W states are maximally entangled states with excellent robustness to loss. They have been studied in ion, photon and waveguide-mode bases, however the entanglement verification has remained challenging. Here, we theoretically study W-state generation by the quantum walk of a single photon through a linearly coupled waveguide array (WGA) that supports self-imaging of light. We design W states in symmetric and asymmetric arrays with even and odd number of waveguides. Bipartite entanglement is formally proven using the von Neumann entropy of the reduced density matrix. We further use the self-imaging to construct an entanglement witness based on the exclusion principle. A key to verification is the interferometer which extends the length of a W-state generator to the revival length where the photon is fully recombined into a single waveguide mode. In addition, W-state coherence is proven by numerically demonstrating the far-field interference. The sensitivities of the proposed W-state generation and verification protocols to the fabrication tolerances are numerically evaluated in glass, silicon nitride and silicon-on-insulator WGAs, indicating the feasibility of their realisation by high-precision e-beam lithography and laser writing.

U ovom radu istražujemo različite srčane ritmove primenom formalizma i teorije kompleksnih sistema na EKG signale. Rezultati pokazuju da se metrike zasnovane na RR intervalima, varijabilnost srčanog ritma i Šenonova entropija, mogu koristiti za razlikovanje periodičnih od neperiodičnih ritmova, dok se periodični ritmovi dodatno klasifikuju po frekvenciji srčanih otkucaja. Veličine koje u obzir uzimaju i amplitude signala, kao što su parametri Poenkareovih dijagrama i multifraktalnih spektara, daju nove informacije i indikatore kompleksnosti EKG signala, te predstavljalju potencijalne nove biomarkere aritmija. Prikazani rezultati predstavljaju korak ka sistematičnom povezivanju dinamičkih parametara EKG signala sa biomarkerima korisnim u kliničkoj praksi.

The potential of time-domain Raman spectroscopy in space exploration is discussed. This work is motivated by the emergence of robust, space-qualified femtosecond lasers and by the fact that time-domain detection allows the design of very compact instruments. As is shown, time-domain Raman spectroscopy gives access to the same fingerprint spectrum of minerals as conventional Raman spectroscopy, while avoiding problems such as fluorescence or ambient light backgrounds.

We propose an innovative approach to W-state generation and verification based on the self-imaging of light in coupled waveguide arrays. Provided is also a formal proof of the W-state entanglement.

Demand for densely packed wavelength demultiplexers has increased due to the rapid developments in information systems and sensing for biomedical and space applications. The required miniaturisation is problematic due to the crosstalk in high-density photonic circuits, while the feature size complicates design at sub-micrometer wavelengths. As a solution, we propose wavelength demultiplexers based on wavelength-dependent self-imaging in linearly coupled finite optical lattices. The novel semi-analytical design allows for intuitive and efficient control of their spectral characteristics, notably the bandwidth control by changing the number of waveguides in the lattice. The principle is validated using femtosecond laser fabrication of visible/near-infrared demultiplexers in borosilicate glass. The insertion loss did not exceed 0.43 dB with 0.1-0.15 dB for most devices and the crosstalk was lower than 30 dB. The applicability of the proposed design to other fabrication platforms and wavelength ranges is demonstrated by numerical simulations of silicon-on-insulator demultiplexers at telecom wavelengths with highly competitive insertion loss and crosstalk of 0.13 dB and -82 dB, respectively.

