A 3X3 plastic optical fiber (POF) twisted coupler has been fabricated as a compact sensor of multiple variables. The POFs are twisted into a combined body and the clad was removed by chemical method. Three LEDs of red, green, and blue colors can be used to shape a broad spectrum. Each led was connected at a different input port of the coupler. Since the twisted coupler makes the coupling of light from the input ports, we have a wide spectrum at each one output port. We develop a different sensor at each one output coupler: mass concentration (At the output-1), and curvature (At the output-2). The multi-sensing proposed in this work can increase the number of sensors as increase the number of output ports, and the bandwidth increase as increase the colors of light sources. On the other hand, we can use a wide spectrum lamp in a single input port and in the same way make multiple sensors in the output ports. The variation is evident in all wavelengths of the spectrum for measurements of sugar concentrations and fiber curvature. However, we can directly associate the sugar concentration variations with the spectrum in a range from 570 to 600 nm; and across the full spectrum for curvature measurements.
We present a calibration approach for rotating polarizer-analyzer polarimeter dedicated to retardance measurements. The rotating polarizer-analyzer polarimeter is based on retrieving a partial Mueller matrix measurement of a transparent sample to be later associated with its phase retardation properties. Through the Mueller matrix approach, we developed a calibration procedure considering the initial orientation of the two linear polarizers used, and we present experimental results showing the feasibility of our calibration approach.
We propose to use the fast Fourier transformation (FFT) to analyze the spectral data of passively mode-locked fiber lasers, with the purpose of characterizing and classifying the different pulsed regimes arising in these lasers. The results show temporal information at the sub-ps scale. Specially, in the Fourier domain, the spectra of bound solitons depict several solitons with relative phases of π/2 and close to 0, distributed into a window that extends beyond the limited span of the autocorrelator. Besides, the FFT amplitude traces can help to classify the multi-pulse regimes generated by the laser; in particular, the exponential decay of intensity in such amplitude traces can be a fingerprint of noise-like pulses. Furthermore, the amplitude traces show some modulation that we attribute to Kelly’s sidebands. The proposed technique allows examining spectra from a mode-locked fiber laser independently of the active medium or laser cavity configuration without the need to use ultrafast photo- detectors.
In this work, we proposed a procedure for the calibration of 3D surface shape measurement system, which is based on fringe projection and phase shifting algorithms. Our approach consists in the use of temporal phase unwrapping methods to determine the phase-to-height mapping relationship. In particular, we propose the use of the two-step temporal phase-unwrapping algorithm. For that, two sequences of fringe patterns (low and high sensitivity) are projected onto the reference plane, which is shifted perpendicularly to the camera-projector plane. Then, the phase maps at each shifting step are retrieved from acquired sequences of sinusoidal intensity patterns using the two-step temporal unwrapping formula. Finally, using the phase maps at well-known in a least-squares scheme, the system parameters, nonlinear model of calibration, are estimated, i.e. the phase-to-height mapping relationship. Validation experiments are presented.
In this paper, we report an experimental study of the supercontinuum (SC) generated by molecules of solitons (MS) and noise-like pulses (NLP) in two different types of optical fibers: 500m of standard fiber (SMF-28, Corning) and 100m of High-Nonlinearity Fiber with a zero dispersion-slope (HNLF-ZS, Furukawa). We extracted information on the inner structure of SC by using a nonlinear optical loop mirror (NOLM) as an intensity filter. The NOLM suppresses pulses with low peak power, which is especially pronounced for wavelengths longer than ~1750 nm for both fibers, and particularly in the region between 1450 nm and 1640 nm for the High-Nonlinearity fiber. It is worth mentioning that depending on the application, the required properties of SC light can vary considerably. Therefore, it is the main importance to know the properties of the different SC sources.
In this work, we proposed the usage of a rotating polarizer-analyzer polarimeter to retrieve retardance parameters of a sample by treating it as an elliptical retarder that can be characterized by three parameters: total retardance, fast axis orientation and an ellipticity related parameter. By employing the Mueller matrix approach, we developed the demodulation algorithm to retrieve each parameter with the association of the Fourier series analysis. We present experimental results considering dextrose concentrations diluted in distilled water scaling in a range from 30mg/dl to 45mg/dl. For comparison purposes, we employed the method of rotating an analyzer and compare the optical activity variation for both methods.
We report dual-wavelength mode-locked operation of a passively mode-locked Er-doped fiber laser (EDFL) including two sections of a fiber with equal length, one right hand twisted and another left hand twisted, and a double-pass amplifier with Faraday Mirror (FM). The configuration allows cancellation of the influence of both linear and circular birefringence and strict control of the polarization of pulses in the cavity. Depending on the polarization azimuth we observed synchronous dual-wavelength, 1532 nm and 1560 nm, noise-like pulses (NLP), and desynchronized soliton emission.
Passively mode-locked fiber lasers are capable of generating a variety of optical pulses, depending of the pump power and cavity adjustments, which makes them attractive for research in multidisciplinary fields. In this paper, we analyze the experimental results of a fiber laser operating in passively mode-locked regime. The figure-eight laser cavity configuration uses 4 m of a co-doped Er/Yb double clad fiber, as a gain medium, pumped by a 976 nm diode laser. The cavity is completed by an isolator for ensure unidirectional propagation, two quarter-wave retarders (QWR), and a nonlinear optical loop mirror (NOLM) with 120 m of twisted standard single-mode fiber in the loop acting as saturable absorber. We used a couple of quarter-wave retarders (QWR) QWR1 at the NOLM input and QWR2 into the NOLM loop. By carefully adjusting of the QWRs the laser generates noise-like square pulses at the 1.54 μm range. With the increase of the pump power, the laser generates harmonics of the mode-locking fundamental mode with repetition frequency of 1.38 MHz, from which we can obtain the second, third and fourth harmonic in a controlled mode.
We report a linear cavity all-fiber passive Q-switched thulium-doped fiber laser operating at the 2 μm wavelength range. The laser configuration is based on a thulium-doped fiber used as a gain medium and an unpumped segment of holmium-doped fiber which acts as a fiber saturable absorber. The cavity is formed by a fiber optical loop mirror and the flat end facet of the holmium-doped fiber. The fiber segments as saturable absorber is a 1-m long single mode doubleclad holmium-doped fiber. Q-switched pulses are obtained at the wavelength of 2024.5 nm with a pulse width of 1.1 μs. The pulse repetition rate increases as a linear function of the applied pump power. The maximum pulse repetition rate of 100 kHz was obtained with a pump power of 2.4 W.
We report the dynamics of multi-pulse in a ring cavity passively mode-locked fiber laser with a strict control of the polarization state. We study the relation between the polarization state of the pulses propagating in the cavity and the regimes of generation. We have found that small ellipticities, the laser generates one bunch of pulses in the cavity, while at higher ellipticities the laser generates multiple bunches. At constant ellipticity we rotated the polarization azimuth and observed a regime transition from the generation of a bunch of solitons to that of noise-like pulses (NLP).
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