F. Domingues

Threshold power of fiber fuse effect for different types of optical fiber

In this work we measured the threshold power level for the fiber fuse effect ignition and propagation for different types of optical fibers. We verified that the threshold power is not proportional to the fiber mode field diameter.

Thermal Effects in Optical Fibres

Optical fibres are essential components in the modern telecommunication scenario. From the first works dealing with the optimization of optical fibres transmission characteristics to accommodate long distance data transmission, realized by Charles Kao (Nobel Prize of Physics in 2009), until the actual optical fibre communication networks, a long way was paved. The developments introduced in the optical communication systems have been focused in 3 main objectives: increase of the propagation distance, increase of the transmission capacity (bitrate) and reduction of the deployment and operation costs. The achievement of these objectives was only possible due to several technological breakthroughs, such as the development of optical amplifiers and the introduction of wavelength multiplexing techniques. However, the consequence of those developments was the increase of the total optical power propagating along the fibres. Moreover, in the last years, the evolution of the optical networks has been toward the objective of deploying the fibre link end directly to the subscribers home (FTTH – fibre to the home). Thus, the conjugation of high power propagation and tight bending, resulting from the actual FTTH infrastructures, is responsible for fibre lifetime reduction, mainly caused by the local increase of the coating temperature. This effect can lead to the rupture of the fibre or to the fibre fuse effect ignition with the consequent destruction of the optical fibre along kilometres. In this work, we analyze the thermal effects occurring in optical fibres, such as the coating heating due to high power propagation in bent fibres and the fibre fuse effect. We describe the actual state of the art of these phenomena and our contribution to the subject, which consists on both experimental and numerical simulation results.

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.

Monitorization of sea sand transport in coastal areas using optical fiber sensors

Novel optical fiber sensors for monitoring the dynamic variations of the sea bed level in the nearshore were developed. The sensors are based on fiber Bragg gratings embedded in a polyurethane resin. For this solution sensitivities of 0.50±0.02 nm/m were achieved. The sensor was tested under controlled laboratory conditions and during an observational survey on the Algarve (Portugal) coastline.

Halting the fuse discharge propagation Using optical fiber microwires

We report and analyze the halting of the fuse effect propagation in optical fiber microwires. The increase of the mode field diameter in the tapered region decreases the optical intensity resulting in the extinction of the fuse effect. This fiber element presents a low insertion loss and can be introduced in the optical network in order to protect the active equipment from the damage caused by the fuse effect.

Recycling optical fibers for sensing

Optical fiber sensors has become one of the most promising sensing technologies. Within all the optical fiber sensing technologies, the Fabry-Perot interferometer (FPI) micro-cavities are one of the most attractive, due to the size, linearity and higher sensitivity. In this work we present the recent results, achieved by our group, regarding the production of optical sensors, by recycling optical fibers destroyed through the catastrophic fuse effect. This enabled the production of FPI sensors, in a cost effective way, tailored for the monitoring of several physical parameters, such as relative humidity (RH), refractive index (RI) and hydrostatic pressure.

Configuration for detecting the fiber fuse propagation using a FBG sensor

Here, we propose a new configuration to remotely detect the fiber fuse propagation. This configuration uses a Fiber Bragg Gratings (FBG) as temperature sensor to monitor the displacement of the thermal wave associated with the fuse effect.

Evaluation of the fuse effect propagation velocity in bend loss insensitive fibers

In this work we investigate the dynamics of the fuse effect propagation in bend loss insensitive fibers. The fuse velocity, threshold power and void period values were compared with those obtained for standard single mode fibers. The results show that the power dependent optical discharge velocity coefficient is 32% higher in G.657 fibers than that in G.652 fibers.

Failure probability of optical fiber under high optical power and small bend diameters

In this work, we investigate the time to failure and the failure probability of optical fiber submitted to small bent diameters and high optical powers. The bent diameters under study were 2.9, 3.1 and 3.3mm and the optical powers injected in the bent fiber had the values of 1.0, 1.5 and 2.0 W. For the bending diameter of 3.1 mm the failure probability presented a Weibull parameter of −0.279±0.021 for the optical power of 1.5 W and −1.38±0.158 for the optical power of 1.0 W. For the injected optical power of 2 W the failure probability presented a Weibull parameter of −0.307±0.025 for a bending diameter of 3.1 mm and −0.617±0.036 for a bending diameter of 3.3 mm.

Impact of the maritime environment on the aging of optical fibers

The effect of the maritime environment on the aging of optical fibers coatings was studied. The obtained stress decay rate was 29.05 days, however, this value is higher than for a pure water saturate environment.