This PDF file contains the front matter associated with SPIE Proceedings Volume 11358, including the Title Page, Copyright Information, Table of Contents, Author and Conference Committee lists.

Detection of a single nanoparticle on a bare silicon wafer has been a challenge in the semiconductor industry for decades. Currently, the most successful and widely used technique is dark-field microscopy. However, it is not capable of detecting single sub-10 nm particles owing to a low signal-to-noise ratio (SNR). As a new approach, we suggest using the second harmonic generation (SHG) to detect a single nanoparticle. The second harmonic generation in centrosymmetric materials, like silicon, is forbidden except for a thin and additionally increase local field factors, allowing for their persistent detection. Choosing the proper surface and increasing SNR. We demonstrate the feasibility of the nonlinear dark-field microscopy concept by detecting an isolated 80-nm silicon nanoparticle on the silicon wafer.

Optical nanofibers have recently emerged as attractive nanophotonic platforms for several applications ranging from quantum technologies to nonlinear optics due to both the tight optical confinement and their wide evanescent field. In this work, we report on a theoretical and experimental investigation of the optical Kerr effect in the evanescent field of silica nanofibers immersed in several highly nonlinear liquids such as ethanol, acetone and water and we further compare them with air cladding. We provide formula of the effective nonlinear coefficients including the contribution of the nanofiber silica core and of the evanescent field for varying nanofiber diameter and for different surrounding media. Our results show that the contribution of the silica core inversely scales with the effective mode area, while the cladding contribution via the evanescent field depends both on the taper diameter and the nonlinear properties of the liquid. More specifically, it is shown in a silica nanofiber immersed in acetone that the evanescent field contribution to the total Kerr effect is greater than that of the silica core for a taper diameter smaller than 560 nm. We further report the observation of a strong evanescent Kerr effect through measurements of the stimulated Raman-Kerr scattering in a silica nanofiber immersed in acetone. The evanescent Kerr effect is shown to give rise to a strong asymmetric spectral broadening of the first Raman order generated in the nonlinear liquid. Finally, the evanescent Kerr and Raman effects demonstrated in this work may find potential applications to ultra-sensitive liquid sensing and Raman spectroscopy, as the optical mode propagating in the nanofiber essentially interacts with the outer environment without any major contribution from the nanofiber itself.

Non-Hermitian photonics and exceptional points

Time-lenses were developed rapidly over the last year. They enable measurements of ultrafast signals which were not measured before with limited electronics detectors. Time-lens enable to image ultrafast signals from sub picosecond time-scales to nanosecond time-scale while preserving the intensity, phase and state of polarization. However, most time-lenses are focus only on the time-domain and ignore the spatial domain. This hinder many ultrafast phenomena which combine the dynamics in time and space together. In this proceeding, we demonstrate the measured results of the mode splitter which is a crucial device for achieving a time-lens which combines time and space.

Optomechanical coupling produced by high finesse optical micro-cavities has led to a plethora of nonlinear observations in silicon photonics due to the coherent nature of the interaction. We have investigated optomechanical coupling in the dielectric-like cavity modes of photonic crystal edge defects. These structures exhibit extreme sensitivity to changes of the edge defect width, allowing for scaling of the edge length and a reduction of the optical finesse required to produce different phenomena independent of the edge width. The edge defect structures presented have relatively simpler fabrication relative to other optomechanical designs of comparable coupling strength. We report frequency combing in long linear edge defects and optical bi-stability in shorter, hexagonally coupled edge defect devices. These results indicate that photonic crystal edge defects offer an exciting platform for the development of new optomechanical devices.

We consider a system of coupled Raman fiber lasers which exhibit PT-symmetric or PT-broken symmetry properties depending on phase shifts between coupled cavities and pump power. We numerically study temporal properties of radiation of this system. We found that besides laminar and turbulent generation regimes of different PT-properties, the coupled lasers allows generation of pulses. The pulsed generation properties are varying from noise-like pulses to stable hundreds of ps-scale pulses depending on pump power and PT-symmetry of the system. We track the transitions between different pulsed regimes and also found that these regimes could co-exist at the same time.

Quantum states of light for quantum metrology, computing and communication

We report on light trapping by a moving refractive index front inside a silicon waveguide, the so-called optical push broom effect. The front generated by a fast pump pulse collects and traps the energy of a signal wave with smaller group velocity tuned near to the band gap of the waveguide with hyperbolic dispersion. The energy of the signal wave is accumulated inside the front and distributed in frequency. The presented effect can be utilized to compress signals in time and space.

We propose a taper design for a silicon-core fiber for the purpose of generating a supercontinuum (SC) from a 2.1μm pulsed fiber laser. The design is tailored to maximise the conversion efficiency (CE) to the 3-4μm region, which is important for environmental sensing as it includes several key greenhouse gas absorption lines. There is a need for compact, low-power and efficient solutions. Aluminium nitride photonic-chip waveguides have been shown to generate 0.3mW in the 3-4μm region with an 80mW input. Although this is sufficient power for some applications, the system only offers a 0.4% CE. More recently a silicon nitride planar waveguide was used to transfer energy from a commercial 2.1μm femtosecond laser to targeted wavelengths in the 3-4μm region through dispersive wave generation. To cover the entire region, it is estimated that an input of 40mW would be needed to generate ~1mW (CE of 2.5%). Compared to these materials silicon has a higher nonlinearity and, despite multi-photon absorption, is highly efficient at transferring energy to different wavelengths with modest input powers. Moreover, silicon-core fibers can be tapered using established post-processing procedures, which can be used to control the phase-matching conditions to concentrate energy in a required wavelength range. We have designed a silicon-core fiber taper that can take the input from a 2.1μm fiber laser and efficiently transfer the energy to cover the entire 3-4μm range. We simulated SC generation using the generalised nonlinear Schrödinger equation including wavelength-dependent loss terms (linear, TPA and 3PA). From these simulations we estimate that ~0.8mW average power can be generated covering the entire 3-4μm region, with only 15mW input power, a CE of 5%.

