Mikel Bravo

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.

Internal modulation of a random fiber laser

A characterization of a modulated random mirror laser has been experimentally carried out. Unlike conventional internally modulated fiber lasers, no distortion of the modulating frequency or self-mode-locking effects were measured. The behavior of the laser using pulsed and analog modulation up to 12 GHz is shown.

Suspended-core fiber Sagnac combined dual-random mirror Raman fiber laser

In the present work, a multiwavelength fiber laser based in the combination of a double-random mirror and a suspended-core Sagnac interferometer is presented. The double-random mirror acts by itself as a random laser, presenting a 30dB SNR, as result of multiple Rayleigh scattering events produced in the dispersion compensating fibers by the Raman amplification. The suspended-core fiber Sagnac interferometer provides the multi peak channeled spectrum, which can be tuned by changing the length of the fiber. The result of this combination is a stable multiwavelength peak laser with a minimum of ~25dB SNR, which is highly sensitive to polarization induced variations.

Real-Time FFT Analysis for Interferometric Sensors Multiplexing

In this paper, a theoretical and experimental study of two interferometric sensor multiplexing schemes has been carried out by means of the fast Fourier transform (FFT) analysis. This study addresses one of the main drawbacks of photonic crystal fiber (PCF) sensors, that is, its multiplexing capability. Using a commercial optical interrogator combined with a simple FFT measurement technique, the simultaneous real-time monitoring of several PCF sensors is achieved. A theoretical analysis has been performed where simulations matched with the experimental results. For the experimental verification, highly birefringent (HiBi) fiber sections that operated as sensing elements were multiplexed and tested in two configurations. Due to the FFT analysis, both multiplexing schemes can be properly interrogated by monitoring the FFT phase change at the characteristic spatial-frequency of each sensor. For this purpose, a commercial interrogator and a custom Matlab program were used for computing the FFT and for monitoring the FFT phase change in real time (1 Hz).

Fully switchable multiwavelength fiber laser assisted by a random mirror

A real-time switchable and reconfigurable multiwavelength laser has been experimentally carried out. The laser cavity is based on a random distributed mirror and a novel real-time reconfigurable filter mirror structure. The proposed laser has been demonstrated to generate any combination of wavelengths at the 50 and 100 GHz International Telecommunications Union (ITU) grids specifications. By simultaneously using Er-doped fiber and Raman amplification, a 15 nm wide lasing window at the C band can be utilized to create up to 18 different lasing wavelengths into the ITU grid that can be switched automatically and in real time when desired.

Ultralong 250 km remote sensor system based on a fiber loop mirror interrogated by an optical time-domain reflectometer

A 253 km ultralong remote displacement sensor system based on a fiber loop mirror interrogated by a commercial optical time-domain reflectometer is proposed and experimentally demonstrated. The use of a fiber loop mirror increases the signal-to-noise ratio, allowing the system to interrogate sensors placed 253 km away from the monitoring system without using any optical amplification. The displacement sensor was based on a long period grating spliced inside of the loop mirror, which modifies the mirror reflectivity accordingly to the applied displacement.

Ultra-Long Laser Systems for Remote Fiber Bragg Gratings Arrays Interrogation

This letter proposes and demonstrates two, 100 and 200 km, long distance fiber laser systems for fiber Bragg grating (FBG) sensors multiplexing. The first system is based on a fiber ring laser and reaches 100 km, whereas the second one is composed by a random fiber laser with a reach of 200 km. Both of them are able to multiplex 11 FBGs. In addition, because of the mode operation of the systems, they are low noise configurations.

Hybrid OTDR-Fiber Laser System for Remote Sensor Multiplexing

We report the experimental demonstration of a new hybrid multiplexing network for optical fiber sensors using a long-distance multiwavelength lasing system and an optical time domain reflectometry (OTDR) to interrogate displacement sensors based on microbenders. With this design, simultaneous interrogation of displacement and temperature is carried out 50 km away from the system header. An improved version of the system which avoids cladding-modes coupling is also presented.

An in-reflection strain sensing head based on a Hi-Bi photonic crystal fiber.

A photonic crystal fiber-based sensing head is proposed for strain measurements. The sensor comprises a Hi-Bi PCF sensing head to measure interferometric signals in-reflection. An experimental background study of the sensing head is conducted through an optical backscatter reflectometer confirming the theoretical predictions, also included. A cost effective setup is proposed where a laser is used as illumination source, which allows accurate high precision strain measurements. Thus, a sensitivity of ∼7.96 dB/ms was achieved in a linear region of 1,200 με.

Multiplexing of six micro-displacement suspended-core Sagnac interferometer sensors with a Raman-Erbium fiber laser.

This work experimentally demonstrates a long-range optical fiber sensing network for the multiplexing of fiber sensors based on photonic crystal fibers. Specifically, six photonic crystal fiber sensors which are based on a Sagnac interferometer that includes a suspended-core fiber have been used. These sensors offer a high sensitivity for micro-displacement measurements. The fiber sensor network presents a ladder structure and its operation mode is based on a fiber ring laser which combines Raman and Erbium doped fiber amplification. Thus, we show the first demonstration of photonic crystal fiber sensors for remote measurement applications up to 75 km.