Optical injection modulation of quantum-dash semiconductor lasers by intra-cavity stimulated Raman scattering.

We report the optical injection modulation of semiconductor lasers by intra-cavity stimulated Raman scattering. This mechanism manifests itself as sharply enhanced modulation bandwidth in InAs/InGaAlAs/InP quantum-dash lasers when the injected photons are 33 +/- 3 meV more energetic than the lasing photons. Raman scattering measurements on the quantum-dash structure and rate equation models strongly support direct gain modulation by stimulated Raman scattering. We believe this new bandwidth enhancement mechanism may have important applications in optical communication and signal processing.

Cavity design and characteristics of monolithic long-wavelength InAs/InP quantum dash passively mode-locked lasers.

By extending the net-gain modulation phasor approach to account for the discrete distribution of the gain and saturable absorber sections in the cavity, a convenient model is derived and experimentally verified for the cavity design of two-section passively mode-locked quantum dash (QDash) lasers. The new set of equations can be used to predict functional device layouts using the measured modal gain and loss characteristics as input. It is shown to be a valuable tool for realizing the cavity design of monolithic long-wavelength InAs/InP QDash passively mode-locked lasers.

Dynamic behavior of an injection-locked quantum-dash Fabry-Perot laser at zero-detuning.

This work investigates the behavior of a zero-detuned optically-injected quantum-dash Fabry-Perot laser as the injected field ratio is increased from near-zero to levels resulting in stable locking. Using a normalized model describing optically-injected semiconductor lasers, variations in the slave laser's free-running characteristics are shown to have a strong impact on the coupled system's behavior. The theoretical model is verified experimentally using a high resolution spectrometer. It is found that the quantum-dash laser has the technological advantage of a low linewidth enhancement factor at low bias currents that suppresses undesirable Period-2 and chaotic behavior. Such observations suggest that optically-injected quantum-dash lasers can be used as an enabling component for tunable photonic oscillators.

Reconfigurable quantum dot monolithic multisection passive mode-locked lasers.

We investigate the dynamical response of a quantum dot photonic integrated circuit formed with a combination of eleven passive and active gain cells operating when these cells are appropriately biased as a multi-section quantum dot passively mode-locked laser. When the absorber section is judiciously positioned in the laser cavity then fundamental frequency and harmonic mode-locking at repetition rates from 7.2GHz to 51GHz are recorded. These carefully engineered multi-section configurations that include a passive wave-guide section significantly lower the pulse width up to 34% from 9.7 to 6.4 picoseconds, as well increase by 49% the peak pulsed power from 150 to 224 mW, in comparison to conventional two-section configurations that are formed on the identical device under the same average power. In addition an ultra broad operation range with pulse width below ten picoseconds is obtained with the 3rd-harmonic mode-locking configuration. A record peak power of 234 mW for quantum dot mode-locked lasers operating over 40 GHz is reported for the first time.

Autocorrelation measurement of femtosecond laser pulses by use of a ZnSe two-photon detector array.

We demonstrate autocorrelation measurements of 85-fs Ti:sapphire laser pulses, using a 32-pixel ZnSe detector array in a single-shot geometry. The two-photon photoconductor is fabricated by deposition of an array of interdigitated gold fingers on a single-crystal ZnSe substrate.

Femtosecond autocorrelation measurements based on two-photon photoconductivity in ZnSe.

Two-photon photoconductivity in ZnSe is used to record femtosecond autocorrelation functions. This technique requires <100 muW of average power of a typical mode-locked femtosecond Ti:sapphire laser and distinguishes itself by a dynamic range over several decades and great conversion bandwidth, permitting the sensitive correlation of pulses of a few femtoseconds.

A simulator-based approach to training in aeronautical decision making.

The effectiveness of a simulator-based approach to training pilot skills in risk assessment and decision making was evaluated in a sample of pilots enrolled in a university aviation science program. The 16 experimental group subjects received 4 hours (h) of classroom instruction designed to enhance pilot judgment skills, followed by 4 simulated cross-country flights during which several critical inflight events occurred. Subjects in the control group received classroom instruction in basic instrument flying, followed by simulator sessions emphasizing instrument flight. Measures of pilot judgment were obtained on all subjects before and after the training, and subjects in the experimental judgment-trained group performed significantly better on the posttraining simulation than did control group subjects. The findings suggest that significant gains in pilot decision-making skill can be obtained through the use of the judgment training materials along with simulator practice.