Singlemode-Multimode-Singlemode Fiber Structures for Sensing Applications – A Review

A singlemode-multimode-singlemode (SMS) fiber structure consists of a short section of multimode fiber fusion-spliced between two SMS fibers. The mechanism underpinning the operation of an SMS fiber structure is multimode interference and associated self-imaging. SMS structures can be used in a variety of optical fiber systems but are most commonly used as sensors for a variety of parameters, ranging from macro-world measurands such as temperature, strain, vibration, flow rate, RI and humidity to the micro-world with measurands such as proteins, pathogens, DNA, and specific molecules. While traditional SMS structures employ a short section of standard multimode fiber, a large number of structures have been investigated and demonstrated over the last decade involving the replacement of the multimode fiber section with alternatives such as a hollow core fiber or a tapered fiber. The objective of replacing the multimode fiber has most often been to allow sensing of different measurands or to improve sensitivity. In this paper, several different categories of SMS fiber structures, including traditional SMS, modified SMS and tapered SMS fiber structures are discussed with some theoretical underpinning and reviews of a wide variety of sensing examples and recent advances. The paper then summarizes and compares the performances of a variety of sensors which have been published under a number of headings. The paper concludes by considering the challenges faced by SMS based sensing schemes in terms of their deployment in real world applications and discusses possible future developments of SMS fiber sensors

Multipoint gas detection using range resolved interferometry

The ability to detect and quantify gas in multiple locations is important in environmental and safety monitoring situations. This thesis describes the first application of Range Resolved Interferometry to the problem of gas sensing at multiple locations. Range resolved interferometry (RRI) is an interferometric signal processing technique that allows the separation of individual interferometric signals from superpositions of multiple interferometers and the rejection of interferometers other than those of interest. This allows the interrogation of the light intensity passing through each interferometer of interest which in turn allows a measure of the absorption of light by gas present within the interferometer arms. The application of the Beer-Lambert Law allows the measurement of a gas concentration from this information. Unlike previous interferometric techniques for multipoint gas measurement, RRI uses injection current modulation of a DFB laser and is therefore, cost effective. The process of applying a ramp modulation to RRI in order to extract spectroscopic information is described along with the post-processing needed to extract gas concentrations from multiple locations simultaneously. Three sensing regions ² < 0.95) and with the ability to measure methane at a concentration of 200ppm with no averaging time. Allen-Werle analysis showed that with sufficient averaging time, a limit of detection as low as 4ppm could be achieved. Cross talk experiments showed that the presence of gas in other sensing regions had no effect on gas concentration measurements. The first use of RRI for spectroscopic measurements required extensive postprocessing to account for the DFB laser’s non-uniform response to sinusoidal modulation as the driving injection current was varied to sweep the laser output wavelength. Application of an envelope function to the sinusoidal modulation provided a stable wavelength response to the sinusoidal modulation and so allowed real-time gas detection with no post processing required. Experiments were performed to establish that the most suitable deployment topology for multipoint sensing is a serial-bus topology and that the amplitude of the sinusoidal modulation must be chosen to provide the chosen balance between the spatial resolution of the system and the signal strength provided by the measurement of light absorption by the gas under test. The ability of RRI to distinguish between interferometers of interest and parasitic interferometers was used to extract the absorption measurements from a gas detection system with optical fringing and was shown to reduce the unwanted signal by a factor of 18

Interference Pattern Representation on the Complex s-Plane

In this work, the normalized interference pattern produced by a coherence interferometer system was represented as a complex function. The Laplace transform was applied for the transformation. Poles and zeros were determined from this complex function, and then, its pole-zero map and its Bode diagram were proposed. Both graphical representations were implemented numerically. From our numerical results, pole location and zero location depend on the optical path difference (OPD), while the Bode diagram gives us information about the OPD parameter. Based on the results obtained from the graphical representations, the coherence interferometer systems, the low-coherence interferometer systems, the interferometric sensing systems, and the fiber optic sensors can be analyze on the complex s-plane

High Temperature Sapphire Optical Fiber Sensor

A sapphire fiber optic sensor for ultra-high temperature is developed, which owns the advantages of high temperature tolerance and compact. The detecting fiber is manufactured by fusing the sapphire fiber for detector head. The developed infrared radiation light is detected and the high temperature optical fiber sensor is placed in the ultra-high temperature furnace. The sensor signal will be transmitted to the display device through a photoelectric conversion module, and data acquisition module. As a result, the temperature response sensitivity is 2.292 uV1/2/K The measurement results show that the repeatability of the sensor is good. The maximum temperature measured by the sensor is 1823 K. The sensor can withstand 10 hours at high temperature and the error is less than 1 %. The development of common optical fiber sensor can stably exist at high-temperature. The sensor owns the advantage of simple, compact, easy to fabricate, what’s more, it can tolerate ultrahigh temperature for a long time

