Maria Angeles Quintela

Comparison of the Stability of Ring Resonator Structures for Multiwavelength Fiber Lasers Using Raman or Er-Doped Fiber Amplification

An experimental comparison of the stability performance of two multiwavelength lasers, based on either an erbium-doped fiber or Raman amplification, is reported. Both systems employ fiber Bragg gratings to select the operating wavelengths within the resonant ring cavity. The aim of this study is to compare the output power stability of the lasers and also their optical SNR ratios.

Tunable Dual-Wavelength Random Distributed Feedback Fiber Laser With Bidirectional Pumping Source

A stable tunable dual-wavelength random fiber laser is presented in this paper. It is based on the combination of an erbium-doped fiber and a Raman gain amplifier as an active medium and a single-mode fiber as distributed mirror forming a cavity with the fiber Bragg gratings using Rayleigh scattering as random distributed feedback with bidirectional pumping from a unique pump source. An output power instability as low as 0.11 dB has been attained. The 3-dB line-width is 0.13 nm, the optical signal-to-noise ratio is up to 50 dB and the dual-wavelength tunable band is over 9 nm.

A Switchable Erbium Doped Fiber Ring Laser System for Temperature Sensors Multiplexing

In this paper, a proof of concept of a switchable erbium-doped fiber ring laser (EDFRL) system that demonstrates temperature sensors multiplexing is carried out showing a high linearity and a sensitivity of 1.55

DBR Fiber Laser Sensor With Polarization Mode Suppression

{\rm GHz}/^{\circ}{\rm C}

Spectroscopic analysis technique for arc-welding process control

. The system is based on the detection in the electrical domain of the resulting beat signal of two different laser lines generated by an EDFRL that operates in single longitudinal mode regime (SLM). The SLM operation is achieved by the use of phase shift fiber Bragg gratings with ultranarrow bandwidths of 6 pm. Two independent cavities for the reference signal and sensor signal generation are used to avoid the wavelength competition and to improve the stability. This configuration allows the control of the temperature operation point of the system by adjusting the temperature in the reference side.

Study of Fiber Bragg Grating Spectral Overlapping for Laser Structures

A distributed Bragg reflector fiber laser sensor based on a commercial high-birefringence Er-doped fiber has been proposed. The spectral overlap of two uniform fiber Bragg gratings has been employed as filtering technique to achieve a sensing head that operates in the single longitudinal mode regime. The high-birefringence Er-doped fiber has been employed to remove a polarization mode, only allowing the oscillation of a single polarization mode. In this way, a single frequency operation with a very stable laser output has been achieved. The proposed fiber laser exhibits a linear response for both strain and temperature variations, keeping the SLM regime and the polarization mode suppression.

Sensor System Based on a Brillouin Fiber Laser for Remote in Series Fiber Bragg Gratings Interrogation

The spectroscopic analysis of the light emitted by thermal plasmas has found many applications, from chemical analysis to monitoring and control of industrial processes. Particularly, it has been demonstrated that the analysis of the thermal plasma generated during arc or laser welding can supply information about the process and, thus, about the quality of the weld. In some critical applications (e.g. the aerospace sector), an early, real-time detection of defects in the weld seam (oxidation, porosity, lack of penetration, ...) is highly desirable as it can reduce expensive non-destructive testing (NDT). Among others techniques, full spectroscopic analysis of the plasma emission is known to offer rich information about the process itself, but it is also very demanding in terms of real-time implementations. In this paper, we proposed a technique for the analysis of the plasma emission spectrum that is able to detect, in real-time, changes in the process parameters that could lead to the formation of defects in the weld seam. It is based on the estimation of the electronic temperature of the plasma through the analysis of the emission peaks from multiple atomic species. Unlike traditional techniques, which usually involve peak fitting to Voigt functions using the Levenberg-Marquardt recursive method, we employ the LPO (Linear Phase Operator) sub-pixel algorithm to accurately estimate the central wavelength of the peaks (allowing an automatic identification of each atomic species) and cubic-spline interpolation of the noisy data to obtain the intensity and width of the peaks. Experimental tests on TIG-welding using fiber-optic capture of light and a low-cost CCD-based spectrometer, show that some typical defects can be easily detected and identified with this technique, whose typical processing time for multiple peak analysis is less than 20msec. running in a conventional PC.

Methane detection using Wavelength Modulation Spectroscopy and a multiline quantitation method

In this letter, different parameters of the spectral overlapping filtering technique have been analyzed for laser structures. Despite the promising preliminary experimental results obtained using this filtering technique, the optimization of the fiber Bragg grating (FBG) parameters to reduce the bandwidth of the achieved filter depending on the fiber laser requirements and configuration, should be performed. The simulated results have been confirmed during the experimental tests, where the same bandwidths and power evolutions have been measured using a ring laser configuration. This technique has been also tested for very narrow filtering purposes by achieving the single longitudinal mode operation with a ring cavity of L ≈ 8 m, using only two uniform FBGs.

Virtual FBGs Using Saturable Absorbers for Sensing with Fiber Lasers

A simple sensor system designed to monitor the temperature or strain of a certain number of critical points along a structure is presented and demonstrated. It is based on the remote interrogation of fiber Bragg gratings (FBGs) placed in series by means of a Brillouin fiber laser. Three FBGs were interrogated 50 km from the processing unit using 8 mW of Brillouin pump. Heterodyne detection brings forth a signal-to-noise ratio of approximately 40 dB in our measurements.

Ultrahigh Temperature Raman-Based Distributed Optical Fiber Sensor With Gold-Coated Fiber

In this paper the application of the Inverse Least Squares algorithm (ILS) to the detection of methane using its behaviour in the near-infrared band is presented. In order to test the effectiveness of this method, different methane concentrations were measured. Wavelength Modulation Spectroscopy (WMS) was employed to obtain the first and second harmonics of the modulation signal. The use of both harmonics in spectroscopy eliminates the dependence of the measured absorbance on parameters such as: fiber misalignments, optical power fluctuations, etc. This property greatly increases the accuracy of the concentration readings. The benefits of analysing multiple lines in gas detection are discussed together with the capabilities of the ILS algorithm. The ILS algorithm is based on the Beer-Lambert law. This law is extended to include multiple wavelengths and rearranged in such a way that the concentration of the chemical species depends on the measured absorbances. In order to apply the previous algorithm, three absorption lines centered at 1665.961 nm, 1666.201 nm and 1666.483 nm were used. The obtained results are compared with the most usual single-line calibration method based on linear regression. This comparison shows that ILS gives a superior performance. Specifically, results indicate that the ILS multiline algorithm is less noise dependent and has a higher reliability than single-line calibration methods.