E. Oomura

Low threshold InGaAsP/InP buried crescent laser with double current confinement structure

An InGaAsP/InP laser diode emitting at 1.3 μm with a crescent shaped active region is described. The active region is completely embedded in InP by a two-step LPE technique, and a double current confinement scheme is incorporated with two reverse biased p-n junctions at both sides of the active layer. A threshold current as low as 20 mA has been achieved in CW operation at room temperature. Fundamental transverse mode operation with linear light output-current characteristics and single longitudinal mode oscillation have been obtained.

InGaAsP/InP buried crescent laser diode emitting at 1.3 µm wavelength

The fabrication procedure, designing of an active region and a p-n-p-n current blocking structure, characteristics and the aging results of an InGaAsP/InP buried crescent (BC) laser diode are described. The BC laser diodes exhibit high laser performances, such as a low-threshold current, a fundamental transverse mode oscillation with linear light output-current characteristics. CW operation at as high as 100°C is achieved with a junction up configuration as a result of the improvement in the current blocking structure. A stable CW operation at 80°C has been realized with a constant optical output power of 5 mW.

Position of the degradation and the improved structure for the buried crescent InGaAsP/InP (1.3 μm) lasers

We have found a degradation of the buried crescent (BC) InGaAsP/InP lasers that occurs when the p‐n junction plane coincides with the surface exposed in the high‐temperature H2 ambient before the melt contact during the liquid phase epitaxial growth. To eliminate the degradation, we have fabricated a new structure of the BC laser and have obtained stable cw operation at 80 °C.

Internal Loss of InGaAsP/InP Buried Crescent (λ=1.3 µm) Laser

The temperature dependence of the internal loss α of the InGaAsP/InP buired crescent (λ=1.3 µm) laser is presented in the temperature range 20~80°C. α is about 18 cm-1 and no apparent temperature dependence of α is observed in this temperature range. This indicates that the temperature-sensitive behavior of the threshold current in 1.3 µm laser is not due to the internal loss. The decrease in the external quantum efficiency with increasing temperature is attributed to the decrease in the internal quantum efficiency, which is possibly caused by some leakage current.

Internal loss of InGaAsP/InP buried crescent (λ = 1.3 μm) laser

The temperature dependence of the internal loss α of the InGaAsP/InP buried crescent laser is presented in the temperature range 20–80 °C. α is about 18 cm−1, and no apparent temperature dependence of α is observed in this temperature range. This indicates that the temperature‐sensitive behavior of the threshold current in InGaAsP/InP long‐wavelength lasers is not due to the temperature dependence of internal loss. The decrease in the external quantum efficiency with increasing temperature is attributed to the decrease in the internal quantum efficiency.

TJS laser with buried p-region for high temperature CW operation

A transverse-junction-stripe (TJS) laser with a buried p-region in a substrate has been newly developed. The temperature dependence of the threshold current is much improved so that it can operate continuously up to 110°C. Even when mounted upside up it can show a CW operation at a temperature as high as 80°C.

Low Threshold Current 1.3 µm InGaAsP Buried Crescent Lasers

The threshold current and beamwidth of the fundamental transverse mode have been examined of the buried crescent (BC) laser. The active region with less than 2.0 µm wide was successfully grown inside the channel prepared on the InP substate and the minimum threshold current of 8 mA has been obtained at room temperature (cavity length L=300 µm). An analytical expression for the beamwidth of far field patterns parallel to the junction plane (θ//) has been obtained and it was confirmed that a good agreement is shown between the theoreitcal calculation and the experimental result.

AlGaAs TJS Lasers with Very Low Threshold Current and High Efficiency

The TJS lasers with the threshold current of approximately 20 mA can be obtained when the active region thickness is controlled to be 0.2 µm. The TJS laser chips mounted upside up on copper heat sinks can operate continuously at room temperature. Under this condition, the power output of more than 10 mW is obtained and the differential external quantum efficiency is approximately as high as 36%. The lives of the lasers with upside up configuration are over 1,000 hours.