H. Imai

Stability in single longitudinal mode operation in GaInAsP/InP phase-adjusted DFB lasers

A single longitudinal mode (SLM) operating condition for phase-adjusted (PA) DFB lasers has been made clear both experimentally and theoretically. As expected, we got a high SLM operation yield of 80 percent in a moderate coupled case up to a light output power of 10 mW. However, in the strongly coupled cases, the two-mode operation with the TE0 mode and the TE + 1 mode occurred frequently. To explain the two-mode operation and to optimize the PA-DFB laser structure, we have developed a theory. Taking the spatial hole burning along the laser axis into account, we succeeded in explaining the longitudinal mode behavior. From our theory, moderate coupling ( kL = 1.25 ) was found to be optimum to maintain the large threshold gain difference above threshold.

Analysis of threshold temperature characteristics for InGaAsP/InP double heterojunction lasers

This paper presents a theoretical study of threshold temperature characteristics of InGaAsP/InP double heterojunction lasers, from the standpoint of carrier leakage from the quaternary active region into the InP confining layers. The leakage carrier concentration flowing beyond the heterobarrier of the InP confining layer is evaluated through an analysis of heterojunction energy‐band structure. Analytical results indicate that, for an emission wavelength of 1.3 μm, the sharp increase in threshold current near room temperature is caused by carrier leakage. The contribution of carrier leakage is also discussed in relation to various wavelength InGaAsP lasers.

V-grooved substrate buried heterostructure InGaAsP/InP laser emitting at 1.3 µm wavelength

Details of the fabrication, optimization of the dimensions of the active region, characteristics, and the aging results of the V - grooved substrate buried heterostructure (VSB) InGaAsP/InP laser are described. It is shown that the VSB laser can be fabricated in one-step epitaxy as well as two-step epitaxy. The active region width below 2.5 μm and the thickness of 0.15-0.2 \mu m are shown to give stable fundamental mode operation and good temperature characteristics. The fundamental mode operation up to the optical output of 20 mW/facet at 25°C and the CW operation above 100°C are obtained. The pulse response showed the strongly damped relaxation oscillation with a frequency as high as 4.5 GHz. The spectral width under the modulation of 400 Mbit/s RZ single is as narrow as 25 A in full width at half maximum. Highly stable aging characteristics at an elevated temperature of 50°C are obtained in both two-step epitaxy lasers and one-step epitaxy lasers.

Catastrophic degradation of GaAlAs DH laser diodes

The catastrophic degradation of GaAlAs DH laser diodes is examined with the application of pulsed or dc current. The dependence of the pulsewidth on the degradation is measured using samples with or without facet coating. The light output PD at which the catastrophic degradation occurs decreases with an increase in the pulsewidth in the pulsewidth range 100 nsec to 10–50 μsec, and PD is constant over the pulsewidth of 10–50 μsec. The sample with an Al2O3 film coating has the highest PD. Photoluminescence patterns of the active layer in degraded samples both with and without facet coating show the growth of DLD’s in the 〈110〉 direction from the vicinity of a facet in the stripe region.

Analysis of electrical, threshold, and temperature characteristics of InGaAsP/InP double- heterojunction lasers

This paper presents an extensive study of the fundamental characteristics of InGaAsP/InP double-heterojunction (DH) lasers with a wavelength of 1.3 μm. The confinement properties of injected carriers in the quaternary active region, the electrical properties such as leakage current and diode current versus voltage, the threshold characteristics, and the threshold temperature characteristics are determined through an analysis of the heterojunction energy band structure. The threshold temperature characteristics and the carrier leakage from the active region into the confining layers are examined in detail. To clarify the dependence of carrier leakage on lasing wavelength in InGaAsP/InP DH lasers and to explain the difference between GaAlAs/GaAs DH and InGaAsP/InP DH lasers, the barrier heights required to effectively confine the injected carriers and the effective carrier masses in the active region are discussed. Various possible explanations for the observed threshold temperature characteristics are considered.

Deep level associated with the slow degradation of GaAlAs DH laser diodes

The deep‐level emission at 1.0 eV is analyzed to be associated with the slow degradation of GaAlAs DH laser diodes. The intensity of this deep‐level emission increases at the same rate as the increase in the threshold current during the slow degradation. The carrier lifetime does not change correspondingly to the increase in the threshold current. This deep level is considered to act as the photon‐absorption center to cause the increase in the threshold current.

Ultra-High speed InGaAsP/InP DFB lasers emitting at 1.3 µm wavelength

A bandwidth of 13 GHz has been attained in a 1.3 μm DFB laser at 25 °C. A mesa structure was introduced to reduce the parasitic capacitance and the lasing wavelength was detuned from the gain peak to increase the differential gain. This bandwidth is the widest so far reported in 1.3 μm DFB lasers.

Semi‐insulator‐embedded InGaAsP/InP flat‐surface buried heterostructure laser

A new structure semi‐insulator‐embedded flat‐surface buried heterostructure 1.3 μm InGaAsP/InP laser has been developed using chloride vapor phase epitaxy. cw threshold currents as low as 18 mA and high‐temperature cw operation up to 100 °C have been obtained. Small‐signal response above 4 GHz has been achieved and no remarkable roll‐off has been observed, which is due to small parasitic capacitance.

Distributed feedback laser emitting at 1.3 µm for gigabit communication systems

A distributed feedback (DFB) laser emitting at 1.3 μm for gigabit lightwave communication systems has been developed. The distributed feedback structure has been introduced in a newly developed buried heterostructure and designs for stable single-mode operation, high speed modulation, and low noise have been done. Threshold current of 10-15 mA, differential efficiency of around 0.28 mW/mA, low noise, small signal modulation bandwidth of 13.9 GHz, and satisfactory modulation waveform at 5-Gbit/s NRZ modulation have been attained with high single-mode operation yield.

High temperature characteristics of stripe-geometry InGaAsP/InP double-heterostructure lasers

This paper presents high temperature characteristics of stripe-geometry InGaAsP/InP double-heterostructure lasers with an emission wavelength of 1.3μm. To evaluate how thermal characteristics such as heat dissipated power, thermal resistance, and temperature increase in the quaternary active region contribute to CW operation, and to derive conditions for stable operation at high temperatures, these thermal characteristics were analyzed for gain-guiding lasers and refractive index-guiding lasers as a function of stripe width and cavity length. Using proton bombarded lasers and self-aligned lasers, oscillation behavior was examined at above room temperature and compared with the analytical results.