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In this paper, we propose a highly sensitive temperature sensor based on two cascaded Mach–Zehnder interferometers (MZIs) that work using the Vernier effect. The all-fiber MZIs were assembled by splicing a segment of capillary hollow-core fiber (CHCF) between two sections of multimode fibers (MMFs). This cascaded configuration exhibits a temperature sensitivity of 1.964 nm/°C in a range from 10 to 70 °C, which is ~67.03 times higher than the sensitivity of the single MZI. Moreover, this device exhibits a high-temperature resolution of 0.0153 °C. A numerical analysis was carried out to estimate the devices’ temperature sensitivity and calculate the magnification of the sensitivity produced by the Vernier effect. The numerical results have an excellent agreement with the experimental results and provide a better insight into the working principle of the MZI devices. The sensor’s performance, small size, and easy fabrication make us believe that it is an attractive candidate for temperature measurement in biological applications.

In this paper, we propose and experimentally demonstrate a simple technique to enhance the curvature sensitivity of a bending fiber optic sensor based on anti-resonant reflecting optical waveguide (ARROW) guidance. The sensing structure is assembled by splicing a segment of capillary hollow-core fiber (CHCF) between two single-mode fibers (SMF), and the device is set on a steel sheet for measuring different curvatures. Without any surface treatment, the ARROW sensor exhibits a curvature sensitivity of 1.6 dB/m−1 in a curvature range from 0 to 2.14 m−1. By carefully coating half of the CHCF length with polydimethylsiloxane (PDMS), the curvature sensitivity of the ARROW sensor is enhanced to −5.62 dB/m−1, as well as an increment in the curvature range (from 0 to 2.68 m−1). Moreover, the covered device exhibits a low-temperature sensitivity (0.038 dB/°C), meaning that temperature fluctuations do not compromise the bending fiber optic sensor operation. The ARROW sensor fabricated with this technique has high sensitivity and a wide range for curvature measurements, with the advantage that the technique is cost-effective and easy to implement. All these features make this technique appealing for real sensing applications, such as structural health monitoring.

We proposed and demonstrated a compact, simple-to-construct and highly sensitive optical fiber sensor capable of simultaneously measuring refractive index (RI) and temperature (T) based on surface plasmon resonance (SPR) effect. The device structure consists of a single mode fiber (SMF) spliced between two multimode fibers where whole SMF was coated with chromium and gold. The thicknesses of the layers of chromium and the gold were 5 nm and 30 nm, respectively. By covering half of the sensing region of the device with a polymer with high thermo-optic coefficient (TOC), it is feasible to detect RI and T changes with sensitives of 2664.540 nm/RIU and -2.852 nm/°C, respectively.

As information technologies move from electron-to photon-based systems, the need to rapidly modulate light is of paramount importance. Here, we study the evolution of the electric-field-induced ali ...

An ultracompact, cost-effective, and highly accurate fiber optic temperature sensor is proposed and demonstrated. The sensing head consists of Fabry-Perot microcavity formed by an internal mirror made of a thin titanium dioxide (TiO2) film and a microscopic segment of single-mode fiber covered with Poly(dimethylsiloxane) (PDMS). Due to the high thermo-optic coefficient of PDMS the reflectance of the fiber-PDMS interface varies strongly with temperature which in turn modifies the amplitude of the interference pattern. To quantify the changes of the latter we monitored the visibility of the interference pattern and analyzed it by means of the fast Fourier transform. Our sensor exhibits linear response, high sensitivity, and response time of 14 seconds. We believe that the microscopic dimensions along with the performance of the sensor here presented makes it appealing for sensing temperature in PDMS microfluidic circuits or in biological applications.

