Single-to-four core optical fiber coupling using a two-photon polymerization produced waveguide.

Optical coupling between single core to multi-core optical fibers usually takes place by means of optical fiber fan-ins / fan-outs, delicate free space optics, or laser inscribed freeform waveguides. In the present work, the two-photon polymerization technique is used for the first time to create a waveguide manifold on top of a four-core optical fiber tip as a means to couple light into and from a single core optical fiber, in a fast and low-cost fashion. It is demonstrated that the performance is influenced by the numerical aperture mismatch between the fabricated and the coupled waveguides. Insertion losses below 5 dB are observed when the numerical aperture mismatch is minimized, with further reduction potential, making this approach applicable to sensing or tweezer applications.

Optically formed rubbery waveguide interconnects.

Light induced self-written waveguides (LISWs) with unique elongation characteristics and low optical loss are formed in a monodispersed polyisoprene solution using a low-power laser photopolymerization process, while their light transmission characteristics are exemplified in the flexible interconnection of two single-mode optical fibers operating in the visible/near infrared wavelengths. The LISWs formed exhibit rubbery properties, allowing extensibilities upon cases from 400% to 800%, while still retaining significant optical transmission. The rubber elasticity enables sustaining LISWs at stressed lengths longer than 500 µm propagation losses from 1.0 to 2.9 dB/mm.

Monitoring of Torque Induced Strain in Composite Shafts with Embedded and Surface-Mounted Optical Fiber Bragg Gratings.

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.

Sensitivity Analysis of Acoustic Emission Detection Using Fiber Bragg Gratings with Different Optical Fiber Diameters.

Acoustic Emission (AE) detection and, in particular, ultrasound detection are excellent tools for structural health monitoring or medical diagnosis. Despite the technological maturity of the well-received piezoelectric transducer, optical fiber AE detection sensors are attracting increasing attention due to their small size, and electromagnetic and chemical immunity as well as the broad frequency response of Fiber Bragg Grating (FBG) sensors in these fibers. Due to the merits of their small size, FBGs were inscribed in optical fibers with diameters of 50 and 80 µm in this work. The manufactured FBGs were used for the detection of reproducible acoustic waves using the edge filter detection method. The acquired acoustic signals were compared to the ones captured by a standard 125 µm-diameter optical fiber FBG. Result analysis was performed by utilizing fast Fourier and wavelet decompositions. Both analyses reveal a higher sensitivity and dynamic range for the 50 µm-diameter optical fiber, despite it being more prone to noise than the other two, due to non-standard splicing methods and mode field mismatch losses. Consequently, the use of smaller-diameter optical fibers for AE detection is favorable for both the sensor sensitivity as well as physical footprint.

A double guidance mechanism, nitroaniline based microstructured optical fiber.

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.

Differential loss magnetic field sensor using a ferrofluid encapsulated D-shaped optical fiber.

A ferrofluid immersed, D-shape optical fiber exhibits differential loss up to 12 dB with respect to an azimuthally rotating magnetic field placed around its longitudinal axis, manifested in its measured transmission power. Investigating the magneto induced refractive index and loss changes by using ferrofluid overlaid diffractive elements a differential loss mechanism is revealed, associated with the relative light polarization direction and the magnetic field application direction. The results were used for performing modal profile simulations of ferrofluid immersed D-shape optical fiber. It is demonstrated that such an optical system can act as a magnetic field sensor with field angle and intensity sensing capabilities.

Fabrication of Bragg gratings in microstructured and step index Bi-SiO2 optical fibers using an ArF laser.

An ArF excimer laser was used to fabricate Bragg gratings in fibers with Bi-SiO(2) core and microstructured or F-doped claddings without fiber presensitization. Average and modulated refractive index changes of 2.7 × 10(-4) and 1.0 × 10(-4) were induced in pristine microstructured fiber while 1.0 × 10(-4) and 0.7 × 10(-4) were observed in the F-doped-cladding fiber. Fiber luminescence was also measured under 1064 nm pumping for both fibers. Photosensitivity and luminescence were compared to a Bi-Al(2)O(3)-SiO(2) core optical fiber.

Fabrication and thermal decay of fiber Bragg gratings in pristine and H2-loaded Bi-Al co-doped optical fibers.

A cw-244-nm-Ar(+) laser was used to fabricate Bragg gratings in pristine and H(2)-loaded Bi-Al-SiO(2) optical fibers with index changes as high as 3.6 × 10(-4) and 19.3 × 10(-4), respectively. For comparison, fiber Bragg gratings in pristine and H(2)-loaded SMF-28e showed index changes of 13.6 × 10(-4) and 63.3 × 10(-4). Continuous isochronal thermal annealing revealed higher thermal stability for the H(2)-loaded Bi-Al-SiO(2) fiber compared to the pristine one. The SMF-28e fibers, with and without hydrogen, were more stable than the Bi-Al-SiO(2) fibers.