Michał Dudek

This work presents the comparison of an optical fiber–based quantum random number generation system with two detectors and a single detector. The presented quantum random number generator was based on branching path approach with spatial superposition principle. It consisted of pulsed laser source attenuated to single photons, optical fiber splitter with 50/50 splitting ratio and two single–photon detectors. The main differences between two setups are described and analyzed in terms of parameters influencing the Shannon entropy of both systems. To determine the quality of randomness of the numbers generated in both systems, statistical tests were performed, i.e., NIST Statistical Test Suite. The analytical relations for the probability of possible output quantum states depending on the initial properties of the systems are presented. Also, description of the experimental setups based on the aforementioned models is provided together with the comparison of the results obtained by means of numerical modeling and real measurements. Both quantum random number generators described in this study may be suitable to be used as an input to the quantum key distribution systems.

In the face of increasing security requirements, threat identification requires technology with uncompromising sensitivity and responsiveness. This article presents a sensor with enhanced sensitivity, designed to detect rotational ground movement. Its physical basis on the Sagnac effect provides an absolute measurement of rotation. From a geotechnical and engineering perspective, the configuration of several such sensors enables precise determination of the epicentral coordinates of seismic events and identification of local material degradation zones, where differences in signal transit time and amplitude between individual network nodes provide the basis for mapping discontinuities in the studied medium. The primary goal of the presented research was to verify the feasibility of creating an integrated sensor array capable of precisely monitoring a defined area. Using highly correlated sensors with time synchronization of the order of 10 ns we obtained signals from artificial disturbances. The time-of-arrival analysis of recorded sensor signals successfully demonstrated the ability to quickly determine the locations of explosions. The presented solution offers new perspectives for early warning systems, providing not only threat detection but also accurate spatial positioning of threats using highly sensitive rotational sensors.

This article describes an external refractive index (RI) sensor based on a spectral analysis of the light transmission through a long tapered side-hole optical fiber (S-H OF). A section of the S-H OF was fusion-spliced with SMFs at both ends and connected to a supercontinuum source at the input and an optical spectrum analyzer (OSA) at the output. To investigate the effect of the external RI on the spectral characteristics, immersion liquids with refractive indices in the ranges of 1.32–1.35 and 1.37–1.42, with increments of 0.01, were used. Power loss measurements were carried out for each liquid in two wavelength ranges: 600–1200 nm and 1200–1800 nm. The highest sensitivity obtained in this study was 622 ± 11 nm/RIU in the near-infrared region. This result highlights the suitability of longtapered S-H OFs for spectral-interrogation-based RI sensing, offering a promising yet simpler alternative to more complex interferometric or plasmonic configurations.

In this work, we present a study of a quantum random number generation system based on a branching path approach with spatial superposition principle, realised using fibre optics. The analysis of the experimental system was supported by the development of a stochastic model of the entropy source, which, to the best of the authors’ knowledge, has not yet been properly described. This resulted in the analytical equations for the probability of possible output quantum states depending on the initial properties of the system. Based on the presented model, the quantum efficiency and the Shannon entropy were calculated and compared with experimentally obtained values, which resulted in full agreement between these data. Additional statistical tests were performed on random numbers obtained theoretically and experimentally to confirm their high degree of randomness and their usability in cryptographic applications. The fact that the developed system is based on fibre optics allows it to operate in stable conditions with a final efficiency at the level of 15%, which provides a random number generation rate of about 8 kb/s. The developed system is used as an input to the quantum key distribution system, which has possible applications in cryptography or military and commercial secure communications.

An intensity-based refractive index (RI) sensor using a laser micromachined side-hole optical fibre (S-H OF) is presented in this paper. To achieve this, a microcavity was cut into a side surface of the S-H OF, providing access to one of the air holes within its structure. The geometrically modified fibre was then connected at both ends to a single-mode fibre for structure investigation in a system containing a supercontinuum laser and an optical signal analyser. In the next step, an immersion liquid was applied to a microcavity for RI values ranging from 1.30 to 1.57 in increments of 0.02. Power loss measurements were conducted for each RI value. Based on the obtained results, it can be concluded that an RI sensor has been successfully developed, which holds potential applications in biochemistry.

