Abstract Analysis of the state of polarization of light guided by structures recorded in lithium niobate and lithium fluoride crystals indicates that the recording method is determinant in the formation of birefringent structures. Each structure was written with a single and continuous translation of the crystal transversally to the laser beam. Birefringence was observed in the structures recorded in both crystals, despite the lack of intrinsic birefringence in lithium fluoride. The recorded structures are anisotropic showing regions with different birefringence. The structure generated with femtosecond laser is directly linked to the recording method and the crystalline lattice. This characteristic can be advantageous for application in photonic devices.

AbstractIn this work, a refractometric fiber sensor for the liquid fuels sector is described. The use of etched FBGs produced in multimode fibers is proposed to overcome the drawbacks associated with sensing high refractive index samples employing fiber transducers. The transducer sensitivity can be tailored by adjusting the final diameter of the etched Bragg grating. Due to a trade-off between the signal-to-noise ratio and the sensitivity, operational parameters of the sensor must be designed to match the expected refractive index dynamic range for specific applications. Metrological properties of the sensor are determined, resulting in resolution from 5.6 % v/v to 0.4 % v/v for refractive indexes ranging from 1.4562 to 1.4729. Specific applications regarding the quality assessment of biodiesel and conformity analysis of diesel-biodiesel blends are discussed.

This paper reports an effective method of packaging a fiber Bragg grating (FBG) for the simultaneous measurement of temperature and strain. The technique consists of embedding two fiber Bragg grating sensors inside a polymeric material with different geometrical characteristics. The mechanical and thermal characterizations of the optical transducer were performed. Then a matrix equation used measurements of the wavelength shifts from the two sensors and yielded information about the temperature and strain coefficients. The preliminary results demonstrate the feasibility of the encapsulation technique allowing measurements of temperature and strain in smart structures and harsh environments. The experimental procedure provides robustness to the sensor and the matrix equation approach has the potential to determine simultaneously the strain and temperature coefficients.

An approximated technique to quickly optimize the gain profile of multi-pump broadband hybrid amplifiers under residual pump recycling in WDM systems is proposed. It is based on the amplifier spectral equalization by adjusting the flexible gain profile of a multi-pump Raman amplification stage to compensate the Erbium-doped stage gain variation within the C-band. In order to increase the pump power efficiency, the Erbium-doped fiber section recycles the residual Raman pump. Three different cases considering, respectively, one, two, and three pumps are analyzed to demonstrate the effectiveness of the proposed technique. The characterization of the Raman+EDFA hybrid amplifier has been performed in terms of global gain, ripple, and noise figure. The proposed optimization method for the Raman pump sets allows ripple figures to be reduced by half of their original values in single pumped configurations. Our results also suggest that two pump lasers is the best configuration when the maximum gain, minimum ripple, and pump power efficiency are simultaneously considered.

We report the use of an optical fiber sensor to measure the soybean oil concentration in samples obtained from the mixture of pure biodiesel and commercial soybean oil. The operation of the device is based on the long-period grating sensitivity to the surrounding medium refractive index, which leads to measurable modifications in the grating transmission spectrum. The proposed analysis method results in errors in the oil concentration of 0.4% and 2.6% for pure biodiesel and commercial soybean oil, respectively. Techniques of total glycerol, dynamic viscosity, density, and hydrogen nuclear magnetic resonance spectroscopy were also employed to validate the proposed method.

We adopt a three-level scheme for the pump - amplification process in 1.48 mum pumped Erbium-Doped Fiber Amplifiers, which reproduces the main experimental features of amplifiers with short and long fiber lengths. Continuous wave amplification in a simplified slab waveguide structure is simulated by means of the scalar Beam Propagation Method, taking into account signal and pump propagation through the waveguide. Results from the simulation are compared with measurements done by the COST 217 Project Group. The method may be well suited for the project of Integrated Optics Optical Amplifiers based on rare earth doped waveguides.