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The ballistocardiogram (BCG) is a graphic representation of the movements of the body associated with cardiac activity. In this article, a 10-min BCG has been captured for ten different volunteers with a polymer optical fiber (POF) specklegram sensor. This transducer, which is composed of a charge-coupled device (CCD) camera, a laser emitting diode, and two meters of POF, allows capturing the BCG by analyzing how the induced speckle pattern changes over time. These changes are related to cardiac activity. Several processing methods have been compared to determine which method achieves the best performance: complex cepstrum, power of spectral density (PSD), Pam-Tompkins algorithm, wavelet, autocorrelation, Savitzky?Golay filter, mean absolute deviation, and Hilbert transform. Accuracy and resource consumption have been characterized and compared for these methods. Hilbert, PSD, and Savitzky-Golay exhibit both small errors and computational costs. This article describes a baseline for the main frequency determination of POF-based BCG signals in real-time. This work was supported by the Project PID2019-107270RB-C21 through MCIN/ AEI /10.13039/501100011033.

In recent years, the Industry 4.0 paradigm has gained special relevance, focused on the integration of smart structures to increase the efficiency of processes. Photonics, with laser advanced manufacture and light-based sensors, can offer great possibilities in this field. Within advanced manufacturing, femtosecond lasers allow inscribing different optical structures. Waveguides are one of the most widely used structures in photonic sensors. This work proposes the design, simulation and manufacture of symmetric cladding waveguides in optical fibers using the slit beam shaping technique. Cladding waveguides characterized by their low losses (0.21 dB/cm), quasi?step-index refractive index profile, and circular cross-section are used to couple evanescent light from the core of a single-mode fiber to each of the four cores of a multicore fiber. This work has been supported by the Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (PID2019-107270RB- C21), the Ministerio de Educación, Cultura y Deporte of Spain (PhD grant FPU2018/02797), and FEDER funds.

In this paper, diffractive elements in one and two dimensions have been inscribed at the end-face of single and multicore optical fibers using femtosecond lasers. Different sensing applications have been also presented on the basis of their projected far-field patterns. The manufacturing of 2D structures was achieved using two approaches: line writing and its equivalent point-by-point technique in order to speed up the process. Specific properties of both the techniques have been exploited by inscribing 2-direction and circular gratings. When diffraction grating is inscribed at the end-face of a four core fiber, the 2D interference pattern is transferred into diffraction orders with the possibility of decoupling the interferometric contribution of selected core. Particularly, with a circular diffraction grating, the multicore far-field pattern exhibits two perpendicular and independent interference patterns, as only opposite cores are interfering with each other. These patterns exhibit period and, hence, sensitivity with phase perturbation, proportional to diffraction order angle. The 2D diffraction grating inscribed in the single mode fiber has been employed for bidimensional displacement insensitive sensing, exhibiting linear response, while aforementioned structures written in multicore fiber have been proposed for bending vector sensing, thereby showing higher sensitivity than that of its pristine counterpart.

In this letter, an annealing process of UV-written fiber Bragg gratings (FBGs) has been employed to achieve FBGs with narrower reflection spectra to be employed in fiber lasers. These FBGs have been used to design distributed Bragg relfector (DBR) laser sensors working on the single longitudinal mode (SLM) regime even at high temperatures. A fiber laser sensor working on multimode regime has been written into commercial Er-doped fiber before annealing its mirror FBGs, removing the unstable UV-induced modulation part and narrowing the FBGs’ combined response. This process obtains a DBR fiber laser sensor working on SLM regime at high temperatures ( $T=500~^{\circ }\text{C}$ ), and also exhibiting a remarkably good linearity and stability. The achieved results confirm the empirically adjusted aging model and prove its usefulness to design high precision devices able to work at high temperatures.

In this study, several multiplexing techniques have been combined to achieve a fiber specklegram multiplexed sensor. Using a single CCD camera as detector, two lasers of different wavelengths have been launched into two multimode polymer optical fibers and then combined through a 2 x 2 coupler before their interrogation. Both coupler exit fibers have been projected to different CCD positions and by analyzing each color of the video sequence, the four fiber channels can be independently obtained. In addition, the speckle sensitivity has been also studied analyzing different properties of speckle patterns such as their contrast or the speckle size. The achieved results will be very useful to the development of new fiber specklegram sensors with several sensing areas using only a CCD camera as detector, making possible low cost sensing devices.

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.

This paper presents a new stable dual-wavelength fiber-ring laser based on erbium-doped fiber amplification. The wavelength selection is made by a combination of fiber Bragg gratings and phase shift fiber Bragg gratings. Two laser emission lines were obtained simultaneously in single-longitudinal-mode operation showing a power-instability lower than 0.35 dB, an OSNR higher than 55 dB, a narrow-linewidth of 13 KHz and an optical output power around 0 dBm for both wavelengths. This proposed configuration allows the individual control of the loss of each channel.

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.

In this paper a proof of concept of a switchable erbium doped fiber ring laser (EDFRL) system, demonstrated for temperature sensors multiplexing, was carried out showing a high linearity and a sensitivity of 1.55 GHz/°C. 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 (PSFBGs) with ultra-narrow bandwidths (BW) 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. The authors are grateful to the Spanish government project TEC2010-20224-C02, to the Spanish Ministry of Education and Culture, and to the grant AP2009-1403.

The recently proposed hierarchical temporal memory (HTM) paradigm of soft computing is applied to the detection and classification of foreign materials in a conveyor belt carrying tobacco leaves in a cigarette manufacturing industry. The HTM has been exposed to hyperspectral imaging data from 10 types of unwanted materials intermingled with tobacco leaves. The impact of the HTM architecture and the configuration of internal parameters on its classification performance have been explored. Classification results match or surpass those attained with other methods, such as Artificial Neural Networks (ANNs), with the advantage that HTM are able to handle raw spectral data and no preprocessing, spectral compression, or reflectance correction is required. It is also demonstrated that an optimized configuration of the HTM architecture and internal values can be derived from the statistical properties of the hyperspectral data, allowing the extension of the approach to other classification problems.