Magnesium titanate ceramics were prepared by reactive spark plasma sintering (SPS) at 1200 degrees C for 5 min. Prior to sintering, MgO and TiO2 powders were mixed by high energy ball milling (HEBM) for 15, 30, or 60 min. The effect of milling time on phase composition was analyzed by X-ray diffraction (XRD) for milled powders and sintered specimens. The morphology of the sintered ceramics was investigated by scanning electron microscopy (SEM), while elemental distribution was determined by energy dispersive spectroscopy (EDS). The presence of the MgTi2O5 phase was detected in XRD and was confirmed by EDS analysis. Microcracking was observed for specimens prepared with longer milling times and attributed to the coefficient of thermal expansion (CTE) mismatch dominantly due to the anisotropic crystal structure of MgTiO3 phase. The sample milled for 15 min showed the highest Vickers hardness due to less or no microcracking and nearly full density. The dielectric measurements in the range of 10 Hz-250 MHz demonstrated extremely high dielectric permittivity, as high as 104 at 1 kHz. An increase in loss tangents was observed due to oxygen vacancy formation, which was promoted by the vacuum environment during SPS. Oxygen vacancy-related dielectric relaxation was also detected and explained.

Zigzag boundary shaping of the rhombic photonic graphene lattice imparts the capability to selectively excite topologically protected edge modes with distinct spatial distributions. Concurrently, the introduction of a vortex sublattice distortion gives rise to novel vortex-pivoted zero modes. The resulting diversity of zero modes facilitates precise control over the propagation of light — an essential prerequisite for practical applications. We systematically investigate the dynamics of these zero modes in the presence of nonlinear lattice response and various types of disorder, revealing their remarkable resilience to weak nonlinearity and disorder, with negligible mode cross-talk. Furthermore, we establish the conditions of efficient vortex-zero mode lasing achieved through saturable-nonlinear driving from a background noise. The results indicate possibilities for multi-mode lasing in a rhombic lattice, as opposed to a hexagonal lattice, thus advancing a novel category of topological photonic lasers.

Flat band lattice systems promote the appearance of perfectly compact bulk states, whereas topology favors edge localization. In this work, we report the existence of compact topological edge states on flux-dressed photonic graphene ribbons. We found that robust localization is achieved through a synergy of AharonovBohm caging and topological protection mechanisms. The topological nontriviality of the compact edge states is characterized through both theoretical derivations and experimental observations of an integer Zak phase obtained from the mean chiral displacement. Experiments are performed using direct laser writing of a graphene ribbon photonic lattice having 0 or pi effective magnetic fluxes. Mode stability is demonstrated by the exceptional localization of the edge compact mode and its resilience to fabrication tolerances and input phase deviations. Our findings demonstrate the existence of perfectly compact topological edge states, as a concrete and promising example of synergy in between flat band physics and topology.

In the present work, we study the nonlinear dynamics of a microtubule, an important part of the cytoskeleton. We use a two-component model of the relevant system. A crucial nonlinear differential equation is solved with semi-discrete approximation, yielding some localized modulated solitary waves called the breathers. A detailed estimation of the existing parameters is provided. The numerical investigation shows that the solutions are robust only if the carrier velocity of the breather wave is higher than its envelope velocity. That disproves the previously accepted solutions based on the equality of these velocities.

Ceramic/polymer composites can be chemically stable, mechanically strong, and flexible, which make them candidates for electric devices, such as pressure or temperature sensors, energy storage or harvesting devices, actuators, and so forth. Depending on the application, various electrical properties are of importance. Polymers usually have low dielectric permittivity, but increased dielectric permittivity can be achieved by the addition of the ceramic fillers with high dielectric constant. With the aim to enhance dielectric properties of the composite without loss of flexibility, 5 wt% of BaTiO3-Fe2O3 powder was added into a polyvinylidene fluoride matrix. The powder was prepared by different synthesis conditions to produce core/shell structures. The effect of the phase composition and morphology of the BaTiO3-Fe2O3 core/shell filler on the structure and lattice dynamics of the polymer composites was investigated. Based on the results of the thermal analysis, various parameters of ceramic/polymer composites were determined. Differences in the phase composition and morphology of the filler have an influence on the formation of various polyvinylidene fluoride allomorphs and the degree of crystallinity. Furthermore, the dielectric performances of pure polyvinylidene fluoride and the polymer/ceramic composites were measured. Synthesis and properties of the PVDF-BTF composites.image

