Dynamics of helical-wave emission in a fiber-coupled diode end-pumped solid-state laser

We have generated TEM_0,l ^* modes in an end-pumped microchip laser using a standard fiber-coupled diode. A rich set of dynamic behaviors, such as periodic and quasi-periodic self-modulation, chaotic pulsing and frequency locking was observed in the generated TEM_0,l ^* modes. Experimental results confirm the theoretical predictions that the locking occurs as a subcritical bifurcation and that a region of coexisting locked and unlocked states exists. Received: 14 November 2000 / Revised version: 22 January 2001 / Published online: 23 May 2001     

Exponential recovery of low frequency fluctuations in a diode laser with optical feedback

We show that the recovery after each power drop on the chaotic low frequency fluctuations in a semiconductor laser with optical feedback follows an exponential envelope. The time constant for such exponential behavior was experimentally measured. This recovery time constant and the average time interval between consecutive drops have different dependences when measured as function of the pump current.     

Toward passive mode locking by nonlinear polarization evolution in a cascaded Raman fiber ring laser

We demonstrate a cascaded Raman fiber ring laser delivering a pulsed fourth-order Stokes component. Periodic emission of subnanosecond pulses is achieved from the interplay between nonlinear polarization evolution and Raman cascade process.     

Abrupt turn-on and hysteresis in a VCSEL with frequency-selective optical feedback

The emission characteristics of a vertical-cavity surface-emitting laser (VCSEL) operated in a single-transverse mode and coupled to an external cavity with a diffraction grating as a frequency-selective element are analyzed experimentally, numerically and analytically. The experiments yield a rather abrupt turn-on of the VCSEL to a high-amplitude emission state and hysteresis phenomena. The experimental results are explained by numerical simulations and analytical calculations demonstrating the possibility of bistability between lasing and non-lasing states close to threshold. Hence, the scheme might be useful in all-optical photonic switching applications. A detailed bifurcation analysis near threshold is given by superimposing the numerical results with analytical steady-state curves. The mode selection and switching behavior obtained in the simulations can be interpreted from the point of view of the preference of states with the minimal total losses.     

Passive harmonic mode-locking in a fiber laser with nonlinear polarization rotation

On basis of numerical simulation and analytical treatment, we investigate the multiple pulse passive mode-locking of a fiber laser with nonlinear loss due to the nonlinear polarization rotation technique. Various additional mechanisms resulting in the ordering of ultrashort pulses inside the laser resonator and in the realization of harmonic passive mode-locking are analyzed. Among which are the active harmonic modulation of the intracavity loss or of the refractive index, the passive modulation of the index due to the inertial properties of intracavity elements, and the amplification modulation due to the depletion and the relaxation of the gain. The velocity of pulses relative to each other is determined, it results in attractive or repulsive pulse-pulse interaction, and allows to evaluate the conditions of ordering of the pulses inside the cavity.     

Control of basins of attraction in a multistable fiber laser

We study how the basins of attraction of coexisting states can be controlled by either harmonic modulation or small noise applied to the pump parameter in a multistable erbium-doped fiber laser. The results of numerical simulations using the three-level laser model display good agreement with previously reported experimental studies on attractor annihilation by periodic modulation. In the laser with stochastic modulation, the attraction basins' volumes have a noise-dependent probabilistic character displaying some resonances for each of the coexisting attractors.     

Comparison of laser models via laser dynamics: The example of the Nd:YVO4 laser

Several models for the Nd³⁺:YVO₄ laser are compared in terms of their performance to describe the turn on transients of the laser. A blind search comparison performed using a genetic algorithm shows that the longitudinal hole burning effect must be included while Auger effect may be neglected.     

Solitons and vortices in lasers

We give in this article the mathematical background for pattern formation in nonlinear active resonators, elucidating the relation of optics with other fields of physics, and demonstrate experimentally the existence, properties, and dynamics of: (i) vortices in lasers, (ii) bright spatial solitons in lasers with saturable absorber, and (iii) spatial solitons in degenerate parametric mixing. All these structures are by definition bistable so that they are potentially useful for parallel optical information processing. Received: 8 June 1998     

Synchronization of chaos in unidirectionally and bidirectionally coupled multiple time delay laser diodes with electro-optical feedback

We report on chaos synchronization in both unidirectionally and bidirectionally coupled multiple time delay laser diodes with electro-optical feedback. We derive existence and sufficient stability conditions for the synchronization regimes. We calculate the Lyapunov exponents, information dimension, and Kolmogorov-Sinai entropy for a single and double delay time lasers to demonstrate that multiple time delay laser system can offer higher complexity than a single time delay laser. We demonstrate that in coupled multiple time delay lasers additional feedback(s) can play a stabilizing role. We compare the synchronization quality for closed loop and open loop receiver laser configurations and find better synchronization quality for partially open loop receiver (when the receiver laser has only one feedback loop), than the open loop receiver configuration (when the receiver contains no feedback loops). We also study the effect of the feedback phase on the correlation coefficient between the interacting laser systems. Analytical results are fully supported by numerical simulations.     

On control of chaos in the Kerr lens mode locked Ti:Sapphire laser

In this paper, I present the numerical demonstration of a simple way to reduce the pulse duration of a Kerr lens mode locked Ti:Sapphire laser. The core of the method lies in the low dimensional deterministic chaos that displays the laser. By adding an acousto optic modulator and applying an adequate control algorithm, it is possible to reduce the pulse duration by a factor of two with a laser that otherwise operates in the range of 40 fs.     

