Shouichi Ogita

Tapered thickness MQW waveguide BH MQW lasers

We propose and demonstrate a novel 1.3 /spl mu/m InGaAsP/InGaAsP multiple-quantum-well (MQW) BH Fabry-Perot laser diode monolithically integrated with a MQW tapered thickness waveguide. A selective area growth (SAG) technique is used to fabricate the tapered thickness waveguide with low absorption loss and to integrate it with the MQW gain region with a high coupling efficiency. We achieve very narrow vertical and lateral far-field FWHM of 11.8/spl deg/ and 8.0/spl deg/, with low threshold current of 19 mA and high slope efficiency of 0.25 mW/mA.<<ETX>>

FM response of narrow-linewidth, multielectrode lambda /4 shift DFB laser

Flat FM response from 100 kHz to 15 GHz was achieved in a multielectrode distributed-feedback (DFB) laser. A lambda /4-shifted corrugation and a 1200- mu m-long cavity were very effective not only in reducing the linewidth to less than 1 MHz, but also in making FM response flat by selective current injection.<<ETX>>

Long-cavity multiple-phase-shift distributed feedback laser diode for linewidth narrowing

A long-cavity multiple-phase-shift distributed-feedback (MPS-DFB) laser diode with three phase shifts in the corrugation for linewidth narrowing is discussed. The threshold gain difference and the field uniformity along the laser cavity of the MPS-DFB laser are analyzed by varying the amount and the position of phase shifts using the coupled-wave theory. It is shown that a large threshold gain difference and a uniform field distribution are obtained in the MPS-DFB laser with some special amount and position of phase shifts. Based on the analysis, a MPS-DFB laser with a 1200- mu m-long cavity and three phase shifts was fabricated. This MPS-DFB laser exhibits stable single-mode operation and shows a very narrow linewidth of 830 kHz at an optical output power of 25 mW. >

Experimental analysis of temperature dependence of oscillation wavelength in quantum-well FP semiconductor lasers

We experimentally evaluated the temperature dependence of the oscillation wavelength in 1.3-/spl mu/m GaInAsP-InP strained multiple-quantum-well (MQW) semiconductor lasers compared to bulk lasers. The temperature dependence of the oscillation wavelength can be characterized by two newly introduced coefficients /spl alpha//sub 1/ and /spl alpha//sub 2/ which are the gain peak wavelength shift coefficients under the constant current condition and under the constant temperature condition, respectively. These two coefficients of various MQW structure lasers are the same as those of bulk lasers. This result means that the oscillation wavelength shift coefficient d/spl lambda//dT is only a function of the characteristic temperature T/sub 0/. The higher T/sub 0/ induces the large temperature dependence of the oscillation wavelength, When the characteristic temperature T/sub 0/ is equal to the characteristic temperature T/sub ltr/ of the transparency current I/sub tr/, the oscillation wavelength shift coefficient d/spl lambda//dT takes the maximum value which is determined by the thermally induced bandgap narrowing effect d/spl lambda//sub g//dT. One possibility to solve the paradox between a high characteristic temperature T/sub 0/ and the small temperature dependence of the oscillation wavelength is the introduction of the temperature-independent leakage current.

Effect of recombination in separate-confinement heterostructure (SCH) layers on temperature characteristics of semiconductor lasers

We investigated the effect of recombination in separate-confinement heterostructure (SCH) layers on the temperature characteristics of lasers. It was found that the large dependence of recombination on the threshold carrier density can be used to greatly reduce the characteristic temperature T/sub 0/. A reduction of recombination in the SCH layer is essential for a high-optical confinement factor in each well. To obtain a high-optical confinement factor in wells at a 1.3-/spl mu/m emission, we fabricated a laser having a wide bandgap cladding layer by introducing a hetero-epitaxial buffer layer. This laser exhibited a temperature characteristic between that of short and long-wavelength lasers, as was expected from the optical confinement factor per well.

Influence of asymmetric nonlinear gain on the transient intensities of longitudinal modes in long wavelength Fabry-Perot laser diodes

The intensity transients of the longitudinal modes in a modulated 1.3-/spl mu/m Fabry-Perot laser diode are analyzed theoretically and experimentally. A simulation of the transient spectra, based on a 21-mode rate-equation model, shows that nonlinear gain strongly affects the intensities of longitudinal modes during transients. The simulation results are confirmed by time-resolved spectrum measurements. From a comparison of measurements and the simulations, the self- and cross-saturation coefficients are estimated. Our simulations also show that the transient spectrum strongly depends on the bit interval during digital modulation.

Narrow-beam divergence 1.3-/spl mu/m multiple-quantum-well laser diodes with monolithically integrated tapered thickness waveguide

This paper describes the optimum design, fabrication, and performance of a 1.3-/spl mu/m multiple-quantum-well (MQW) laser diode monolithically integrated with a tapered thickness spot-size transformer. The dependence of the lasing characteristics on the thickness distribution of the core layer and on the current injection profile of the device were analyzed. This integrated laser with its optimized structure performed at a low threshold current of 22.2 mA, even at 85/spl deg/C. The integrated spot-size transformer effectively reduced the lateral and vertical far-field FWHMs to 8/spl deg/ and 9/spl deg/, respectively. A very long lifetime of over 1/spl times/10/sup 5/ h was estimated at 85/spl deg/C and 8 mW under CW operation.

Optimum asymmetric mirror facet structure for high-efficiency semiconductor lasers

A design theory for asymmetric mirror facet structure lasers that takes into account the spatial hole burning (SHB) effect along the cavity is presented. It is shown that the SHB effect reduces the external quantum efficiency in asymmetric mirror facet structure lasers, and the front facet reflectivity has an optimum value depending on the internal loss for high-efficiency operation. A slope efficiency of more than 50% has been obtained in lasers based on the new design theory. It is noted that nonuniform current injection is one of the most useful methods for increasing the external quantum efficiency, which is reduced by the SHB effect. >

Influence of separate confinement heterostructures on the effective carrier recombination coefficient in quantum well laser structures

We analyzed the carrier recombination coefficient of quantum well laser structures by combining two-level ambipolar rate equations and a carrier diffusion equation for the separate confinement heterostructure (SCH) layer. We derived a new analytical expression for the effective carrier recombination coefficient (Beff) in quantum well laser structures. From our analysis, we found out that the dominant factor that determines Beff is not the diffusion across the SCH layer but the ratio of confined carriers in the well to the total carriers in both the well and the SCH layers. Our new expression well explained the measured results of 1.3 μm strained-layer quantum well lasers with SCH layers of different thicknesses.

1.3 /spl mu/m high T/sub 0/ strained MQW laser with AlGaInAs SCH layers on a hetero-epitaxial InGaAs buffer layer

The 1.3 /spl mu/m InGaP clad laser with AlGaInAs SCH layer was fabricated on a hetero-epitaxial InGaAs QW buffer layer. Due to high optical confinement, this laser showed a high characteristic temperature T/sub 0/ of 110 K.