Rogério N. Nogueira

POF metrology in physics medicine and rehabilitation

Three optical monitoring joint angle devices with the ability of real-time assessment of the knee, elbow and ankle movements are presented. All devices were tested in different selected tasks and its performance evaluated. Results have shown that these side-polished plastic optical fiber based systems are a valid technique and suitable to aid physicians in the diagnosis and rehabilitation of joint injuries, to monitor the performance of high competition athletes or even to quantify daily activities. The wearable sensor systems have properties such as low-cost, friendly operation and less effect to human which are important topics in biomechanics and clinical applications.

Analysis of Bragg grating written in high-birefringence fiber optics

Bragg gratings written in high birefringence (HiBi) fibre optics can be used as sensors for multiple parameters, such as stress along different axis and temperature. Their use as sensors require the characterization of the HiBi fibres, because the specific fibre parameters can induce different responses to the sensor system. In this work we analyse, using finite elements methods, stress effects over three types of the HiBi fibres: Bow tie, PANDA and internal elliptical cladding. We also characterize the spectral response of gratings written in HiBi fibre as a function of the input states of the polarization. The obtained results are discussed.

Precise characterization of fiber Bragg gratings for photonic communications systems

A new class of structures based on fibre Bragg gratings enable the next generation of lightwave communication systems. However, these devices require precise recording and determination of the fibre Bragg gratings characteristics for optimized performance. In this paper we present a technique for a precise spatial characterization of gratings based structures. A theoretical model as well as the corresponding experimental setup are presented and compared.

Regeneration of FBGs during the HFCVD diamond-fiber coating process

In this work, the regeneration of saturated fiber Bragg gratings during the diamond coating of the fiber is presented. Due to the high temperatures characteristic of the hot filament chemical vapor deposition (HFCVD) process (around 800 ºC), uniform fiber Bragg gratings (FBGs) are not appropriate to be coated. Nevertheless, regenerated Bragg gratings are a suitable solution for this drawback. Its production process involves the inscription of a saturated FBG followed by a time consuming heat treatment. Here it is proposed to take advantage of the high temperatures characteristic of the HFCVD process to simultaneous regenerate the grating and coat the fiber with diamond.

Theoretical modeling of an U-shaped SPR fiber sensor in 1550 nm spectral range for sensing applications

Currently, the surface plasmon resonance (SPR) based sensors are mainly focused in visible frequencies, being a barrier for a better integration with the typical fiber optical communication transmission bands. Here, it is presented a theoretical analysis of a SPR based fiber optic sensor with a uniform gold coating on a U-shaped probe. The sensor does not require any fiber etching treatment which eases and improves the control of the overall process. The response of the device to refractive index variations was investigated and a resolution of 10-8 is foreseen for refractive indices around 1.413, becoming the proposed sensor a useful tool for biological and chemical applications.

Polymer Optical Fiber Sensors and Devices

This chapter will present a review of polymer optical fiber-based sensors and techniques. The main characteristics of optical fibers will be briefly summarized, with special focus on POFs. Since POF end face termination plays an important role in the coupling efficiency, the recent technologies used to prepare the POF end face will be described. Finally, the most recent advances in sensing technologies employing POFs will be reviewed. R. Oliveira ( ) • F. Sequeira • L. Bilro • R. Nogueira Instituto de Telecomunicações, Campus Universitário de Santiago, Aveiro, Portugal e-mail: oliveiraricas@av.it.pt; fsequeira@av.it.pt; lucia.bilro@av.it.pt; rnogueira@av.it.pt

In-series fiber Bragg gratings and multimode interferometers for sensing applications

Bragg gratings and multimode interferometers are used for monitoring strain, refractive index, temperature and liquid level. Resolutions of 4.3μϵ, 1.6oC and 4x10^-4 were obtained for strain, temperature and refractive index respectively. Liquid level measurements revealed a 0.25dB/mm sensitivity.

Simultaneous regeneration of seed FBGs during the HFCVD diamond-grating coating process and its thermal monitoring

In this work, the simultaneous regeneration of seed fibre Bragg gratings (FBGs) during the diamond-grating coating and the thermal monitoring of that process is presented. The diamond was deposited through the hot filament chemical vapour deposition (HFCVD) process, and due to the high temperatures characteristics of this method (above 800 ºC), regenerated FBGs are suitable samples to be coated. The advantages of this study are the possibility to regenerate the seed gratings during the coating process, becoming the fibre more resistant and the procedure less time consuming, and to control the temperature, a critical parameter for the morphology of the deposited layers.

Fast inscription of Bragg grating arrays in undoped PMMA mPOF

In this work, the inscription in few seconds of a Bragg grating array in undoped PMMA mPOF using the phase mask technique is reported. The fast growth was possible through the use of a 248 nm UV laser, with suited laser parameters, allowing the creation of a core refractive index modulation without damaging the fiber surface. The Bragg gratings were written in the IR region presenting good spectral properties, achieving for the best case 30 dB reflectivity and 0.2 nm bandwidth. The Bragg grating array was characterized to strain and results are in agreement with the values reported in literature.

Surface-core fiber gratings

In this paper, we report, to our knowledge, the first demonstration of the induction of long-period and Bragg gratings on surface-core optical fibers. Surface-core fibers described herein were fabricated from commercial silica tubes and germanium-doped silica rods by employing a very simple procedure. Being the core on the fiber surface, it can be sensitive to refractive index variations in the environment in which the fiber is immersed. Thus, results concerning the sensitivity of these gratings to environmental refractive index variations are presented. Besides, simulation data are presented for comparison to the experimental behavior and for projecting future steps in this research.