Instability and satellite pulse of passively Q-switching Nd:LuVO4 laser with Cr:YAG saturable absorber

This work presents experimental results concerning a passively Q-switching Nd:LuVO₄ laser with a Cr⁴⁺:YAG saturable absorber operated in a three-element cavity. When the pump power exceeded 5.47 W, the system transfers stable pulse train into spatial-temporal instability. Furthermore, the chaotic pulse train accompanied the generation of a satellite pulse. The experimental results reveal that the mechanisms of instability and generation of the satellite pulse are governed by the multitransverse mode competition.     

High frequency fiber laser emission generated by pump spiking

A stable and short pulse train of ∼100 MHz repetition frequency was obtained from an erbium doped fiber laser excited by a “continuous” semiconductor laser and by using a linear cavity defined by a Bragg grating pair. The operation frequency of the fiber laser was greater (∼5-15 times) than the cavity round-trip frequency. Emission properties obtained from the erbium doped fiber laser were correlated with those taken from the pump laser, which presented a particular optical noise (very short pulses) added to the continuous emission. From the temporal and radio-frequency analysis of both systems, we conclude that the pump emission characteristics are the responsible of the fiber laser pulsed behaviour.     

Transverse effects and mode couplings in OPOS

00 pump field. The corresponding differential equations for the time evolution of the self-consistent mode amplitudes are derived for typical cavity geometries including the propagation integrals within the crystal. We discuss the new physical effects introduced by these couplings in some typical cases. This includes a change of the OPO threshold and stable simultaneous oscillation of several mode pairs with fixed relative phases as well as oscillating self-pulsing type solutions. Received: 12 January 1998/Accepted: 11 February 1998     

A continuous-mode model of the mode locking in a pump-modulated laser

The active mode-locking process of the multimode laser with an external pump modulation is theoretically investigated in the frequency domain within the framework of the continuous-mode approximation. Intermode interaction and mode-coupling effects, including both AM and FM modulations, are naturally considered in a hierarchical equation of the mode components derived from the multimode Maxwell-Bloch equations. It is reduced to a continuous-mode equation that can be solved analytically in a stationary case, and used to discuss the spectral line shape and the phase dynamics of mode-components as a function of modulation amplitude and detuning of the modulation frequency. We predict a novel oscillation existing below the threshold of the ordinary complete mode-locking: The intensity of the total electric field yields a stable pulse train but its phase varies irregularly in time. This semi-locked state is characterized by a nonlinear chirping, an asymmetric spectrum, and drifting phases of the field mode-components.     

Suppression of Nonlinear Patterning Effect in Wavelength Conversion Based on Transient Cross-Phase Modulation in Semiconductor Optical Amplifier Assisted with a Detuning Filter

Nonlinear patterning （NLP） effect in wavelength conversion based on transient cross-phase modulation （XPM） in semiconductor optical amplifier （SOA） assisted with a detuning filter is theoretically investigated. A non- adiabatic model is used to estimate the ultrafast dynamics of gain, phase and electron temperature in the SOA. Simulation results show that the NLP can be greatly suppressed by introducing an assist light, especially for the probe wavelength distant from gain peak. Furthermore, the results also indicate that the improvement is more evident for long wavelength probe light and assist light in counter-propagating configuration.     

Passive mode locking of a ruby laser using a birefringent crystal and a fractional-commensurate cavity length

Mode-locked operation has been observed in a Q-switched, ruby laser using a quartz crystal as the passvie mode-locking element and a laser cavity length which is a whole fraction of that which is commensurate in mode-frequency spacing with the lowfrequency stimulated Brillouin scattering (lf S BS) in the crystal element. In addition, high-bit-rate operation has been observed, suggesting that the passive modulation of the lf S BS process is sufficiently strong to maintain a fixed-phase relation between several neighboring oscillating modes of the laser.     

A single-mode KrF laser

Single-mode operation of a KrF laser oscillator has been achieved for the first time. The laser medium is pumped by an electron beam which allows excitation for a much longer duration than with discharge pumping. The long excitation time, together with the use of a short oscillator cavity with a low single-pass gain, allows many roundtrips before saturation is reached. This makes line-narrowing easier and single-mode operation has been achieved using only two intracavity etalons.Technical Research Centre of Finland, Helsinki, Finland     

Simulation of turbulence in mode-locked lasers

We establish the connection between a paper by Kartner et al. [F.X. Kartner, D.M. Zumbuhl, N. Matuschek, Phys. Rev. Lett. 82 (1999) 4428] entitled “Turbulence in mode-locked lasers”, and earlier work on the role of noise in mode-locked laser systems. We present numerical results that broadly support the analytical results of Kartner et al.     

Intensity noise of pump-enhanced continuous-wave optical parametric oscillators

4 (RTA), which provides a threshold pump power of 16 mW. The maximum signal wave power is 23 mW at a wavelength of 1243 nm. The spectral bandwidth of the signal wave is less than 750 kHz. Received: 3 February 1998     

Chaos in photovoltaic HgCdTe detectors under laser irradiation

Chaos in photovoltaic HgCdTe detectors irradiated by a low-power stable continuous-wave laser is found in our experiment. The detectors give a chaotic output in the laser irradiation power density range a little higher than their saturation threshold. Chaos is diagnosed by calculating the power spectrum and the Lyapunov exponent with experimental data of the detectors’ output signals vs. time. We conclude with a qualitative discussion of the possible causes of the observed chaotic behavior. Received: 3 April 2002 / Revised version: 8 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. (Fax: +86-0731/4514127, E-mail: maliqin01@263.net)