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In this research, we investigated common machine learning algorithms to estimate the highest sensitivity of a D-shaped PCF SPR sensor by optimizing the performance parameters. Extreme gradient boosting (XGBoost), random forest model, and PyTorch neural network machine learning algorithms were compared to build a model and accurately predict the results, and sensor parameters were optimized through Non-dominated Sorting Genetic Algorithm (NSGA-II). The XGBoost technique demonstrated exceptional prediction capability, achieving an impressive R2 value of 99.64% and the trained model served as the objective function. The maximum sensitivity of 4529.75 nm/RIU was achieved in the standard optimization approach, However, with the guidance of NSGA-II, this sensitivity increased to 4814.14 nm/RIU, representing an improvement of 6.28%. The developed model enables rapid, reliable, and computationally cost-effective parameter predictions. Additionally, it provides a comprehensive understanding of the intricate relationships between input parameters and sensitivity, thus contributing significantly to the existing literature in the quest for optimal parameter identification through the application of machine learning algorithms. • A novel optimization approach for a highly sensitive D-shaped PCF SPR RI sensor is presented. • The significance of the sensor features and the correlations between them are investigated. • The best parameter ranges are discovered with an ML-based trained model. • XGBoost showed the highest performance with R2 and MSE values of 0.99 and 305.7, respectively. • NSGA-II optimization technique achieved 6.3% better sensitivity compared to the classical method. [ABSTRACT FROM AUTHOR]

Quanta of light (single photon) play as one of the building blocks of photonic based quantum computations, sensing, and communications. This makes a necessity to develop practical approaches for tuning, guiding, and coupling of single photons in photonic circuits for viable applications. Interaction and coupling efficiency of single photon into optical fibers is a technical bottleneck of quantum optics and should be addressed by novel design and materials. Here, we introduce a fiber-based micro-photonic design to directly coupling of the emitted single-photon to the core of a single mode fiber (SMF). The results of the simulation indicate that the emission of single photon source on a D-shaped SMF coated by a thin plasmonic film, provide remarkable amplifying of the evanescent field by confined surface plasmons into the SMF. The numerical analysis of different types and thicknesses of plasmonic materials by finite element method (FEM) is conducted to study the propagation vectors along the SMF as a function of the emission angle and wavelength of the single photon source. The results revealed that by the optimum thickness of the tantalum layer as novel plasmonic material, the best record of coupling efficiency can be achieved in the fiber optics communication region (λ ∼ 1550 nm). This approach sheds light on novel plasmonic-assisted coupling and promises a functional strategy for single photon manipulation in various fields of quantum optics. [ABSTRACT FROM AUTHOR]

• An optimal IA-PCF with only single material has three ZDWs (1061 nm/1598 nm/1904 nm) in 800–2400 nm. • The flat dispersion fluctuation of ± 2.05 (ps/nm·km) in the range of 1509 nm-1955 nm is obtained. • The continuous SC exists in 750 nm-2430 nm at the pump wavelength 1064 nm with power range of −40 dB. • The broadband SC appears in 1235 nm-3470 nm at the pump wavelength 1550 nm with power range −43 dB. • The flat SC with power range −26.8 ∼ -18.6 dB is obtained in 1331 nm-2315 nm at a pump wavelength 1080 nm. This paper proposes an Interlayer Air-hole Photonic Crystal Fiber (IA-PCF) consisting of five air-hole layers with a single material, which means compatibility checking between the core and cladding material need not be required. The optical fiber is designed using COMSOL software. Further more, the dispersion, nonlinearity, effective mode area, and confinement loss characteristics of the proposed IA-PCF structure are numerically analyzed using the finite element method (FEM). The results indicate that the proposed IA-PCF has three zero dispersion wavelengths (ZDW) within 800–2400 nm. Through continuous structural optimization, a flat dispersion optimal IA-PCF with a dispersion fluctuation of ± 2.05 (ps/nm·km) in the range of 1509 nm-1955 nm is obtained. The three zero dispersion wavelengths (ZDW) of the optimal IA-PCF are 1061 nm, 1598 nm, and 1904 nm, respectively. Four input 50 fs pulses both in the normal and anomalous dispersion regimes are explored to analyze the spectral evolution process of SC in a 30 cm lenth IA-PCF. The results indicate that the continuous SC exists in the range of 750 nm-2430 nm at the pump wavelength of 1064 nm with power range of −40 dB. While the continuous broadband SC exists in the range of 1235 nm-3470 nm at the pump wavelength of 1550 nm with power range of −43 dB. In addition, a broadband, flat SC spectrum with a power range of −26.8 dB to −18.6 dB is obtained in the wavelength range of 1331 nm-2315 nm at a pump wavelength of 1080 nm. The IA-PCF provides a new structure and approach for generating a broadband, flat and SC spectrum. The supercontinuum belongs to a wide range of applications in optical communication, optical coherence tomography, optical frequency comb etc. [ABSTRACT FROM AUTHOR]

