arXiv subjects

N. S. Kostyuchenko

Publications and source records attributed to N. S. Kostyuchenko.

4 recordsLinked to original sources

arXiv2026

Control of eigenmode localization and coupling anisotropy by multiscan femtosecond laser writing

The multiscan method is widely used in femtosecond laser writing of waveguide systems to increase the refractive index contrast and to control the eigenmode shape. Here, we investigate multiscan writing with a constant effective writing speed and show that the displacement between adjacent scans provides an additional degree of freedom for controlling eigenmode confinement. By optimizing the multiscan parameters, the effective mode area can be reduced, enabling an up to eightfold increase in fabrication speed compared to conventional single-scan writing. We further demonstrate that careful tuning of the multiscan geometry substantially reduces the anisotropy of inter-waveguide coupling. These findings are applied to the fabrication of three-dimensional waveguide arrays operating at wavelengths of 808 nm and 1450 nm, where reduced coupling anisotropy is achieved. The proposed approach may be useful for three-dimensional waveguide arrays employed in topological photonics experiments, where low coupling anisotropy is desired.

physics.optics↗

arXiv2026

Observation of topological vortex solitons on disclinations

Vortex-carrying wave fields play a crucial role in photonics due to unusual propagation properties and interactions with matter, which enable numerous practical applications ranging from optical tweezers and imaging to information encoding and transmission. Localized vortex-carrying beams propagating in nonlinear optical media may form self-sustained excited states-vortex solitons-which are, however, usually prone to instabilities and require high powers for their stabilization in non-topological materials. Using fs-laser written aperiodic waveguide arrays, we demonstrate that photonic topological insulators with disclinations admit the formation of stable and thresholdless vortex solitons with tunable shapes. These unique materials belong to a class of higher-order topological insulators and allow the propagation of localized, topologically protected excitations at the disclination core, enabling disorder-resistant transmission of signals and energy. We show that vortex solitons bifurcate from the superposition of topologically protected linear edge states at the disclination core and remain stable in the entire forbidden topological gap. Realized topological vortex solitons with symmetries that are inaccessible in periodic lattices are the first example of excited soliton states with non-trivial phase structure in a topological insulator. Our findings shine a light on the interplay between nonlinearity, the angular momentum degree of freedom of light, and the material topology.

physics.optics↗

arXiv2025

Observation of linear and nonlinear light trapping on topological dislocations

Topological dislocations in otherwise periodic lattices represent global structural defects that, nevertheless, typically leave the lattice periodicity intact far from the dislocation. Such dislocations arise in diverse physical systems ranging from crystalline solids, acoustic and photonic lattices and crystals to matter waves in optical lattices. Dislocations drastically affect the evolution of wave excitations in their vicinity, enabling novel mechanisms for trapping on topological defects and controlling the energy flow. Moreover, when combined with nonlinearity, such systems give rise to new types of self-sustained states of topological origin that have never been observed to date. Here we demonstrate experimentally, for the first time at optical frequencies, the waveguiding at various types of topological edge dislocations, resulting in the formation of localized photonic eigenstates with distinct and tunable shapes. Using femtosecond laser-writing techniques, we fabricated waveguide arrays with precisely tailored dislocation parameters, enabling full control over the degree of localization and internal structure of the associated modes. We further demonstrate both theoretically and experimentally that in the high-power regime, the families of thresholdless dislocation solitons bifurcate from such modes, which inherit shape diversity of their linear counterparts. Our results reveal a nontrivial interplay between nonlinearity and global lattice deformations and establish dislocation solitons as a new class of nonlinear topological states. They may stimulate the observation of new types of nonlinear states and interaction scenarios for excitations in nonlinear physical systems, where lattices with controllable global deformations can be created.

physics.optics↗

arXiv2025

Observation of Light Localization at the Edges of Quasicrystal Waveguide Arrays

Quasicrystals are unique systems that, unlike periodic structures, lack translational symmetry but exhibit long-range order dramatically enriching the system properties. While evolution of light in the bulk of photonic quasicrystals is well studied, experimental evidences of light localization near the edge of truncated photonic quasicrystal structures are practically absent. In this Letter, we observe both linear and nonlinear localization of light at the edges of radially cropped quasicrystal waveguide arrays, forming an aperiodic Penrose tiling. Our theoretical analysis reveals that for certain truncation radii, the system exhibits linear eigenstates localized at the edge of the truncated array, whereas for other radii, this localization does not occur, highlighting the significant influence of truncation on edge light localization. Using single-waveguide excitations, we experimentally confirm the presence of localized states in Penrose arrays inscribed by a femtosecond laser and investigate the effects of nonlinearity on these states. Our theoretical findings identify a family of edge solitons, and experimentally, we observe a transition from linear localized states to edge solitons as the power of the input pulse increases. Our results represent the first experimental demonstration of localization phenomena induced by the selective truncation of quasiperiodic photonic systems.

physics.optics↗