J. R. Guzman-Sepulveda

Fiber Optic Sensor for High-Sensitivity Salinity Measurement

A highly sensitive salinity sensor based on a two-core optical fiber is demonstrated for both high- and low-concentration regimes. Salinity of several aqueous solutions is measured in the ranges from 0 to 5 mol/L and from 0 to 1 mol/L with sensitivities of 14.0086 and 12.0484 nm/(mol/L), respectively. The achieved sensitivity is ~19 times higher than that recently reported for polymide-coated photonic crystal fibers.

A Highly Sensitive Fiber Optic Sensor Based on Two-Core Fiber for Refractive Index Measurement

A simple and compact fiber optic sensor based on a two-core fiber is demonstrated for high-performance measurements of refractive indices (RI) of liquids. In order to demonstrate the suitability of the proposed sensor to perform high-sensitivity sensing in a variety of applications, the sensor has been used to measure the RI of binary liquid mixtures. Such measurements can accurately determine the salinity of salt water solutions, and detect the water content of adulterated alcoholic beverages. The largest sensitivity of the RI sensor that has been experimentally demonstrated is 3,119 nm per Refractive Index Units (RIU) for the RI range from 1.3160 to 1.3943. On the other hand, our results suggest that the sensitivity can be enhanced up to 3485.67 nm/RIU approximately for the same RI range.

Highly Sensitive Liquid Core Temperature Sensor Based on Multimode Interference Effects.

A novel fiber optic temperature sensor based on a liquid-core multimode interference device is demonstrated. The advantage of such structure is that the thermo-optic coefficient (TOC) of the liquid is at least one order of magnitude larger than that of silica and this, combined with the fact that the TOC of silica and the liquid have opposite signs, provides a liquid-core multimode fiber (MMF) highly sensitive to temperature. Since the refractive index of the liquid can be easily modified, this allows us to control the modal properties of the liquid-core MMF at will and the sensor sensitivity can be easily tuned by selecting the refractive index of the liquid in the core of the device. The maximum sensitivity measured in our experiments is 20 nm/°C in the low-temperature regime up to 60 °C. To the best of our knowledge, to date, this is the largest sensitivity reported for fiber-based MMI temperature sensors.

Passive optical mapping of structural evolution in complex fluids

Self-assembling complex systems exhibit properties that involve a broad spectrum of thermal, structural, morphological, and optical transitions. Various techniques have been used to assess different aspects of the phase transitions in these complex systems. However, because of inherent technical constraints, structural information is usually provided only within narrow ranges of concentrations and temperatures. We show here that by effectively suppressing multiple scattering, low-coherence dynamic light scattering permits assessing the aggregation dynamics of self-assembling systems in a completely passive manner and over ranges of concentration and temperatures well beyond the limits of traditional approaches. The power spectral analysis of scattered intensity fluctuations permits a reliable characterization of multiple relaxation times. We demonstrate that the entire phase diagram can be covered in a consistent way and structural phase transitions can be mapped over a broad optical regime from weak to strong scattering.

Fiber Optic Bending Sensor Based on Multimode Interference (MMI) Effects

Here we report a fiber bending sensor based on multimode interference effects. Sensing is achieved through losses induced in the propagating modes, which directly affects the intensity of the imaged formed by the multimode fiber.

Full Characterization of Colloidal Dynamics at Low Péclet Numbers.

Although critical in applications, the dynamics of colloidal systems at low Péclet numbers is poorly understood. Here we introduce an optical technique that permits for the first time a complete characterization of this regime through a continuous and independent measurement of both the diffusive and the advective components of a systems dynamics. For the particular example of gravity-driven colloids, we demonstrate experimentally that the hydrodynamic size and the mass density of particulate suspensions can be measured simultaneously. The proven capabilities are of particular interest for studying the spatial and temporal properties of inhomogeneous colloidal systems where aggregation and structural evolution play major roles.

Multimode interference dynamic light scattering

We present a robust implementation of a fiber-based, single-mode, common-path interferometer assisted by multimode interference effects in which light is efficiently collected from larger coherent regions while maintaining a high signal-to-noise ratio.

Parkinson's disease: Improved diagnosis using image processing

An intensity-based texture segmentation approach for the detection of regions with abnormal texture characteristics in magnetic resonance imaging is presented. Our algorithm is tested over several images taken from The Parkinsons Progression Markers Initiative (PPMI-database), and the results suggest that this approach is suitable for the successful identification and extraction of regions of interest whose properties can be potentially related to signature features of Parkinson disease.

Passive athermalization of multimode interference devices for wavelength-locking applications

In this paper we demonstrate the passive, material-based athermalization of all-fiber architectures by cascading multimode interference (MMI) devices. In-line thermal compensation is achieved by including a liquid-core multimode section of variable length that allows ensuring temperature-independent operation while preserving the inherent filter-like spectral response of the MMI devices. The design of the temperature compensation unit is straightforward and its fabrication is simple. The applicability of our approach is experimentally verified by fabricating a wavelength-locked MMI laser with sensitivity of only -0.1 pm/°C, which is at least one order of magnitude lower than that achieved with other fiber optics devices.

Fiber Optic Sensors Based on Multicore Structures

We present a review of the fundamentals and applications of fiber optic sensors based on multicore coupled structures. The fundamentals of these coupled structures are approached in general for arbitrary distributions of N cores on the foundations of coupled mode theory. The principle of operation of fiber optic sensors using this type of architectures is illustrated via numerical simulations of the simplest coupled structure—the two-core fiber. Illustrative experimental results using fiber optic sensors based on two- and seven-core multicore fibers are shown for a number of applications including temperature, curvature, and refractive index sensing. The main aspects of the performance of multicore fiber sensors are highlighted throughout this chapter and their characteristics, especially their sensitivity, are compared to those of other existing fiber sensing architectures such as fiber Bragg gratings, long period gratings, and photonic crystal fibers, among others.