We propose, analyze and simulate a microwave photonic system for generation of damped sinusoidal and ultra- wideband (UWB) microwave waveforms based on an optoelectronic approach. In the proposed system, a pulsed laser source (PLS) of 1 fs pulse width generates pulses at a repetition rate of 1 Tbps. These train of pulses are fed as input to a silicon-on-insulator microring resonator of radius 10µm. . The wavelength of the pulsed laser source is tuned to the resonance wavelength (1555.8 nm) of microring resonator (MRR) due to which the pulses are coupled into the ring cavity and emerge at the drop port of MRR. In order to compensate for the propagation losses within the cavity, an Erbium doped fiber amplifier (EDFA) is used to amplify the signal appearing at the drop port of the MRR. This amplified signal is then detected by an InGaAs photodetector of bandwidth 40 GHz and responsivity 0.85 A/W. The generated signal at the photodetector is reshaped by a bandpass Butterworth filter. In other words, the generated photocurrent acts as an impulse to the filter, the response to which results in different shapes of microwave waveforms for different characteristics of the filter. In this paper, a bandwidth of 6 GHz and order 34 results in a damped sinusoidal waveform when the repetition rate of PLS is 1 Tbps. Variations in repetition rate of PLS results in delayed damped sinusoidal waveforms. Maintaining the bandwidth to be 6 GHz and decreasing the order of the filter results in suppression of the damped oscillations of the damped sinusoidal waveform. When the order of the filter is reduced to 4, the resultant waveform at the filter is reshaped to an ultra-wideband waveform. The frequency spectra of the generated UWB waveform covers half of the UWB frequency band spanning from 3.2 to 6 GHz. The repetition rate of the generated microwave waveforms is found to be 1 GHz. The generated damped sinusoidal waveforms and UWB waveforms will be suitable for medical imaging and high data rate, short range indoor wireless communication applications respectively.

Coherently refreshing acoustic phonons for light storage

Slow and fast light are achieved in two experiments using SPS photorefractive crystal at room temperature. We report that the photorefractive gain achieved by the two wave mixing (TWM) method can control the group velocity of the transmitted light pulses at visible wavelength. It is shown theoretically and experimentally that the time delay and the shape of the output pulse change as a function of the photorefractive gain. The beam fanning has also been used to control the velocity propagation of a single light pulse in the same crystal at λ = 1064 nm. Depending on the orientation of the polar axis, it is possible to accelerate or decelerate a short pulse with duration of order of μs in the crystal.

Supercontinuum generation in the long pulse regime exhibits large shot-to-shot spectral variation and chaotic time domain consisting of soliton peaks emerging with random statistics. Under particular conditions, the noise-seeded dynamics may lead to the generation of a small number of extreme red-shifted rogue solitons that are associated with highly skewed “rogue wave” statistics. To overcome the restrictions in the experimental measurements, we here use the techniques of machine learning to predict the peak power and temporal shift of extreme red-shifted rogue solitons from single-shot spectral intensity profiles of supercontinuum without any phase information. The possibility to combine machine learning approaches with real-time spectral measurements to obtain temporal characteristics information without direct time-domain measurements which are often complex and limited to specific regimes of operations offers completely new avenues for the study of ultrafast dynamics in general.

2D Ruddlesden-Popper-phase perovskites (2D RPPs) have recently been shown to not only exhibit excellent photoabsorptive properties for light harvesting and photovoltaics, but also a strong third-order nonlinear response. This work is about a more detailed characterisation of this third-order nonlinearity of 2D RPPs with different chemical composition around their excitonic bandgaps using a Z-scan technique. As the key result the 2D RPPs are found to exhibit a strong enhancement of the nonlinear response and a sign change of the nonlinear refractive index around the excitonic bandgap with peak values on the order of 10^-14 m^2/W for n2 and -0.1 cm/kW for beta_eff, which is several orders of magnitude higher than previously reported values for highly nonlinear chalcogenide glasses. The investigated flakes differ in their inorganic layer thicknesses and hence exciton confinement, resulting in different spectral positions of the excitonic bandgap. In terms of their chemical composition, the flakes are lead halide RPPs, with both iodide and bromide-containing flakes being studied. The spectral positions of the excitonic bandgap in these flakes cover most of the visible spectrum, with bandgaps ranging from about 400 nm to 650 nm. The optical response at the excitonic bandgap is dominated by saturable absorption for all flakes. This effect was particularly prominent in a lead halide flake with the inorganic layer just consisting of one monolayer, with a more than 15x increase in transmission. In summary, the studied 2D RPPs exhibit an extremely strong nonlinear optical response in the visible and are promising candidates for applications in all-optical switching or frequency conversion.

Laser cavity-soliton microcombs

We developed original model describing the process of frequency comb generation in the self-injection locking regime and performed numerical modelling of this process. Generation of dissipative Kerr solitons in the self-injection locking regime at anomalous GVD was observed and studied numerically. It was proposed that self-injection locking may provide easy way for generation of frequency comb at normal group velocity dispersion. This idea was investigated in detail and platicon generation was demonstrated. Parameter range providing platicon excitation was found.

