The dynamical complexity of optically injected semiconductor lasers

We consider a laser with an injected signal, in which the polarization can be adiabatically eliminated, we study the stability of the steady-state solutions, and we discuss the time-dependent solutions. For the laser alone, the only possible solution is constant intensity. However, the introduction of an external field, with an amplitude that does not satisfy the injection-locking condition, destabilizes the system. In such a case, numerical results show the existence of a self-Q-switching process, which induces relaxation oscillations. The frequency of the giant pulses is directly related to the amplitude of the external field, whereas the frequency of the relaxation oscillations depends on the damping rates. We show also that, depending on the value assigned to control parameters, the interaction between these frequencies leads to a chaotic behavior through intermittency or period-doubling bifurcations. Finally, topological equivalence between our laser system and a unidimensional circle map is shown for some values of control parameters.

Instabilities in lasers with an injected signal

Polarization self‐modulation at frequencies up to 6 GHz is observed in a vertical‐cavity surface‐emitting laser. This self‐oscillation is observed when a portion of the laser output power is injected back into the laser after having rotated its polarization by 90° with respect to the initial laser polarization state. Our experiment demonstrates a simple technique for generating an ultrahigh frequency optical clock. New applications in optical storage are also envisioned.

High‐frequency polarization self‐modulation in vertical‐cavity surface‐emitting lasers

Publisher Summary This chapter discuses the dynamical instabilities and pulsations in lasers. The laser instabilities are of interest in the research efforts. The characteristics of laser pulsations are in accord with the predictions of the early maser models. The chapter discuses the laser phenomena. The semiclassical theory of the laser was developed in response to the limited success of the rate equations in dealing with issues such as coherence, spectral purity, and the spiking phenomenon. The most analyzed laser model is a single-mode resonant system. The single-mode equations are the prototype example of an unstable laser model. The experimental realization of a single-mode, homogeneously broadened laser is attractive from the point of view of laser physics because the Lorenz model itself has no close realization in hydrodynamic systems. Neodymium glass lasers are inhomogeneously broadened because of differences in the local fields at the site of the active atoms. Most gas lasers operating in the visible and near-infrared regions of the spectrum are inhomogeneously broadened because of the Doppler shift suffered by the moving atoms. The combination of lasers and saturable absorbers has been proposed. Most experimental lasers are designed to operate as Fabry–Perot resonators.

I Dynamical Instabilities and Pulsations in Lasers

Using an injection-locking technique, we obtain high-power single-frequency emission from a multimode argon-ion laser. Furthermore, a phase-control loop permits the stable, coherent summation of the beams from the two lasers.

Injection locking of argon-ion lasers

A multimode He–Ne laser can be forced to oscillate in a single mode by injecting a narrow-band signal into the resonator. We show experimentally that the minimum injected intensity required for single-mode operation occurs at an injection frequency detuned from line center. This is in agreement with the results from a semiclassical theory of an inhomogeneously broadened injection-locked laser.

Single-mode operation of Doppler-broadened lasers by injection locking.

The output of a single-mode He–Ne laser with internal mirrors is usually linearly polarized in one of two orthogonal directions. This polarization state may be selected by a tunable injected signal or by feedback from a tunable secondary optical resonator. The laser will remain in the selected polarization even after the injected signal or the feedback from the secondary resonator is removed. This effect has potential applications as a fast switch or as an optical memory. An explanation based on intracavity birefringence is given for this bistable behavior in the polarization.

Observation of bistable behavior in the polarization of a laser.

In this Letter, we show that the fundamental pulsation frequency of the mode-locked laser can be multiplied by an integer number by simply changing the length of a secondary cavity formed by the AOM and an external mirror. Furthermore, we show that a mode-locked laser may be used to enhance the SNR in passive ring gyroscopes by matching multiple modes of the laser to those of the passive cavity.

James G. Small

Papers

Single-mode operation of Doppler-broadened lasers by injection locking.

Observation of bistable behavior in the polarization of a laser.

Gas laser mode-locking using an external acoustooptic modulator with a potential application to passive ring gyroscopes

Polarization bistability in lasers (A)