VCSEL-based optical transceivers in data centers meet the increase in data traffic by increasing the data transmission rate. A single-channel PAM-4 data rate of >100 Gb/s is already in high demand. For 100Gb/s operation a low relative intensity noise (RIN) significantly gains importance. The challenge is to reduce the RIN without impeding the other static and dynamic VCSEL performance parameters. We demonstrate up to 20 dB/Hz RIN reduction of commercial VCSELs that are approaching the shot noise limit and give an outlook on datacom VCSELs for higher order modulation formats for single channel data rates of 100 Gb/s and beyond.
Energy efficient 200+ Gbit/s single fiber data transmission systems can be realized by wavelength multiplexing the directly modulated Vertical-Cavity Surface-Emitting Lasers (VCSELs) presented here, emitting at the four wavelengths 850 nm, 880 nm, 910 nm, and 940 nm. Large energy efficiency defined by a heat to data ratio (HBR) of only 240 fJ/bit @ 50 Gb/s is observed. Tuning the cavity photon lifetime is demonstrated to lead to an increase of the data rate in concert with a reduction of the HDR. The large linearity of our L-I-characteristics will allow easily higher order modulation rates. Our results might impact ongoing discussions of new physical layer standards for IEEE 802.3cm and cd coarse wavelength multiplexing standards across OM5 multimode fiber enabling up to 400 Gbit/s error-free transmission.
We reduce the epitaxial design complexity of our conventional single-cavity oxide-aperture vertical-cavity surfaceemitting lasers (VCSELs) to reduce manufacturing costs while still meeting our internal 980 nanometer VCSEL performance goals via simplicity-in-design principles. We achieve maximum static single-mode optical output powers exceeding 4 milliwatts with small-signal modulation bandwidths exceeding 30 gigahertz at an ambient temperature of about 25 degrees Celsius for VCSELs with an oxide-aperture diameter of about 4 micrometers. Neighbor VCSELs with oxide-aperture diameters above 15 micrometers have maximum room temperature multiple-mode optical output powers of about 20 milliwatts with small-signal modulation bandwidths exceeding 20 gigahertz. The performance of our conventional oxide-confined 980 nanometer simplicity VCSELs exceeds the performance of our previously-reported and more complex 980 nanometer VCSEL epitaxial designs where we previously achieved maximum small-signal modulation bandwidths of about 26 gigahertz with oxide-aperture diameters of about 4 to 6 micrometers.
Energy-efficient oxide-confined vertical-cavity surface-emitting lasers (VCSELs) emitting at 980 nm, particularly well suited for optical interconnects operating at up to 85°C are presented. The modulation bandwidth f3dB of our VCSELs increases at low currents with increasing temperature up to 23 GHz at 85°C. The impact of cavity photon lifetime and oxide-aperture diameter on the energy efficiency, temperature stability, and static and dynamic properties of our VCSELs are analyzed. Error-free 40 Gb/s operation at 85°C with an energy-to-data ratio below 100 fJ/bit and a current density close to 10 kA/cm2 is predicted based on small signal modulation experiments.
Vertical-cavity surface-emitting lasers (VCSELs) are decisive cost-effective, energy-efficient, and reliable light sources for short-reach (up to ~300 m) optical interconnects in data centers and supercomputers. To viably replace copper interconnects and advance to on-chip integrated photonics, reliable VCSELs ideally must be able to operate highly energy efficient, but at large bit rates and without cooling up to 85 °C, with immunity to temperature variations. Our 980 nm VCSELs achieve such temperature-stable, energy-efficient, and high-speed operation coincidently. Record low 139 fJ/bit of dissipated heat for 35 Gbit/s error-free data transmission at 85 °C is reported. Careful design of both the VCSEL’s epitaxial structure and device geometry is of essence. Introducing a suitable gain-to-etalon wavelength offset simultaneously improves the temperature-stability, the maximum bit rate at high temperatures, and the energy efficiency. Tuning the photon lifetime additionally increases the bandwidth by changing the relation between damping and resonance relaxation frequency. Systematic temperature-dependent and oxide aperture-diameter-dependent measurements, including static L-I-V curves and emission spectra, small signal analysis, and data transmission experiments are reported. The modulation bandwidth, the parasitic cut-off frequency, the relaxation resonance frequency, lumped-circuit elements, and the K- and D-factors are derived, useful for energy-efficient optical interconnects based on 980 nm VCSELs.
The use of Internet has increased and continues to increase exponentially, mostly driven by consumers. Thus bit rates in networks from access to WDM and finally the computer clusters and supercomputers increase as well rapidly. Their cost of energy reaches today 5-6 % of raw electricity production. For 2023 a cross over is predicted, if no new "green" technologies or "green" devices" will reduce energy consumption by about 15% per year. We present two distinct approaches for access and computer networks based on nanophotonic devices to reduce power consumption in the next decade.
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.
