RESUMEN
Experimental optimization of all fiber Mach-Zehnder interferometers based on concatenated tapers is presented. The experimental optimization was realized by the application of the four parameters Taguchi algorithm, and the insertion loss of comb filters operating around the 1064 nm wavelength was taken as the parameter to be optimized. The out of band losses were reduced from around 2.5 dB (43.7%) to a minimum of 0.45 dB (9.84%) in one case, and from 2.9 (48.71%) to 0.4 dB (8.79%) by using a fixed tapers pair's geometry with 1 mm×1 mm×1 mm of up-taper length/waist length/down-taper length, respectively, and a waist diameter of 40 µm.
RESUMEN
A compact, highly sensitive optical fiber displacement and curvature radius sensor is presented. The device consists of an adiabatic bi-conical fused fiber taper spliced to a single-mode fiber (SMF) segment with a flat face end. The bi-conical taper structure acts as a modal coupling device between core and cladding modes for the SMF segment. When the bi-conical taper is bent by an axial displacement, the symmetrical bi-conical shape of the tapered structure is stressed, causing a change in the refractive index profile which becomes asymmetric. As a result, the taper adiabaticity is lost, and interference between modes appears. As the bending increases, a small change in the fringe visibility and a wavelength shift on the periodical reflection spectrum of the in-fiber interferometer is produced. The displacement sensitivity and the spectral periodicity of the device can be adjusted by the proper selection of the SMF length. Sensitivities from around 1.93 to 3.4 nm/mm were obtained for SMF length between 7.5 and 12.5 cm. Both sensor interrogations, wavelength shift and visibility contrast, can be used to measure displacement and curvature radius magnitudes.
RESUMEN
A compact, low loss, and highly sensitive optical fiber curvature sensor is presented. The device consists of a few-millimeter-long piece of seven-core fiber spliced between two single-mode fibers. When the optical fiber device is kept straight, a pronounced interference pattern appears in the transmission spectrum. However, when the device is bent, a spectral shift of the interference pattern is produced, and the visibility of the interference notches changes. This allows for using either visibility or spectral shift for sensor interrogation. The dynamic range of the device can be tailored through the proper selection of the length of the seven-core fiber. The effects of temperature and refractive index of the external medium on the response of the curvature sensor are also discussed. Linear sensitivity of about 3000 nm/mm(-1) for bending was observed experimentally.
RESUMEN
Fiber filters based on periodic cascaded tapered fiber sections are demonstrated. The filters consist of up to seven tapered sections separated periodically by more than 3 mm from center to center, with nominal tapered sections of 1 mm×1 mm×1 mm longitudinal dimensions. The transmission spectrum consists of discrete notches, resembling those observed in long-period fiber gratings, which differs from the observed spectrum in Mach-Zender interferometers based on cascaded tapers. Its sensitivity to external perturbations, such as refractive index or mechanical stress, made the device potentially very useful as a sensor or tunable filter.
RESUMEN
We report on a functional optical microfiber mode interferometer and its applications for absolute, temperature-insensitive refractive index sensing. A standard optical fiber was tapered down to 10 µm. The central part of the taper, i.e., the microfiber, is connected to the untapered regions with two identical abrupt transitions. The transmission spectrum of our device exhibited a sinusoidal pattern due to the beating between modes. In our interferometer the period of the pattern-an absolute parameter-depends strongly on the surrounding refractive index but it is insensitive to temperature changes. The period, hence the external index, can be accurately measured by taking the fast Fourier transform (FFT) of the detected interference pattern. The measuring refractive index range of the device here proposed goes from 1.33 to 1.428 and the maximum resolution is on the order of 3.7×10(-6).
RESUMEN
A low-loss, compact, and highly sensitive optical fiber curvature sensor is presented. The device consists of two identical low-loss fused fiber tapers in tandem separated by a distance L. When the optical fiber is kept straight and fixed, no interference pattern appears in the transmitted spectrum. However, when the device is bent, the symmetry of the straight taper is lost and the first taper couples light into the cladding modes. In the second taper, a fraction of the total light guided by the cladding modes will be coupled back to the fundamental mode, producing an interference pattern in the transmitted spectrum. As the fiber device is bent, visibility of the interference fringes grows, reaching values close to 1. The dynamic range of the device can be tailored by the proper selection of taper diameter and separation between tapers. The effects of temperature and refractive index of the external medium on the response of the curvature sensor is also discussed.