Ultrafast mode-locked lasers are well-known to display a rich variety of unstable dissipative soliton dynamics resulting from the interplay of nonlinearity, dispersion and dissipation. Although laser instabilities have been known and studied in depth for many years, their properties have recently received greatly renewed attention because of the development of time and frequency domain techniques that allow laser dynamics and instabilities to be measured in real-time. This has allowed the variations in circulating pulse characteristics to be examined on a roundtrip to roundtrip basis, providing a new window into understanding these instabilities and how they develop based on the cavity configuration being used. A technique of this kind that has proven both straightforward to implement and powerful is the photonic time stretch or dispersive Fourier transform (DFT) which has been used in a number of important applications including the measurement of soliton rogue waves, modulation instability and supercontinuum noise. The DFT allows direct access to shot-to-shot measurement of the mode-locked fibre laser spectrum and, via computation of the associated autocorrelation function, can also provide complementary time-domain information in cases where multiple pulse states are observed. In this paper, we report results of DFT measurements which have been used to reveal previously unreported behavior in a mode-locked fiber laser designed to operate with soliton-similariton dynamics. In particular, we observe instabilities including soliton explosions, chaotic evolution and oscillation in the relative phase of bound-state multi-pulse molecules, and what we believe to be a previously-unobserved regime of operation associated with the intermittent appearance of short-lived stable single pulses within of otherwise chaotic dynamics. Our results - obtained in a laser believed to be a particularly stable design - suggest that instabilities such as soliton explosions and intermittence are a universal feature of dissipative soliton systems transitioning from noise to stability.

The generation of dissipative Kerr solitons is experimentally investigated in ring resonators with optical feedback. This new double-resonator geometry allows generating frequency combs with smooth solitonic spectral shape over much broader spectral bandwidths if compared with the standard ring resonator architecture. By using an amplitude modulated pump, the repetition rate of the generated frequency comb is locked to the external modulation and exhibits a stability comparable to the modulating radio frequency signal, i.e. the repetition rate linewidth is very narrow (20 Hz). Furthermore, the energy conversion efficiency (pump-to-frequency comb) can be up to 60%, being a record for microresonators.

We investigated the vectorial nature of ultrafast rogue waves in fiber lasers. In this proceeding, we present the analytical evolution of the nonlinear Schroedinger equation in vector field and show that when considering two Solitons with different state of polarization, they do not stay static which indicates that such Solitons are not a solution of the system.

Emerging nonlinear optical approaches for mid-infrared ultrafast pulse generation

Forecasting the dynamics of chaotic systems from the analysis of their output signals is a challenging problem with applications in most fields of modern science. In this work, we use a laser model to compare the performance of several machine learning algorithms for forecasting the amplitude of upcoming emitted chaotic pulses. We simulate the dynamics of an optically injected semiconductor laser that presents a rich variety of dynamical regimes when changing the parameters. We focus on a particular regime where the intensity shows a chaotic pulsing dynamics, and occasionally an ultra-high pulse, reminiscent of a rogue wave, is emitted. Our goal is to predict the amplitude (height) of the next pulse, knowing the amplitude of the three preceding pulses. We compare the performance of several machine learning methods, namely neural networks, support vector machine, nearest neighbors and reservoir computing. We analyze how their performance depends on the length of the time-series used for training.

Numerical modelling based on purely scalar nonlinear Schröodinger equation propagation is applied to a dissipative soliton laser operating in the soliton-similariton regime and generating parabolic pulses. The model is shown to reproduce a range of instabilities that have been reported in recent experiments. Here, we study in detail the laser stability characteristics as a function of the parameters of the gain medium and the saturable absorber, allowing us to readily identify clear regimes where stable single solitons and soliton molecules are observed. Outside these regimes, we reproduce a wide range of instabilities linked with soliton molecule internal motion, soliton explosions and intermittence.

We report on the experimental realization of optical frequency comb (OFC) generation in a doubly-resonant cavity second harmonic generation (SHG) system. OFCs continue to attract significant interest, offering a wealth of potential applications beyond frequency metrology. Continuously-driven Kerr microresonators, whose nonlinear response is dominated by the third-order nonlinearity, have proven to be viable alternatives to comb sources based on femtosecond mode-locked lasers. Recently, OFCs have also been directly generated through second-order nonlinear interactions in cw-pumped resonators namely, a singly-resonant cavity SHG system and a nearly-degenerate optical parametric oscillator. Theoretical studies have also predicted OFCs in doubly-resonant cavity SHG systems with a much lower threshold with respect to the singly-resonant configurations. Here we report on the first observations of OFCs in such a doubly-resonant system. The experiment is based on a periodically poled lithium niobate crystal, placed in a traveling-wave optical cavity, pumped by a cw Nd:YAG laser emitting 0.5 W at 1064 nm. The cavity is resonant for frequencies around both the fundamental pump and its second harmonic at 532 nm, and an intracavity adjustable silica window is used to separately set the detunings of the pump and its second harmonic. Stable cavity locking to the pump laser is achieved via the Pound-Drever-Hall offset locking technique, thanks to a counterpropagating orthogonally polarized auxiliary beam. We measured a power threshold for comb formation as low as 5 mW, reduced by more than one order of magnitude with respect to singly-resonant configurations. The locking system permitted to explore frequency detunings up to several cavity linewidths, and to correspondingly observe a large variety of comb regimes, with different teeth spacing and spectral span, as well as the contribution of photothermal effect to the whole dynamics. In this regard, we developed an extended theoretical model that includes thermo-optical nonlinearities.

The history of conceptions of light is among the most exciting scientific adventures. It was Fresnel's theoretical work that made it possible to establish the most solid theoretical basis of wave optics. Two centuries ago, his approach was validated by the observation of a counter-intuitive bright spot appearing at the center of the geometric shadow of an illuminated opaque circular object. This phenomenon has remained known as the Arago spot. We propose here to further extend the spatial/temporal analogy that exists between diffraction and dispersion by revisiting the Arago spot formation in the time domain through the temporal dispersive evolution of light after being briefly stopped by an obstacle. The analytical treatment that is possible for linear propagation as well as the experiments based on telecom optical fibers and fast optoelectronics confirm that we observe the emergence of light where it was initially absent. As the power increases and Kerr nonlinearity affects the propagation, the Arago spot intensity is affected by the sign of the dispersion.

The experimental investigation of formation of coherent structures from noise is essential for fundamental understanding of nonlinear systems. Here, we present switch-on dynamics in bidirectional mode-locked laser in spatio-temporal and frequency domains by using Dispersive Fourier Transform for both clockwise and counterclockwise directions. We have calculated cross-correlation of counter-propagating beams that reveals the dissimilarities between formation of the spectra of counter-propagating pulses. From cross-correlation we revealed periodic patterns which manifest complex exchange dynamics between the counter-propagating pulses at different stages of their mutual formation. These results will help to understand complex soliton dynamics and nonlinear systems in general.

