K. Nishi

Low-threshold lasing at 1.3 /spl mu/m from GaAsSb quantum wells directly grown on GaAs substrates

Material systems on GaAs that can emit at 1.3 /spl mu/m have been attracting great interest from the viewpoint of realizing long-wavelength vertical-cavity surface-emitting lasers (VCSELs) that use high-reflectivity GaAs-AlAs distributed Bragg reflectors (DBRs). We previously investigated GaAsSb quantum-well (QW) layers on GaAs. By improving the GaAsSb optical quality and optimizing the laser structure, we have since achieved low-threshold lasing at a longer wavelength of 1.27 /spl mu/m in the GaAsSb-GaAs material system.

GaAsSb/GaAs 1.3-/spl mu/m-VCSELs for 10 G-bit Ethernet

We demonstrated high-performance GaAsSb VCSELs emitting at 1.295 /spl mu/m with a low threshold current of 1.1 mA and a maximum cw operating temperature of 70 C. After the high-frequency modulation characteristics have been validated, the GaAsSb VCSELs should be viable low-cost light sources for high bandwidth fiber communications.

High-performance 1.3-/spl mu/m VCSELs with GaAsSb/GaAs quantum wells

We have demonstrated CW and high-speed performance of GaAsSb/GaAs VCSELs lasing at a wavelength of longer than 1.27 /spl mu/m. 1.295 /spl mu/m lasing was achieved with a threshold of 1.1 mA. Single-mode output of 0.46 mW, and 4.5-GHz bandwidth was obtained at 1.27 /spl mu/m. Thus, GaAsSb/GaAs VCSELs should be viable low-cost light sources for high-capacity optical fiber systems.

Continuous-wave operation of 1.27-/spl mu/m GaAsSb/GaAs VCSELs

1.27-/spl mu/m VCSELs using GaAsSb quantum wells, which operate continuous-wave at and above room temperature (RT), are reported. A threshold current as low as 0.7 mA at RT and a maximum cw operating temperature of 70/spl deg/C are demonstrated. This result was achieved by optimizing the active-layer structure with respect to strain. Thus, GaAsSb VCSELs are viable low-cost light sources for high-bandwidth fiber communications.

GaAsSb-based alloys for long-wavelength lasers

We will review the growth, structural, and optical properties of GaAsSb QWs and the material gain improvement of lasers using modulation doping in the active region and the state-of-the-art device performance of GaAsSb VCSELs. We grew GaAsSb QWs with GaAs barriers on n-GaAs [100] substrates by using gas-source molecular beam epitaxy (GSMBE) and metal-organic vapor phase epitaxy (MOVPE).

Temperature-insensitive luminescence linewidth from highly-uniform strain-reduced InAs quantum dots

Because quantum dots (QDs) grown by self-assembling techniques show high emission efficiency, they are now being incorporated into optical devices such as laser diodes). However, obvious characteristic improvements still have not been made mainly because of a wide inhomogeneous broadening which originates from the dot size distribution. When the dot size uniformity is improved so that the luminescence linewidth becomes narrower than the width of ordinary quantum wells (QWs), a reduced threshold current and a high characteristic temperature will be expected in QD lasers. Recently, highly-uniform InAs QDs have been fabricated by using a strained coverage layer (InGaAs) instead of the usual GaAs-based layer. The strain of InAs is reduced due to expansion toward the surface resulting in long-wavelength emission from structures on GaAs substrates. A narrow linewidth of 21 meV is observed in InAs QDs covered with 7 nm-thick strained In/sub 0.2/Ga/sub 0.8/As, presumably because of suppression of In segregation and interface diffusion. Typical photoluminescence (PL) spectra are reported. The linewidth is reduced by almost half in the GaAs-covered QD structure and is almost comparable to the best results observed in ordinary QW structures. Thus, using these strain-reduced QDs will improve device characteristics by reducing the state density of carriers.

1.3-/spl mu/m GaInNAs VCSELs for 40-Gb/s CWDM systems

This paper reports on the performance of the four-wavelength 10-Gb/s GaInNAs VCSELs for a 40-Gb/s CWDM system. WDM transmission characteristics using a optical multiplexer and a demultiplexer including dielectric thin film filters is also demonstrated.

Room-temperature CW operation of InP-based long-wavelength InAs quantum dot lasers

Long-wavelength quantum-dot lasers were fabricated on InP (311)B substrates by using high-dense InAs quantum dots (9 /spl times/10/sup 10/ cm/sup -2/) as active media, which achieved 1.6-/spl mu/m continuous-wave lasing at room temperature. The lasers had a low threshold current density of 380 A/cm/sup 2/ and a high external differential quantum efficiency of 32%.

New materials for 1.3-/spl mu/m VCSEL smart pixels

Our approaches to developing 1.3-/spl mu/m VCSELs are introduced. The two new materials, Sb QWs and InGaAs-capped InAs QDs, are found to be candidates for the active layers of VCSELs on GaAs substrates. These new GaAs-based materials will be key in making 1.3-/spl mu/m VCSEL pixels and in enlarging the capacity of optical interconnections.