pump powers. These results provide deep understanding of low-repetition-rate pulse laser and an intriguing way to obtain tunable dual-scale synchronous pulses, indicating the high potential for multiple-pulse laser processing and so on.

In the transient high-speed measurement scene, time-stretched dispersion Fourier transform technology is presented as an effective solution to reduce the bandwidth limit of electrical digital-to-analog conversion devices, which can realize the mapping from frequency domain to time domain by introducing sufficient amount of group time delay by dispersion elements, such as single-mode fibers. However, the introduction of long-distance single-mode fiber greatly reduce the intensity of optical signal. In our work, we introduce the Gerchberg-Saxton phase recovery algorithm into the velocity signal analysis to recover the interference signal from the two sufficient diversities incompletely stretched temporal envelope. The two envelopes are stretched by L₁=10 km and L₂=15 km single-mode fiber, which recorded with the dispersion D₁=180 ps/nm and D₂=270 ps/nm respectively. With the additional iterations, the phase error and magnitude tend to be stable, which are both below 0.3. We also compare the error of the algorithm under different dispersion ratios D(=D₁/D₂). The results show that the demodulated error will be affected by the change of the value of D. Our work lays a foundation for the subsequent debugging of the time-stretched photon Doppler velocimetry system, and also provides support for transient high-speed measurement.

We performed numerical simulations based on the generalized nonlinear Schrödinger equation to investigate the coherence of supercontinuum (SC) generated by multi-pulse pumping with varying peak powers in all-normal dispersion (ANDi) fibers. The study explores and explains the nonlinear dynamics responsible for spectral coherence degradation at high peak powers. The results indicate that the spectral coherence of multi-pulse pumped SC is determined by the quality of the spectrum at the moment when pulses begin to overlap in the time domain. High peak powers cause noise to rapidly amplify through the coupling of stimulated Raman scattering (SRS) and four-wave mixing (FWM) during the Stage I evolution, while also accelerating pulse overlap, leading to insufficient coherent photon generation. To mitigate spectral coherence degradation in multi-pulse pumped SC generation, we propose two methods: introducing an initial chirp to the pulse pairs and employing multi-wavelength pulse pumping. Both approaches aim to introduce a frequency difference during Stage I evolution, which accelerates the generation of coherent photons between pulses, ensuring spectral coherence is maintained at the moment of pulse overlap.

This study details the experimental use of a combined error signal (CES) method in Ramsey spectroscopy with a pulsed Rb CPT atomic clock to counteract light shift frequencies. By employing a linear combination of two error signals, generated during different free evolution times in a pulse sequence, this method effectively neutralizes field shift impacts. The precise calibration of coefficient allows for an error signal that remains constant despite varying field shifts. Experimentally, this technique has proven to reduce the effects of fluctuations in optical radiation and modulating microwave signal power, which can significantly enhance the long-term stability of atomic frequency standards.

In present paper we discuss the role of interaction between the pump and generation waves in a fiber laser with randomly distributed feedback due to weak Rayleigh backscattering, operating in the ultra-narrow regime, observed just above the generation threshold. Spectrum in this case consists of narrow (less than 1 MHz) modes, having typical lifetime of 1 ms, decomposing through the nonlinear interaction processes. We demonstrate that cross-phase modulation between narrow mode and the pump wave can lead to demolition of the first if the walk-off length is big enough. Therefore, ultra-narrow regime is dependent on fiber dispersion, as it defines the walk-off parameter of the fiber. Comparison with the experiment proves our conclusion: in random lasers, based on fibers with low dispersion, no narrow generation occurs, while for fibers with larger dispersion coefficient it is steadily observed.

