30cm of spatial resolution using pre-excitation pulse BOTDA technique

A pre-excitation pulse technique in Brillouin optical time domain analysis (PP-BOTDA) for enhancement of the spatial resolution is shown. The technique here exposed is based on the pre-excitation of the stimulated Brillouin scattering and the subtraction of the Brillouin scattering due to the intensity dc level present in the optical pulse. A main optical pulse with 3ns of duration followed by a pulse of 40ns and half the intensity of the main one are used for obtaining 30cm of spatial resolution. The spatial range is 3600m on a standard single mode optical fiber

Quasi-distributed liquid level measurement with adaptable optical fiber transducers

A level and flexible quasi-distributed liquid sensor based on the changes in the light transmittance in a plastic optical fiber cable is proposed. The measurement points are constituted by small areas created by side-polishing on a curved fiber and the removal of a portion of the core. These points are distributed and adapted on each full-turn of a spire of fiber built on a cylindrical tube vertically positioned in a tank. The changes between the refractive indexes of air and liquid generate a signal power proportional to the position and level of the liquid. The sensor system was successfully demonstrated in the laboratory and experimental results of three prototypes with 10, 8, and 5 measurement points and with bend radius of 5mm are presented in this paper

Comparative experimental study of a high-temperature raman-based distributed optical fiber sensor with different special fibers

An experimental study of a high temperature distributed optical fiber sensor based on Raman Optical-Time-Domain-Reflectometry (ROTDR) (up to 450 °C) and optical fibers with different coatings (polyimide/carbon, copper, aluminum and gold) is presented. Analysis of the distributed temperature sensor (DTS) measurements determined the most appropriate optical fiber to be used in high temperature industrial environment over long periods of time. To demonstrate the feasibility of this DTS for an industrial application, an optical cable was designed with the appropriate optical fiber and it was hermetically sealed to provide the required mechanical resistance and isolate the fiber from environmental degradations. This cable was used to measure temperature up to 360 °C of an industrial furnace during 7 days.This work has been supported by the Spanish Government through the Ministry of Economy and Competitiveness project TEC2016-76021-C2-2-R, AEI/FEDER (UE) and ENSA through the FACON project

Switchable dual-wavelength mode-locked fiber laser source for in-PCF parametric frequency conversion applied to CARS microscopy

A self-started, switchable dual-wavelength allpolarization-maintaining mode-locked (ML) fiber laser for optical parametric generation (OPG) in photonic crystal fiber (PCF) applied to coherent anti-stokes Raman scattering (CARS) microscopy is reported in this paper. The complete laser setup is built in an all-fiber structure composed of commercial elements. It is based on a linear cavity with an active medium-namely, Ytterbium-doped fiber (YDF), a pair of fiber Bragg gratings as switchable partial mirrors between 1031.5 and 1049.7 nm, and a semiconductor saturable absorber mirror functioning also as the mode-locking device. The seed laser is amplified to 650 mW average power by two YDF amplifiers. The source delivers a pulse-train output of 30.9 ps at 1031.5 ps and 31.6 ps at 1049.7, a 3.1-MHz repetition rate, and over 200 nJ pulse energy and 6 kW of peak power at fundamental ML operation. The properties of this switchable dual-wavelength source ensures the correct OPG by degenerated four-wave mixing in PCF fulfilling the phase matching condition which corresponds to CARS resonance of 2850 cm -1 (CH3-O molecular bonds) at 1031.5 nm and 1475 cm -1 (CH2 δ molecular bonds) at 1049.7 nm.This work was supported by the Spanish Comisión Interministerial de Ciencia y Tecnología within project TEC2016-76021-C2—R and Feder funds and the Spanish Ministry of Education and Culture, within the scholarship FPU14/02196

Optimal design and implementation of a temperature and strain optical transducer using FBGs and fiber taper hybrid structure

A temperature and strain optical fiber transducer and its optimal design are presented. The hybrid structure is composed of two Fiber Bragg Gratings (FBG) in a fused taper. Using the same phase mask one of the FBG is written outside of the taper, and the other one in the middle of the taper, in the area with constant diameter. The taper diameter and the structure length play a key role on the transducer behaviour. Useful results to optimize the transducer structure design, from a theoretical and experimental investigation, are reported in this paper

