The precise control over optical pulse parameters in fiber systems is crucial in many applications. Our research focuses on optimizing optical femtosecond pulses for nonlinear optics, addressing challenges in fiber-based systems with dispersion and nonlinearity. Utilizing spectral phase control and optimization algorithms like particle swarm and simulated annealing, we fine-tune a complex phase mask for desired pulse shapes. Our method involves custom phase-profile optimization via spectral-domain phase modulation to compensate for nonlinear effects in pulse delivery. Using a chirped femtosecond source and a fiber amplifier, our implemented optimization scheme produces near-transform-limited pulses after propagation in polarization-maintaining fiber. This approach accommodates diverse pulse durations, showcasing the effectiveness of off-the-shelf programmable components with optimization algorithms in nonlinear optics and optical signal processing applications.

In this study, hollow whispering gallery resonators were filled with an aqueous solution containing magnetospirillum magneticum (strain AMB-1) bacteria and the response to an external magnetic field was investigated. Magnetotactic bacteria can align with the field lines when exposed to a magnetic field. This changes the effective refractive index of the resonator and leads to shifts in the resonance frequencies of the whispering gallery modes, depending on the applied magnetic field strength. This work investigates the potential of a microbubble resonator platform for biosensing applications and the use of magnetotactic bacteria as a novel magnetic field-sensing substance.

Silicon one-dimensional optomechanical cavities offer a cost-effective and highly scalable solution for the study and implementation of non-linear phenomena. By modifying the refractive index of silicon through thermal or free-carrier effects, it becomes possible to optically drive these resonators into a state of high-amplitude and coherent self-sustained mechanical oscillation. The nonlinearity stemming from this amplification mechanism provides significant adaptability in adjusting the frequency of mechanical resonators, enabling experiments such as injection locking, synchronization, and the study of chaotic dynamics. In this work, we show different novel configurations for the synchronization between mechanical flexural modes of silicon nanobeams and their locking to an external reference signal. The results hold great promise for applications in the distribution of clock signals in future photonic integrated circuits, as well as for establishing extensive networks of optomechanical resonators for studying complex non-linear dynamics.

We consider a resonator with two optical modes, excited with counter-propagating light of equal intensities. Recently, it was shown that the natural symmetry of this optical system can lead to spontaneous symmetry breaking of its steady states. We show that this symmetry property also applies to chaotic attractors, leading to different types of self-switching oscillations. We demonstrate that transitions between such attractors occur when the system exhibits a Shilnikov bifurcation. We employ a dynamical system approach to identify distinct switching behaviors as characterized by symbolic information and associated Shilnikov bifurcations.

In this work, we experimentally demonstrate the capacity of the photorefractive (PR) crystal to control the group velocity of light pulses, specifically at the telecommunication wavelength, by using the so-called beam fanning at room temperature. Significantly, we show for the first time that this method can effectively decelerate a modulated signal propagating through this material at 1310 nm. Furthermore, we illustrate that the performance of this slow light system can be adjusted by changing the intensity, duration, and angle of polarization of the input pulse. The results obtained through this technique can potentially improve the performance of specific components in telecommunication networks.

Integrated optical phased arrays (OPAs), fabricated in advanced silicon-photonics platforms, enable manipulation and dynamic control of free-space light in a compact form factor, at low costs, and in a non-mechanical way. This talk will highlight our work on developing OPA-based platforms, devices, and systems that enable chip-based solutions to high-impact problems in areas including augmented-reality displays, LiDAR sensing for autonomous vehicles, optical trapping for biophotonics, 3D printing, and trapped-ion quantum engineering.

We demonstrate integrated optical continuous-travelling-wave parametric amplifiers that significantly surpass the amplification bandwidth of traditional Erbium-Doped Fiber Amplifiers. Using a 5.55-cm-long integrated gallium phosphide waveguide, we achieve up to 35 dB of parametric gain in the small-signal regime, and more than 10 dB of off-chip net gain in the wavelength window spanning approximately 140 nm and centered at 1550 nm, with the maximum value of net gain reaching 25 dB. This is, to our knowledge, the first demonstration of such a large and broadband continuous-wave net gain in a photonic integrated waveguide.

