Abstract
The fibre optic current sensor demonstrated here uses the intrinsic temperature and wavelength dependence of the Verdet constant of a terbium gallium garnet (TGG) magneto-optic material and the two micro-optic linear polarizers attached, to simultaneously extract the values of temperature and the optical Faraday rotation (induced by the presence of the magnetic field due an electric current on a conductor) without any extra optical component attached to the optical sensor head. The simultaneous measurement is achieved by illuminating the sensor head with a broadband optical source and by careful signal processing of the originated channelled-spectrum, compensate the sensor's temperature dependence.

Abstract
It is presented a study of the dependence between the free spectral range (FSR) and the cavity length in Fabry-Perot interferometers. Furthermore, the effect of frequency modulation on the FSR is studied when an optical spectrum analyser (OSA) is used as an interrogator. For low frequency range it is possible to observe this behaviour in the OSA and using an appropriate processing signal it is possible to use the white light interferometry technique.

Abstract
In this paper, we study the implementation of a secure key distribution system based on an ultra-long fiber laser with a bi-directional erbium-doped fiber amplifier. The resilience of the system was tested against passive attacks from an eavesdropper. A similarity was observed in the spectra for both secure configurations of the system and no signature that would allow an eavesdropper to obtain the secure state of the system was observed during the state transitions.

Abstract
The decoupling of temperature and refractive index measurements was achieved by exploiting the properties of the asymmetric spectrum generated by Fano resonance, resulting from the interference between the Bragg reflection of the grating and the Fresnel reflection at the fiber tip. This spectral asymmetry enabled the implementation of a combined wavelength-based and intensity-based interrogation scheme. By separating the influence of each parameter in the spectral response, it was possible to measure the refractive index independently, without interference from temperature variations. A refractive index sensor with a minimum detectable change of d = 1.2 × 10?4 RIU was demonstrated. In addition to introducing a novel structure that leverages Fano resonance, the sensor was also applied as an evaporation rate sensor. The results demonstrate its potential for a wide range of applications, serving as a foundation for the development of future optical sensing technologies. © 1983-2012 IEEE.

Abstract
A refractive index sensor was designed using a novel approach to sensing based on a cleaved standard fiber Bragg grating (FBG) at the grating region, which enables the FBG to interact with its surrounding environment. The sliced-FBG (SFBG) exhibits a variable phase shift in the reflection response due to the length of the last grating's pitch, which differs from the rest. At the SFBG, the signal is the result of interference between the reflected wave from the grating and the transmitted spectrum returned due to Fresnel reflection at the final pitch, and the intensity of this signal depends on the refractive index of the surrounding medium. Based on this phenomenon, an intensity-based refractive index sensor with self- referencing technique was employed in this experiment, whereby the grating peak maximum point served as the signal reference, while the minimum of the Fresnel peak from each measurement functioned as the signal input. The proposed sensor demonstrated the ability to measure refractive indices within the range of 1.333-1.339, with a resolution of approximate to 10(-3), and a minimum detectable value of 6x10(-4) RIU (the data yielded a linear response with R-2=0.990). This study presents an innovative data sensing approach compared to existing techniques found in literature, which typically employ wavelength variation in the reflected wave to extract the desired information.

Abstract
This work analyzes the sensitivity of an optical system consisting of two fiber Fabry-Perot ( FP) interferometers and the apparent increase in sensitivity due to the harmonics of the Vernier effect. Two scenarios are examined: (1) when the larger FP cavity acts as the sensor, and (2) when the smaller FP cavity acts as the sensor. The computation analysis reveals that in the first scenario, higher-order spectral harmonics yield greater sensitivity for maxima and minima of the same order. In the second scenario, however, the sensitivity remains constant and does not depend on the harmonic order. Moreover, it is demonstrated that the sensitivity curve is identical for both scenarios, regardless of the harmonic order. This outcome occurs because the use of spectral harmonics simply reduces the free-spectral range in certain situations, bringing the extrema closer to the maximum sensitivity condition (i.e., Delta L = 0) and thereby increasing sensitivity. Consequently, if points on the envelope other than maxima or minima are used, the sensitivity achieved is the same for both scenarios.