Broadband continuously tunable all-fiber laser based on OPG for CARS imaging

A broadband continuously tunable SESAM all-fiber laser based on optical parametric generation (OPG) for Coherent anti-Stokes Raman Scattering (CARS) imaging applications is presented in this article. This laser structure is built on all-polarization maintaining fibers yielding high environmental stability. The OPG is based on PM photonic crystal fiber as parametric gain pumped by a wavelength-tunable (1025 nm to 1055 nm) and repetition rate-tunable (3 MHz to 500 KHz) Yb-doped pulsed fiber laser. The all-fiber structure features free polarization adjustment in slow-axis tunable operation with a wavelength range from 770 to 940 nm for signal radiation and 1225 to 1510 nm for idler radiation. The pump and signal pulses (CARS-Stokes and CARS-pump respectively) are intrinsically overlapped, both spatially and temporarily, due to the four-wave mixing (FWM) generation and emitted from a single fiber end. The CARS-Stokes and CARS-pump pulse duration vary between 25 to 32 ps and 21 to 24 ps respectively in the whole band, ensuring a good overlap of the generated signals, and both exhibit a Gaussian profile with high spatial beam quality. The frequency conversion allows to obtain a frequency difference between the generated signals from 1100 to 3300 cm-1. The reported low-cost laser source is ideal for bio-imaging applications, especially in CARS imaging, due to its compactness, simplicity, robustness and ease of handling. A patent has been filed based on this technology.This work was supported by the Spanish Comisión Interministerial de Ciencia y Tecnología within project TEC2016-76021-C2-2-R (AEI/FEDER, UE) and project PID2019-107270RB-C21/AEI/10.13039/501100011033

Comparison between a symmetric bidirectional-pumping and a unidrectional-pumping configurations in an erbium fiber ring laser

An experimental comparative study between two wide-band wavelength-tunable erbium doped fiber ring lasers (EDFRLs) with the same active fiber length but with two different pumping configuration (forward unidirectional pumping and symmetric bidirectional pumping) is reported in this paper. Both fiber lasers cover almost the whole C-band and L-band with a single setup laser. The signal wavelength can be tuned in a wide range of 60 nm with the two presented lasers. Nevertheless, experimental results verify that a higher output power is obtained with the bidirectional pump configuration

Tunable fiber laser using concatenated non-adiabatic single-mode fiber tapers

An erbium doped fiber ring laser (EDFRL) that incorporates four non-adiabatic concatenated single-mode fiber tapers (acting as tunable filter in the laser cavity) is presented. These concatenated fiber tapers integrates a filter with a narrower band-pass and a higher modulation depth than a single taper. The tuning of this filter was implemented applying a controlled perturbation in the fiber taper. The proposed laser architecture was successfully demonstrated in the laboratory in which a tuning range of 20.8nm (1544.5nm-1565.3nm) were measured

Strain and temperature transducer based in FBG and tapers: design and implementation

RESUMEN: Se presenta el diseño, optimización, implementación y comprobación practica de un transductor de deformación y temperatura basado en redes de difracción en fibra óptica y fibras estrechadas. Usando una única mascara de fase se graban dos redes de difracción con el mismo periodo, cada una en una zona de la fibra estrechada con diferente diámetro, pero constante. Tanto la longitud del transductor como el diámetro mínimo de la zona estrechada de la fibra determinan el comportamiento y prestaciones del transductor. En el artículo se estudia teóricamente como es esa influencia, para posteriormente corroborar de manera práctica las conclusiones obtenidas.ABSTRACT: A temperature and strain optical fiber transducer and its optimal design are presented. The hybrid structure is composed of two Fiber Bragg Gratings (FBG) in a fused taper. Using the same phase mask one of the FBG is written outside of the taper, and the other one in the middle of the taper, in the area with constant diameter. The taper diameter and the structure length play a key role on the transducer behavior. Useful results to optimize the transducer structure design, from a theoretical and experimental investigation, are reported in this paper

Angle transducer based on fiber Bragg gratings able for tunnel auscultation

In this paper an angle transducer based on Fiber Bragg Grating (FBG) is presented. Two gratings are glued to a metallic platen, one in each side. It is insensitive to temperature changes, given that the temperature shifts affect equally to both FBG. When the platen is uniformly bent an uniform strain appears in both sides of the platen. It depends on the bend angle and the platen length and thickness. The transducer has been designed to be used in the auscultation of tunnels during their construction process and during their live time. The transducer design and its characterization are presented