In this work we expand on the practical side of using periodic refractive index modulation – photonic crystals – to control the spatial dispersion curvature in a way that could suppress filamentation, by discussing some of the key issues arising in their fabrication. Fabrication of such photonic crystals poses some unique challenges due to the small feature size and large-scale requirement. Bessel beam writing is shown to be a valid method for the fabrication of such photonic crystals. Use of an annular beam to form the Bessel beam is shown to significantly reduce the errors in fabrication, allowing the formation of photonic crystals of sufficiently high quality for further experimental study.

We present theoretical and experimental findings related to a significant increase in efficiency for the gain-through-filtering process utilized in the generation of sidebands and frequency combs within driven normal dispersion fiber cavities incorporating a slow-gain amplifier.

We have characterized the supercontinuum generation along a tapered silica optical fiber using a highly-sensitive distributed measurement technique. Based on a confocal Raman micro-spectrometer, this method involves far-field point-by-point Rayleigh scattering analysis along the waveguide, providing micrometer spatial resolution and high spectral resolution. This non-destructive and non-invasive technique enables the observation of each step of supercontinuum generation along the fiber taper.

We predict the existence of a novel type of modulation instability within passive ring fiber Kerr cavities. This instability, which exhibits a period-4 pattern, is accessible to observation utilizing experimentally realistic parameters.

In this investigation, we conducted a study on the amplification of ultra-low repetition rate pulses, specifically in the 0.5 to 16 MHz range, utilizing gain-managed nonlinear techniques. The research was centered around the implementation of a 1064 nm all-polarization-maintaining fiber mode-locked laser, which was seeded with an acoustic-optical pulse picker to regulate the pulse repetition rate. This experimental approach significantly enhanced the nonlinear pulse propagation effects across various pulse repetition rates at 1064 nm, offering new insights into the dynamics of GMN amplification in ultra-low repetition rate regimes.

In this work, we theoretically investigate the nonlinear light dynamics in dual-core fiber passive-driven resonators. Utilizing coupled Ikeda maps and Lugiato-Lefever equations, we analyze bistability and modulation instability, unveiling notable differences from single-core fiber cavities. Specifically, we highlight the difference in modulation instability maximum gain frequency between supermodes. Our discoveries pave the way for multicore fibre cavity experimental setup design, and modelling.

The field of nonlinear optics (NLO) has been continuously growing over the past decades, and several NLO data tables were published before the turn of the century. After the year 2000, there have been major advances in materials science and technology beneficial for NLO research, but a data table providing an overview of the post-2000 developments in NLO has so far been lacking. Here, we introduce a new set of NLO data tables listing a representative collection of experimental works published since 2000 for bulk materials, solvents, 0D-1D-2D materials, metamaterials, fiber waveguiding materials, on-chip waveguiding materials, hybrid waveguiding systems, and THz NLO materials. In addition, we provide a list of best practices for characterizing NLO materials. The presented data tables and best practices form the foundation for a more adequate comparison, interpretation, and practical use of already published NLO parameters and those that will be published in the future.

Polycrystalline silicon germanium (SiGe) core fibers offer great potential as flexible nonlinear platforms. Compared to Si core fibers, the SiGe material offers higher nonlinear coefficients, extended mid-infrared wavelength coverage, and the possibility to tune the bandgap and index of refraction through varying the Ge concentration. Here SiGe core fibers with 10% Ge were fabricated using the molten core drawing method, followed by CO₂ laser irradiation. The transmission properties of the fibers were subsequently improved further using a fiber tapering method, to tailor the core diameter and enhance the crystallinity. The resulting tapered SiGe fiber had linear losses of 2.17 dB cm^-1 at 1.5 μm and 4 dB cm^-1 at 2.5 μm, significantly lower than previous reports. Nonlinear characterization of the fibers reveals that the nonlinear coefficients are higher than standard Si core fibers, as expected due to the introduction of germanium. The significantly higher value of the nonlinear figure of merit calculated for the SiGe fiber for wavelengths above 2 μm indicates that this new fiber platform could find numerous applications in mid-infrared nonlinear photonics.

