Philip Moser

81 fJ/bit energy-to-data ratio of 850 nm vertical-cavity surface-emitting lasers for optical interconnects

Extremely energy-efficient oxide-confined high-speed 850 nm vertical-cavity surface-emitting lasers for optical interconnects are presented. Error-free performance at 17 and 25 Gb/s via a 100 m multimode fiber link is demonstrated at record high dissipation-power-efficiencies of up to 69 fJ/bit (<0.1 mW/Gbps) and 99 fJ/bit, respectively. These are the most power efficient high-speed directly modulated light sources reported to date. The total energy-to-data ratio is 83 fJ/bit at 25 °C and reduces to 81 fJ/bit at 55 °C. These results were obtained without adjustment of driving conditions. A high D-factor of 12.0 GHz/(mA)0.5 and a K-factor of 0.41 ns are measured.

44 Gb/s VCSEL for optical interconnects

Highly temperature-stable, high-speed 980-nm VCSELs for optical interconnects are presented. Error-free performance up to 44 Gb/s at 25°C and 38 Gb/s at 85°C is demonstrated. These are the highest data-rates for VCSELs reported to date.

99 fJ/(bit

We present extremely energy-efficient oxide-confined 850-nm single-mode vertical-cavity surface-emitting lasers (VCSELs) for optical interconnects. Error-free transmission at 17 Gb/s across 1 km of multimode optical fiber is achieved with an ultra-low energy-to-data ratio of 99 fJ/bit, corresponding to a record-low energy-to-data-distance ratio of 99 fJ/(bit ·km). This performance is achieved without changing any of the driving parameters up to 55 °C. To date our VCSELs are the most energy-efficient directly modulated light-sources for data transmission across all distances up to 1 km of multimode optical fiber.

\cdot

The design, fabrication, and performance of the presently most energy-efficient oxide-confined 850 nm vertical-cavity surface-emitting lasers (VCSELs) for optical interconnects are presented. We employ a novel current spreading layer to reduce differential resistance. Compared to our previous designs, a higher indium content is used in the InGaAs quantum wells to increase the differential gain at low injected current densities. The influence of the oxide aperture diameter on the energy efficiency is determined by comparing the key performance parameters for a batch of VCSELs produced on the same epitaxial wafer, but with varying aperture diameters from 2.5 to 9.0 μm. The static light output power-current-voltage characteristics, small-signal modulation response, and large signal performance of our VCSELs are investigated in detail. The parameters important for energy-efficient operation are analyzed including threshold current, differential quantum efficiency, and differential resistance. We observe that our single-mode VCSELs are more energy efficient than our multimode VCSELs, although our multimode VCSELs typically exhibit a larger maximum static wallplug efficiency. Error-free (defined as a bit error ratio <;1 × 10 -12) data transmission at 25 Gb/s with a record-low dissipated heat energy of only 56 fJ/bit is achieved using a single-mode VCSEL with an oxide aperture diameter of 3.5 μm.

km) Energy to Data-Distance Ratio at 17 Gb/s Across 1 km of Multimode Optical Fiber With 850-nm Single-Mode VCSELs

We have studied the modulation properties of a vertical cavity surface-emitting laser (VCSEL) coupled to an electrooptical modulator. It is shown that, if the modulator is placed in a resonant cavity, the modulation of the light output power is governed predominantly by electrooptic, or electrorefraction effect rather than by electroabsorption. A novel concept of electrooptically modulated (EOM) VCSEL based on the stopband edge-tunable distributed Bragg reflector (DBR) is proposed which allows overcoming the limitations of the first-generation EOM VCSEL based on resonantly coupled cavities. A new class of electrooptic (EO) media is proposed based on type-II heterostructures, in which the exciton oscillator strength increases from a zero or a small value at zero bias to a large value at an applied bias. A EOM VCSEL based on a stopband-edge tunable DBR including a type-II EO medium is to show the most temperature-robust operation. Modeling of a high-frequency response of a VCSEL light output against large signal modulation of the mirror transmittance has demonstrated the feasibility to reach 40 Gb/s operation at low bit error rate. EOM VCSEL showing 60 GHz electrical and ~35 GHz optical (limited by the photodetector response) bandwidths is realized.