Via experimental results supported by numerical modeling we report the energy-efficiency, bit rate, and modal properties of GaAs-based 980 nm vertical cavity surface emitting lasers (VCSELs). Using our newly established Principles for the design and operation of energy-efficient VCSELs as reported in the Invited paper by Moser et al. (SPIE 9001-02 ) [1] along with our high bit rate 980 nm VCSEL epitaxial designs that include a relatively large etalonto- quantum well gain-peak wavelength detuning of about 15 nm we demonstrate record error-free (bit error ratio below 10-12) data transmission performance of 38, 40, and 42 Gbit/s at 85, 75, and 25°C, respectively. At 38 Gbit/s in a back-toback test configuration from 45 to 85°C we demonstrate a record low and highly stable dissipated energy of only ~179 to 177 fJ per transmitted bit. We conclude that our 980 nm VCSELs are especially well suited for very-short-reach and ultra-short-reach optical interconnects where the data transmission distances are about 1 m or less, and about 10 mm or less, respectively.
A new record for energy-efficient oxide-confined 850 nm vertical-cavity surface-emitting lasers (VCSELs) particularly suited for optical interconnects is presented. Error-free performance at 25 Gb/s is achieved with only 56 fJ/bit of dissipated energy per quantum of information. The influence of the oxide-aperture diameter on the energy-efficiency of our VCSELs is determined by comparing the total and dissipated power versus the modulation bandwidth of devices with different aperture diameters. Trade-offs between various parameters such as threshold current, differential quantum efficiency, wall plug efficiency and differential resistance are investigated with respect to energy-efficiency. We show that our present single-mode VCSELs are more energy-efficient than our multimode ones.
The bandwidth-induced communication bottleneck due to the intrinsic limitations of metal interconnects is inhibiting the
performance and environmental friendliness of today´s supercomputers, data centers, and in fact all other modern
electrically interconnected and interoperable networks such as data farms and "cloud" fabrics. The same is true for
systems of optical interconnects (OIs), where even when the metal interconnects are replaced with OIs the systems
remain limited by bandwidth, physical size, and most critically the power consumption and lifecycle operating costs.
Vertical-cavity surface-emitting lasers (VCSELs) are ideally suited to solve this dilemma. Global communication
providers like Google Inc., Intel Inc., HP Inc., and IBM Inc. are now producing optical interconnects based on VCSELs.
The optimal bandwidth per link may be analyzed by by using Amdahl´s Law and depends on the architecture of the data
center and the performance of the servers within the data center. According to Google Inc., a bandwidth of 40 Gb/s has
to be accommodated in the future. IBM Inc. demands 80 Tbps interconnects between solitary server chips in 2020. We
recently realized ultrahigh bit rate VCSELs up to 49 Gb/s suited for such optical interconnects emitting at 980 nm. These
devices show error-free transmission at temperatures up to 155°C and operate beyond 200°C. Single channel data-rates
of 40 Gb/s were achieved up to 75°C. Record high energy efficiencies close to 50 fJ/bit were demonstrated for VCSELs
emitting at 850 nm. Our devices are fabricated using a full three-inch wafer process, and the apertures were formed by
in-situ controlled selective wet oxidation using stainless steel-based vacuum equipment of our own design. assembly,
and operation. All device data are measured, recorded, and evaluated by our proprietary fully automated wafer mapping
probe station. The bandwidth density of our present devices is expected to be scalable from about 100 Gbps/mm² to a
physical limit of roughly 15 Tbps/mm² based on the current 12.5 Gb/s VCSEL technology. Still more energy-efficient
and smaller volume laser diode devices dissipating less heat are mandatory for further up scaling of the bandwidth.
Novel metal-clad VCSELs enable a reduction of the device's footprint for potentially ultrashort range interconnects by 1
to 2 orders of magnitude compared to conventional VCSELs thus enabling a similar increase of device density and
bandwidth.
State-of-the-art vertical-cavity surface-emitting laser (VCSEL) based optical interconnects for application in high
performance computers and data centers are reviewed. Record energy-efficient data transmission is demonstrated with
850 nm single-mode VCSELs for multimode optical fiber lengths up to 1 km at bit rates up to 25 Gb/s. Total power
consumption of less than 100 fJ/bit is demonstrated for VCSELs for the first time. Extremely temperature stable 980-nm
VCSELs show lasing up to 200 °C. Error-free 44 Gb/s operation at room temperature and 38 Gb/s up to 85 °C is
achieved with these devices. We present record-high bit rates in a wide temperature range of more than 160 °C. Record
energy-efficient data-transmission beyond 30 Gb/s is achieved at 25 °C for this wavelength range. In view of the high
speed and advanced temperature stability we suggest long wavelength VCSELs for energy-efficient short and very short-distance
optical interconnects for future high performance computers.
The copper-induced communication bottleneck is inhibiting performance and environmental acceptance of
today's 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.
Record energy-efficient oxide-confined 850-nm single mode and quasi-single mode vertical-cavity surface-emitting
lasers (VCSELs) for optical interconnects are presented. Error-free performance at 17 Gb/s is achieved with record-low
dissipated power of only 69 fJ/bit. The total energy consumption is only 93 fJ/bit. Transmission lengths up to 1 km of
multimode optical fiber were achieved. Our commercial quasi-single mode devices achieve error-free operation at
25 Gb/s across up to 303 m of multimode fiber. To date our VCSELs are the most energy-efficient directly modulated
light-sources at any wavelength for data transmission across all distances up to 1 km of multimode optical fiber.
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