The damage threshold of femtosecond laser mirrors is critical in the construction of femtosecond laser systems. Therefore, we developed a uniform and efficient test method for femtosecond mirrors for the most relevant laser wavelengths of 266 nm, 400 nm, 800 nm and 1030 nm and tested various broadband metal and metal-dielectric hybrid mirrors. With this, damage threshold values as high as 1 J/cm² were observed for laser pulses with pulse lengths between 70 and 90 fs.

We present a comprehensive investigation of Raman scattering (RS) and supercontinuum (SC) generation in high-index doped silica glass integrated optical waveguides under diverse femtosecond pumping wavelengths and input polarization states. We first report the observation based on a confocal Raman microscope of new Raman peaks different from fused silica at 48 THz and 75 THz, respectively. We then demonstrate broadband supercontinuum generation from 700 nm to 2500 nm when pumping into the anomalous dispersion regime at 1200 nm, 1300 nm, and 1550 nm, respectively. Conversely, narrower SC spectra were generated when pumping in the normal dispersion regime at 1000 nm of self-phase modulation and optical wave breakup. A good agreement is found with numerical simulations of a nonlinear Schrödinger equation including the new Raman response. We also study the impact of the TE/TM polarization modes of the integrated waveguide on SC generation.

We demonstrate transitional dimensionality crossover of radial discrete diffraction in optically induced radial-elliptical Mathieu photonic lattices. Varying the order, characteristic structure size, and ellipticity of the Mathieu beams used for the photonic lattices generation, we control the shape of discrete diffraction distribution over the combination of the radial direction with the circular or elliptic. We also investigate the transition from one-dimensional to two-dimensional discrete diffraction by varying the input probe beam position. Discrete diffraction is the most pronounced along the crystal anisotropy direction.

Miniaturization of nonlinear optical elements is one of the major trends of modern photonics. In particular, in the ‘flatoptics’ geometry, the sample is ultrathin along the light propagation direction. For nonlinear optical effects in such samples, phase matching is satisfied automatically, which allows for the use of materials with giant nonlinear susceptibilities. The tiny thickness reduces the efficiency but it can be compensated for by using geometric and material resonances. Recently also spontaneous parametric down-conversion (SPDC), leading to the generation of entangled photons, has been implemented in ultrasmall sources: subwavelength layers, metasurfaces, even nanoantennas. The lifted constraint of phase matching gives to SPDC even more freedom than to classical frequency conversion effects. The reason is that SPDC, as a spontaneous effect, is stimulated by quantum vacuum fluctuations, which populate all modes uniformly. SPDC in ultrathin samples demonstrates very broad spectral and angular width, extremely high degrees of continuous-variable entanglement, tunable polarization entanglement, and orders of magnitude enhancement of photon pair production rate due to the geometric resonances of dielectric metasurfaces.

We experimentally generate twin beams through cascaded quadratic processes in a nonlinear χ⁽²⁾ crystal, leading to an internally pumped optical parametric oscillation, in a doubly resonant second-harmonic generation system. The exploration of the non-classical properties of these beams enabled the observation of up to 5 dB of noise reduction in their intensity difference below the standard quantum limit.

Sub-micron tapered fibers have been proposed to be a suitable platform for the implementation of third-order spontaneous parametric down conversion (TOSPDC). Starting with the derivation of expressions for quantized fields in optical fibers, we devise an exact theoretical treatment of the expected triplet generation rate.

