P. Moser

85 °C error-free operation at 38 Gb/s of oxide-confined 980-nm vertical-cavity surface-emitting lasers

Extremely temperature stable oxide-confined high-speed 980-nm vertical-cavity surface-emitting lasers (VCSELs) for optical interconnects are presented. Error-free performance at 38 Gb/s and 40 Gb/s is demonstrated at temperatures as high as 85 °C and 75 °C, respectively. No adjustment of driving conditions was found to be necessary from room temperature up to 85 °C. In addition, energy-efficient 35 Gb/s operation at a very low pump current of only 4 mA is demonstrated with a low dissipated heat-to-bit rate ratio of 233 mW/Tbps. These are by far the highest bit rates reported for VCSELs at such temperatures.

Temperature-Dependent Small-Signal Analysis of High-Speed High-Temperature Stable 980-nm VCSELs

980-nm VCSELs based on submonolayer growth show for 20-Gbit/s large-signal modulation clearly open eyes without adjustment of the driving conditions between 25degC and 120degC. To access the limiting mechanism for the modulation bandwidth, a temperature-dependent small-signal analysis is carried out on these devices. Single-mode devices are limited by damping, whereas multimode devices are limited by thermal effects, preventing higher photon densities in the cavity.

Quantum dot insertions in VCSELs from 840 to 1300 nm: growth, characterization, and device performance

Presently VCSELs covering a significant spectral range (840-1300 nm) can be produced based on quantum dot (QD) active elements. Herein we report progress on selected QD based vertical-cavity surface-emitting lasers (VCSELs) suitable for high-speed operation. An open eye diagram at 20 Gb/s with error-free transmission (a bit-error-rate < 10-15) is achieved at 850 nm. The 850 nm QD VCSELs also achieve error-free 20 Gb/s single mode transmission operation through multimode fiber without the use of optical isolation. Our 980 nm-range QD VCSELs achieve error free transmission at 25 Gb/s at up to 150°C. These 980 nm devices operate in a temperature range of 25-85°C without current or modulation voltage adjustment. We anticipate that the primary application areas of QD VCSELs are those that require degradation-robust operation under extremely high current densities. Temperature stability at ultrahigh current densities, a forte of QDs, is needed for ultrahigh-speed (> 40 Gb/s) current-modulated VCSELs for a new generation of local and storage area networks. Finally we discuss aspects of QD vertical extended-cavity surface emitting lasers with ultra high power density per emitting surface for high power (material processing) and frequency conversion (display) applications.

Energy efficient 850 nm VCSELs operating error-free at 25 Gb/s over multimode optical fiber up to 600 m

We demonstrate error-free 25 Gb/s optical interconnects with 850 nm vertical-cavity surface-emitting lasers. At 25°C through 100, 303, and 603 meters of fiber we achieve record heat-to-bit-rate ratios of 99, 122, and 188 mW/Tbps, respectively.

980-nm VCSELs for optical interconnects at bandwidths beyond 40 Gb/s

The copper-induced communication bottleneck is inhibiting performance and environmental acceptance of todays supercomputers. Vertical-cavity surface-emitting lasers (VCSELs) are ideally suited to solve this dilemma. Indeed global players like Google, Intel, HP or IBM are now going for optical interconnects based on VCSELs. The required bandwidth per link, however, is fixed by the architecture of the data center. According to Google, a bandwidth of 40 Gb/s has to be accommodated. We recently realized ultra-high speed VCSELs suited for optical interconnects in data centers with record-high performance. The 980-nm wavelength was chosen to be able to realize densely-packed, bottom-emitting devices particularly advantageous for interconnects. These devices show error-free transmission at temperatures up to 155°C. Serial data-rates of 40 Gb/s were achieved up to 75° C. Peltier-cooled devices were modulated up to 50 Gb/s. These results were achieved from the sender side by a VCSEL structure with important improvements and from the receiver side by a receiver module supplied by u2t with some 30 GHz bandwidth. The novel VCSELs feature a new active region, a very short laser cavity, and a drastically improved thermal resistance by the incorporation of a binary bottom mirror. As these devices might be of industrial interest we had the epi-growth done by metal-organic chemical-vapor deposition at IQE Europe. Consequently, the devices were fabricated using a three-inch wafer process, and the apertures were formed by proprietary in-situ controlled selective wet oxidation. All device data were measured, mapped and evaluated by our fully automated probe station. Furthermore, these devices enable record-efficient data-transmission beyond 30 Gb/s, which is crucial for green photonics.

High speed VCSELs for energy-efficient data transmission

High-speed 850nm VCSELs are suitable for energy-efficient error-free multimode fiber data transmission over extended distances (>;600m at 25Gb/s and >;100m at 40Gb/s). Large coupling tolerances and fulfillment of the encircled flux condition are demonstrated.

High-speed directly and indirectly modulated VCSELs

Recent results on directly modulated VCSELs, including high efficiency 980 nm devices operating error free at 20 Gbit/s without current adjustment between 25 and 85degC, will be reviewed. In addition, a novel electro-optically modulated (EOM) VCSEL concept employing an EOM Bragg reflector based on the Quantum Confined Stark Effect will be proposed and preliminary data presented.

Energy efficient 850 nm vcsels for error-free 30 gb/s operation across 500 m of multimode optical fiber with 85 fj of dissipated energy per bit

Error-free operation at 25 and 30 Gb/s across 1 km and 500 m of multimode fiber is achieved with 100 and 85 fJ of dissipated energy per bit using narrow spectral-width 850 nm vertical-cavity surface-emitting lasers.

120 °C 20 Gbit/s operation of 980 nm single mode VCSEL

Single mode 980 nm VCSEL show under 20 Gbit/s large signal modulation clearly open eyes without adjustment of the laser current and modulation voltage between 25 and 120 degC.

Comparative study of contact geometry for bottom-emitting 980-nm VCSELs

Substrate-emitting GaAs based oxide-confined 980-nm vertical-cavity surface-emitting lasers (VCSELs) with top-surface high-frequency ground-source-ground contact pads are designed, fabricated, and characterized. The devices are composed of standard top and bottom epitaxially-grown AlGaAs distributed Bragg reflectors (DBRs). The top (p)DBR is capped with p-contact Ti then Au thin-film metals for uniform current injection and laser emission is through the GaAs substrate. The devices are realized on a single epitaxial wafer with n-ohmic-contacts placed on a thick (n+)GaAs buffer layer beneath the bottom (n)DBR and alternatively with the n-ohmic-contacts placed on an (n)GaAs intra-cavity layer lying within the same bottom (n)DBR. Static device parameters including threshold current and rollover current, differential resistance, peak optical output power, and wall-plug efficiency are extracted for VCSELs with oxide-aperture diameters ranging from about 3 to 9-µm and at different temperatures. At room temperature threshold currents are achieved from the sub-mA range up to about 3.5-mA with maximum output powers exceeding 15-mW. Increasing the temperature up to 85 °C slightly increases the threshold current while the peak output power is about halved. The differential resistance at the thermal rollover current is comparable for standard and intra-cavity n-metal-contacts. Small-signal analysis is performed for different bias currents, temperatures, oxide-aperture diameters, and the two n-contact options. Under optimal bias conditions the 3-dB bandwidth exceeds 15 GHz. Direct current modulation-based on-off keying signal generation is investigated from 10 to 40-Gb/s. The influence of an anti-reflection-coated substrate, a thinned substrate, and the combination of both is investigated and discussed.