Although the interaction of electromagnetic waves with dispersed systems has been studied for many decades, a number of important problems still remain unresolved. This primarily applies to systems with nonlinear properties composed of smaller particles, such as nano- and meso-particles. Also, since the interaction of electromagnetic waves with dispersed media leads to various induced effects, modeling the disperse media properties requires the problems of the interaction of the electromagnetic wave with disperse particles have to be solved simultaneously with the coupled heat and mass transfer problem with accounting for heating, evaporation and other effects, which that appear, for example, during interaction of the electromagnetic field with liquid crystal particles. The interaction of electromagnetic waves with nano- and meso-particles is particularly important when modeling and designing numerous technologies of nanomaterial manufacturing. In this work, the interaction of electromagnetic waves with a two-layer spherical nanostructure was investigated. The propagation of longitudinal electromagnetic waves, the influence of which can be very important in the case of meso- and nano-sized particles, and the influence of electromagnetic radiation on thermophysical processes were studied simultaneously. A new algorithm for modeling the interaction of longitudinal electromagnetic waves with the systems being studied here was developed using the solution of the Maxwell-Schrödinger equations. Several relevant examples of the interaction of electromagnetic waves with nonlinear media were investigated and the possibility of the Aharonov-Bohm effect for longitudinal waves, associated with the influence of the quantum nature of nanoparticles, was pointed out. The possibility of a noticeable contribution of longitudinal waves as components of the electromagnetic field in the case of meso- and nanosystems was pointed out. The densities of the heat sources caused by transverse and longitudinal waves were derived, heat exchange with these heat sources was studied, and the possibilities of phase transitions such as melting and evaporation caused by the heat sources were also explored. Here we also show that near the critical point, the relationship for the heat capacity in the form of a power function of the ratio of the difference between the critical temperature and the media temperature to the critical temperature can be expressed in terms of the densities of the heat sources caused by the transverse and longitudinal waves.

Optical bistability and multistability are very important phenomena that are used as basic principles in the design of optical devices. In this work, a three-layer structure (substrate, film and coating), in which the film is an optically nonlinear liquid crystal, was investigated. The structure was exposed to the laser radiation field with power I0 and frequency ω. The dependence of the film dielectric constant on the modulus of the electric vector was expressed by via a polynomial function, which includes the second and fourth powers of the modulus. Expressions for the electrical intensity vector in each layer and, based on them, the power P of the energy flow were obtained using solutions to the Maxwell’s equations. In some cases, these solutions, expressed via Jacobi functions, transform into soliton solutions. We found that the power P depends nonlinearly on the effective refractive index. The bistability and multistability phenomena, which play an important role in designing and manufacturing new materials with controlled optical properties, which serve as media in which bi- or multi-stability phenomena occur, have been studied. In these cases, the corresponding solutions may vary widely due changes in the boundary conditions, which, in turn, affect the boundaries of the stability regions.

In this paper, we investigate the propagation of electromagnetic radiation in a model planar three-layer waveguide with a nonlinear dielectric layer (film) with accounting for the absorption of radiation in each layer and the second-order dependence of the dielectric permittivity on the electric field amplitude. In this model, absorption was taken into account as an imaginary component of the dielectric permittivity and electric field strength. In order to compute the electric field strength, Maxwell's equations, the finite-difference method and matrix sweep method with simple iterations were used. The energy flux of guided waveguide modes was determined using the Poynting vector, which depends on the amplitude of the electric field strength. A nonlinear dependence of the electromagnetic radiation flux on the effective refractive index, which characterizes the wave velocity, was pointed out and optical bistability, where the same value of the flux corresponds to two values of the effective refractive index, was revealed. The developed model, which explicitly account for the impact of the absorption coefficient on the transmission of electromagnetic radiation, can be used to design optoelectronics and integrated optics, such as nonlinear waveguides, optical switches, and various optical devices based on the use of optical bistability. It was shown how the regions of optical bistability change depending on the thickness of the nonlinear layer and the dielectric constants of the waveguide components. Since waveguide layers considered here are of micro- and nano-size, the Casimir force can play an important role in the propagation of electromagnetic waves, which, at a certain ratio of the dielectric constants of the waveguide layers, manifests itself as a repulsive force arising between the dielectric layers of the waveguide. The nonlinear nature of the transfer of electromagnetic waves was found to lead to a bistable dependence of the Casimir-Lifshitz repulsive force on the effective refractive index. The change in the film layer thickness due to the Casimir-Lifshitz repulsive force was also investigated. It was found that the presence of multimode waveguide modes for wavelengths of ~ 10 nm can significantly reduce energy losses during the propagation of electromagnetic waves in nanostructures.