Kay Schuster

All Fiber Mach–Zehnder Interferometer Based on Suspended Twin-Core Fiber

An all fiber Mach-Zehnder interferometer using suspended twin-core fiber is described. Due to the birefringence of the fiber cores, two interferometers are obtained when the fiber is illuminated by a polarized light. Applying curvature or temperature to the sensing head, different sensitivities are observed. In order to discriminate curvature from temperature in the suspended twin-core fiber Mach-Zehnder sensor, the matrix method is used.

Temperature- and strain-independent torsion sensor using a fiber loop mirror based on suspended twin-core fiber

In this Letter, we present a fiber loop mirror configuration based on a suspended twin-core fiber for sensing applications. Using the suspended twin-core fiber, the fringe pattern is due to the differential optical patch of the light in the two cores associated with a refractive index difference of approximately 10(-3), which indicates an advantage of this approach compared with those based on high-birefringent fibers, namely, the possibility of using a small length of fiber. The sensing configuration was characterized for torsion, temperature, and strain. Using the fast Fourier transform technique, it is possible to obtain measurand-induced amplitude variations of the fringe pattern. The results obtained indicate the viability of a temperature- and strain-independent torsion sensor.

Fabry–PÉrot Cavity Based on a Suspended-Core Fiber for Strain and Temperature Measurement

A fiber-optic Fabry-Perot sensing structure based on the utilization of a suspended-core fiber is presented. The interferometric structure is formed when a small length of the suspended-core fiber is spliced to the end of a standard single-mode fiber. The interfering waves are generated by the refractive-index mismatches between the two fibers in the splice region and at the end of the suspended-core fiber. Thermal and strain responses of two different sensing heads associated with suspended-core fibers with three and four holes are characterized.

High-reflectivity draw-tower fiber Bragg gratings—arrays and single gratings of type II

Fiber Bragg gratings (FBG) were manufactured during the fiber drawing process [draw tower grating (DTG)] with excellent reflectivity values. This was done in the region of 1550 nm by single pulses of a 248-nm excimer laser applied during the fiber drawing process of single mode fibers. An improved setup for the writing process and special photosensitive fibers enable the manufacture of type I DTG arrays with a reflectivity of up to 40% and type II DTGs with a reflectivity near 100%. Details of the setup and results of the DTG arrays and DTGs of type II are reported.

Fabry–Perot cavity based on a diaphragm-free hollow-core silica tube

A Fabry-Perot (FP) cavity of simple design and based on a pure silica diaphragm-free hollow tube is proposed. Its operation is based on a first reflection of light at the end of the single-mode fiber that illuminates the silica rod and in a second reflection that takes place at the end of the rod. The FP cavity is characterized for high temperature, pressure and refractive index sensing, showing useful characteristics for the measurement of these three parameters. The diaphragm-free configuration simplifies the measurement of the refractive index of fluids.

High precision micro-displacement fiber sensor through a suspended-core Sagnac interferometer

A sensing system for micro-displacement measurement based in a suspended-core fiber Sagnac interferometer is presented. The suspended-core fiber characterization was made through the use of an optical backscatter reflectometer, screening its multimodal and birefringent behavior. Its sensitivity to displacement measurements is shown to be due only to birefringence, being that core-cladding mode coupling is negligible. High precision (~0.45 μm) was obtained using three different measurement instruments, showing an extremely high stability and high insensitivity to temperature, demonstrating that the sensing system has the ability for low cost applications.

Temperature Fiber Laser Sensor Based on a Hybrid Cavity and a Random Mirror

In the present work, a simple temperature fiber laser sensor configuration is proposed. The temperature fiber laser sensor is based in the combination of a Fabry-Perót hybrid cavity and a random mirror. The Fabry-Perót hybrid cavity is fabricated by splicing a single mode fiber with a small piece of suspended-core fiber. The random mirror is created by multiple Rayleigh scattering events running along the dispersion compensation fiber, as a direct consequence of Raman gain in this fiber. In the proposed configuration, the Fabry-Perót cavity presents simultaneously a double function: laser reflective mirror and temperature sensing cavity. The proposed temperature fiber laser sensor presents maximum output power of ~4 mW in a 15nm wavelength range while providing a temperature sensibility of ~6 pm/°C, in a 200°C temperature range.

Whispering gallery mode microsphere resonator integrated inside a microstructured optical fiber

Here we report on a novel in-fiber microresonator coupler, which combines a microstructured optical fiber (MOF) and a polystyrene microsphere (PM), embedded into one of its empty capillaries. The MOF consists of a germanium-doped silica core (~2.5 m), suspended within three hollow channels with a maximum dimension of ~11 m. The microsphere has a diameter of 10.4 m and a refractive index n=1.59 at 589 nm. After selection of a single PM from a glass micropipette and its controllable infiltration inside the fiber capillary with the help of a liquid solvent, the microsphere is placed inside the MOF, in contact with the core, ~3 cm from the fiber endface. The operation of the coupler when radiation is guided along the fiber has been investigated under two different launch/collection schemes, i.e. in the core-input/sphere-output (C/S) and the sphere-input/core-output (C/S) mode.

Multicore fiber with integrated fiber Bragg gratings for background-free Raman sensing

In the last years a variety of fiber optic Raman probes emerged, which are only partly suited for in vivo applications. The in vivo capability is often limited by the bulkiness of the probes. The size is associated with the required filtering of the probes, which is necessary due to Raman scattering inside the fibers. We employed in-line fiber Bragg gratings (FBG) as notch filter for the collection path and integrated them in a novel type of Raman probe. Multicore singlemode fibers (MCSMF) were designed and drawn integrating 19 singlemode cores to achieve better collection efficiency. A Raman probe was assembled with one excitation fiber and six MCSMF with inscribed FBGs as collection fibers. The probe was characterized regarding Raman background suppression, collection efficiency, and distance dependence. First Raman measurements on brain tissue are presented.

Inner cladding microstructuration based on symmetry reduction for improvement of singlemode robustness in VLMA fiber

Very large mode area, active optical fibers with a low high order mode content in the actively doped core region were designed by removing the inner cladding symmetry. The relevance of the numerical approach is demonstrated here by the investigation of a standard air-silica Large Pitch Fiber, used as a reference. A detailed study of all-solid structures is also performed. Finally, we propose new kinds of geometry for 50 μm core, all-solid microstructured fibers enabling a robust singlemode laser emission from 400 nm to 2200 nm.