Supercontinuum light (SC) is a broadband source with unique properties as the result of cascaded nonlinear dynamics when intense light propagates in a nonlinear material [1]. Recently, the generation of broadband SC sources operating in the mid-infrared (MIR) has attracted significant interest due to a wide range of potential applications in spectroscopy [2], microscopy, molecular fingerprinting [3], environmental monitoring and LIDAR [4], just to name a few. Fibers made of non-silica soft glasses such as fluoride, tellurite and chalcogenide are good candidates for SC generation in the MIR due to their high intrinsic nonlinearity and wide transparency window in this wavelength range. Supercontinuum generation in the MIR is typically achieved by propagating femtosecond pulses into the anomalous dispersion regime of a single-mode soft glass fibers. This typically leads to SC sources which are limited in terms of average power due to the low damage threshold associated with soft glasses and susceptible to noise due to the anomalous pump regime. These inherent limitations can be detrimental for many applications such as e.g. optical coherence tomography (OCT), photoacoustic imaging [5], or spectroscopy where the performance critically depends on the power and noise properties of the light source. In this work, we demonstrate for the first time the generation of a low noise high power SC in the MIR by injecting 350 fs pulses from an optical parametric amplifier into the normal dispersion regime of a one meter-long multimode step-index chalcogenide fiber with 100 µm core diameter. We show the generation of SC spanning from 1700 nm to 4800 nm for a pump wavelength at 3500 nm (located in normal dispersion regime of the used fiber) and an input peak power of 570 kW. A systematic study of the SC intensity noise is performed as a function of different pump parameters and for different output wavelengths show that the initial fluctuations on the pump laser are at most amplified by a factor of 2 at the spectral edge of the SC. Although the output beam in this case is multimoded, it can still be used for many practical applications such as long-distance remote sensing for which high power and low noise are more essential than the actual beam profile quality. Our results open novel perspective for the generation of high power low-noise broadband light sources in the MIR.

Phase mismatch and group velocity mismatch are two dispersion effects which limit the effectiveness of optical frequency conversion processes. Here we propose a condition for a high harmonic generation in which a phase mismatch and a group-velocity mismatch work together through constructive inter sub-cycle interference to provide an efficient, phase-matched optical frequency conversion. This condition, which we call an anomalous phase matching (APM) can be valuable to the emerging extreme non-linear optics regime of a long wavelength drive field and a high gas pressure. The APM condition is fulfilled once both phase mismatch and group velocity mismatch (GVM) are present in the optical system, which is the most general case to consider. The effect of a phase mismatch is that after a propagation of one coherence length the emission start to destruct coherently, leading to a decrease in the up-conversion efficiency. The effect of the GVM is that after a particular harmonic order is being generated by the fundamental pulse, it starts to drift away from its creation time in the reference frame moving with the pump pulse, due to different group velocities between the pump and that harmonic. If a harmonic emission arrives, due to GVM, to an emission with the opposite polarity after traversing a coherence length the interference of both emissions would be constructive. Actually, this condition ensures constructive interference over the whole interaction length allowing for an increased HHG flux. We derive a mathematical condition for an APM and show numerically that APM can be achieved and wavelength-tuned in several different setups: by varying the peak intensity of the pump laser in a pre-ionized gaseous medium, by varying the wave-guide radius in a hollow wave guide filled with a neutral gas and by varying the pressure of a neutral gas in a gas cell at moderate pressures and long fundamental beam wavelengths.

High harmonic generation (HHG) provides a table-top source of extreme ultraviolet (XUV) and soft x-ray radiation. HHG pump-wavelength dependence is of significant practical interest for laser system design as HHG efficiency scales with pump wavelength to the power of P. First experiments suggested P=-6.5 while theoretical models predict P=-4.7 to -6.0. These investigations exploited single-atom models; insight into efficiencies for full experimental setups will further guide HHG laser designs. We developed a model that simulates the HHG process in full for an argon-filled capillary including all Ti:sapphire pump pulse and XUV propagation effects. With this we compare HHG of two geometries: a thin slice of argon, and an argon-filled capillary. For the thin slice with pump wavelengths 820-1890nm we found P=-4.5 scaling when the harmonic energies were integrated between 16 and 45eV. However, further analysis revealed a dependence of P=-6.4 for longer pump wavelengths (1500-1890nm), but P=-4.0 for shorter wavelengths (820-1500nm). By contrast, HHG in a 7-cm long capillary was found to scale with P=-3.4 (800-1850nm). We attribute this to phase-matching effects over longer propagation distances and nonlinear pump propagation distorting the pulse. Different scaling is observed when the energy of a single harmonic is calculated. In the thin slice the energy in the first harmonic above 20eV yields P=-6.1 (820-1890nm), P=-5.7 (820-1500nm), and P=-7.8 (1500-1890nm). For the whole capillary the corresponding value is P=-4.1 (800-1850nm). High-energy harmonics also exhibit very different scaling with pump wavelength as they cross the classical harmonic cutoff energy. For example, for the first harmonic beyond 41eV no value of P provides a good fit to the simulated HHG efficiencies, neither for the thin slice nor the whole capillary. Our simulations highlight pump-wavelength dependence of HHG efficiency is complex, with many contributing factors such as exact experimental geometry, optical nonlinearity, phase matching, and classical cutoff.