Distributed Fiber Ultrasonic Sensor and Pattern Recognition Analytics

Ultrasound interrogation and structural health monitoring technologies have found a wide array of applications in the health care, aerospace, automobile, and energy sectors. To achieve high spatial resolution, large array electrical transducers have been used in these applications to harness sufficient data for both monitoring and diagnoses. Electronic-based sensors have been the standard technology for ultrasonic detection, which are often expensive and cumbersome for use in large scale deployments. Fiber optical sensors have advantageous characteristics of smaller cross-sectional area, humidity-resistance, immunity to electromagnetic interference, as well as compatibility with telemetry and telecommunications applications, which make them attractive alternatives for use as ultrasonic sensors. A unique trait of fiber sensors is its ability to perform distributed acoustic measurements to achieve high spatial resolution detection using a single fiber. Using ultrafast laser direct-writing techniques, nano-reflectors can be induced inside fiber cores to drastically improve the signal-to-noise ratio of distributed fiber sensors. This dissertation explores the applications of laser-fabricated nano-reflectors in optical fiber cores for both multi-point intrinsic Fabry–Perot (FP) interferometer sensors and a distributed phase-sensitive optical time-domain reflectometry (φ-OTDR) to be used in ultrasound detection. Multi-point intrinsic FP interferometer was based on swept-frequency interferometry with optoelectronic phase-locked loop that interrogated cascaded FP cavities to obtain ultrasound patterns. The ultrasound was demodulated through reassigned short time Fourier transform incorporating with maximum-energy ridges tracking. With tens of centimeters cavity length, this approach achieved 20kHz ultrasound detection that was finesse-insensitive, noise-free, high-sensitivity and multiplex-scalability. The use of φ-OTDR with enhanced Rayleigh backscattering compensated the deficiencies of low inherent signal-to-noise ratio (SNR). The dynamic strain between two adjacent nano-reflectors was extracted by using 3×3 coupler demodulation within Michelson interferometer. With an improvement of over 35 dB SNR, this was adequate for the recognition of the subtle differences in signals, such as footstep of human locomotion and abnormal acoustic echoes from pipeline corrosion. With the help of artificial intelligence in pattern recognition, high accuracy of events’ identification can be achieved in perimeter security and structural health monitoring, with further potential that can be harnessed using unsurprised learning

Applications of Ring Resonators and fiber delay lines for sensors and WDM Networks

En esta tesis doctoral, se presentan diversas aportaciones científicas en el ámbito de las aplicaciones de la fibra óptica y de las comunicaciones ópticas. En primer lugar, la tesis doctoral describe nuevas técnicas de medida remota y multiplexación en longitud de onda (WDM), a través de fibra óptica monomodo, para sensores ópticos. Las técnicas de medida están orientadas a sensores de intensidad óptica y se basan en configuraciones ópticas implementadas mediante redes de Bragg en fibra y líneas de retardo en fibra recirculantes (anillo resonante) y no recirculantes. En el documento se describen matemáticamente dichas técnicas y se presentan medidas experimentales que verifican los modelos teóricos. En segundo lugar, la tesis contiene diversas contribuciones novedosas al diseño y simulación por ordenador de filtros fotónicos compuestos basados en el anillo resonante con interferómetro Sagnac, para la compensación de la dispersión cromática en enlaces de transmisión digital con fibra óptica. Por último, el documento incluye un listado de todas las referencias empleadas, un listado de los acrónimos empleados, así como las publicaciones y patentes obtenidas por el autor hasta la fecha.Los proyectos de la Comisión Interministerial de Ciencia y Tecnología (CICYT): TIC2003-03783 (DISFOTON) y TEC2006-13273-C03-03-MIC (FOTOCOMIN). El programa de I+D+i de la Comunidad Autónoma de Madrid: FACTOTEM-CM (S-0505/ESP/000417). La Acción Integrada Hispano-Portuguesa del Plan Nacional de I+D+i 2004-2007: Self-referenced fibre optic intensity configurations for single and multi-sensors (HP2007-0093). El proyecto cofinanciado por la Universidad Carlos III de Madrid y la Comunidad Autónoma de Madrid: Fotónica en visualización, comunicaciones y sensores (CCG06-UC3M/TIC-0619). Las ayudas a la movilidad de investigadores en formación que me concedió la Universidad Carlos III de Madrid en 2006 y 2007. La Red Temática Europea SAMPA (HPRN-CT-2002-00202) del 5º Programa Marco de la Unión Europea. La Acción Europea FIDES (COST Action 299) del 6º Programa Marco de la Unión Europea. Y las Redes de Excelencia Europea ePhoton/ONe+ (FP6-IST-027497) y BONE (FP7-ICT-216863), del 6º y 7º Programa Marco de la Unión Europea, respectivamente