Abian B. Socorro

Tapered Single-Mode Optical Fiber pH Sensor Based on Lossy Mode Resonances Generated by a Polymeric Thin-Film

Lossy mode resonances can be generated with certain polymeric nanostructures, such as those obtained with a multilayered assembly of poly(allylamine hydrochloride) and poly(acrylic acid). This coating is adsorbed by the electro-static self-assembly technique onto a tapered single-mode optical fiber, in order to evaluate its performance when detecting pH. According to the results reported in this paper, the high sensitivity given by a tapering process in a single-mode optical fiber is increased by the effect of this kind of electromagnetic resonances. Particularly, in a pH range from 4.0 to 6.0, the overall wavelength shift of this sensor reaches 200 nm, and the transmission at the resonance wavelengths can fall down to -50 dB. These data provide results which can be taken into account to detect pH with high accuracy.

Mode transition in complex refractive index coated single-mode–multimode–single-mode structure

By coating a single-mode-multimode-single-mode (SMS) structure with a high refractive index thin-film it is possible to obtain a transition of modes for specific combinations of thin-film thickness, thin-film refractive index and surrounding medium refractive index, which permits to develop devices with a high sensitivity to specific parameters. In order to gain a better knowledge of the phenomenon the experimental results are corroborated numerically with the Transfer-Matrix-Method. The influence of losses in the thin-film has also been studied. The results obtained prove that a thin-film coated SMS structure is a simple and cost-effective platform for development of sensors and optical filters.

Optimization of Sensors Based on Multimode Interference in Single-Mode–Multimode–Single-Mode Structure

By coating a single-mode-multimode-single-mode (SMS) structure with a complex refractive index thin-film the central wavelength of the transmission and attenuation bands of the optical spectrum can be shifted. By adequate selection of multimode segment length and diameter, the thin-film thickness and the thin-film refractive index, the sensitivity of the device to the surrounding medium refractive index, the thickness of the thin-film or the refractive index of the thin-film can be optimized. Experimental results are corroborated numerically with the transfer matrix method.

Refractometric sensors based on multimode interference in a thin-film coated single-mode–multimode–single-mode structure with reflection configuration

Thin-film coated single-mode-multimode-single-mode (SMS) structures have been analyzed both theoretically and experimentally with the aim of detecting different refractive indices. By adequate selection of the thickness of the thin film and of the diameter of the multimode segment in the SMS structure, a seven-fold improvement can be obtained in the sensitivity of the device to the surrounding medium refractive index, achieving a maximum sensitivity of 1199.18  nm/refractive index unit for the range of refractive indices from 1.321 to 1.382. Using layer-by-layer self-assembly for deposition, both on the cladding and on the tip of the multimode segment, allows the reflected power to increase, which avoids the application of a mirror on the tip of the multimode segment.

Sensitivity optimization with cladding-etched long period fiber gratings at the dispersion turning point

This work presents a refractive index sensor based on a long period fiber grating (LPFG) made in a reduced cladding fiber whose low order cladding modes have the turning point at large wavelengths. The combination of these parameters results in an improved sensitivity of 8734 nm/refractive index unit (RIU) for the LP0,3 mode in the 1400-1650 wavelength range. This value is similar to that obtained with thin-film coated LPFGs, which permits to avoid the coating deposition step. The numerical simulations are in agreement with the experimental results.

Influence of Waist Length in Lossy Mode Resonances Generated With Coated Tapered Single-Mode Optical Fibers

In this work, the generation of electromagnetic resonances due to the deposition of a nanocoating on a tapered single-mode optical fiber is analyzed. The layer-by-layer technique is used to control the thickness of the nanocoating. According to the results that have been obtained, the depth of the resonance depends on the length of the waist region. Variations in the transmitted optical power of 40 dB are observed in just a few layers. This can be considered in the fabrication of both highly sensitive resonance-based sensors and optical filters.

Micro and Nanostructured Materials for the Development of Optical Fibre Sensors

The measurement of chemical and biomedical parameters can take advantage of the features exclusively offered by optical fibre: passive nature, electromagnetic immunity and chemical stability are some of the most relevant ones. The small dimensions of the fibre generally require that the sensing material be loaded into a supporting matrix whose morphology is adjusted at a nanometric scale. Thanks to the advances in nanotechnology new deposition methods have been developed: they allow reagents from different chemical nature to be embedded into films with a thickness always below a few microns that also show a relevant aspect ratio to ensure a high transduction interface. This review reveals some of the main techniques that are currently been employed to develop this kind of sensors, describing in detail both the resulting supporting matrices as well as the sensing materials used. The main objective is to offer a general view of the state of the art to expose the main challenges and chances that this technology is facing currently.

Temperature sensor based on a hybrid ITO-silica resonant cavity

Integrated optical devices comprised of multiple material systems are able to achieve unique performance characteristics, enabling applications in sensing and in telecommunications. Due to ease of fabrication, the majority of previous work has focused on polymer-dielectric or polymer-semiconductor systems. However, the environmental stability of polymers is limited. In the present work, a hybrid device comprised of an indium tin oxide (ITO) coating on a silicon dioxide toroidal resonant cavity is fabricated. Finite element method simulations of the optical field in the multi-material device are performed, and the optical mode profile is significantly altered by the high index film. The quality factor is also measured and is material loss limited. Additionally, its performance as a temperature sensor is characterized. Due to the high thermo-optic coefficient of ITO and the localization of the optical field in the ITO layer, the hybrid temperature sensor demonstrates a nearly 3-fold improvement in performance over the conventional silica device.

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.

Lossy Mode Resonance-based pH sensor using a tapered single mode optical fiber coated with a polymeric nanostructure

This contribution presents a pH sensor based on the combination of two technologies: tapered standard-single mode optical fiber (S-SMF) and an electromagnetic resonance phenomenon called Lossy Mode Resonance (LMR). This last phenomenon is produced by coating the optical structure with a thin polymeric film, which for specific values of the coating refractive index and thickness causes a maximum coupling of light guided in the tapered S-SMF region. Layer-by-layer electrostatic self assembly technique was used for the fabrication of a polymeric sensing nanostructure. The construction process was optimized in order to visualize the LMR behavior with a device length of 5 mm. The sensing combination produces a 250 nm wavelength-shift and a 20 dB attenuation variation of the LMR when varying the pH from 4 to 6.