José A. Sanchez-Martin

Erbium-Doped-Silica Photonic Crystal Fiber Characterization Method: Description and Experimental Check

The present paper reports and discusses a characterization method for erbium-doped-silica photonic crystal fibers based on the measurement of pump power attenuation and gain together with the McCumber theory. The absorption and emission cross sections and the passive losses of the fiber were obtained from a fitting procedure of theoretical to experimental values. The method was checked by means of a home-made photonic crystal fiber to verify its reliability. Finally, it was found that the characteristic parameters obtained by this method can be used to accurately simulate the performance of the fiber and therefore to design devices based on it.

Amplifiers and Lasers Based on Erbium-Doped Photonic Crystal Fiber: Simulation and Experiments

In this paper it is shown that, once a particular erbium-doped-silica photonic crystal fiber has been fabricated, the characteristic parameters obtained by means of the technique developed by the authors can be used to properly simulate the main features of optical amplifiers and lasers made of this fiber. This requires assuming that the finite size of the air-holes microstructure makes the overall passive losses per unit length to exhibit an effective dependence on the fiber length. Measurements are performed on a variety of amplifiers and lasers built with pieces of different lengths of two home-made fibers to check the simulation method. A good agreement is found between experimental and simulated results. This means that the proposed method is useful to design optimized erbium-doped photonic crystal fiber amplifiers and lasers for particular applications.

Temperature dependence of birefringence in ethanol-filled suspended core fiber.

The temperature dependence of the birefringence in a suspended core fiber (SCF) has been experimentally analyzed by using a polarimetric setup. The used configuration consists of two linear polarizers and the SCF as birefringent medium. A theoretical study based on Jones matrices has been carried out to analyze the experimental observed behavior. For this, a polarimetric all-fiber configuration was used whose sensitivity depends on the wavelength variation with temperature. Results obtained show that it is strongly affected when the air holes of SCF are partially filled with ethanol.

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.

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.

Er-doped photonic crystal fibre characterization method based on McCumber theory

Characterization and modeling of Er-doped fibres [1] allowed in the past years fruitful developments of amplifiers and lasers. Since in a conventional fibre monomodal propagation of light is achieved in a very short length (once energy of other modes has been radiated) the cutback technique has been successfully used to determine absorption cross sections at the pump and gain band wavelengths. Emission cross sections have been usually determined instead from the measurement of gain or amplified spontaneous emission (ASE) spectrum together with the use of theoretical models. In a photonic crystal fibre (PCF) the limited size of the air-holes lattice originates energy radiation from the highest order confined mode [2]. Therefore, in order to avoid radiation from the fundamental mode, a bimodal structure with an effective monomodal behavior is sometimes preferred. In this case monomodal propagation is not achieved in a short length and the use of the cutback technique to determine absorption cross sections is prevented. On the other hand fusion splicing of PCFs to other components made of conventional fibres originates non negligible losses [3] that cannot be easily measured.

Correlation between the chaotic emissions of two coupled erbium-doped fibre ring lasers

We present experimental and numerical results of the correlation between the chaotic emissions of two coupled erbium-doped fibre ring lasers whose pump powers are modulated with a sine-wave signal. Experimentally, it is observed that correlation does not increase monotonously as the coupling becomes stronger: for certain intermediate coupling conditions, a correlation minimum is found. This non-monotonic dependence is also found in the numerical simulations performed, which in general provide an acceptable qualitative agreement with the experimental results.