Layered two-dimensional (2D) transition metal chalcogenides have attracted incredible interest due to their intriguing electronic, electrical, and optical properties. Liquid phase exfoliation (LPE) technique has been employed for the synthesis of ultrathin tin sulfide (SnS) sheets. A many body process, exciton-exciton annihilation was found to be significant in such anisotropic nanosheets of reduced dimensionality. Moreover, femtosecond Z-scan measurement infers that these 2D materials exhibit saturable absorption property because of optical transitions, which result in band filling from low to high energy band. The value of non-linear absorption coefficient was found greater and saturation intensity was found lower than that of other 2D materials. By taking the advantage of high nonlinear absorption coefficient and low saturation intensity ultrathin SnS nanosheets may prove to be a suitable candidate for various applications like saturable absorber, Q-switching.

Plasma based particle accelerators driven by either lasers are the future of the particle accelerators technology, due to the fact, that this technology can overcome the limit of the standard accelerators given by the physicalchemical properties of the material used for the construction as well as by the huge size and the financial costs. Nevertheless, a stable synchronization of the electron bunch and of the plasma wakefield in the range of few femtoseconds is necessary in order to optimize the acceleration. Therefore, for SINBAD a shot to shot synchronization system is planned, that should be able to synchronize the electron bunch with the plasma exciting laser pulse with a time resolution of less than 1 fs. In a first step, stable Terahertz (THz) pulses should be performed by optical rectification of high energy laser pulses in a nonlinear crystal. These pulses allow an energy modulation of the electron bunch in order to achieve the required resolution This paper focuses on the first step of the feedback system, i.e. the generation of THz pulses using a periodically poled lithium niobate crystal LiNbO3 (PPLN) and we investigate the in uence of the optical properties of the material on the stability and efficiency of this process. We present systematic calculations of the optical properties of the crystal and of their in uence on the efficiency and on the optimum crystal length for the generation of THz pulses. We compare different models and approximation for the dielectric function (full Sellmeier equation or linear approximation, FC implementation or neglecting, different description of the FC saturation, depletion of the pump) and different modeling of the generation dynamic (full second order calculation or first order slope varying approximation) in order to obtain a detailed diagnostic for the THz generation and to optimize our feedback system.

The generation of high quality pulse trains at repetition rates of several tens of GHz remains a crucial step for optical telecommunications, optical sampling or component testing applications. Unfortunately, the current bandwidth limitations of optoelectronic devices do not allow the direct generation of well-defined optical pulse trains with low duty cycles. A linear solution is based on a direct temporal phase modulation that is then converted into an intensity modulation thanks to a dispersive element. However, this approach suffers from a limited extinction ratio or from the presence of detrimental temporal sidelobes. We introduce here theoretically and experimentally an alternative scheme where the quadratic spectral phase is replaced by a triangular one. With such a specific phase processing, Fouriertransform limited structures are obtained, with properties that may present some similarities with Akhmediev breathers at the point of maximum focusing. Experimental validation carried at repetition rates between 10 and 40 GHz confirm that high-quality close-to-Gaussian pulse trains can be achieved with an excellent extinction ratio and with a duty cycle below 1/4, in full agreement with our numerical simulations and analytical predictions. The resulting pulse train exhibits a remarkable stability. The proposed approach can be extended to process several wavelengths simultaneously as demonstrated by the experimental generation of 4 interleaved pulse trains in the conventional C-band. The versatility of the proposed scheme also enables the generation of pulse trains with varying pulse-to-pulse delays or durations.

In this work, an ultra-long single-span 10Gbps SDH optical communication system was built up and tested. The 10G signal transmitted from the bit error tester with an additional 10G XFP transponder module, and looped back to the bit error tester. All the conditions and results presented were verified as error-free for over 12h. The 10G XFP module was used to perform an optical-electric-optical (OEO) conversion, so that the modulation parameters can be adjusted for nonlinearity optimization, which will be discussed elsewhere. The total distance of the fiber is over 220km, and the maximum power of the signal injected into fiber is over 17dBm, indicating that the SBS threshold is suppressed over 17dBm with the help of the 10G XFP optimization. What is interesting is, a clear wide shoulder was observed in the output signal spectrum at the transmission fiber output, provided that the fiber input power exceeds 17dBm. After careful analysis and simulation, we attributed this shoulder generation to the intra-band FWM effect, which is caused due to the FWM interaction between the carrier wave and the modulation wave within the band. The error tester will identify the shoulder as the noise level, and the maximum input power is restrained by equivalent optical signal noise ratio (OSNR) due to the intra-band FWM effect. So that the maximum transmission distance will be restricted even if the stimulated Brillouine scattering (SBS) threshold can be further enhanced. Other nonlinear effects including self-phase modulation (SPM), and group velocity dispersion (GVD) are also analyzed.

We demonstrated how the nonlinear Fourier transform based on the Zakharov-Shabat spectral problem can be used to characterise coherent structures in dissipative systems. We consider as a particular, albeit important practical example model equation that is widely used to analyse laser radiation and demonstrate that dissipative solitons can be described by a limited number of degrees of freedom { discrete eigenvalues. Our approach can be applied for signal processing in a number of optical systems, from lasers to micro-resonators.

We have investigated the ultrafast third-order nonlinear optical (NLO) properties of a novel chalcone derivative, 3-(4- methoxyphenyl)-1-(4-nitrophenyl)prop-2-en-1-one (abbreviated as MNC) by Z-scan and degenerate four-wave mixing (DFWM) techniques using femtosecond Ti:Sapphire laser system (~70fs, 1 kHz, 800 nm). The molecular structure of the synthesized chalcone by Claisen-Schmidt condensation reaction was confirmed by FT-IR and ¹H NMR spectroscopic techniques. The thermal stability was studied by thermogravimetric/ differential thermal analysis (TG/DTA) technique and melting point was found to be 177 °C. The linear absorption spectra suggest that the MNC chalcone is optically transparent in the Vis-NIR region. The open aperture Z-scan demonstrated two-photon absorption, evident from the reverse saturable absorption type mechanism, while the closed aperture Z-scan demonstrated a positive nonlinear refraction due to self-focusing effect. Further, the chalcone exhibited optical limiting (OL) and optical switching properties. The onset optical limiting threshold fluence was measured at 9.15 mJ/cm² and the figures of merit for all-optical-switching were satisfied. From DFWM data we measured the magnitude of NLO coefficients, nonlinear response time and dephasing time. The third-order NLO susceptibility and molecular hyperpolarizability were calculated to be 1.39×10^-14 esu and 6.89×10^-34 esu, respectively, using Z-scan and 6.53×10^-14 esu and 32.7×10^-34 esu, respectively, using DFWM techniques. From both these techniques the magnitude of NLO coefficients were found to be in good agreement. The time-resolved DFWM studies revealed that the nonlinear response time of MNC was very short (~112 fs). These results indicate that the MNC chalcone is a potential material for optical limiting and all-optical-switching applications.