—In this work photonic crystal fibers of different cross-sectional patterns are studied. Dirac points of these various lattices are explored, propagation diagrams showing positions of the Dirac spectrums are obtained, and their application in fiber guiding is discussed. A quasi-3D FDTD simulation method, which is simpler and more efficient than a commercial 3D FDTD simulation software, is developed for photonic crystal fiber. This method is then applied to the new photonic crystal fiber proposed in [Fiber guiding at the Dirac frequency beyond photonic bandgaps, Light Sci. & App. 4 (2015) e304.]. Dirac-point guidance, which is based on Dirac localization of photons, is verified for these fibers. • Dirac point guiding exists in lattices possess triangular and inversion symmetries. • Multiple vector Dirac modes form far away from the light line. • Quasi-3D FDTD is much more efficiency than 3D FDTD in computer memory and time. • Dirac mode enables remote coupling, results in new coupling and sensing features. [ABSTRACT FROM AUTHOR]

• A Fabry–Pérot interferometer optofluidic sensor is proposed for simultaneous measurement of temperature and refractive index. • The liquid channel within microstructured optical fiber offers an ideal platform for liquid analysis with low sample consumption. • The proposed sensor enables dual-parameter measurement of temperature and refractive index based on the transfer matrix method. The majority of biology and chemistry takes place in solution, in which refractive index (RI) and temperature sensing underlie molecular detection and profiling. All-in-fiber integrated devices are uniquely suited to detecting the properties of samples, which allows liquids to flow and react in the fiber cavities. Here we use a single-hole dual-core fiber (SHDCF) based Fabry–Pérot interferometer (FPI) to simultaneously detect the refractive index and temperature of solution, with high sensitivity enhanced by the vernier effect. The inlets and outlets are built by splicing C-shaped fiber and fiber capillary between SHDCF. A detection region inside the microscopic hole of SHDCF obtained after splicing is constructed. Our method offers high sensitivities of 6851.89 nm/RIU and 0.493 nm/℃ for RI and temperature in a liquid solution, respectively. Notably, the cross-sensitivity of RI and temperature can be eliminated by constructing a transmission matrix. New in-fiber integrated ways of revealing properties of low-volume samples may have extensive potential for applications in the biological and chemical sciences. [ABSTRACT FROM AUTHOR]

• A refractive index insensitive, directional bending sensor is proposed based on microstructure optical fibre with dumbbell shape core. • Sensing characteristics of this specialty fibre based Mach-Zehnder interferometer are systematically studied and analyzed. • It displays different response to bending along x and y direction, giving out a maximum bending sensitivity of 2.57 nm/m−1 ranging of 0–3.79 m−1. • The peak wavelength is almost insensitive to the refractive index change. With the development of information society, more and more special occasions are calling for a wide range of sensors with special properties. In this work, a refractive index insensitive directional bend sensor is proposed based on a specialty microstructure optical fiber with dumbbell shape core, which works as a dual core fiber (DCF). Firstly, this specialty microstructure optical fiber with dumbbell shape core has been fabricated with self-pressurised drawing technique. Then, it has been constructed as a Mach-Zehnder interferometer (MZI) sensor. Consequently, its bend sensing characteristics has been investigated from both theory and experiment. The response of the proposed sensor to the bending evidently displays the directional dependence. In the bending along x direction, the interference peak wavelength is almost insensitive to the curvature. But the transmission is sensitive, which almost obeys the exponential function. Correspondingly, in the bending along y direction the wavelength almost linearly varies with curvature, giving out an averaged sensitivity of 2.44 nm/m−1 in the curvature range of 0–3.79 m−1. But the peak transmission fluctuates without typical principle. In addition, the response of the proposed sensor to the refractive index variation has been checked. It is found that the peak wavelength is almost insensitive to the change of refractive index from 1.33 to 1.45, and the peak transmission fluctuates without clear principle. All these results demonstrate that the proposed sensor has great potential for future internet of things (IoT) applications. [ABSTRACT FROM AUTHOR]