Candido Bariain

Optical fiber humidity sensor based on a tapered fiber coated with agarose gel

Abstract An optical fiber humidity sensor (OFHS) has been fabricated using a hydrophilic gel (agarose) deposited on the thinner zone of a biconically tapered single-mode optical fiber. A variation of up to 6.5 dB of the transmitted optical power was obtained with relative humidity (RH) changes between 30% and 80%. Furthermore, the sensor shows an invariant behavior with time. This inexpensive material showed a good reproducibility with low hysteresis and its use with tapered optical fiber makes it useful for industrial and environmental applications.

Experimental study of a thermochromic material based optical fiber sensor for monitoring the temperature of the water in several applications

This paper describes the use of a thermochromic material (2,4,5-triphenylimidazole or also called Lophine) for the fabrication of temperature optical fiber sensors. First, an experimental study of this material at different temperatures is presented and subsequently its behavior in two different schemes (variations of the reflected optical power and of the transmitted optical power) is analyzed. The characterization of both low cost sensors is discussed comparing the experimental results and analyzing their advantages and disadvantages. Besides, all the measurements taken were immune to humidity obtaining ideal sensors for monitoring the temperature of the water in several applications.

Long-range hybrid network with point and distributed Brillouin sensors using Raman amplification.

We propose a novel concept for hybrid networks that combine point and distributed Brillouin sensors in a cost-effective architecture that also deploys remote distributed Raman amplification to extend the sensing range. A 46-km proof-of-concept network is experimentally demonstrated integrating point vibration sensors based on fiber Bragg gratings and tapers with distributed temperature sensing along the network bus. In this network the use of Raman amplification to compensate branching and fiber losses provides a temperature resolution of 0.7 degrees C and 13 m. Moreover, it was possible to obtain good optical signal to noise ratio in the measurements from the four point vibration sensors that were remotely multiplexed in the network. These low-cost intensity sensors are able to measure vibrations in the 0.1 to 50 Hz frequency range, which are important in the monitoring of large infrastructures such as pipelines.

Resilient Amplified Double-Ring Optical Networks to Multiplex Optical Fiber Sensors

In this paper, we report the experimental demonstration of an amplified optical fiber double-ring network for the multiplexing of sensors. The network is designed to be inherently resilient to fiber failures because it enables simultaneous interrogation of all the optical fiber sensors using both rings. We demonstrate the feasibility of so-called ldquodedicated protectionrdquo for fiber optic intensity sensors. Raman amplification is used to overcome the losses of the couplers used in the rings, providing power transparency. In this novel configuration, Raman pumping is activated only when a fiber failure occurs. We demonstrate how the topology allows the received powers from the sensors to be equalized.

Volatile-organic-compound optic fiber sensor using a gold-silver vapochromic complex

We describe a new gold-silver complex based on 2,2-bipyridine, whose formula is Au2Ag2C6F54C5H4N-C5H4N2n, used to detect volatile organic compounds VOCs such as ethanol, methanol, and acetic acid. This organometallic material is presented in the form of bright yellow powder, and suffers a change in its optical properties when it is exposed to VOCs. A new fiber optic sensor is pre- sented based on the properties of a new vapochromic material. The sensor works in a reflection configuration and consists of an optic fiber pigtail core diameter is 200 m and cladding is 230 m on the cleaved end of which the vapochromic material, previously mixed with a commer- cially available solvent, Liquicoat ® , is deposited by using the dip-coating technique. Using an optical source and a photodetector, it is possible to detect and quantify the change in reflected intensity-modulated signal when the sensor is exposed to VOC inside a sealed chamber. This be- havior can be related to the VOC concentration. The study of the sen- sors response is made at a specific wavelength for different VOC con- centrations. Limits of detection of 2.16, 1.73, and 3.73 mg/L of vapors of ethanol, methanol, and acetic acid vapors, respectively, are attained.

Application of gold complexes in the development of sensors for volatile organic compounds

Two different kinds of sensors have been developed by using the same kind of vapochromic complexes. The vapochromic materials [Au2Ag2(C6F5)4L2]n have different colours depending on the ligand L. These materials change, reversibly, their optical properties, colour and fluorescence, in the presence of the vapours of volatile organic compounds (VOCs). For practical applications, two different ways of fixing the vapochromic material to the optical fibre have been used: the sol-gel technique and the electrostatic self-assembly method (ESA). With the first technique the sensors can even be used to detect VOCs in aqueous solutions, and using the second method it has been possible to develop nanosensors.

Low-cost optical amplitude modulator based on a tapered single-mode optical fiber.

A new, to our knowledge, modulator based on a tapered single-mode optical fiber is introduced. The electro-optic device consists of a tapered optical fiber placed on a resonator made of a piezoelectric material. An electrical signal applied to the piezoelectric material makes the taper bend, and that displacement produces a modulation in the intensity of the optical signal traveling through the fiber. This device is very easy to build and is low in cost. Because of its nature, this new device might be very useful in optical fiber sensors. Its performance is analyzed, and the results are discussed.

Experimental results toward development of humidity sensors by using a hygroscopic material on biconically tapered optical fiber

A novel humidity optical fiber sensor have been developed using an hygroscopic material, deposited on the thinner zone of a biconically tapered single mode optical fiber. Relative humidity variations form 40 percent to 90 percent have been detected producing up to 5dB optical power change.

Optical Fiber Sensors Array to Identify Beverages by Their Odor

Four optical fiber sensors have been grouped in an array which is able to distinguish odors of different drinks. The sensing materials employed have been deposited onto optical fibers following the electrostatic self assembly method. The responses have been characterized in terms of reflected optical power; more specifically, the dynamic range and the recovery of each device have been used to discriminate between the samples. Data mining techniques based on the combination of principal component analysis and artificial neural networks are performed. The final system is trained to distinguish between grape juice, wine, and vinegar by using a set of one hundred samples of each one. Furthermore, the array can be located at up to 6 km away from the optical header, offering the possibility of in situ measurements.

Experimental design rules for implementing biconically tapered single mode optical fibre displacement sensors

Tapered optical fibers are used to design couplers, wavelength division multiplexers, near field scanning optical microscopy, just to mention a few. Moreover, and due to its strong transmission dependence to external medium the tapered fiber may also be used to sense distinct parameters such as temperature, humidity, PH, etc. In this work bending effects in tapers are exploited to achieved displacement sensors and to present design rules for implementing these sensors according to the desired both range and sensitivity.