Showing papers by "Yasuharu Suematsu published in 1977"

Measurement of spontaneous-emission factor of AlGaAs double-heterostructure semiconductor lasers

Abstract: In this paper, experimental determination of the spontaneous-emission factor of an injection laser is presented. For a lot of conventional AlGaAs DH stripe lasers, spontaneous-emission factors of about 10-5were obtained from the measurement of the light intensity of a lasing mode versus the injected current. These values are in good agreement with the theoretical prediction based upon the classical wave theory. Brief discussion of the magnitude of the spontaneous-emission factor is given relating to the direct modulation characteristics of a semiconductor laser, which shows that the damping oscillation can be decreased in a laser consisting of very small active region.

Coupling coefficient in strongly coupled dielectric waveguides

Abstract: The coupling properties between two strongly coupled parallel dielectric slab waveguides are investigated using an analytical method based on waveguide theory. Coupling properties between two waveguides which have different geometrical configurations are given. To specify the strongly coupled waveguides, the coupling coefficient used in this paper is defined as the power transfer ratio. As a result of the analysis, it is shown that a complete power transfer between strongly coupled waveguides cannot exist even if the phase velocities are matched, and therefore an uncoupled factor, defined here, is important. When waveguide parameters are chosen properly, the coupling coefficient becomes insensitive to the structure deviation, and therefore the tolerances in the fabrication processes of the coupled waveguides and related devices can be relaxed.

Suppression of relaxation oscillation in light output of injection lasers by electrical resonance circuit

Abstract: It is shown that relaxation oscillation in the light outputs of injection lasers can be suppressed by an external electrical circuit. This method can be applicable to high-speed pulse modulation. For this purpose, an electrical resonant circuit connected to the laser diode (LD) and tuned to the relaxation oscillation is considered as an example. Frequency response of direct modulation and the device-transient characteristics are analyzed. These results were verified experimentally. A brief discussion on the upper limit of the repetition frequency of pulse modulation is given and it is shown theoretically that stable pulse modulation of an LD up to a few Gbit/s may be obtained by applying this method.

Fast pulse behaviour of InGaAsP/InP double-heterostructure lasers emitting at 1.27 μm

Abstract: The fast pulse behaviour of InGaAsP/InP d.h. lasers prepared on (100) InP substrates by liquid phase epitaxy has been studied. The possibility of high-speed direct modulation at a few gigahertz has been deduced from the relaxation oscillation characteristics.

Axial-mode selectivities for various types of integrated twin-guide lasers

Abstract: Wavelength dependencies of the gains, namely the axial-mode selectivities, of various types of integrated twin-guide (ITG) injection lasers are given theoretically. The double-resonator type, the distributed Bragg reflector (DBR), and the two tandem-connection types of ITG lasers are considered. The axial-mode selectivities are also discussed briefly in relation to the efficiencies.

GaAs-Al x Ga 1-x As integrated twin-guide lasers with distributed Bragg reflectors

Abstract: A GaAs-Al x Ga 1-x As integrated twin-guide (ITG) laser with distributed Bragg reflectors (DBR) was fabricated. The DBR was in the form of a third-order grating which was chemically etched on the surface of the output waveguide. The ITG lasers with distributed Bragg reflectors (DBR-ITG lasers) operating at room temperature showed single mode oscillation up to 1.5 times the threshold current and the half-side external quantum efficiency was 1 ∼ 2 percent.

Analysis of an integrated twin-guide laser with coupled-wave theory

Abstract: The integrated twin-guide (ITG) laser consists of two parallel waveguides for the laser gain and the light output. Light-wave coupling between the two waveguides is analyzed with the help of coupled-wave theory, and the frequency-dependent oscillation conditions are obtained in an explicit form. It is concluded that single axial-mode oscillation is more realizable in an asymmetrical structure with shorter cavity length than in a symmetrical structure. This method of analysis can be applied to integrated optical circuits consisting of twin-guide structures.