Surface plasmon-polaritons (SPP) excited in periodic metallic gratings provide strong electromagnetic field localization at the interface. The applications of plasmonic structures are mainly sensors for magnetic and biochemical measurements. Besides such nanostructures are widely used in the laser technique applications, e.g. for lowering the threshold of the laser fluences sufficient for all-optical switching and optical demagnetization processes. The possibility to tune an SPP resonance (SPR) in real time is very attractive for fundamental and practical needs. It may be provided by active plasmonics studying the opportunities of SPR control using external stimulus. Here we experimentally study the influence of nanostructure profile depth on the ultrafast SPR control capabilities. It is shown that moderate fluence of 6 mJ/cm2 can induce ultrafast charge carriers dynamics in all considered nanostructures resulting in their optical and magnetooptical response modulation. The latter is visualized using the pump-probe technique in the transverse magnetooptical Kerr effect (TMOKE) configuration. A 1-KHz Ti:Sapp regenerative amplifier is a pump source, and a super-continuum pulse is a probe. The modification of the SPP wave vector under the pump pulse irraditation may be considered as the physical reason of modulation in both non-magnetic and magnetic cases. The peak reflectance and TMOKE spectra modulation values in the spectral area of SPR are affected by the surface corrugation depth of the plasmonic crystal. Their highest achieved values for the set of studied MPCs are of 10% and 0.7% respectively. The durations of laser-induced charge carriers thermalization and relaxation processes are also profile-dependent. Their typical values are of 400 fs for electron thermalization, of 1 ps for electron-phonon relaxation, and of several tens of ps for phonon-phonon relaxation process. This research was supported by the Russian Foundation for Basic Research (Grants No. 17-52-560011, No. 18-52-45023) and MSU Quantum Technologies Center.

Dynamics of light bullets in the Raman active and ionizing gas was analyzed with the help of moment method. We obtained the system of ordinary differential equations for the pulse’s parameters such as amplitude, temporal duration, chirp parameter, temporal delay, phase, frequency shift, transverse size and curvature. Numerical analysis of this system shows that quasi-stable regime takes place when exist balance between dispersion and nonlinearity, photoionization and stimulated Raman self-scattering with simultaneous suppression of diffraction and ionization divergence by self-focusing.

Silica nanoparticles have been studied for several applications since they can be obtained from rice husk biomass. These nanoparticles are dope with different metals for industry applications or as adsorbent of impurities. Quantitative analysis of them is carried out for evaluating their efficiency as adsorbents. LIBS technique can analysis this kind of samples by fixing the powder for the study. Two different methods of fixation (pressed tablets and fixation by carboxymethyl cellulose) were studied in this work with silica nanoparticles doped with Cu and Fe. Calibration curves were made and a simple linear regression was performed for obtain the correlation coefficient and slope of the linear fit for each method and metal. Limits of detection were calculated and the prediction ability of the models were evaluated by the analyzed of “unknown” samples. Results showed that pressed tablets had better correlation coefficients and prediction ability than fixation by CMC. Also, this method showed a good repeatability and reproducibility. Despite that, fixation by CMC showed a better LOD for copper but for iron.

Due to circumstances beyond the presenter's control, an audio recording was not possible for this presentation.

Moving refractive index fronts in waveguides with dispersion is a special type of spatio-temporal modulation leading to the change of signal frequency and wavenumber. The interaction of light with such fronts allows frequency conversion, light stopping, optical delays as well as bandwidth and pulse duration manipulation. We will present theoretical and experimental examples of signal transmission, reflection and trapping by the front and highlight special situations such as light stopping, time reversal or optical push broom effect. We will geometrically consider indirect transitions in the dispersion relation using the phase continuity relation at the front and present numerical solutions of the linear Schrödinger equation which follows from the slowly varying envelope approximation of the wave equation. In particular, for highly dispersive waveguides a temporal evolution of the spatial wave envelopes are considered in contrast to conventional spatial evolution of temporal envelopes. Further, we will present an overview of experimental results and estimate the maximal achievable effects for each of the application in different waveguide systems.

During the last decade generation of frequency combs and different types of dissipative solitons was demonstrated and well-studied in high-Q optical microresonators with Kerr nonlinearity. However, recently, it was shown that it is also possible in microresonators with quadratic nonlinearity. In our work, we studied numerically the generation of coherent frequency combs in quadratically nonlinear microresonators via conventional frequency scan method for both second harmonic generation and downconversion processes. We revealed that under particular conditions it is possible to generate two-color flat-top solitonic pulses, platicons, using pump amplitude modulation or controllable mode interaction approach, if the signs of the group velocity dispersion (GVD) coefficients at interacting harmonics are opposite. For SHG process at each combination of GVD coefficients platicon generation was observed at both positive and negative pump frequency detunings from the linear microresonator resonance. Platicon generation was also demonstrated for the downconversion process. Platicon excitation was observed at positive detunings for the normal GVD at pump frequency and at negative detunings in the opposite case. For both SHG and downconversion processes, for the efficient platicon excitation one needs simultaneous accurate matching of the free spectral ranges at interacting harmonics and resonant eigenfrequencies. Excitation conditions and platicon generation domains were revealed for different generation methods, and properties of generated platicons were studied for various combinations of medium parameters.