Compact sources of short pulses with high-repetition-rates are highly desirable for a wide range of applications such as optical coherent tomographic, metrology, optical communication, two photon microscopy, and optical clocks. This thesis is focus on the research and development of fiber lasers that emit short optical pulses. Here we purpose to use Polydimethylsiloxane (PDMS) and SU8-2075 polymers to fabricate thin films doped with SWCNTs that work like a saturable absorber. Moreover, the nonlinear behavior of these films was investigated by using an all-fiber power dependent transmission setup. Using this setup a PDMS/SWCNT film (thickness 200 μm) and SU8-2075 film (thickness 100 μm) were tested. The saturation intensity and the modulation depth of the PDMS/SWCNT and SU8-2075 films are 5.1 MW/cm2, 0.7MW/cm2, 12.3 % and 10 %, respectively. Passively mode-locked Erbium fiber ring lasers have been implemented by using PDMS/SWCNT and SU8-2075 films, the first one produces pulses at a repetition rate of 22.73 MHz with a pulse duration of 1.26 ps assuming a sech2 pulse profile. The second one has a repetition rate of 21.27 MHz with a pulse duration of 871 fs assuming a sech2 pulse profile. A hybrid mode-locked Erbium-doped fiber laser that provides very short pulse-widths while achieving high repetition rates is proposed and experimentally demonstrated. This hybrid configuration is realized by using a PDMS/SWCNT thin film composite as saturable absorber, which is inserted within an active mode-locked laser system using angled connectors. Therefore, the effect of the PDMS/SWCNT composite is to effectively narrow the width of the pulses generated by the active system without modifying its repetition rate. A pulse-width of 730 fs was generated at a repetition rate of 4 GHz, while achieving an average output power of 4 mW. A reduction in the noise of the photodetected RF spectrum was also observed in the hybrid system. Finally, a passively-Q-switching laser has also been built up by using a SU8-2075/SWCNT film. The maximum average power, peak power, and pulse energy were 160 μW, 7.3 mW, and 5.1 nJ, respectively.

A stable optofluidically tunable fiber laser based on Multimode Interference (MMI) effect is experimentally demonstrated. The tuning mechanism relies on modifying the effective width of the multimode fiber (MMF) using a liquid with a specific refractive index, which in turns tunes the peak wavelength of the filter. We easily demonstrate a tunability of almost 40 nm with a side-mode suppression ratio (SMSR) of 47 dBm, and a 3dB bandwidth of 0.4 nm. The laser was operated at room temperature without any thermal control and the wavelength peak was very stable.

El efecto de fuerza foto-electromotriz se ha empleado para determinar amplitudes de vibración (desplazamiento) ocasionadas por una onda ultrasónica al propagarse a través de un material. En el presente trabajo se propone introducir una señal de referencia para cuantificar los desplazamientos. Debido a que van a existir dos señales en el efecto de fuerza fotoelectromotriz, se hace un análisis experimental que consiste en observar el espectro de frecuencias de la señal y compararlo con el espectro de un interferómetro de Mach-Zehnder con dos frecuencias (se modula la fase de cada haz por medio de una señal senoidal). Otros resultados de este análisis son: Se obtienen las curvas que exhiben la relación entre la corriente de la señal del efecto de fuerza foto-electromotriz y la amplitud de modulación para dos moduladores; se observa que estas dos curvas son iguales dentro de los errores experimentales. Además, se muestra experimentalmente que el cociente entre los voltajes de las señales de salida del efecto de fuerza foto-electromotriz son independientes de la intensidad. Por último, se exponen los resultados obtenidos al determinar la amplitud de vibración de una onda ultrasónica al emplear el efecto de fuerza foto-electromotriz con una señal de referencia.

We demonstrate the capability of an air cavity Fabry-Perot interferometer (FPI), built with a tapered lead-in fiber tip, to measure three parameters simultaneously, distance, group refractive index and thickness of transparent samples introduced in the cavity. Tapering the lead-in fiber enhances the light coupling back efficiency, therefore is possible to enlarge the air cavity without a significant deterioration of the fringe visibility. Fourier transformation, used to analyze the reflected optical spectrum of our FPI, simplify the calculus to determine the position, thickness and refractive index. Samples made of 7 different glasses; fused silica, BK7, BalF5, SF2, BaF51, SF15, and glass slides were used to test our FPI. Each sample was measured nine times and the results for position, thickness and refractive index showed differences of ± 0.7%, ± 0.1%, and ± 0.16% respectively. The evolution of thickness and refractive index of a block of polydimethylsiloxane (PDMS) elastomer due to temperature changes in the range of 25°C to 90°C were also measured. The coefficients of the thermal expansion and thermo-optic estimated were α = 4.71x10(-4)/°C and dn/dT = -4.66 x10(-4) RIU/°C, respectively.

We present a novel technique to fabricate a saturable absorber thin film based on Polydimethylsiloxane doped with Single Wall Carbon Nanotubes. Using this film a passive mode-locked fiber laser in a standard ring cavity configuration was built by inserting the film between two angled connectors. Self-starting passively mode-locked laser operation was easily observed. The generated pulses have a width of 1.26 ps at a repetition rate of 22.7 MHz with an average power of 4.89 mW.