Juan A. Valles

Analysis of channel addition/removal response in all-optical gain-controlled cascade of erbium-doped fiber amplifiers

Application of the all-optical gain-controlled (AOGC) erbium-doped fiber amplifier (EDFA) for protection surviving channels in a multiwavelength network in which several EDFAs are cascaded is studied. The effects of addition and/or dropping of wavelength channels in a network comprising six concatenated EDFAs have been analyzed by numerical simulation. Only the first EDFA in the cascade is gain clamped using a ring laser configuration. A large-signal EDFA model which incorporates time variation numerical effects and the downstream propagation of signal and pump and downstream and upstream propagation of amplified spontaneous emission (ASE) has been used. In particular, the effects of relaxation oscillations from the gain-controlled EDFA on the surviving channel protection are investigated. It is shown that power excursions caused in an eight-channel wavelength division multiplexed (WDM) network by the loss/addition of 6 channels will be lower than 1 dB and free of relaxation oscillations if the gain-controlled EDFA is strongly inverted and the average normalized population density of the metastable level does not drop below 0.74.

In situ measurement of absorption and emission cross sections in Er/sup 3+/-doped waveguides for transitions involving thermalized states

An application to transitions involving thermalized states of a procedure based on the McCumber theory to determine emission and absorption cross sections in waveguides from transversal fluorescence spectra is presented. The procedure is tested in Er-doped Ti:LiNbO/sub 3/ waveguides to provide accurate cross-section values for the recently attractive 550-nm band. We also study the excited-state absorption transition around 860 nm and present, to our knowledge, the first published cross-section values for this transition.

Determination of emission and absorption cross sections of in waveguides from transversal fluorescence spectra

A procedure for the determination of emission and absorption cross sections in integrated waveguides from transversal fluorescence spectra is presented. It is based on an approximate treatment of McCumbers theory, which was demonstrated to provide accurate values for -doped silica fibres. Results on the transition of in waveguides pumped by a 980 nm laser diode are shown and compared to results from attenuation measurements. Advantages over other procedures for waveguide characterization (less dependence on experimental inaccuracies, all measurements are made on the waveguide, consideration of codoping influence and no pump interference around ) are discussed in detail.

Modeling, characterization, and experimental/numerical comparison of signal and fluorescence amplification in Ti,Er:LiNbO/sub 3/ waveguides

A complete model for signal and fluorescence amplification in Ti,Er:LiNbO/sub 3/ waveguides under 1480 and 980 nm excitation, which includes transitions involving high energy levels, is presented. Most of the waveguide parameters that the model requires have been determined or checked in situ. In order to numerically solve the proposed model, the overlapping factors method has been adapted to these waveguides and improved, obtaining a large computing time reduction with sufficiently accurate results. Finally, results from signal gain and ASE spectral measurements and numerical simulations have been compared. The remarkable agreement confirms both the model assumptions and the used characterization techniques. Moreover, the unusually short computing time which is consumed makes the model suitable for design and optimization processes.

In situ assessment and minimization of nonlinear propagation effects for femtosecond-laser waveguide writing in dielectrics

The effect of nonlinear propagation on the shape of the focal volume has been assessed by in situ plasma emission imaging during the subsurface processing of a commercial phosphate glass. The sample was processed with an elliptically shaped femtosecond-laser beam at 1 kHz repetition rate and scanned transversely with respect to the writing beam axis. As a consequence, optimal conditions for minimizing undesirable nonlinear propagation effects during the production of optical waveguides by direct laser writing have been determined. Under these conditions, it is possible to induce structural transformations and still preserve the focal volume shape associated with the linear propagation regime. While at low pulse energy a single scan laser-written structure does not support a guided mode, the use of multiple scans with minimized nonlinear propagation effects enables the production of optical waveguides. The latter show a significantly improved performance in terms of the refractive index change and propagation losses when compared to single scan waveguides.

Modeling of integrated erbium-doped waveguide amplifiers with overlapping factors methods

An analysis of the applicability of overlapping factors methods to the modeling of integrated erbium-doped waveguide amplifiers is presented. These methods offer as main advantage a considerable seduction in computation time without a decrease in their effective accuracy. We propose an extension of previous overlapping factors methods in order to model highly erbium-doped waveguide amplifiers. New sets of parameters related to the relevant upconversion and cross-relaxation mechanisms are introduced. Some numerical examples illustrate both working-conditions dependent and independent overlapping factors main dependences, which are fully explained. Finally, the accuracies of the results obtainable by both methods are examined and interpreted and the reduction in computation time is considered.

Full characterization of packaged Er-Yb-codoped phosphate glass waveguides

We present a procedure for the characterization of packaged Er-Yb-codoped phosphate glass waveguides. The procedure is based on precise measurements of the output optical powers when the waveguide is diode-laser pumped at 980 nm. The dependence of these optical powers on the input pump power is then fitted to the results from a numerical model that describes in detail the propagation of the optical powers inside the waveguide. The best fit is obtained for the following parameters: the signal wavelength scattering losses are /spl alpha/(1534)=8.3/spl times/10/sup -2/ dB/cm, the Yb/sup 3+/ absorption and emission cross sections (/spl ap/980 nm) are 5.4/spl times/10/sup -25/ m/sup 2/ and 7.0/spl times/10/sup -25/ m/sup 2/, the Er/sup 3+/ absorption and emission cross sections (/spl ap/980 nm) are 1.6/spl times/10/sup -25/ m/sup 2/ and 1.2/spl times/10/sup -25/ m/sup 2/, the Yb/sup 3+/--Er/sup 3+/ energy-transfer coefficient is 1.8/spl times/10/sup -23/ m/sup 3//s and the cooperative-upconversion coefficient is 8/spl times/10/sup -25/ m/sup 3//s. An approximate method is introduced that allows the determination of the absorption and emission cross section distributions for the erbium /sup 4/I/sub 13/2//spl hArr//sup 4/I/sub 15/2/ transition from the amplified spontaneous emission power spectrum.

Method for Accurate Gain Calculation of a Highly

The performance of a highly Yb3+/Er3+-codoped phosphate glass femtosecond-laser written waveguide amplifier is numerically analyzed using a macroscopic rate-equation propagation model where concentration-dependent rates for the interatomic migration-assisted energy-transfer mechanisms are considered. The Er3+-upconversion rate is obtained by a rigorous microscopic statistical modeling of the migration-assisted homogeneous upconversion, and the concentration dependence of the experimental Yb3+-sensitization rate utilized reflects the presence of migration among the Yb3+ ions. The results of the amplifier gain dependence on the dopant concentrations illustrate the influence of migration and the need of a careful modeling of interatomic energy-transfer mechanisms for high-concentration rare-earth-doped fiber or waveguide active devices.

{\rm Yb}^{3+}/{\rm Er}^{3+}

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.

-Codoped Waveguide Amplifier in Migration-Assisted Upconversion Regime

The amplifying and filtering performance of a highly Yb/Er-codoped phosphate glass add-drop filter is numerically analyzed. The use of the microscopic statistical formalism to describe energy-transfer inter-atomic mechanisms allows determining realistic optimum parameters and working conditions. In order to optimize the device performance and achieve a significant signal power gain in both through and drop ports, in addition to a careful previous design, moderate input pump powers (>;50 mW) and comparatively high erbium concentrations (>;5 × 1026 m-3) are required. The optimal parameters present a strong dependence on the input pump power. This dependence confirms the necessity of considering the energy-transfer inter-atomic mechanisms for any optimization design process.