Design and analysis of highly sensitive solid core gold-coated hexagonal photonic crystal fiber sensor based on surface plasmon resonance

In this article, a surface plasmon-based hexagonal photonic crystal fiber sensor is numerically computed and studied. Metallic layer thickness and lattice period are optimized to 30 nm and 1.75 µm respectively to enhance the sensor performance. Sensor sensitivity is obtained by employing the finite element method by enclosing the structure with a perfectly matched layer. This studied sensor uncovers the wavelength sensitivity of 8000nm/RIU, amplitude sensitivity of 3959 /RIU, and minimum detection ability of 1.25x10− 5 RIU for the analyte refractive index range from 1.36 to 1.40. The simulated results’ variations are also analyzed by altering the metallic layer thickness, lattice period, and air hole diameter. The computed PCF sensor might be a promising aspirant in the area of chemical sensing, bio-molecule detection, and biological sample recognition.

Effect of Hole Shift on Threshold Characteristics of GaSb-Based Double-Hole Photonic-Crystal Surface-Emitting Lasers

Photonic-crystal (PC) surface-emitting lasers (SELs) with double-hole structure in the square-lattice unit cell were fabricated on GaSb-based type-I InGaAsSb/AlGaAsSb heterostructures. The relative shift of two holes was varied within one half of the lattice period. We measured the lasing wavelengths and threshold pumping densities of 16 PC-SELs and investigated their dependence on the double-hole shift. The experimental results were compared to the simulated wavelengths and threshold gains of four band-edge modes. The measured lasing wavelength did not exhibit switching of band-edge mode; however, the calculated lowest threshold mode switched as the double-hole shift exceeded one quarter of the lattice period. The identification of band-edge lasing mode revealed that modal gain discrimination was dominated over by its mode wavelength separation.

Тепловое расширение кристаллов Pb-=SUB=-1-x-=/SUB=-Cd-=SUB=-x-=/SUB=-Te

The values of the lattice period and the linear coefficient of thermal expansion (alfa) of Pb1-xCdxTe solid solutions are determined depending on the cadmium content and temperature using high-temperature X-ray diffractometry. Аn increase in the concentration of cadmium in Pb1-xCdxTe in the range x = 0.02–0.08 leads to a significant increase in the linear coefficient of thermal expansion. A change in temperature range T = 293–673 K leads to decrease in the linear coefficient of thermal expansion. Besides, an increase in temperature does not affect the value alfa of the undoped PbTe in the indicated temperature range.

Twist-angle dependence of moiré excitons in WS2/MoSe2 heterobilayers

Moiré lattices formed in twisted van der Waals bilayers provide a unique, tunable platform to realize coupled electron or exciton lattices unavailable before. While twist angle between the bilayer has been shown to be a critical parameter in engineering the moiré potential and enabling novel phenomena in electronic moiré systems, a systematic experimental study as a function of twist angle is still missing. Here we show that not only are moiré excitons robust in bilayers of even large twist angles, but also properties of the moiré excitons are dependant on, and controllable by, the moiré reciprocal lattice period via twist-angle tuning. From the twist-angle dependence, we furthermore obtain the effective mass of the interlayer excitons and the electron inter-layer tunneling strength, which are difficult to measure experimentally otherwise. These findings pave the way for understanding and engineering rich moiré-lattice induced phenomena in angle-twisted semiconductor van der Waals heterostructures.

Endlessly single-mode photonic crystal fiber with high birefringence for sensing applications

A novel type of highly birefringent photonic crystal fiber is designed, which yields to promise a very large birefringence [Formula: see text] with flat dispersion at the operating wavelength 1550 nm. By employing the FDTD method, other properties, such as dispersion, walk-off effect and [Formula: see text]-parameters, are highly optimized using lattice period of air holes.

Структурные, оптические и фоточувствительные свойства пленок PbS, осажденных в присутствии CaCl-=SUB=-2-=/SUB=-

Polycrystalline lead-sulfide (PbS) films doped with calcium are synthesized on sitall and glass substrates by chemical bath deposition with the use of thiocarbamide and a CaCl_2 additive at concentrations of up to 5 mM. Introduction of the CaCl_2 additive into the reaction solution greatly prolongs the induction period of the process of synthesis. The thicknesses of the PbS and PbS(Ca) films are, correspondingly, 200 and 150 nm at an average crystallite dimension of ~100 nm. The maximum calcium content in the films is 0.06 at % for layers on sitall substrates and 0.11 at % for layers on glass substrates. Doping with calcium does not influence the crystal structure of lead sulfide (the cubic B 1 structure, space group Fm 3 $$\bar {m}$$ ) but brings about an increase in the crystal-lattice period from a = 0.59343(2) nm to a = 0.59413(1) nm, an increase in microstrains, and partial ordering of the crystallites forming the film. Upon the introduction of calcium, the band gap decreases from E _ g = 0.40 eV at 295 K (0.38 eV at 90 K) to E _ g = 0.38 eV (0.37 eV). The introduction of up to 5 mM of CaCl_2 into the reaction mixture increases the voltage–power sensitivity of the films by a factor of ~1.7, which is attributed to oxygen-containing compounds formed in the films as a result of the increase in the induction period of the process of synthesis.