In this study, silica glass, optical fiber Bragg gratings (FBGs) are used for torque-induced strain monitoring in carbon fiber reinforced polymer (CFRP) hollow shafts toward the development of a methodology for structural load monitoring. Optical fibers with gratings are embedded during shaft manufacturing, by an industrial filament winding process, along different orientations with respect to its central axis and surface mounted after production. Experimental results are supported by numerical modeling of the shaft with appropriate boundary conditions and homogenized material properties. For an applied torque up to 800 Nm, the strain sensitivity of an embedded grating positioned along the reinforcing fibers’ direction winded under 55° is in the order of 3.6 pm/Nm, while this value is more than 4× times higher than the other examined orientations. The study also shows that surface-mounted optical fiber Bragg gratings along the reinforcing carbon fibers’ direction perform equally well in monitoring strains in composite shafts under torque.

A new type of all-solid, photonic bandgap fiber exhibiting a wavelength dependent guidance mechanism and second harmonic generation capabilities is presented. A silica glass microstructured optical fiber was infiltrated with 2-methyl 4-nitroaniline for creating the composite material optical fiber. This optical fiber was characterized over a broad wavelength range, revealing that a transition from photonic bandgap guidance to modified total internal reflection propagation occurs from short to longer wavelengths, attributed to the dispersion characteristics of the low Abbe number nitroaniline. Annealing post-processing was used for tuning the morphology of the solidified nitroaniline inside the capillaries of the silica glass microstructured optical fiber which increased the extinction ratio of the transmission bandgaps. This composite material optical fiber also exhibits second harmonic generation capabilities under 1064 nm laser excitation, with conversion characteristics dependent upon the packing of the nitroaniline inside the optical fiber capillaries. As the pump and generated light fall into different guidance regimes of the optical fiber, such a device could be potentially used as an all optical gate or light conversion device.

An accurate (≤5°) and straightforward implementation optical method for determining the azimuthal lattice orientation of a microstructured optical fiber with respect to the side illumination beam used for Bragg grating recording is presented. This method is based on the diffraction pattern generated backward of the photonic crystal fiber cladding upon a continuous-wave visible laser light illumination. This optical fiber alignment and coordination method is experimentally demonstrated, describing in detail characteristic light scattering patterns used for the azimuthal orientation of the fiber with respect to the side-coming laser beam. Moreover, this alignment method is theoretically validated using standard ray tracing beam scattering software. Bragg grating recordings performed in this photonic crystal fiber (PCF) using 193-nm excimer laser radiation are also presented to depict the impact of the azimuthal alignment of the fiber with the inscription beam on the photosensitivity refractive index changes induced in the optical fiber.

A hybrid, microstructured optical fiber (MOF) comprised of a silica glass, endlessly single mode optical fiber infiltrated with 2-methyl, 4-nitroaniline (MNA) is subjected to electric field poling for enhancing non-linear wavelength conversion properties. Different poling conditions (temperature, and electric field) are applied, resulting in significant changes manifested in the transmittance and second harmonic generation (SHG) behavior of this hybrid optical fiber. The origins material and guidance changes induced by the electric poling are investigated by scanning electron microscopy, back-scattered SHG microscopy and modal imaging as a function of the polarization state of a 1064nm, pulsed laser pump. Results show that the improved crystallinity, induced by the poling of the MNA material infiltrated into the MOF capillaries surrounding the optical fiber core, play a dominant role in both SHG efficiency and the transmission performance of these hybrid optical fibers, opening new prospects in the development of in-fiber light switching and wavelength conversion devices.