Abstract
A micromachined low finesse Fabry-Perot interferometer for measuring dc and ac electrical current is presented. Interrogation of the microcavity is achieved by a dual-wavelength fiber Bragg grating technique working in quadrature. A linear relation between the dc electrical current and the optical phase defined by the microcavity was detected. Large enhancement of the sensitivity of the microcavities is presented with the use of a planar coil instead of a power line. The sensitivity of the sensor with the planar coil configuration is 7.9 rad/A and resolution of similar to0.18 mA/rootHz is achieved when the distance between the planar coil and the transducer head is 2 mm. The response of the sensor for ac measurements is 0.14 V/A with a resolution of 6 mA/rootHz when the distance between the power line and the transducer head is 5.5 cm.

Abstract
Singlemode-multimode-singlemode fiber structures (SMS) based on distinct sections of a pure silica multimode fiber (coreless-MMF) with diameters of 125 and 55 mu m, were reported for the measurement of curvature and temperature. The sensing concept relies on the multimode interference that occurs in the coreless-MMF section and, in accordance with the length of the MMF section used, two fiber devices were developed: one based on a bandpass filter (self-image effect) and the other on a band-rejection filter. Maximum sensitivities of 64.7 nm.m and 13.08 pm/degrees C could be attained, for curvature and temperature, respectively, using the band-rejection filter with 55 mu m-MMF diameter. A proof of concept was also explored for the simultaneous measurement of curvature and temperature by means of the matrix method.

Abstract
Theoretical and experimental results of three different high-birefringent fiber loop mirrors with output ports are analyzed. For theoretical model, the Jones matrix analysis is used. The theoretical studies present similar results for all experimental configurations. The last configuration is tested as an interrogation system where the spectral response arises from the combination of the reference signal modulated by the sensor signal. The configuration is characterized in strain with the phase changes recovered from two quadrature phase signals, providing a sensitivity of 16 mrad/mu epsilon with a resolution of 1.9 mu epsilon.

Abstract
Different multiwavelength Raman fiber lasers based on a hybrid cavity setup are proposed. The lasing schemes are based in highly birefringent photonic crystal fiber loop mirrors combined with random cavities. The Hi-Bi PCF loop mirrors are characterized by an interferometric output; whereas the random mirrors are created by cooperative Rayleigh scattering due to Raman gain. This configuration allows suppression of Rayleigh associated noise growth, while taking advantage of it as an active part of the laser cavity, enhancing the achievable gain. The proposed fiber lasers present stable operation at room temperature although different output maxima and shapes depending on the fiber loop mirror/random mirror combination.

Abstract
sThe interrogation of a Fabry-Perot cavity through a dual wavelength Raman fiber laser is reported. The proposed sensing system is based on the use of a dual wavelength Raman fiber laser to generate two quadrature phase-shifted signals that allow the recovery of the temperature change sensed by the Fabry-Perot interferometric cavity. The dual wavelength Raman fiber laser is based on fiber Bragg gratings combined with a distributed mirror. The Fabry-Perot cavity is fabricated by splicing a short length of a suspended-core microstructured fiber to a single mode fiber. The use of this sensing system allows a passive and accurate interrogation of the temperature, while taking advantage of the Rayleigh scattering growth as a distributed mirror in the laser.

Abstract
A technique for interrogating multiplexed FBG sensors using all-fiber low-cost devices is demonstrated. It is based on spectral filtering employing a fused biconical wavelength-division multiplexer and on amplitude-to-phase optical conversion to perform power referencing. Four FBG sensors are wavelength multiplexed in the network, and a 3-nm-wide tunable optical filter is, employed at the detection block for sensor demultiplexing. With this technique an operation range of more than 2 nm is demonstrated for the sensors with achievable wavelength static resolution ranging from 1.9 to 13.4 pm/Hz(1/2) with no observable hysteresis. As for power referencing, the system is proven to be unaffected by power variations as high as 75% of the total power launched by the source. Finally, output-phase variations due to crosstalk are shown to be under 1% of-the total output phase range, with more than 29-dB optical isolation between channels.