Abstract
We investigate the third-order nonlinearity of DANS and DAN2 side-chain polymers by tunable third-harmonic generation and nonlinear distributed coupling. The large third-order susceptibility can be interpreted in terms of microscopic cascading of second-order hyperpolarizabilities.

Abstract
In this work, a fibre loop mirror for the simultaneous measurement of strain and temperature is presented. The loop mirror contains a section of a small core microstructured fibre characterized for strain and temperature sensing. Due to the small core geometry and using a small section length, the structure presents high birefringence and also intermodal interference. The spectral response of this configuration shows the presence of three interferometers. One of them corresponds to the interference of light that propagates in the fast and slow axes (group birefringence) and the others are associated with the interference of light in the two lowest order spatial modes in each of the fibre eigenaxis. These interferometers present distinct sensitivities to strain and temperature for different wavelengths.

Abstract
A Temperature-independent strain sensor based on Four-Wave Mixing (FWM) using Raman fiber Bragg grating (FBG) laser sensor with cooperative Rayleigh scattering is proposed. Two FBG were used to form two linear cavities laser sensors based on Raman amplification combined with cooperative Rayleigh scattering. Due to the low dispersion coefficient of the fiber, it is possible to obtain the FWM using the two Raman FBG laser sensors. This configuration allows the operation as a temperature-independent strain sensor where both sensors are sensitive to temperature but only one of the FBG is sensitive to strain. The FWM efficiency is thus dependent on the applied strain but independent to the temperature.

Abstract
Suspended core fiber tapers with different cross sections (from 70 mu m to 120 mu m diameter) were produced by filament heating. Before obtaining the taper, the spectral behavior of the suspended core fiber presents multimode interference. When the taper is made an intermodal interference is observed. This effect is clearly visible for high taper reduction. The spectral response of the microtaper inside the suspended core fiber is similar to a beat of two interferometers. The microtaper was subjected to strain, and an increase of sensitivity with the reduction of the transverse area was observed. When the taper was immersed in liquids with different refractive indices or subjected to temperature variations, no spectral change occurred.

Abstract
Tapering single mode-multimode-single mode structures to enhance sensitivity is proposed and experimentally demonstrated. 50 mm-long coreless MMF sections are spliced between SMFs and tapered. They are characterized in strain and an increase in strain sensitivity is obtained with taper diameter reduction. Sensitivities as high as -23.69 pm/mu epsilon for the 15 mu m taper are attained. A combination of an untapered and tapered SMS is proposed as a sensing system for the simultaneous measurement of strain and temperature.

Abstract