Plasmonic nanoantennas offer the possibility to confine light in sub-wavelength volumes and to strongly enhance local fields. The latter is highly beneficial for nonlinear optics, as the efficiency of second- and third-order nonlinear processes increases with increasing field strength. While third-order processes may occur in any material, symmetry breaking is required for second-order processes. This is achieved by utilising materials with non-centrosymmetric unit cells or by exploiting the symmetry breaking of surfaces when using centrosymmetric materials. In this work, gold nanoantennas with a strong surface nonlinearity and broad plasmonic resonances at 1500 nm and 750 nm are combined such that they efficiently couple to far-field radiation, even for second-order processes, thanks to a non-centrosymmetric arrangement of the antennas. The key idea of this work is to use this structure to support two nonlinear processes of different order for characterising two unknown pulses at the same time, which is in contrast to conventional techniques where nonlinear crystals that are optimised for only one specific process allow for the characterisation of only one pulse at a time, either by nonlinear interaction with itself or with another known reference pulse. Here, Sum-Frequency generation (SFG) and Four-Wave-Mixing (FWM) spectra from the structure were plotted against the time delay between the interacting input pulses to yield a double spectrogram with enough independent information to simultaneously characterise both pulses. Advantages of pulse characterisation with our plasmonic nanoantennas are the broad spectral range - the pulses were separated by almost an octave - and relaxed phase-matching constraints in the sub-wavelength interaction volume. The main limitations are the damage threshold of the particles and the plasmonic dephasing time of about 10 fs.

Time-lenses in general proved to be useful for many applications and specifically when utilizing them for temporal imaging schemes where they can image ultrafast signals that cannot be detected by any electronic based device. Over the last few years, we demonstrated that when joining together several time-lenses into a single time-lens array, it is possible to gain more information on the input signal. Such as measuring temporal depth imaging, the state of polarization of the input signal as a function of time, and retrieving the phase dynamics. However, when designing an array of time-lenses, there is a trade-off between joining large number of small time-lenses, so each signal will interact with many time-lenses but each one has low resolution, and joining small number of large time-lenses, so each has better temporal resolution but on the expanse of interacting with smaller number of time-lenses in the array. We showed that one way to overcome this drawback is to overlap adjacent timelenses. Thus it is possible to both have large number of time-lenses without compromising on the size of each time-lens and obtaining high temporal resolution. In this proceeding, we overlap two time-lenses and measure the spectrum of the idler. We compare the numerical simulations of the frequency domain of the idler to the measured spectrum of the idler.

Temporal imaging system have enabled imaging of ultrafast phenomena with high temporal resolution different ultrafast phenomena. Specifically, time-lenses which are based on nonlinear interaction of four-wave mixing have a wide field of view together with high F-number. These offers temporal imaging system with large magnifications in the time-domain. However, when considering a time-lens based on four-wave mixing interaction, the input signal must be synchronized to the pump wave which makes it challenging for measuring any ultrafast phenomena with unknown time-of-arrival. Therefore, we developed a temporal imaging system which does not require this synchronization between a signal and a pump wave. This is done by generating time-lenses with high repetition-rate. Therefore, any input signal will interact with one of the time-lenses and it will be imaged in time with high probability. In this proceeding, we demonstrate how our temporal scheme is able to measure with high temporal resolution the start-up dynamics of pulsation in a fiber laser.

Limonene (C₁₀H₁₆) is the most common six-membered ring monoterpene that is daily consumed through the digestive system of humans and most living substances. The chiro-optical properties of chiral molecules are optimally investigated by employing the nonlinear optical method known as vibrational circular dichroism (VCD). In this paper, the spectra of differential infrared (IR) absorption between left-and right circularly polarized light of limonene’s R and S mirror-image configurations are presented for the vibrational energy levels. Furthermore, high resolution and well-resolved temperature-dependent infrared absorption spectra of limonene’s individual enantiomers are also reported and thoroughly discussed. Lastly, a comparison will be drawn between the density functional theory calculations of the IR and VCD (correlation function type B3LYP with basis set aug-cc-pVDZ) for limonene’s most possible individual conformers (Eq (T), Eq (C) and Ax (T)) against corresponding experimental results.

A 5 Gb/s 32-QAM data transmission over a hybrid standard single-mode fibre (SSMF) and free-space optics (FSO) link has been experimentally demonstrated in the 42 − 90 GHz range for 5G networks deployment. Four-wave mixing (FWM) nonlinear effect in a semiconductor optical amplifier (SOA) experienced by a carrier suppressed double sideband modulated signal has been employed to photonically generate millimetre wave (mmW) signals with reduced electronics bandwidth. Both simulation and experimental results have been shown to describe the error vector magnitude (EVM) performance of the system. Large operation bandwidth is shown in our experimental setup, where measured penalties for 42 and 66 GHz are below 1 dB whereas 90 GHz leads to 3 dB penalty at 12 % EVM threshold. Sensitivity has also been estimated for optical back-to-back (OB2B), after SSMF and hybrid link transmissions for different mmW frequencies.

Highly-resolved spectra of (2+1) resonance-enhanced multiphoton ionization (REMPI) for nozzle-jet expanded molecular beams of H₂O and D₂O molecules seeded in Ar and He gases of 1% concentration are presented. The third Harmonic output (λ=355 nm) of a seeded Q-switch Nd:YAG laser was employed to pump an OPO laser, consequently, the VUV output of frequencydoubled OPO radiation was directly used to photo-ionize the jet-cooled sample molecules. By monitoring the H₂O⁺ and D₂O⁺ parent ions signals, highly resolved mass and photoionization spectra were recorded by probing the C-band via a (2+1) REMPI process and over the spectral range 80400 – 81000 cm^-1. In this study, highly resolved mass and REMPI spectra of the C-band of H₂O and D₂O will be presented. Moreover, the effect of seeding gas effect on sample molecules as well as the nature of the photoionization spectra will be discussed.

