The direct modulation of semiconductor lasers has received considerable attention for application to high speed optical communication systems. In this paper, discussed are dynamic properties of the semiconductor las-ers with emphasis on the achievable modulation bandwidth. It is revealed that the increase of differential gain leads to significant improvements in these properties, as well as the increase of the photon density and the de-crease of the photon lifetime. Other physical mechanisms which limit the modulation bandwidth are also dis-cussed.

View full abstract

1μm wavelength distributed feedback (DFB) lasers are suitable for high-bit-rate lightwave transmission systems. Spatial hole burning is a key factor to obtain the good single longitudinal mode lasing yield. Their corrugation depth has been optimized to raise the reproducibility of stable single longitudinal mode lasing. For asymmetric reflectivity structure, it is important to suppress Fabry-Perot mode lasing. Optimized front facet re-flectivity has minimized relative intensity noise and linewidth. Typical characteristics of these lasers emitting at 1.3μm wavelength include a threshold current of 13m A, a differential efficiency of 0.29 m W/m A, and a 3-d B bandwidth of 2-3 GHz. Long term reliabity is under test.

View full abstract

Atomic layer epitaxy (ALE) of Ga As has been achieved by switching laser MOVPE. It is found that a selectivep hotocatalytice nhancemento f the decompositionf or adsorbed TMG on As atomicl ayer with no en-hancement on Ga atomic layer occurs under Ar ion laser irradiation. This mechanism is an essential point to realize an ideal ALE in which suspension of Ga deposition at 100% coverage is required.

View full abstract

Fundamental studies on the power transmission by laser beam have been done. Experimental resultsabout a plasma direct converter (PDC) from laser energy to electricity are reported.
It is found that laser-produced plasma is far from the perfect ionized plasma. Using a 5m-long chamber, electrostatic separation of ions and electrons in the PDC has been done almost completely, and the conversion efficiency of the PDC η₃ has been improved using a venetian-blind collector. And it is found that the conversion efficiency from laser energy to plasma η₁ is increased and the maximum conversion efficiency η_3max is decreasedwith increasing laser energy.

View full abstract

To obtain high performance In Ga As P visible laser diodes, suitable composition z of Ga As_1-zP_z substrate is theoretically anlyzed with the approximation of k-selection rule. New approximative method is presented to evaluate the electron mobility in each valley. Keeping a band gap of active layer constant, 1.92 e V, a As_0.7P_0.3 substrate is found to be most suitable for fabrications of visible laser diodes. These devices are applicable to optical communication with plastic optical fibers.

View full abstract

The geometrical form factor (GFF) of a lidar system with the stepwise laser beam profile is investigated theoretically and in computer calculation for the case with a narrow-band interference optical filter. A case of a portable lidar is chosen as a model of the calculation, and the effects of distance between optical axes of the laser and the telescope, their crossing angle, and the iris position are considered. In addition, optimum design of the lidar construction is discussed.

View full abstract