Temperature and pressure sensitivities of the highly birefringent photonic crystal fiber with core asymmetry

We investigated a particular design of a highly birefringent PCF with attractive features for pressure sensing applications. A plane-wave method together with the finite element method were used to numerically calculate phase and group modal birefringence, pressure and temperature sensitivities of our fiber. The simulation results together with the experiments demonstrate a considerable difference between a very high phase birefringence (B ∼ 10⁻³) and a very low negative group birefringence (G −10⁻³). Our fiber exhibits a low and positive temperature sensitivity (K_T < 0.1 rad/(K⋅m)), and relatively high and negative mechanical (pressure) sensitivity (K_p ≤ −10 rad/(MPa⋅m)), which supports its possible use as a mechanical sensor that does not require any temperature compensation.     

Birefringent photonic crystal fibers with zero polarimetric sensitivity to temperature

We designed, fabricated, and characterized birefringent holey fibers with zero polarimetric sensitivity to temperature. The sensitivity measurements were carried out in a wide spectral range of 0.68–1.55 μm in fibers with different hole and pitch values and with birefringence induced by a pair of large holes adjacent to the core. Our results show that zero sensitivity to temperature can be obtained at certain wavelengths for the bare fibers with properly adjusted geometrical parameters. Moreover, the spectral measurements of the sensitivity to temperature are in good agreement with the modeling results for all the investigated fibers.     

Long period gratings and rocking filters written with a CO2 laser in highly-birefringent boron-doped photonic crystal fibers for sensing applications

In this work, we demonstrate the possibility of fabricating short-length long-period gratings and rocking filters in highly birefringent Photonic Crystal Fiber using a CO₂ laser. In our experiments both kinds of gratings were made in the same Boron doped highly birefringent PCF using similar exposure parameters. We also present the sensing capabilities of both fabricated gratings to temperature, strain and hydrostatic pressure by interrogation of the wavelength shifts at different resonances.     

Measurements of sensitivity to hydrostatic pressure and temperature in highly birefringent photonic crystal fibers

We report on experimental studies of polarimetric sensitivity to hydrostatic pressure and temperature in two highly birefringent index guided photonic crystal fibers, in which birefringence is induced by one row of the cladding holes with diameters smaller than the other cladding holes. The sensitivity measurements were carried out in the spectral range from 0.6 μm to 1.6 μm. Our results show that absolute value of the polarimetric sensitivity to hydrostatic pressure can reach 23 rad/MPa × m, which is almost one order of magnitude higher than in conventional fibers with elliptical core. Simultaneously, polarimetric sensitivity to temperature is at least two orders of magnitude lower than in conventional highly birefringent fibers. Moreover, we proved experimentally that one of the investigated fibers is completely insensitive to temperature at certain wavelength.     

Influence of the core size on light propagation in photonic liquid crystal fibers

In this paper analyses of mode distribution, confinement and experimental losses of the photonic crystal fibers with different core sizes infiltrated with liquid crystal are presented. Four types of fibers are compared: with single-, seven-, nineteen- and thirty seven solid rods forming the core in the same hexagonal lattice of seven “rings” of unit cells (rods or capillaries). The experimental results confirming the influence of the core diameter on light propagation are also included. The diameter of cores determines not only the number of modes in the photonic liquid crystal fiber but also is correlated with experimentally observed attenuation. For fibers with larger cores confinement losses are expected to be higher, but the measured attenuation is smaller because the impact of liquid crystal material losses and scattering is smaller.     

Preparation and physicochemical characterisation of functionalised multi-walled carbon nanotubes

A series of new functionalised carbonaceous materials were prepared by means of oxidation and ammoxidation of commercially available multi-walled carbon nanotubes. The effect of oxygen and nitrogen doping on the textural, surface as well as thermal properties of the prepared adsorbents was tested. The materials were characterized by elemental analysis, low-temperature nitrogen sorption, determination of the surface oxygen groups content as well as by coupled thermogravimetric and spectroscopic methods (TG/DSC/MS). Depending of the variant of raw nanotubes modification, the final products were oxygen- and nitrogen-doped materials of medium-developed surface area and mesoporous structure, showing highly diverse acidic-basic character of the surface, from the weakly acidic to slightly alkaline.     

D-shape polymer optical fibres for surface plasmon resonance sensing

We experimentally studied three different D-shape polymer optical fibres with an exposed core for their applications as surface plasmon resonance sensors. The first one was a conventional D-shape fibre with no microstructure while in two others the fibre core was surrounded by two rings of air holes. In one of the microstructured fibres we introduced special absorbing inclusions placed outside the microstructure to attenuate leaky modes. We compared the performance of the surface plasmon resonance sensors based on the three fibres. We showed that the fibre bending enhances the resonance in all investigated fibres. The measured sensitivity of about 610 nm/RIU for the refractive index of glycerol solution around 1.350 is similar in all fabricated sensors. However, the spectral width of the resonance curve is significantly lower for the fibre with inclusions suppressing the leaky modes.     

Methodology of splicing large air filling factor suspended core photonic crystal fibres

We report the methodology of effective low-loss fusion splicing a photonic crystal fibre (PCF) to itself as well as to a standard single mode fibre (SMF). Distinctly from other papers in this area, we report on the results for splicing suspended core (SC) PCF having tiny core and non-Gaussian shape of guided beam. We show that studied splices exhibit transmission losses strongly dispersive and non-reciprocal in view of light propagation direction. Achieved splicing losses, defined as larger decrease in transmitted optical power comparing both propagation directions, are equal to 2.71 ±0.25 dB, 1.55 ±0.25 dB at 1550 nm for fibre SC PCF spliced to itself and to SMF, respectively.