This paper presents a tunable, switchable multi-wavelength emission from an erbium-doped fiber ring laser, enabled by adjusting the spectral fringe visibility of a fiber interferometer filter. The filter is formed with specially designed concatenated tapered fibers to configure a Mach-Zehnder fiber interferometer (MZFI). The laser emission is highly flexible and reconfigurable, allowing for tuning between single- and dual-wavelength operation. The laser can switch sequentially from one up to six wavelengths by fixing the curvature and adjusting the polarization state. The lasing emission is generated over a stable wavelength range between 1559.59 nm and 1563.54 nm, exhibiting an optical signal-to-noise ratio (OSNR) exceeding ~35 dB. The performance of amplitude and wavelength fluctuations were evaluated, indicating an appropriate stability of ~3 dB and a shift less than 0.1 nm within a 45 min period at room temperature. A detailed comparison with the literature is given.

A fiber optic curvature sensor based on a tapered single-mode optical fiber coated with a polyester polymer (T-SMF-CPP) is proposed and experimentally demonstrated. Fabrication of the tapered optical fibers was realized by heating and stretching by a flame, and an airbrush was used to coat the surface of the tapered fiber with the polymer. The operating principle of the sensor was based on the interaction of the evanescent wave with the polyester polymer deposited on the tapered fiber. By adopting intensity demodulation in experiments, average sensitivities of -5.017 dB/m-1 and 5.862 dB/m-1 in the curvature ranges from 1.23 to 4.44 m-1 and from 4.64 to 7.54 m-1, respectively, were obtained for a fixed wavelength of $\lambda =1572.45$ nm. The curvature of the sensor did not show a temperature dependence in the range [24-90 °C].

A multiwavelength Q-switched erbium-doped fiber ring laser based on a section of Tm-Ho codoped fiber as a saturable absorber, assisted by a tapered optical fiber filter to stabilize the lasing performance is reported. The tapered fiber structure acts as a comb filter that allows us simultaneous lasing wavelengths at 1529.69, 1531.74, and 1533.48 nm with high stability. By adjusting the pump power, optical pulses with repetition rates from 10.46 to 61.8 kHz were obtained. The maximum average output power was 27.61 mW, while 496.34 nJ for the maximum pulse energy. The fiber laser exhibits a power deviation of ± 0.376 dB, an OSNR of 54 dB, and a spectral width of lasing lines of 0.06 nm, with stable multiwavelength lasing.

Corrosion monitoring is essential to assess the integrity of metal structures and prevent critical failures. Corrosion increased in coastal areas by the chemical reaction between moisture and sodium chloride. Because of this, different techniques have been developed for monitoring and contributing to the integrity in metal structures. However, more effort is needed to assess structural integrity in different industries. In this work, a tapered optical fiber sensor for monitoring corrosion processes in the X70 pipeline steel immersed in natural seawater is proposed and experimentally demonstrated. A DC electrochemical test was carried out to obtain potentiodynamic polarization curves, which are associated with different corrosion processes occurring in the metal samples at different electrode potentials. The fabrication process of the tapered optical fibers consisted mainly of heating the fiber with a flame and stretching it. The operating principle of the sensor was based on the interaction of the evanescent wave with corrosion products dissolved in seawater at 50 °C. The fiber optic sensor response was related to regions of the potentiodynamic polarization curve of X70-PS in seawater at 50 °C. Therefore, from 0.12 to 0.0285 μW correspond to the anodic and cathodic regions at potentials of the electrode between −2 and −0.5 V and −0.5 and 1 V, respectively. Moreover, this optical response could be correlated with some corrosion processes experienced by the metallic samples such as pre-passivation and passivation.