Hideto Iwaoka

Purely gain‐coupled distributed feedback semiconductor lasers

We propose a new distributed feedback (DFB) laser structure in which almost pure gain coupling can be embodied in principle, without sacrificing low threshold operation. An analysis of coupling coefficients has revealed the condition for canceling index‐coupling component. Utilizing organometallic vapor phase epitaxy, we have fabricated GaAlAs/GaAs ridge waveguide distributed feedback lasers having this structure. Excellent single longitudinal mode oscillation independent of facet reflection has been obtained along with low threshold current. The single‐mode spectrum has exhibited distinctive characters of purely gain‐coupled DFB lasers.

Fabrication and characteristics of gain-coupled distributed feedback semiconductor lasers with a corrugated active layer

A distributed feedback (DFB) semiconductor laser structure in which pure gain coupling can be realized is proposed. The fabrication procedure of this structure makes use of a special feature of organometallic vapor phase epitaxy. Lasers of this structure were fabricated to show the validity of the proposal. Coupling coefficients of DFB lasers were calculated considering the gain-coupling component. Using the results, a DFB laser was designed to obtain pure gain coupling. The parameters of the actual structure observed under a scanning electron microscope showed good agreement with those designed. Device characteristics predicted for purely gain-coupled DFB lasers were achieved. For greater gain coupling and lower threshold current operation, an optimization of the Al composition of the pattern-providing layer and the thickness of the active layer in the structure has been carried out. >

Ultralow chirping short optical pulse (16 ps) generation in gain‐coupled distributed feedback semiconductor lasers

We describe optical short pulse generation in novel gain‐coupled distributed feedback (GC‐DFB) semiconductor lasers by using a simple electrically pumped gain switching method. An optical pulse as short as 16 ps has been obtained from a 130 ps current pulse. The most exciting result is that the lasers keep single longitudinal mode oscillation with very low wavelength chirping (∼0.12 nm) during the gain switching operation. From the optical pulse width and the amount of the wavelength chirping, we have estimated the α parameter of the GC‐DFB laser to be less than 1.6.

InGaAs/InP Gain-Coupled Distributed Feedback Laser with a Corrugated Active Layer

With InGaAs/InP materials, we have fabricated gain-coupled distributed feedback lasers having grating corrugation on the active layer itself, using two-step organometallic vapor phase epitaxy. Single longitudinal mode properties have been achieved. Self-consistent calculation of coupling coefficients and threshold gain difference for these lasers has also been carried out.

An Anomalous Transient Behavior of the Sealed CO 2 Laser

An anomalous transient behavior was observed in a narrow bore sealed CO2 laser. The laser tube was pulsed transiently just after the discharge was started. And after a long non-lasing interval, it began to re-oscillate gradually. Electron temperatures, electron densities, side light emissions from CO molecules and laser gains were measured and discussed. As a result, the phenomena was attributed to the dissociation and the re-construction of CO2 molecules in the tube.