Guy Stéphan

EVIDENCE OF A SATURABLE-ABSORPTION EFFECT IN HEAVILY ERBIUM-DOPED FIBERS

A new configuration for erbium-doped fiber lasers in which two different connected fibers are used is studied: one is heavily and the other weakly doped. It is demonstrated that the dynamics of such a system depends on the fiber into which the pump is injected. The experimental results are interpreted in the framework of an ion-pair interaction model.

Whispering-gallery-mode laser at 1.56 μm excited by a fiber taper

We report the observation of whispering-gallery-mode lasers based on Er(3+) -doped ZBLAN microspheres coupled with half-tapered and tapered optical fibers. A multimode lasing effect is observed at 1.56mu when the taper diameters are properly adjusted so that their fundamental propagation constants match those of the resonant modes of interest. Overlap between the pump and the laser geometrical modes is optimized by pumping at 1.48mu .

Laser characteristics at 1535 nm and thermal effects of an Er : Yb phosphate glass microchip pumped by Ti : sapphire laser

An Er:Yb codoped phosphate glass microchip laser has been studied under pumping with a Ti:sapphire laser ranging from 945 to 990 nm. The characteristics (threshold, slope efficiency) are first described for an optimized laser. The gain spectrum is calculated for the transition 4I13/2→4I15/2 around 1535 nm from fundamental spectroscopic data and from experimental results. Red-shift effect on the frequency of a single mode is experimentally observed when the pump power is increased, originating from thermal effects. Temperature inside the microchip cavity and thermal expansion coefficient were determined by employing the intensity ratio of two green upconversion emission line centered at 530 and 554 nm, respectively, which quantitatively explain this red shift.

Room-temperature continuous-wave upconversion laser at 455 nm in a Tm 3+ fluorozirconate fiber

A room-temperature blue upconversion laser operating at 455 nm is demonstrated in a Tm(3+) -doped fluorozirconate fiber when the laser is excited simultaneously at 645 and 1064 nm, permitting as much as 3 mW of cw blue laser output.

Antiphase dynamics and chaos in self-pulsing erbium-doped fiber lasers

We present experimental evidence of antiphase dynamics in self-pulsing erbium-doped fiber lasers operating simultaneously at 1.536- and 1.55-microm wavelengths. Autonomous chaos is also observed for several ranges of pumping rates. The fractal dimension of the chaotic attractor, calculated from experimental data by use of the Procaccia method, is found to depend on the pumping ratio but always remains smaller than 4.1, regardless of the chaotic regime considered.

Influence of ion pairs on the dynamical behaviour of Er3+-doped fibre lasers

We demonstrate experimentally the influence of ion-pair concentration on the dynamical behaviour of erbium-doped fibre lasers. At low pair densities, the laser has a CW output, while at higher densities it exhibits a self-pulsing behaviour. For intermediate pair concentrations, the output intensity evolves continuously from an infinite train of pulses to a CW steady state as the pumping ratio is increased.

Switching between polarized modes of a vertical-cavity surface-emitting laser by isotropic optical feedback

Experiments are described that show that polarization of light in a vertical-cavity surface-emitting laser subjected to isotropic optical feedback can jump regularly back and forth between two orthogonal states when the injection current is increased. The polarization-resolved light-current characteristic curves are thus channeled. This effect occurs when the dichroism of the laser is weak enough to allow the effective (isotropic) reflectance to impose the polarization. A comparison of a model introduced by San Miguel [Phys. Rev. A52, 1728 (1995)] and the standard equations indicates that the best description is given when no spin relaxation is included.

Quasi-periodic route to chaos in erbium-doped fiber laser

We present experimental evidence of quasiperiodic route to chaos in erbium-doped fiber laser operating simultaneously at 1.550 /spl mu/m and 1.536 /spl mu/m. Starting from a CW state for high pumping rates the system becomes T-periodic, 2T-periodic, 3T-periodic and chaotic for decreasing pumping ratios. The low-frequency spectra shows two fundamental frequencies. The nT-periodic regimes correspond to a frequency locking of the low frequency on a subharmonic of the high frequency. An adapted model based on the rate equations is numerically investigated and leads to a good qualitative agreement with the experimental data. >

Self-pulsing in Er3+-doped fibre laser

The output intensity of an erbium-doped fibre laser was studied. Experiments were performed with three pumping wavelengths: 514.5 nm, 810 nm and 980 nm. The laser output intensity exhibits three different dynamical behaviours: steady-state, sinusoidal variation or self-pulsing. In particular, in a bad (high-loss) cavity configuration, when the pumping ratio is increased above the lasing threshold the output intensity changes continuously from a steady-state to an infinite train of pulses. We also show that, depending on the cavity configuration, the transient oscillations display different forms.

Dynamics of the transient buildup of emission in Nd/sup 3+/-doped fiber lasers

The two-stage process of the transient buildup of emission in Nd/sup 4+/-doped fiber lasers is described both experimentally and theoretically. After switching on the pump, spontaneous emission increases first until the gain becomes sufficient to compensate for the cavity losses; the laser field then develops and reaches the steady state after more or less regular oscillations. During this second stage, an almost chaotic spiking is obtained either for high pumping rates and/or at low temperatures. The whole set of these dynamical scenarios is not described under the usual assumptions of uniform cavity losses over the whole field spectrum and of pure homogeneous broadening for the transition line, but rather a modified form of the Maxwell-Bloch equations which retains some frequency dependence for the losses in the cavity and the inhomogeneous broadening as well is proposed. >