Integrated duobinary VCSEL driver for ultra-fast short-range electro-optical transmitters (DUET)
Final Report Abstract
To accommodate the ever-increasing internet and data center traffic, short-range optical interconnects based on vertical-cavity surface-emitting lasers (VCSELs) have gained huge attention in the last decade. While they enable low-cost and power-efficient data transmission, they have bandwidths <30 GHz, which limit the non-return-to-zero (NRZ) data rates to ≈40 Gb/s. Several techniques have been proposed to overcome this limitation. Pulse amplitude modulation with four levels (PAM-4) doubles the NRZ data rate, but comes along with increased system complexity, power penalty and reduced tolerance to noise and nonlinearity. The fastest VCSEL-based NRZ data transmission of 71 Gb/s was achieved by using signal equalization, which comes at the cost of high energy consumption of 13.4 pJ/bit. Therefore, in DUET, we investigated novel concepts and alternative integrated drivers for direct VCSEL modulation with a duobinary (DB) signal. This 3-level modulation is as spectrally efficient as PAM-4, but more tolerant to noise and nonlinearity, and offers a simpler and thus more energy-efficient implementation. It has been mainly applied in copper-based and longrange optical links for up to 100 Gb/s. However, the DB signal generation was often enabled by laboratory instruments or offline digital signal processing, which is not suitable for a system implementation with low power consumption. For VCSEL-based links almost no works on DB modulation were available and only one integrated driver at 5 Gb/s was reported. In DUET, we investigated three novel concepts for DB modulation of VCSELs with 20-GHz bandwidth and designed drivers in the fastest available SiGe BiCMOS technology with maximum transistor oscillation frequencies of 650 GHz. 1) With a pre-/encoder-based concept we achieved the first and fastest integrated DB VCSEL driver for data rates of up to 56 Gb/s. 2) For further performance enhancement, this driver was extended with an equalizer to compensate the VCSEL’s low-pass behavior. While the data rate could be increased by 10%, the power consumption increased by 50%. Due to the degraded energy efficiency, this concept was not pursued. 3) A novel encoder-less driver design, which exploits the low bandwidth behavior of the VCSEL for a first optical DB signal generation, achieved a data rate of >66 Gb/s at an energy efficiency of better than 2.5 pJ/bit. The results based on 1) and 3) improve the performance, efficiency as well as the state of the art of VCSEL-based optical transmitters.
Publications
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A High-Speed 130-nm SiGe BiCMOS Integrated Duobinary Driver for Data Rate Capacity Enhancement in VCSEL-Based Optical Links. IEEE Access, 12, 28343-28352.
Giuglea, Alexandru; Belfiore, Guido; Protze, Florian; Henker, Ronny & Ellinger, Frank
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A 60 Gbit/s Integrated Encoderless Duobinary VCSEL-Driver. IEEE Transactions on Circuits and Systems II: Express Briefs, 73(1), 58-62.
Froitzheim, Maximilian; Protze, Florian; Dürrwald, Franz Alwin; Henker, Ronny & Ellinger, Frank
