Juan Carlos Martín

Bistability in an Erbium-Doped-Fiber Laser Controlled by a Coupled External Signal

A sine-wave-modulated erbium-doped-fiber laser with an external signal coupled into its cavity has been studied. In particular, an analysis on how the time-dependent laser emission changes as a function of the external signal power has been conducted. Under appropriate working conditions, different bistable behaviors have been found. In some cases, the system behaves as a pilot lamp, which, once activated by the occurrence of a certain event, remains on until reset. For other working conditions, the system behaves as a binary memory whose states can be easily switched.

Optical bistability via an external control field in all-fiber ring cavity

We demonstrate a new scheme for realizing the Optical Bistability (OB) inside an all-fiber ring cavity with an external control field. In the absence of the external control field, the pump power is fixed below the threshold value of laser, and there is no laser in the cavity. However, when the control signal of 1505 nm to 1520 nm is injected into the cavity, laser begins to oscillate and OB appears. We found that the wavelength and power of the control signal can affect the OB behavior dramatically, which can be used to manipulate efficiently the threshold intensity and the hysteresis loop. We also give an explanation of the bistability phenomenon based on numerical simulations, which are agreed very well with our experimental results. Our scheme may provide some new possibilities for technological applications in optical power limiters, switches or memories.

Response of an EDF to a coupled low-frequency modulated signal: Calculation procedure and comparison with experimental data

Abstract The capacity of the erbium-doped fibre models to predict output signal and amplified spontaneous emission power in time-dependent situations is studied. In the initial stage, we demonstrate the usefulness of a model based on overlapping factors for time-dependent calculations, which allow one to save computation time, apart from other advantages. In the second stage, we compare theoretical predictions with experimental measurements in several time-dependent cases. We find an acceptable agreement.

Study of the use of methanol-filled Er-doped suspended-core fibres in a temperature-sensing ring laser system

We report on an experimental/numerical investigation into the use of methanol-filled Er-doped suspended-core fibres (SCFs) in temperature-sensing ring laser systems. We have adopted a ring laser configuration that includes an Er-doped SCF as a temperature-dependent attenuator (TDA) with a step-index Er-doped fibre (EDF) as the laser active medium. The laser performance dependence on the temperature was measured both in continuous wave (CW) and transient regimes. CW laser output power and build-up time values are compared with those of similar laser systems based on other types of Er-doped PCFs or using other laser configurations. A notable variation of 0.73% °C−1 was achieved in CW operation. Then, by means of parameters obtained by numerically fitting the experimental results, the potential sensing performance of the laser configuration with an SCF as a TDA is studied. Moreover, two ring cavity laser configurations (with the SCF acting basically as an attenuator or also as the active media) are compared and the influence of the position of the coupler inside the ring cavity and the contribution of the erbium doping to improve the sensor features are analysed. The longer interaction lengths compatible with laser action using the Er-doped SCF as a TDA could provide variations of laser output power up to 8.6% °C−1 for 90 mW pump power and a 1 m methanol-filled SCF.

Study of upconversion in PCFs with high erbium concentration

We report on a comparison of characterization techniques for high concentration erbium-doped photonic crystal fibres (PCFs). A highly erbium-doped-silica PCF was fabricated and an amplifier based on the PCF was built. Then, measurements on the amplifier output optical powers were carried out. To model the amplifier, three different formalisms were assumed for the Er3+-ion upconversion mechanism and the numerical results were fitted to the experimental ones. The sets of best-fit parameters are compared and the use of these techniques for active PCF characterisation is discussed.

Analysis of the Polarization Influence on the Erbium-Doped Fiber Laser Transient Behavior

Abstract We studied the erbium-doped fiber laser transient behavior dependence on the pump polarization state or on the cavity polarization eigenvalues. Several series of measurements are shown in which the changes in the transient laser response can be appreciated as the pump polarization state, or the cavity polarization eigenvalues are modified by means of polarization controllers. Results are fitted to a model considering polarization hole burning. It is shown that including this effect is fundamental for a correct erbium-doped fiber laser transient model. On the other hand, the validity of the models fitting parameters under pump or cavity polarization changes is analyzed.