Systems with engineered flatband spectra are a postulate of high-capacity transmission links and a candidate for high-temperature superconductivity. However, their operation relies on the edge or surface modes susceptible to fluctuations and fabrication errors. While the mode robustness can be enhanced by a combination of Aharonov-Bohm caging and topological insulation, the design of the corresponding flatbands requires approaches beyond the standard $k$-vector-based methods. Here, we propose a synthetic-flux probe as a solution to this problem and a route to the realization of ultra-stable modes. We prove the concept in a laser-fabricated graphene-like ribbon photonic lattice with the band-flattening flux induced by "P" waveguide coupling. The topological non-triviality is witnessed by an integer Zak phase derived from the mean chiral displacement. Mode stability is evidenced by excellent mode localization and the robustness to fabrication tolerances and variations of the input phase. Our results can serve as a basis for the development of multi-flat-band materials for low-energy electronics.

A major challenge in inverse design of optical splitters is to efficiently reach platform nonspecific designs constrained to multiple functional requirements: arbitrary splitting ratio, low insertion loss, broad bandwidth and small footprint. While the traditional designs fail to fulfill all these requirements, the more successful nanophotonic inverse designs require substantial time and energy resources per device. Here, we present an efficient inverse design algorithm that provides universal designs of splitters compliant with all above constraints. To demonstrate the capabilities of our method, we design splitters with various splitting ratios and fabricate 1 × N power splitters in a borosilicate platform by direct laser writing. The splitters show zero loss within the experimental error, competitive imbalance of <0.5 dB and broad bandwidth in the range 20 - 60 nm around 640 nm. Remarkably, the splitters can be tuned to achieve different splitting ratios. We further demonstrate scaling of the splitter footprint and apply the universal design to silicon nitride and silicon-on-insulator platforms to achieve 1 × 5 splitters with the footprints as small as 3.3 µm × 8 µm and 2.5 µm × 10.3 µm, respectively. Owing to the universality and speed of the design algorithm (several minutes on a standard PC) our approach renders 100 greater throughput than nanophotonic inverse design.

Rapidly increasing demand for higher data bandwidths has motivated exploration of new communication channels based on spatially multiplexed in-fibre and on-chip coupled light guides. However, the conventionally used periodically arranged coupled waveguides display complicated light propagation patterns, ranging from quasiperiodic to nearly chaotic. Taking a different approach, we spectrally engineer interwaveguide coupling to instigate self-imaging of the input light state at the array output and thus enable construction of novel high-fidelity interconnects. Simple implementation via modulation of the interwaveguide separations makes these interconnects realizable in all fabrication platforms. Their competitive advantages are negligible crosstalk-induced information loss, high density that exceeds the current standards by an order of magnitude, and compatibility with both classical and quantum information encoding schemes. Moreover, the wavelength-dependent self-imaging opens up new possibilities for wavelength and spatial division demultiplexing. The proposed analytical designs are supported by extensive numerical simulations of silicon-on-insulator, silicon nitride and silica glass waveguide arrays, and a statistical feasibility study.

Optical fibre sensors have attracted much attention as noninvasive electrically immune multiparameter diagnostic tools. Optical fibre gratings – resonant structures inside fibres, enable localized and distributed high-precision measurement schemes for the use in cardiology, pulmonology, prosthetics, obstetrics, etc. Particular niche market is reserved for broadband LPG sensors, which expel light from the fibre core to the cladding and thus enable sensitive measurement of the external refractive index and curvature. With the new costcutting LPG fabrication methods on the raise the question of the source and detector cost gets into focus. While the broadband coherent sources are usually used in laboratory, the source and spectrum analyser costs are prohibitive for many field applications. In this paper, we evaluate the performance and cost-benefit of the incoherent source application. The sensor performance is assessed in terms of sensing precision and signal-to-noise signal quality for broadband and lateral edge sensing schemes. It is sufficient for basic heart and respiration rate monitoring, but fails to satisfy stricter requirements for medical diagnostics.

