R. Jager

Design and analysis of single-mode oxidized VCSELs for high-speed optical interconnects

Oxide-confined vertical-cavity surface-emitting laser diodes (VCSELs) are fabricated for applications in high-performance optical interconnects. Both 980-nm as well as 850-nm wavelength devices in one- and two-dimensional arrays are investigated. Noise properties of single- and multimode devices under different operation conditions are relative intensity noise of single-mode devices can be as low as -150 dB/Hz at output powers of about 1 mW and feedback levels up to -30 dB. Data rates up to 12.5 Gb/s with bit error rates below 10/sup -11/ are achieved with VCSELs showing stable single-mode emission at large-signal modulation, combined with modulation bandwidths exceeding 10 GHz. Arrays with 4/spl times/8 elements flip-chip mounted on Si CMOS driver chips ready for use in parallel data transmission systems are presented.

Efficient single-mode oxide-confined GaAs VCSEL's emitting in the 850-nm wavelength regime

Single- and multimode vertical-cavity surface-emitting lasers (VCSELs) with three unstrained GaAs quantum wells (QWs) and emission wavelengths around 850 nm have been fabricated using molecular beam epitaxy (MBE) for crystal growth. Wet chemical etching and subsequent selective oxidation are applied for current confinement. The influence of oxide layer position on lateral index guiding is studied in detail in order to increase maximum single-mode output power. A device of 3-/spl mu/m active diameter and reduced index guiding shows maximum single-mode output power of 2.25 mW with a side-mode suppression ratio (SMSR) of more than 30 dB for high-efficiency oxidized VCSELs.

Noise characteristics of 850 nm single-mode vertical cavity surface emitting lasers

We have measured the noise characteristics of single-mode oxide confined surface emitting vertical cavity laser diodes. For pumping levels of more than 3.5 times threshold current, the relative intensity noise is below −150 dB/Hz up to 5 GHz at output powers near 1 mW. For various frequencies, we observe sub-Poissonian noise.

Single-mode AlGaAs-GaAs lasers using lateral confinement by native-oxide layers

We report on results of wet oxidized narrow-stripe QW laser diodes operating in single lateral and longitudinal mode around an emission wavelength of 850 nm. Devices with an active width of 4-10 /spl mu/m achieved output powers of up to 240 mW in continuous-wave (CW) operation at room temperature.

Analysis of longitudinal mode wave guiding in vertical-cavity surface-emitting lasers with long monolithic cavity

Lasing mode switching between two longitudinal modes is observed in transverse single mode vertical-cavity surface-emitting lasers with an extended cavity. Near- and far-field analyses carried out on devices with 2, 4, and 8 μm cavity spacers show an inherent relation between the transverse mode diameter and the calculated oxide- or thermally induced index guiding for the oscillating modes. Depending on the designed alignment of the optical longitudinal standing wave patterns relative to the oxide layer, mode switching can either be promoted or suppressed. Record-high single mode output powers up to 5.5 mW obtained from devices with 8 μm spacers and 8μm active diameter indicate the potential of the given device concept for low-divergence fundamental mode emission as required for many applications.

63% wallplug efficiency MBE grown InGaAs/AlGaAs broad-area laser diodes and arrays with carbon p-type doping using CBr4

We report on the growth and fabrication of InGaAs/AlGaAs strained quantum-well (QW) laser diodes with a maximum wallplug efficiency of 63%. The epitaxial graded-index separate-confinement heterostructure (GRINSCH) includes a single 8 nm InGaAs quantum well in the active region and AlGaAs cladding layers. For n-type and p-type doping, elemental silicon and CBr 4 as carbon source have been used, respectively. The device benefits from the low diffusion constant and the high free-carrier concentration of the p-type dopant in combination with abrupt doping profiles.

Highly efficient oxide-confined VCSEL arrays for parallel optical interconnects

We have designed and fabricated and VCSEL arrays at 850 and 980 nm operation wavelength, respectively, which are designed for maximum single-mode output power and high-frequency applications. GaAs VCSELs in the array show record high single-mode CW powers up to 4.8 mW. Individual devices of the InGaAs VCSEL array exhibit small-signal modulation bandwidths exceeding 10 GHz.

Applications of VCSELs for optical interconnects

High efficiency and high power VCSELs and arrays have been fabricated for potential applications in optical interconnects. We discuss VCSEL Si CMOS integration, characteristics of VCSEL arrays, few-km distance fiber data transmission and indoor free-space communications.

High performance selectively oxidized VCSELs and arrays for parallel high-speed optical interconnects

We introduce a new layout for high-bandwidth single-mode selectively oxidized vertical-cavity surface-emitting laser (VCSEL) arrays operating at 980 nm or 850 nm emission wavelength for substrate or epitaxial side emission. Coplanar feeding lines and polyimide passivation are used to reduce electrical parasitics in top-emitting GaAs and bottom-emitting InGaAs VCSELs. In order to enhance fundamental single-mode emission for larger devices of reduced series resistance a surface relief transverse mode filter is employed. Fabricated VCSELs are applied in various interconnect schemes.

Highly efficient laterally oxidized /spl lambda/=950 nm InGaAs-AlGaAs single-mode lasers

Results on laser diodes operating in single lateral and longitudinal mode around an emission wavelength of 950 nm are reported. Index guiding and current confinement in these devices are provided by a laterally oxidized aperture. The effective refractive index step of the lateral waveguide can be adjusted by the position and the thickness of the aperture. Structures with different effective refractive index steps and various aperture widths (3-7 /spl mu/m) have been characterized in CW operation at room temperature. Maximum output powers of 170 mW have been achieved. Due to the lower refractive index step compared to ridge-waveguide lasers, a larger lateral width of the optical waveguide can be chosen, preserving single-mode operation. Because of the low series resistance, wall-plug efficiencies up to 638 have been realized with these devices.