Dong-Sun Seo

Self-pulsations in strongly coupled asymmetric external cavity semiconductor lasers

Self-pulsations in asymmetric external cavity semiconductor lasers are studied experimentally and are analyzed using improved rate equations which include multiple reflections. These equations are valid for arbitrary levels of coherent external optical feedback. The dependence of self-pulsation frequencies on injection current, external mirror tilt angle and reflectivity, and external cavity length is explained by small-signal analysis of the rate equations. By numerical integration of the rate equations, self-pulsations are demonstrated theoretically and resonant enhancement of intensity noise is shown to occur when the self-pulsation frequency is an integer fraction of the external cavity resonance frequency. >

Multiple feedback effects in asymmetric external cavity semiconductor lasers

Multiple feedback effects on the output power and spectral characteristics of an external cavity semiconductor laser with asymmetric feedback induced by misalignment of an external mirror are discussed. The external mirror tilt modifies the round-trip phase condition as well as the coupling efficiency. Undulation in power as a function of external mirror tilt have been observed. At particular tilt angles where strong interaction between odd-order round-trip beams and even-order round-trip beams occurs, unique optical spectra featuring double peaks within a compound-cavity mode spectrum or uneven compound-cavity mode spacings have been observed. A quasi-static model for asymmetric external cavity systems explains qualitatively the power undulations and complex spectral characteristics. The model also predicts the existence of two nearby phase-matched mode groups, which may result in complex and chaotic instabilities. >

Compound cavity modes in semiconductor lasers with asymmetric optical feedback

We describe a static model for determining the oscillating modes of an external cavity semiconductor laser with asymmetric feedback induced by external mirror misalignment. The most significant prediction of this model, the existence of double loss minima leading to compound cavity mode splitting, has been confirmed directly by spectral measurements. This result is important for analyzing complex dynamical phenomena in semiconductor lasers with optical feedback.

Low-frequency self-pulsations in asymmetric external-cavity semiconductor lasers due to multiple-feedback effects

We investigate the dynamical stability of external-cavity semiconductor lasers with deliberate tilt asymmetries. Experimentally observed low-frequency self-pulsations are explained by small-signal analysis based on a new rateequation model that uses a time-dependent effective reflectivity to include multiple-feedback effects. We observe and explain the dependence of the self-pulsation frequency on the strength and degree of asymmetry of the feedback, on the injection current, and on the external-cavity length. These results are important in interpreting instabilities, chaos, and other complex dynamical phenomena in external-cavity semiconductor lasers.

Reduction of spectral linewidth and FM noise in semiconductor lasers by application of optical feedback

We describe the theory and practice of using coherent optical feedback from a simple external reflector or self-contained high-finesse resonator to reduce the time-averaged spectral width and FM noise level in a single-mode semiconductor injection laser.

Subharmonic Bifurcation Route to Chaos in Asymmetric External Cavity Semiconductor Lasers

Complex dynamics and chaos in nonlinear optical systems are of considerable theoretical and practical interest.1–4 Semiconductor lasers, which are used extensively in optical communication and data storage, are especially appropriate vehicles for studying complex dynamics. Chaotic behavior in semiconductor laser systems has been induced by gain modulation,5,6 external light injection,7 and coherent optical feedback.8–11 Some of the most interesting phenomena have occurred in high feedback external cavity semiconductor lasers with deliberately induced tilt asymmetries.9–14 Previously, we have observed nearly sinusoidal pulsations and have explained the effects of mirror tilt, injection current, and external cavity length on the self-pulsation frequency using small signal analysis.15 In this paper, we report experimental observation and theoretical analysis of subharmonic bifurcation routes to chaos associated with these self-pulsations.