Optimization of pump absorption in MOF lasers via multi-long-period gratings: design strategies

Brillouin-like amplification in rare-earth-doped optical fibers

We present a theoretical formalism to describe the amplification of two monochromatic waves counter-propagating in a rare-earth-doped optical fiber amplifier. Interaction of the waves through a dynamical population inversion grating inscribed in the active fiber by the waves during their amplification results in a strong power transfer from one wave to another providing a preferable amplification of one wave at the expense of another. In this sense, the effect is similar to stimulated Brillouin scattering and is expected to be observed with both pumped and unpumped rare-earth-doped fibers possessing a finite polarizability difference between the excited and ground states.

NiRu nanoparticles encapsulated in a nitrogen-doped carbon matrix as a highly efficient electrocatalyst for the hydrogen evolution reaction

The design and fabrication of low-cost, efficient, and robust electrocatalysts for the hydrogen evolution reaction (HER) is of great importance in accelerating the development of water electrolysis technology. Herein, NiRu alloy nanostructures embedded in a nitrogen-doped carbon matrix (NiRu@NC) have been fabricated through a facile metal-organic framework-derived (MOF-derived) strategy. Benefiting from their advantages in the unique structures and components, the resulting NiRu@NC possesses excellent activity and durability towards the HER, which exhibits low overpotentials of 85 and 53 mV at a current density of 10 mA cm-2 in acidic and alkaline electrolytes, respectively. Furthermore, NiRu2@NC-600 also exhibits excellent hydrogen oxidation reaction (HOR) activity in an alkaline electrolyte. Therefore, this work provides a facile MOF-derived strategy for the design and synthesis of low-cost and efficient electrocatalysts for the HER.

Advances on Photonic Crystal Fiber Sensors and Applications

In this review paper some recent advances on optical sensors based on photonic crystal fibres are reported. The different strategies successfully applied in order to obtain feasible and reliable monitoring systems in several application fields, including medicine, biology, environment sustainability, communications systems are highlighted. Emphasis is given to the exploitation of integrated systems and/or single elements based on photonic crystal fibers employing Bragg gratings (FBGs), long period gratings (LPGs), interferometers, plasmon propagation, off-set spliced fibers, evanescent field and hollow core geometries. Examples of recent optical fiber sensors for the measurement of strain, temperature, displacement, air flow, pressure, liquid-level, magnetic field, and hydrocarbon detection are briefly described.

Electromagnetic Modelling of Fiber Sensors for Low-Cost and High Sensitivity Temperature Monitoring

An accurate design of an innovative fiber optic temperature sensor is developed. The sensor is based on a cascade of three microstructured optical fibers (MOFs). In the first one a suitable cascade of long period gratings is designed into the core. A single mode intermediate and a rare-earth activated Fabry-Perot optical cavity are the other two sensor MOF sections. An exhaustive theoretic feasibility investigation is performed employing computer code. The complete set-up for temperature monitoring can be obtained by utilizing only a low cost pump diode laser at 980 nm wavelength and a commercial optical power detector. The simulated sensitivity S = 315.1 μW/°C and the operation range ΔT = 100 °C is good enough for actual applications.

Fabrication of fiber optic long period gratings operating at the phase matching turning point using an ultraviolet laser

It is known that optical fiber long period gratings (LPGs) exhibit their highest sensitivity to environmental perturbation when the period is such that the phase matching condition is satisfied at its turning point. The reproducible fabrication of LPGs with parameters satisfying this condition requires high resolution control over the properties of the grating. The performance of an LPG fabrication system based on the point-by-point UV exposure approach is analyzed in this paper, and the control of factors influencing reproducibility, including period, duty cycle, and the environment in which the device is fabricated, is explored.

Narrow bandwidth and polarization independent design of hollow waveguide in-plane mirror with ultrawide tuning-range

A design of an integrated widely tunable in-plane micro-optical mirror based on a hollow waveguide (HWG) consisting of a high index contrast grating (HCG) and a dielectric multilayer distributed Bragg reflector (DBR) is proposed. The in-plane mirror is formed in a variable air-core HWG by loading a SiO(2) Bragg grating on the multilayer (DBR) mirror. Ultrawide tuning of 161 and 150 nm in Bragg wavelengths of TE and TM mode, respectively are reported in simulation with a simple tuning scheme and a single tuning parameter of variable air core. The presence of HCG in the proposed design causes a reduction from 88 nm (for DBR-DBR) to 48 nm (for HCG-DBR) in the 3 dB reflection-bandwidth of the proposed in-plane mirror. Also, a four-time reduction in the difference in the reflectivity of the Bragg wavelengths of TE and TM modes is reported because of the introduction of HCG into the hollow waveguide. The reflections of orthogonal polarizations and hence the polarization characteristics of the in-plane mirror are controlled by the combined effect of HCG and DBR.

Bend measurement using an etched fiber incorporating a fiber Bragg grating

A fiber Bragg grating (FBG) based bend measurement method using an etched fiber is proposed that utilizes the coupling of the core mode to the cladding and radiation modes at the bending region. An etching region of 99 µm diameter that serves as bend sensing head is achieved at 10 mm upstream the FBG through processing in 40% hydrofluoric acid, while the FBG acts as a narrowband reflector to enhance the sensitivity. The power variation curves are obtained for a wide range of bend angles, but the performance is limited due to the presence of the loss peaks. The sensing response is improved by immersing the etching region in a refractive index matching gel. The results are analyzed by using curve fitting formulas and are in good agreement. A large dynamic range of -27° to +27° and sensitivity of 0.43 dBm/deg is achieved, which can be enhanced by reducing the etched diameter.