Paulo André

Mechanical Properties of Optical Fibers

Nowadays, optical communications are the most requested and preferred telecommunication technology, due to its large bandwidth and low propagation attenuation, when compared with the electric transmission lines. Besides these advantages, the use of optical fibers often represents for the telecom operators a low implementation and operation cost. Moreover, the applications of optical fibers goes beyond the optical communications topic. The use of optical fiber in sensors applications is growing, driven by the large research done in this area in recent years and taking the advantages of the optical technology when compared with the electronic solutions. However, the implementation of optical networks and sensing systems in seashore areas requires a novel study on the reliability of the optical fiber in such harsh environment, where moisture, Na+ and Clions are predominant. In this work we characterize the mechanical properties, like the elastic constant, the Young modulus and the mean strain limit for commercial optical fibers. The fiber mean rupture limit in standard and Boron co-doped photosensitive optical fibers, usually used in fiber Bragg grating based sensors, is also quantify. Finally, we studied the effect of seawater in the zero stress aging of coated optical fibers. Such values are extremely relevant, providing useful experimental values to be used in the design and modeling of optical sensors, and on the aging performance and mechanical reliability studies for optical fiber cables.

Experimental Demonstration of a 33.5-Gb/s OFDM-Based PON With Subcarrier Pre-Emphasis

Spectral efficiency is one of the critical issues in passive optical networks (PONs). Thus, next generation PON systems must employ advanced modulation techniques and channel compensation to improve the network performance and provide more bandwidth for end users. In this letter, we have experimentally demonstrated a spectral efficiency improvement in PONs based on the bandwidth scalable orthogonal frequency division multiplexing (BSOFDM-PON), considerably reducing the recommended optical guard band of such direct detection systems. The experimental results show that this efficiency can be achieved in a 33.5-Gb/s BSOFDM-PON on one wavelength channel when subcarrier pre-emphasis is used.

In the trail of a fiber Bragg grating sensor to assess the central arterial pressure wave profile

Cardiovascular diseases are one of the primary causes of death in the world. Hemodynamics is the study of the blood propagation and the physics aspects concerned to it, relating pressure, flow and resistance. One of the most important topics on hemodynamics is the evaluation of arterial wave reflections. Recently this physical parameter of the pressure wave propagation through the arterial tree was considered as a novel strong risk factor for cardiovascular diseases. Arterial pressure reflections can be quantified by central pressure profile analysis. In this work we study in the trial of an optical fibre Bragg grating based sensor of assess the central pressure profile, with the goal of to achieve a superior sensitivity, with a better signal quality than electromechanical probes, measured directly in the carotid artery.

Polymer Optical Fiber Sensors Approaches for Insole Instrumentation

Advantages like electromagnetic field immunity, fracture toughness, high strain limits, flexibility in bending and impact resistance of polymer optical fibers (POFs) are beneficial for applications that involve embedment in flexible structures. Since insoles are one of these flexible structures that may be used in different wearable applications, POFs can be applied and this paper proposes the application of POF sensors in insole instrumentation with two different approaches: intensity variation-based and polymer optical fiber Bragg gratings (POFBGs). Results show that both approaches present low errors with root mean squared errors (RMSEs) of 45.17 kPa for the plantar pressure monitoring with the POFBG-based insole and 5.30 N for the ground reaction force measurement with the intensity variation sensors. These results demonstrate the feasibility of POF sensors applications in flexible structures and in wearable applications such as insoles and soft robotics instrumentation.

Biaxial optical fiber sensor based in two multiplexed Bragg gratings for simultaneous shear stress and vertical pressure monitoring

This work consists on the design and implementation of a compact and accurate biaxial optical fiber sensor (OFS) based on two in-line fiber Bragg gratings (FBGs) for the simultaneous measurement of shear and vertical forces. The two FBGs were inscribed in the same optical fiber and placed individually in two adjacent cavities. In the calibration and performance tests, the response from the optical fiber cells was compared with the values given by a three-axial electronic force sensor. Sensitivity values obtained for the FBG1 are K1V= (14.15±0.10) pm/N (vertical force) and K1S= (-26.02±0.08) pm/N (shear force) and for the FBG2 are K2V= (7.35±0.02) pm/N and K2S= (-24.29±0.08) pm/N. The conversion of the Bragg wavelength shift, given by the optical fiber sensors, into the shear and vertical force values is also presented along with its comparison to the values retrieved by an electronic sensor, yielding to low RMSE values, which shows the high accuracy of the algorithm applied. This work stands out from the others with optical fiber by the simplicity of its structure. The proposed solution represents a compact and reliable device for simultaneous measurement of shear and vertical forces, useful in several areas, such as: incorporation into insoles for plantar pressure and shear force measurement; electronic skin technologies; smart rehabilitation robotic exoskeletons; or even biomimetic prosthesis.

High-quality phase-shifted Bragg grating sensor inscribed with only one laser pulse in a polymer optical fiber

We present the first phase-shifted polymer optical fiber Bragg grating sensor inscribed with only one KrF laser pulse. The phase shift defect was created directly during the grating inscription process by placing a very narrow blocking aperture, in the center of the UV beam. One laser pulse with a duration of 15 ns and energy 6.3 mJ is adequate to introduce a refractive index change of 0.69×10−4 in the fiber core. The high-quality produced Bragg grating structure rejects 16.3 dB transmitted power, thus providing 97.6% reflectivity, which is well suited for photonic applications. The transmission notch depth is about 10 dB and very sharp notches of 3 dB width ranging from 14 pm is reported. The temperature, strain, and pressure response of the sensor has been characterized showing promising results in applications that require high-precision measurements. The ability to inscribe these high-quality sensors effectively can significantly reduce their production cost in industry.

Multiwavelength conversion based on reflective semiconductor optical amplifiers

In this contribution the routing capabilities of time/wavelength codes in Optical Code Division Multiple access are observed by means of the study of two devices for achieving the wavelength part code conversion. Multi-wavelength conversion will be achieved by using a Semiconductor Optical Amplifier and a Reflective Semiconductor Optical Amplifier. The conversion results for the two devices will be characterized and compared in terms of applicability to the conversion in hands and to the referred application.