Recently we have witnessed experimental realization of a Majorana zero-mode bound at vortex distortion induced in bipartite hexagonal photonic lattices. Here, we address an open question of the impact of nonlinearity on the zero-mode dynamics by theoretically investigating the abilities of topologically protected zero-modes to guide, couple and lase light in the presence of nonlinear effects. Light-intensity related nonlinearity enters the scene through a local nonlinear lattice response and driving properties: saturable nonlinear gain and linear loss. We demonstrate an efficient steady zero-mode lasing regime by managing the lattice and driving parameters. Obtained results open up possibilities for design of new topological lasers in length-scalable photonic platforms, such as multicore optical fibers.

We report the preliminary results of a laboratory validation study of a new polycardiographic device for the assessment of cardiovascular function (SensSmartTech). The main principle behind polycardiography is a synchronized measurement of multiple electro- mechanical parameters of the cardiovascular system. The assessment is non-invasive and entails electrocardiography, photoplethysmography, phonography and seismography. The study’s results validate the use of the proposed policardiograph implementation in settings with varying measurement and physiological conditions in both clinical and homecare settings. A simple signal analysis shows that the method is suitable for automated determination of diagnostically relevant features including the heart rhythm, openings and closures of heart valves, heart sounds, and systolic intervals generated as a combination of electrical and mechanical observables.

In recent years, short pulse lasers have made massive progress and space-ready femtosecond laser systems are under development [1]. Moreover, employing time-domain spectroscopy techniques to identify planetary minerals by their spectroscopic fingerprints in the infrared and terahertz frequency range can have technological advantages over conventional spectroscopic techniques such as Fourier-Transform Infrared or Raman spectroscopy. The advantages are compactness, the possibility to replace bulky optical components by electro-optic/acousto-optic photonic techniques and the potential to be chip-integrable. We focus on one particular time-domain technique, coherent phonon spectroscopy (CPS), which is sensitive to Raman-active modes. Here, CPS is demonstrated in single-color operation and thus the simplicity and its insensitivity to fluorescence background add to the advantages of this technique.

Multiarm interferometers can enhance measurement precision and provide multiparameter capability to the measurement. Their realisation requires multiport beam splitters, which has been a long-standing challenge in free-space and integrated optics. Here, we propose a new type of multiport interferometers suitable for implementation on optical chips. Their prospective advantages over the standard directional-coupler architectures: an arbitrary number of arms, planar architecture and two orders of magnitude reduction in footprint, are achieved by the layout based exclusively on the finite modulated photonic lattices. The inverse design of photonic lattices is facilitated by restricting the light propagation to periodic patterns. The corresponding interferometer model predicts the maximum $$1/\sqrt{N}$$ sensitivity scaling with the number of arms N. While the presented design solutions are ubiquitous to all implementations, the advantages are discussed in both the low and high refractive-index contrast platforms. Finally, we provide an outlook on the possibilities for the interferometer applications in distributed classical and quantum measurements.

We challenge the current thinking and approach to the design of photonic integrated circuits (PICs) for applications in communications, quantum information and sensing. The standard PICs are based on directional couplers, that provide a wide range of functionalities but do not fully respond to the major technological challenges: massive parallelisation of transmission channels, low-energy dissipation and small footprint. We propose a new concept for design of PICs with the ultimate downscaling capability, the absence of geometric loss and a high-fidelity throughput. This is achieved by a periodic continuous-time quantum walk of photons through waveguide arrays that leverages on the simple and effective algebraic approach to engineering waveguide couplings. We demonstrate the potential of the new concept by reconsidering the design of basic building blocks of the information and sensing systems: interconnects, multiport couplers, entanglement generators and interferometers. An extensive feasibility check in dielectric and semiconductor fabrication platforms confirmed this potential.