Fluorescent fiber implementation of a high-resolution distributed position sensor

Fluorescent optical fibers employ the luminescence property of fluorescent dyes in order to radiate light as a response to incident illumination. When multiple dyes are used to dope the fiber, fluorescence results from the energy transfer between the donor and acceptor dyes and the reabsorption process. In this work we propose a high-resolution distributed optical sensor for position monitoring developed around a yellow fluorescent fiber. Immunity vs. ambient light variations is achieved by employing the spectral behavior of the donoracceptor energy transfer mechanism and the reabsorption process. This consists in a red shift of the fiber emission peaks vs. distance. Extensive experimentation with the laboratory proof of principle validates the proposed solution. Measurements carried out in laboratory environment under ambient illumination show that the wavelength of the emission peaks is insensitive to the intensity of the incident light, but is dependent on the variation of the ambient light color. Accordingly, rather than monitoring the wavelengths of the emission peaks, the proposed positions sensor evaluates the spectral spacing between the peaks. This provides an accurate estimate of the distance between the fiber end and the incident light application point. The proposed sensor exhibits a monotonous decrease of the spectral spacing vs. distance, which is indeed insensitive to limited variation of the ambient light.

Detailed characterization of a highly Yb-doped double-clad fiber

A characterization method based on the careful measurement of the characteristic parameters and fluorescence emission spectra of a highly Yb-doped double-clad fiber is presented. The method is successfully checked by numerically fitting experimental results of a ring laser based on highly doped double-clad Yb-doped silica fibers with different dopant concentrations, fiber lengths and ring-laser output-coupler rates.

A simple theoretical model for erbium doped PCF ring lasers design

In this paper a simple theoretical model is presented where the energy conservation principle is used. The model is based on semi-analytical equations describing the behaviour of an erbium-doped photonic crystal fibre (PCF) inside a ring laser. These semi-analytical equations allow the characterisation of the erbium-doped PCF. Spectral absorption and emission coefficients can be determined through the measurement of the gain in the PCF as a function of pump power attenuation for several fibre lengths by means of a linear fitting. These coefficients are proportional to the erbium concentration and to the corresponding absorption or emission cross section. So if the concentration is known the erbium cross sections can be immediately determined. The model was successfully checked by means of two different home-made erbium doped PCFs. Once the fibres were characterised the values of the spectral absorption and emission coefficients were used to simulate the behaviour of a back propagating ring laser made of each fibre. Passive losses of the components in the cavity were previously calibrated. A good agreement was found between simulated and experimental values of efficiency, pump power threshold and output laser power for a wide set of experimental situations (several values of the input pump power, output coupling factor, laser wavelength and fibre length).

Erbium-doped photonic crystal fiber chaotic laser

An erbium-doped photonic crystal fiber laser has been designed, constructed and characterized in order to examine the feasibility of this kind of devices for secure communications applications based on two identical chaotic lasers. Inclusion of a tailored photonic crystal fiber as active medium improves considerably the security of the device because it allows customization of the mode transversal profile, very influential on the laser dynamics and virtually impossible to be cloned by undesired listeners. The laser design has been facilitated by the combination of characterization procedures and models developed by us, which allow prediction of the most suitable laser features (losses, length of active fiber, etc.) to a given purpose (in our case, a laser that emits chaotically for a wide assortment of pump modulation conditions). The chaotic signals obtained have been characterized by means of topological analysis techniques. The underlying chaotic attractors found present topological structures belonging to classes of which very scarce experimental results have been reported. This fact is interesting from the point of view of the study of nonlinear systems and, besides, it is promising for secure communications: the stranger the signals, the more difficult for an eavesdropper to synthesize another system with similar dynamics.