Optical frequency combs (OFCs) have been identified as a key building block for many applications ranging from spectroscopy to optical communications. In these applications, the fixed phase relation between the individual spectral components of the comb is a crucial aspect of frequency combs. Recently multi-wavelength lasers that are in essence multimode lasers have shown a promising capability to enable frequency comb multiplication over a broad range of frequency offsets surpassing 1 THz. Despite the robust phase coherence within each comb's lines, there remains a notable lack of phase coherence among distinct sub-combs. In this work, we show that the injecting of an adapted frequency comb, i.e., a narrowband comb comprising five lines and an extra tone separated by a certain frequency offset from the central line of the comb, facilitates cascaded phase locking between three adjacent sub-combs. The interaction between the regenerated comb and the multiplied comb induced by the extra tone initiates a modulation at their beating frequency. By fine-tuning the frequency of the extra tone, we can adjust the position of the resulting beating, and eventually achieve a cascaded phase locking for the third mode. We envision that cascaded phase-locking can advantageously be extended to additional modes leading to cover higher frequency offsets up to a few THz.

Molybdenum disulfide (MoS₂) dots have potential applications as optical limiter and beam modulators. In this work, MoS₂ quantum dots (QDs) prepared via the solvothermal method are studied for their broadband nonlinear optical (NLO) response. The as-prepared dots are few layers thick with lateral size distribution of 2-8 nm. The photoluminescence spectra show dependence on incident pump wavelength. Tunable femtosecond laser based z-scan technique shows reverse-saturable absorption and self-defocusing behavior. The direct bandgap in visible region achieved via quantum confinement effect enhances the NLO response of QDs. The mechanisms of two photon absorption along with thermal nonlinearity have been found to be operating in the system.

The interaction of nonresonant intense periodic optical field shifts the ground state excitonic position which can be understood by Floquet manipulation in Jaynes–Cummings model. The induced shift can be manifested by the optical Stark effect (OSE) and Bloch-Siegert effect (BSE) via controlling the light helicity. It is noteworthy that the energy shift is proportional to field intensity and inversely to the detuning at nearly resonant excitation which understood by rotating wave approximation. Recently, OSE and BSE have observed simultaneously with very large detuning (infrared excitation) for CsPbI₃ quantum dots. However, observing the BSE at near resonance with small detuning is difficult due to the dominance shift by OSE. Here, we have chosen Cu-doped CsPbI₃ nanocrystals and incorporated a helicity-resolved transient absorption spectroscopic technique. Moreover, the dynamical excitonic effect in a small percentage of Cu-doping reduced the binding energy and blueshifted the continuum band without changing the excitonic position. Interestingly we observe blueshift in excitonic position for co (σ+σ+)- and cross(σ+σ-)-polarization of pump and probe at small detuning. We observed a huge BSE shift ~ 122 meV with the ratios of shifts (i.e., Δ_BSE/Δ_OSE) are 0.74 at the lowest detuning, 193 meV Cu-doped CsPbI₃, respectively. Thus, our study advances high-field Floquet engineering with a doping mechanism and can be potentially exploited in strong-field device applications as well as a quantum information process.

Linear spectrophotometric transmittance measurements are widely used for determining the value of molar extinction coefficient and other basic photophysical parameters of dissolved molecular species. However, such measurements usually require prior information about the molar concentration of the studied chromophores, which in many cases such as e.g. genetically encoded self-maturing species, is not readily available. Here we use wavelength-tunable femtosecond pulses to demonstrate that by performing high-accuracy measurement of small intensity-dependent changes induced in the sample transmittance due to absorption saturation we are able to estimate the extinction coefficient without prior knowledge of the concentration.

