P. Sanchez

Design rules for lossy mode resonance based sensors

Lossy mode resonances can be obtained in the transmission spectrum of cladding removed multimode optical fiber coated with a thin-film. The sensitivity of these devices to changes in the properties of the coating or the surrounding medium can be optimized by means of the adequate parameterization of the coating refractive index, the coating thickness, and the surrounding medium refractive index. Some basic rules of design, which enable the selection of the best parameters for each specific sensing application, are indicated in this work.

Generation of lossy mode resonances by deposition of high-refractive-index coatings on uncladded multimode optical fibers

A comparative study of lossy mode resonances generated by depositing two different materials is presented. The two materials selected are indium tin oxide (ITO) and indium oxide. The two materials present different dielectric dispersion, which leads to the generation of single-peak lossy mode resonances with the ITO coated optical fibers and dual-peak lossy mode resonances with the In2O3 coated optical fibers. The obvious advantage of a dual-peak based measurement in the sensors field is enhanced by a sensitivity increase observed in sensors based on In2O3 if compared with those based on ITO. These characteristics are analyzed both theoretically and experimentally.

Dual-Peak Resonance-Based Optical Fiber Refractometers

The fabrication of optical fiber refractometers by means of the deposition of a thin indium-oxide coating onto an optical fiber core is presented. Indium-oxide permits the guided light in the fiber to be coupled from its core to its coating, creating resonances in the infrared and visible regions. These resonances vary as a function of the external mediums refractive index, enabling the fabrication of robust and highly reproducible wavelength-based optical fiber refractometers. Moreover, two differentiated resonances have been obtained from the same device within the 500to 1700-nm spectrum. The central wavelength of the resonances can be adjusted by varying the thickness of the indium-oxide coating. The sensitivity of the dual-peak resonance-based refractometers is within the same order of magnitude when the resonances are situated in the same spectral region. The refractometers that we obtained showed a sensitivity of 4068-nm/refractive index unit (RIU) in the range 1.333-1.392 RIU, comparable to existing ones based on resonances and other techniques, with the advantage of permitting the realization of dual-peak reference measurements in different regions of the spectrum.

Lossy mode resonances toward the fabrication of optical fiber humidity sensors

In this work, the fabrication and characterization of novel humidity sensors based on lossy mode resonances (LMRs) are presented. Indium tin oxide (ITO) and In2O3 coatings fabricated onto an optical fiber are used as the LMR supporting coatings. Poly-acrylic acid and polyallylamin hydrochloride polymeric coatings were used as the sensitive layers. A comparative study between the ITO and the In2O3 devices is made. The In2O3-based humidity sensors show an improvement in the sensitivity if compared with the ITO-based ones within the same working range. Moreover, In2O3-based refractometers enable to carry out dual-reference measurements thanks to the resonances associated with TE and TM light polarizations instead of a single resonance as was the case for the ITO coated devices. In addition to this, the fabrication time has been reduced because the number of bilayers required for deposition of the In2O3 coating is only 13, whereas for deposition of the ITO coating 100 bilayers are necessary.

High sensitive and selective C-reactive protein detection by means of lossy mode resonance based optical fiber devices.

This work presents the development of high sensitive, selective, fast and reusable C-reactive protein (CRP) aptasensors. This novel approach takes advantage of the utilization of high sensitive refractometers based on Lossy Mode Resonances generated by thin indium tin oxide (ITO) films fabricated onto the planar region of d-shaped optical fibers. CRP selectivity is obtained by means of the adhesion of a CRP specific aptamer chain onto the ITO film using the Layer-by-Layer (LbL) nano-assembly fabrication process. The sensing mechanism relies on resonance wavelength shifts originated by refractive index variations of the aptamer chain in presence of the target molecule. Fabricated devices show high selectivity to CRP when compared with other target molecules, such as urea or creatinine, while maintaining a low detection limit (0.0625mg/L) and fast response time (61s). Additionally, these sensors show a repetitive response for several days and are reusable after a cleaning process in ultrapure water.