Energy Efficiency of Directly Modulated Oxide-Confined High Bit Rate 850-nm VCSELs for Optical Interconnects

New oxide-confined 980-nm vertical-cavity surface-emitting lasers (VCSELs) with record temperature-stable small-signal bandwidths of 25.6 to 23.0 GHz at 25 to 85 °C are designed, fabricated, and characterized. Technology-based device parameters essential for system-level models of VCSEL-based short-reach and ultrashort-reach optical interconnects are extracted. These parameters include key intrinsic figures-of-merit, including the -3-dB modulation bandwidth, the bandwidth-to-electrical power ratio, and device input impedance, all as functions of temperature, oxide-aperture diameter, and desired range of bias current or current density. Further, the M-factor, relating the intrinsic VCSEL bandwidth to the error-free bit rate for a given external systems configuration and application, is introduced. Our present 980-nm VCSEL technology is capable of 40 Gb/s operation at 85 °C at a simultaneously low current density of 10 kA/cm2 with an energy of only 100 fJ per bit.

Ultra high-speed electro-optically modulated VCSELs: modeling and experimental results

Vertical-cavity surface-emitting lasers (VCSELs) are particularly suited for energy- efficient optical interconnects in supercomputing. Consequently, several groups are developing VCSELs for energy-efficient interconnects with remarkable success. We give an overview over recent breakthroughs and present devices at the standard wavelength of 850 nm with record-low power consumption and heat dissipation per bit, achieving a value of only 69 mW/Tb/s at 17 Gb/s. This efficiency is exceeding the International Technology Roadmap for Semiconductors (ITRS) projection of 100 mW/Tb/s for 2015. If uncooled operation, ultradense arrays with smallest footprints, and highest ambient temperatures are required, the waveband around 1 μm is advantageous. At 980 nm, we could achieve an efficiency value in this waveband of 233 mW/Tb/s at an error-free 35 Gb/s.

Impact of the Oxide-Aperture Diameter on the Energy Efficiency, Bandwidth, and Temperature Stability of 980-nm VCSELs

Highly temperature stable, high bit rate oxide-confined vertical-cavity surface-emitting lasers (VCSELs) emitting at 980 nm are presented. Error-free data transmission at 38 Gb/s at 25 °C, 45 °C, 65 °C, and 85 °C is achieved without any change of working point and modulation condition. Static and high-speed properties are analyzed experimentally and theoretically. We numerically investigate the temperature dependence of the differential gain of our quantum well (QW) active region design to explain why a -15-nm QW gain-to-etalon wavelength offset facilitates our 980-nm VCSELs to show simultaneously high bit rate, temperature stability, and energy efficiency. Our VCSELs operate error-free at 42 and 38 Gb/s at 25 °C and 85 °C, respectively, with very low power consumption. Record low 175 fJ of dissipated heat per bit is achieved for 35-Gb/s error-free transmission at room temperature and 177 fJ/bit for 38-Gb/s error-free transmission at 85 °C. Such VCSELs are especially well suited for very-short-reach (<;1 m) optical interconnects in high-performance computers and board-to-board and chip-to-chip integrated photonics.

Energy-Efficient VCSELs for Interconnects

Principles of energy-efficient high speed operation of oxide-confined VCSELs are presented. Trade-offs between oxideaperture diameter, current-density, and energy consumption per bit are demonstrated and discussed. Record energyefficient error-free data transmission up to 40 Gb/s, across up to 1000 m of multimode optical fiber and at up to 85 °C is reviewed.

Impact of the Quantum Well Gain-to-Cavity Etalon Wavelength Offset on the High Temperature Performance of High Bit Rate 980-nm VCSELs

We present multioxide-aperture 980 nm-range vertical cavity surface emitting lasers (VCSELs) with highly temperature stable modulation characteristics operating error-free at 25 Gbit/s at 25 and 85 °C. We perform small signal modulation experiments and extract the fundamental physical parameters including relaxation resonance frequency, damping factor, parasitic cut-off frequency, D-factor, and K-factor, leading to identification of thermal processes and damping as the main factors that presently limit high speed device operation. We obtain very temperature-insensitive bandwidths around 13–15 GHz. Presented results clearly demonstrate the suitability of our VCSELs for practical and reliable optical data transmission systems.