Two-photon absorption (2PA) transitions play a key role in numerous photonic applications, where many prominent features in the 2PA spectra of organic fluorophores are due to transitions between electronic-vibrational (vibronic) states. While quantum-chemical calculations excel at modelling purely electronic 2PA transitions, success in predicting vibronic properties remains limited. This is in part due to high computational costs of evaluating 2PA tensor derivatives required for Herzberg-Teller (HT) vibronic interactions, especially if carried out across full vibrational coordinate space of the chromophores. Here, we present a novel highly efficient and cost-effective approach to modelling of HT vibronic two-photon absorption spectra of organic fluorophores by using the latest version of FCclasses3 code combined with judicious pre-selection of symmetry-adapted vibrational subspace. We apply this method to a C_2h inversion-symmetric diketopyrrolopyrrole chromophore, where the 2PA spectrum is dominated by HT terms because Franck-Condon contributions vanish due to LaPorte rule. Our results are in excellent agreement with recently reported experimental 2PA spectra confirming two-photon HT coupling is indeed dominated by, B_u-symmetry modes, and is also consistent with the experimentally observed polarization ratio. However, nominally-forbidden features near the electronic-origin appear significantly larger than HT coupling permits, indicating the presence of additional phenomena.

Exploring optical analogues with paraxial fluids of light has been a subject of great interest over the past years. Despite many optical analogues having been created and explored with these systems, they have some limitations that usually hinder the observation of the desired dynamics. Since these systems map the effective time onto the propagation direction, the fixed size of the nonlinear media limits the experimental effective time, and only the output state is accessible. In this work, we present a solution to overcome these problems in the form of an optical feedback loop, which consists of reconstructing the output state, by using the off-axis digital holography technique, and then re-injecting it again at the entrance of the medium through the utilization of Spatial Light Modulators. This technique enables access to intermediate states and an extension of the system effective time. Furthermore, the total control of the amplitude and phase of the beam at the input of the medium, also allows us to explore more exotic configurations that may be interesting in the context of optical analogues, that otherwise would be hard to create. To demonstrate the capabilities of the setup, we explore qualitatively some case studies, such as the dark soliton decay into vortices with the propagation of shock waves, and the collision dynamics between three flat-top states. The results presented in this work pave the way for probing new dynamics with paraxial fluids of light.

Triamino-heptazines (TAH's) comprise the fundamental building blocks of graphitic carbon nitride, an alluring material with promising applications in optoelectronics. However, the core D_3h molecular symmetry enforces a forbidden lowest-energy excited singlet state, making it a challenge to characterize via conventional spectroscopy. Here, we measure oneand two-photon absorption spectra of an acidic form of triamino-heptazine, 3H-TAH, and use reversible acid/base titration to further probe the symmetry of the low-energy transitions in aqueous solution, which suggests the molecular base structure is dimelem. Two-photon absorption reveals two distinct low-energy transitions in acidic conditions, both of which are one-photon forbidden. The lowest energy state additionally becomes one-photon allowed in basic conditions. Spectroscopic changes can be described according to chromophore symmetry switching, with C_3h, D_3h, or C_s point group symmetry in respective acidic, neutral, or basic environments.

A multimode optical fiber supports the excitation and propagation of a singular, pure optical mode. This mode, characterized by a field pattern that adheres to the boundary conditions, remains constant throughout the length of the fiber. When two such pure optical modes, moving in opposite directions, are initiated, they could interact via the stimulated Brillouin scattering (SBS). In this study, we introduce an analytic theoretical framework to describe the SBS interactions between two counterpropagating optical modes, each selectively excited in an acoustically uniform multimode optical fiber. Using a weakly guiding step-index fiber model, we have formulated an analytical expression that maps the spatial distribution of sound field amplitude within the fiber core. Furthermore, we have investigated the characteristics of the SBS gain spectra, particularly focusing on the interactions between modes of varying orders. Through this approach, we aim to provide comprehensive insights into the sound propagation phenomena associated with SBS in multimode optical fibers, highlighting their unique influences on the SBS gain spectrum.

