R. Rojas-Laguna

Experimental investigation of the nonlinear optical loop mirror with twisted fiber and birefringence bias

We examine the transmission characteristics of a NOLM device using a symmetrical coupler, highly twisted fiber, and a quarter-wave (QW) retarder plate introducing a polarization asymmetry in the loop. We demonstrate high dynamic range with controllable transmissivity, and good stability over long times. We experimentally study the transmission behavior for different input polarization states and distinguish between different polarization components of the output beam. Experiments are in good agreement with our theoretical approach previously published. Appropriate choice of the input and output polarizations allows a very high dynamic range. The adjustment of the QW retarder and input polarization enables tuning the critical power over a wide range.

Laser Temperature Sensor Based on a Fiber Bragg Grating

In this letter, a temperature sensor based on a fiber ring laser is presented. A fiber Bragg grating was used as a sensor head, and a Mach-Zehnder interferometer (MZI) was utilized as a wavelength selective filter to enhance the temperature sensing capability. The MZI was achieved by splicing a piece of photonic crystal fiber between two segments of single-mode fiber. Moreover, it is shown that when the laser emission wavelength is shifted as the temperature is varied, achieving a temperature sensitivity of 18.8 pm/°C at 1550 nm, within the temperature range from 20 °C to 90 °C.

An All Fiber Intrinsic Fabry-Perot Interferometer Based on an Air-Microcavity

In this work an Intrinsic Fabry-Perot Interferometer (IFPI) based on an air-microcavity is presented. Here the air microcavity, with silica walls, is formed at a segment of a hollow core photonic crystal fiber (HCPCF), which is fusion spliced with a single mode fiber (SMF). Moreover, the spectral response of the IFPI is experimentally characterized and some results are provided. Finally, the viability to use the IFPI to implement a simple, compact size, and low cost refractive index sensor is briefly analyzed.

A tunable multi-wavelength laser based on a Mach?Zehnder interferometer with photonic crystal fiber

In this paper a tunable multi-wavelength erbium doped fiber laser, based on a Mach–Zehnder interferometer, is presented. Here the interferometer is achieved by splicing a piece of photonic crystal fiber (PCF) between two segments of a single-mode fiber. The laser can emit a single, double, triple or quadruple line, which can be tuned from 1530 to 1556 nm by controlling the polarization state. Finally it is shown, by experimental results, that the laser has high stability at room temperature.

Stimulated Raman scattering in a fiber with bending loss

Stimulated Raman scattering is investigated in a 100-m long single mode fiber with bend-induced loss which has a steep wavelength dependence. The wavelength dependent loss can be used to suppress the second Stokes conversion resulting in an increased first Stokes intensity. Our experiments with a Q-switch Nd:YAG laser produced a rectangular first Stokes pulse at the fiber output.

Nonlinear optical loop mirror using the nonlinear polarization rotation effect

Abstract The effect of nonlinear polarization rotation in a fiber loop mirror constricted from a low-birefringent fiber was numerically examined. We have shown that it provides in itself the intensity variation of the transmission coefficient from 1 to 0 in the configuration with a 0.5 0.5 coupler and a birefringent bias rotating polarization by π 2 at one end of the fiber. By appropriate choice of the fiber parameters both normal and inverted characteristics of the interferometer can be achieved.

Total internal reflection of spatial solitons at interface formed by a nonlinear saturable and a linear medium

Abstract We study numerically and experimentally the reflection of spatial solitons at the interface between a nonlinear saturable-type medium and a linear one. We emphasize on determining the physical conditions under which the reflected beam at the interface conserve its nondiffracting properties. Depending on the incidence angle, we find three critical regions for spatial soliton conservation after reflection. We numerically show that the nonlinear Goos–Hanchen shift can have a dramatic effect on the diffracting properties of the reflected beam.

All-Fiber Curvature Sensor Based on an Abrupt Tapered Fiber and a Fabry–Pérot Interferometer

In this letter, a highly sensitive curvature sensor arrangement based on an abrupt tapered fiber (ATF) concatenated with an all-fiber micro Fabry-Pérot interferometer (MFPI) is presented. Here, as the ATF is bent, the MFPI spectral fringes contrast decreases. In addition, the curvature sensitivity is considerably enhanced due to the use of the ATF. Finally, it is shown that with this arrangement, at 1530-nm wavelength, it is possible to detect curvature changes with a sensitivity of 11.27 dB/m-1 and a curvature resolution of 8.87 × 10-3 m-1 within the measurement range of 0 - 3.5 m-1.

A tunable multi-wavelength erbium doped fiber laser based on a Mach–Zehnder interferometer and photonic crystal fiber

In this paper a tunable multi-wavelength erbium doped fiber laser, based on a Mach–Zehnder interferometer, is presented. The interferometer is achieved by splicing a piece of photonic crystal fiber between two segments of a single-mode fiber. Here, by changing the curvature radius in the Mach–Zehnder interferometer, the single-, double- or triple-line emissions can be tuned from 1526 to 1550 nm. Finally it is shown, via experimental results, that the laser has high stability at room temperature.

Approximate estimates of limiting errors of passive wireless SAW sensing with DPM

This paper discusses the approximate statistical estimates of limiting errors associated with single differential phase measurement of a time delay (phase difference) between two reflectors of the passive surface acoustic wave (SAW) sensor. The remote wireless measurement is provided at the ideal coherent receiver using the maximum likelihood function approach. Approximate estimates of the mean error, mean square error, estimate variance, and Cramer-Rao bound are derived along with the error probability to exceed a threshold in a wide range of signal-to-noise ratio (SNR) values. The von Mises/Tikhonov distribution is used as an approximation for the phase difference and differential phase diversity. Simulation of the random phase difference and limiting errors also is applied.