This paper investigates the wavelength-dependent sensitivity of a ridge waveguide based on a silicon nitride (Si₃N₄) platform, combining numerical analysis and experimental validation. In the first part, the modal characteristics of a Si₃N₄ ridge waveguide are analyzed in detail, focusing on the effective refractive index (n_eff), evanescent field ratio (EFR), and propagation losses (α_prop). These parameters are critical for understanding the interplay of guided light with the surrounding medium and optimizing waveguide design for sensing applications. In the second part, the wavelength-dependent sensitivity of a racetrack ring resonator (RTRR) based on the Si₃N₄ waveguide is experimentally demonstrated. The results demonstrate a clear increase in the sensitivity of the RTRR, rising from 116.3 nm/RIU to 143.3 nm/RIU as the wavelength shifts from 1520 nm to 1600 nm. This trend provides valuable insights into the device’s enhanced performance at longer wavelengths, underscoring its potential for applications requiring high sensitivity in this spectral range.

This paper presents and discusses the results of numerical studies of multi-layered hyperbolic metamaterials (HMMs). Such structures are built of alternating thin layers of conductive (e.g., metal or alternative conductive material) and dielectric materials. The thicknesses of these layers are much smaller than the operating wavelength, usually of the order of a few or tens of nanometres. Indium tin oxide (ITO), which is an alternative conductive plasmonic material from the group of transparent conductive oxides (TCOs), was used in the conductive layers. Silica (SiO2) was used as a material in the dielectric layers. As a result of a simulation-based optimization, the layer thicknesses of two components forming the structure were chosen to be 20 nm each. Four variants of multilayer structures with different numbers of elementary cells forming the structure, N, for N = 5, 10, 15, and 20, respectively, were investigated by both analytical methods using the transfer matrix method (TMM) and simulation methods using finite-difference time-domain (FDTD). The results confirmed the hyperbolic dispersion of effective electric permittivity and tunability of the structure in the near-infrared (NIR) range. Moreover, a complete agreement of the results confirmed the complementarity of the two methods – both analytical TMM and simulation FDTD. The proposed HMMs structures may have potential applications as tunable edge filters.

This paper aims to present data recorded by a three-axial Fiber-Optic Rotational Seismograph (FORS). The laboratory and field tests showed a high correlation coefficient above 99% between two seismographs signals during the external disturbance, with an amplitude ranging from 0.5 mrad/s to 1.2 rad/s. This is achieved by ensuring a 100 ns time synchronization in the systems. At the same time, the Allan Variance analysis was applied to determine the basic parameters of random errors of the presented seismographs. The performed analysis indicates the angular random walk of 35–45 nrad/s/√Hz and a bias instability below 50 nrad/s. FORS offers the widest dynamic range available, at 170 dB, which is crucial during rotational seismology exploration due to its wide range of interest from seismology to engineering applications. Finally, a field research is also presented during an explosion in a closed limestone quarry in the border area.

In optical communication and sensing, silicon nitride (SiN) photonics plays a crucial role. By adeptly guiding and manipulating light on a silicon-based platform, it facilitates the creation of compact and highly efficient photonic devices. This, in turn, propels advancements in high-speed communication systems and enhances the sensitivity of optical sensors. This study presents a comprehensive exploration wherein we both numerically and experimentally display the efficacy of a SiN-based ring resonator designed for refractive index sensing applications. The device’s sensitivity, numerically estimated at approximately 110 nm/RIU, closely aligns with the experimental value of around 112.5 nm/RIU. The RR sensor’s Q factor and limit of detection (LOD) are 1.7154 × 10⁴ and 7.99 × 10⁻⁴ RIU, respectively. These congruent results underscore the reliability of the two-dimensional finite element method (2D-FEM) as a valuable tool for accurately predicting and assessing the device’s performance before fabrication.