Dipicolinic acid (DPA), bound to calcium (Ca), is a main component of bacterial endospores. Complexation of DPA with lanthanide ions, particularly Terbium (Tb), allows for rapid detection via monitoring the lanthanide luminescence, with applications spanning from cell imaging to contamination and biohazard detection, to sterilization control. Here we present time-resolved luminescence of the Tb-DPA complex upon UV excitation at 266 nm. Our measurements directly monitor the luminescence dynamics and speak for a rise of the luminescence on the ns time scale, which is orders of magnitude faster than previously reported, and raise questions about the details of the energy transfer process in this complex and the states involved. The results are relevant for the design of more sensitive detection schemes for Tb-DPA fluorescence, as well as for the design of novel Tb-based luminescence probes or novel fluorescence probes working as FRET acceptors of Tb energy.

Microplastics contamination in water sources presents a pressing concern for environmental and public health, necessitating accurate detection and quantification methods. We investigate the application of broadband Coherent anti-Stokes Raman Spectroscopy (BCARS) as an innovative, rapid, and label-free spectroscopy method for the detection of microplastics in drinking water. Current methods for detecting microplastics, such as visual inspection, FTIR and spontaneous Raman spectroscopy, and gas chromatography, have limitations in terms of sensitivity, speed, specificity, or destructive analysis. BCARS, however, offers a non-destructive approach with the capability to identify particles smaller than a micron and to discern different types of plastics through chemical analysis. BCARS operates at a significantly faster rate than spontaneous Raman spectroscopy, reducing acquisition time from seconds to milliseconds. BCARS utilizes a dual excitation technique to simultaneously probe both the fingerprint and C-H band regions of the Raman spectrum and allows for the identification of different polymers in a sample, as demonstrated in this study with a mixture of Polystyrene and Poly(methyl methacrylate) (PMMA) micro-beads. Our results highlight the ability of B-CARS to distinguish between different types of polymers in a sample, using resonant peaks at specific wave-numbers to generate a false-color image for easy identification.

We report on the experimental and numerical studies exploring dynamical processes of soliton birth and annihilation of solitons in the laser ring cavity. The specific purpose of the research is focused on the exact control of the pulse repetition rate of a harmonically mode-locked fiber laser. We have demonstrated that the birth of a new pulse occurs from the soliton background (i.e., from the dispersive waves) through its shaping to the soliton or from the existing pulse through its splitting. The injection of external continuous wave (CW) allows one-by-one change of the number of solitons in the laser cavity thus enabling the fine-tuning of the pulse repetition rate. We present new experimental observations of the laser transition dynamics associated with the changes of the soliton numbers and give clear insight into the possible physical mechanisms responsible for these effects.

This study investigates the nonlinear effects on signal integrity in 16-QAM optical communication systems by focusing on received signal distributions without noise interference. Utilizing GPU-based simulations and analyzing “triplets” of consecutive signal points, we uncover that nonlinear interactions generate distinctive patterns in signal behavior, challenging the adequacy of standard Gaussian models. Our analysis employs the Gaussian Mixture Model (GMM), revealing that multi-component models offer a more accurate representation of signal distributions, highlighting the complexity of nonlinear effects. This research not only enhances our understanding of signal behavior under nonlinear conditions but also paves the way for future investigations into improving optical communication system design and reliability.

This article introduces an innovative procedure integrating chromatic dispersion compensation (CDC) and sliding window methodology for ongoing signal processing in optical communications. Our strategy notably elevates the effectiveness of Nonlinear Fourier Transform (NFT) processing.

We report on the results of experimental and numerical studies enabling deep insight into the physical mechanisms underlying the supermode noise suppression in harmonically mode-locked (HML) fiber laser using the resonant continuous wave (CW) injection. In particular, we have proved experimentally that the supermode noise suppression effect is available only with the CW injected to the long-wavelength side of laser spectrum. Injection to the opposite side destroys the HML operation regime and leads to the formation of tight soliton bunch. Our numerical simulations confirm these specific features. To get the result, we have simulated phase-locking between the CW and a single soliton. Then, the developed model has been applied to the laser cavity operating multiple pulses in the presence of the gain depletion and recovery mechanism responsible for harmonic pulse arrangement. We clearly demonstrate how the CW injection accelerates or destroys the HML process enabling the generation of additional inter-pulse forces.