Photo-polymerization is the reaction between monomers to form polymer chains, and these polymer chains have a higher refractive index than the monomer in the photopolymer, and so it is higher in the polymerized areas. There are four main processes that occur during photo-polymerization in the photopolymer, which are Initiation, Propagation, Termination, and Inhibition. Self-written waveguides (SWWs) in photopolymers, and the process of self-focusing and self-trapping, has been seen that certain important areas which require further research. In this article, the effect a SWW has on the transmission of light through the photopolymer is further tested using a PVP as a media with Rhodamine 6G (R6G) as a dye. Simulations were focused on investigating the SWW mechanism, testing different quantities of beams entering the material. The SWW process was seen to be of most interest for the connection and splitting of multiple optical waveguides.

In general, optical spatiotemporal solitons with phase singularities, known as optical vortex bullets, are unstable. In particular, it is very difficult to preserve a vortex structure of a propagating localized wave. In this paper we propose to introduce absorption to the model used for the process description. By means of numerical simulation we study the formation and propagation of an optical vortex bullet at different regimes. Our goal is to find the conditions of bullet stabilization.

If an acousto-optic processor of spectral type, for example, acousto-optic spectrum analyzer (AOSA) with space integration operates in a low-frequency range, the lowest frequencies of the spectrum to be analyzed (which can be related to the transition zone between Raman-Nath and Bragg diffraction modes) may produce higher orders of diffraction. This creates the frequency bandwidth limitation of one octave for such a device. The present paper is devoted to the method allowing to avoid this limitations. The method of data decoding using the inverse part of the device transmission function has been considered in details. The method includes introduction into the Bragg cell on a level with ordinary information signal, also additional signal of double frequencies and second additional signal with uniform frequency spectrum and high enough power. It has been shown that this method application compensates the second diffraction order and allows to increase significantly both the device frequency range and its information productivity.

We study two-color soliton-like propagation of laser radiation in a quadratic nonlinear medium under both second- and thirdorder dispersion (TOD) actions. The main feature of this soliton-like propagation is an asymmetric pulse shape and the presence of nonlinear chirp. We propose approximate formulas for the pulses shapes and their chirps. We clarify the limits of applicability of these formulas on basis of numerical simulation and show that the propagation dynamics matches analytical formulas at a rather long propagation distance. It is remarkable that the pulse amplitude evolution demonstrates an explicit dependence on the TOD coefficient.

Optical rectification is a prominent method to generate a broadband terahertz pulse. It is known that generation is possible at the resonance condition of Zakharov-Benney. To increase generation efficiency, in particular, optical component shortening is applied. Thus, while studying this process analytically and modeling it numerically one should consider non-zero third order dispersion. The case is especially interesting when the carrier frequency of the initial optical radiation is situated near zero value of the second-order dispersion. In this work, using numerical simulation, we study the influence of third-order dispersion on terahertz generation efficiency.

We study with the help of numerical simulation the generation of second optical harmonic neglecting group velocity dispersion but taking into account third order dispersion effect at either fundamental or doubled frequency. At that, a component at another frequency usually undergoes second order dispersion in experiments. Varying values and signs of the third order dispersion at quasi-zero values of the second-order dispersion we reveal the conditions of bullet formation and stable propagation.

Due to circumstances beyond the presenter's control, and audio recording was not possible for this presentation.

Using a 4.5-W average power Cr2+:ZnS laser having a pulse width 43 fs and a spectral bandwidth of 138 nm centred at 2360 nm with a repetition rate of 80 MHz, we have produced femtosecond pulses in yellow wavelength. Using a 1 mm long Type 0 MgO: PPLN crystal in the first stage of our experiment, we have generated a maximum of ~ 2.43 W power of ~ 60 fs pulse width and ~ 39 nm spectral bandwidth centred at 1180 nm with a maximum conversion efficiency as high as ~ 65%. In the second stage, two different crystals, MgO:PPLN and BIBO were used to generate ultrafast coherent yellow source. The 1.18 μm radiation is first frequency-doubled in a multigrating 1 mm long Type 0 MgO:PPLN crystal with grating periods Λ=8.9 - 9.45 μm. A coherent yellow source with wavelength tunability from 577- 589 nm with a spectral bandwidth of ∼ 2 nm and temporal pulsewidth of ∼ 913 fs was achieved. At optimum focussing, we obtained a maximum power of 0.92 W for 2.2 W of pump power having a conversion efficiency of 40%. In order to address the large GVM between 1180 nm and 590 nm wavelength, we used another 1.2 mm long nonlinear crystal BIBO for birefringent phase matching. With BIBO crystal, the near-IR radiation was efficiently frequency doubled into yellow range (~ 591 nm) with average power of ~ 1 W and having a maximum conversion efficiency as high as 47%. The generated beam has a pulse width of ~ 130 fs in Gaussian shaped and ~ 4 nm spectral bandwidth with a time-bandwidth product of 0.45 showing almost no chirp. The output beam is a Gaussian shaped transverse beam profile with measured M2 values of M2x ∼ 1.07 and M2y ∼1.01.

Due to circumstances beyond the presenter's control, and audio recording was not possible for this presentation.

The features of degenerate four-wave mixing by means of two-photon excitation of exciton transitions in a colloidal solution of CdSe/ZnS quantum dots (QDs) were revealed. This process was studied by means of dynamic Bragg gratings creation in colloidal QDs solution. The intensity of the generated pulses as a result of the degenerate four-wave interaction should be proportional to the cube of the incident pulses intensity. However, the 6th degree dependence and the quadratic dependence were experimentally measured for the first half and for the second half of the pulses in the train, correspondingly. To determine the features of the two-photon absorption the dependence of the intensity of the transmitted and self-diffracted pulses on the incident pulses intensity was measured. The experimental results can indicate a simultaneous effect on the transmission and refraction of the colloidal solution of QDs in the case of resonant two-photon excitation of the basic exciton transition as a non-inertial (classical) nonlinearity and resonance nonlinearity associated with a strong exciton absorption.