Sensing Properties of Indium Oxide Coated Optical Fiber Devices Based on Lossy Mode Resonances

In this work, lossy mode resonance (LMR)-based optical fiber refractometers fabricated by using a transparent coating (indium oxide) as the LMR supporting layer are studied. The utilization of the high refractive index indium oxide coatings enables the fabrication of highly sensitive optical fiber refractometers, the resonance of which can be tuned by adjusting the fabrication parameters, such as the coating thickness. The detection technique is based on the wavelength shift of the resonances produced by both TE and TM polarization modes. Here, the influence of the coating thickness on the sensitivity of the device to external refractive index variations is observed. Maximum sensitivities of 2.03e-4 and 2.35e-4 refractive index units (RIU) per nanometer for TE and TM polarizations have been obtained, respectively. The sensitivity of the devices to diverse volatile organic compounds (VOCs), such as ethanol, methanol, isopropyl alcohol, acetone, and ammonia has been studied and the cross-sensitivity to temperature and moisture as well.

Sensors based on thin-film coated cladding removed multimode optical fiber and single-mode multimode single-mode fiber: a comparative study

Two simple optical fibre structures that do not require the inscription of a grating, a cladding removed multimode optical fibre (CRMOF) and a single-mode multimode single-mode structure (SMS), are compared in terms of their adequateness for sensing once they are coated with thin-films. The thin-film deposited (TiO2/PSS) permits increasing the sensitivity to surrounding medium refractive index. The results obtained can be extrapolated to other fields such as biological or chemical sensing just by replacing the thin-film by a specific material.

Considerations for Lossy-Mode Resonance-Based Optical Fiber Sensor

This paper presents the fabrication of optical fiber relative humidity (RH) sensors by means of polymeric thin-films as lossy-mode resonance (LMR) supporting coatings. In particular, LMRs are observed because of the fabrication of polyallylamine hydrochloride (PAH) and polyacrylic acid (PAA) polymeric coatings onto cladding-removed multimode optical fibers on applying the layer-by-layer self-assembly method. More than one LMR can be generated as a function of the coating thickness. The generation of multiple LMRs produces notch band filter with a rejection band in the visible region. To compare the parameters of different LMRs, two devices with PAH/PAA coating thicknesses of 140 and 470 nm, respectively, are fabricated. The thickness and the refractive index of the PAH/PAA film can be modified as a function of the surrounding medium refractive index. Thus, surrounding medium relative humidity can be easily determined through the wavelength shift of the resonance (~ 34 nm between 20% and 80% RH).

Exhaled Breath Optical Fiber Sensor based on LMRs for Respiration Monitoring

In this work, the fabrication and characterization of a small and portable exhaled breath sensor based on Lossy Mode Resonances (LMR) is presented. Tin oxide (SnO2) coatings fabricated onto optical fibers are used as LMR supporting coatings. The principle of operation is based on the measurement of refractive index changes by the LMR device (with an average sensitivity of 8355 nm/RIU) originated by the condensation of micro water droplets in the surroundings of the SnO2 coating during the breath natural process. The sensor shows a repetitive response with less than 100 ms of response time and a wavelength shift of 150 nm from inhalation to exhalation.

Humidity sensor fabricated by deposition of SnO2 layers onto optical fibers

In this work, the fabrication and characterization of novel humidity sensors based on Lossy Mode Resonances (LMR) is presented. Tin oxide (SnO2) coatings fabricated onto optical fibers are used as LMR supporting coatings. The SnO2 based refractometers showed an average sensitivity of 6715 nm/refractive index unit (RIU) in the range 1.333–1.420 RIU. The behavior of this optical fiber device as relative humidity (RH) sensor was also tested, monitoring its response to different surrounding humidity levels. The results show a sensitivity of 0.1 nm/RH% in the range from 20% to 80% RH.