Integrated duobinary VCSEL driver for ultra-fast short-range electro-optical transmitters (DUET)

在DUET项目中，我们希望开发具有双二进制信号的垂直腔面发射激光器（VCSELs）直接调制的新概念和集成驱动器，这将大大提高光发射机的性能，并为下一代光短距离数据通信系统铺平道路。近十年来，随着互联网业务的进步和5G、6G、物联网的发展，为适应日益增长的互联网数据流量，基于vcsel的近距离光互联得到了广泛关注。虽然vcsel可以实现低成本和节能的数据传输，带宽低于30 GHz，但它们将传输的非归零（NRZ）数据速率限制在约40 Gb/s。因此，已经提出了克服这一限制的技术。四电平（PAM-4）的脉冲幅度调制可以使NRZ数据速率提高一倍，但随之而来的是系统复杂性增加、功率损失和对噪声和非线性的容忍度降低。采用信号均衡技术，实现了基于vcsel的最快数据传输速度（71 Gb/s）。然而，这是以13.4 pJ/bit的高能耗为代价的。对于超过71 Gb/s的光学数据速率，目前还没有集成的vcsel驱动程序。双二进制是一种3级调制，其频谱效率是NRZ的两倍。与PAM-4相比，它提供了一个更简单、更节能的实现，并且对噪声和非线性的容忍度更高。它主要应用于铜基链路，也应用于100gb /s的远程光链路。然而，经常使用实验室仪器或离线数字信号处理来产生二进制信号，这并不适合低功耗的系统实现。对于基于VCSEL的链路，几乎没有关于双二进制调制的工作，只有一个集成的5gb /s VCSEL驱动被报道。在DUET中，我们将采用最快的SiGe BiCMOS技术设计基于vcsel的新型发射机，该发射机集成了双二进制驱动器，可提供最大振荡频率为500 GHz的晶体管。将设计三个VCSEL驱动程序，其中包括一个二进制预/编码器，一个均衡二进制驱动程序和一个无编码器的二进制驱动程序。此外，通过使用我们的创新方法同时调谐偏置电流和负载电阻，将研究性能和功率自适应。从密集的系统模拟开始，包括当前高速vcsel的行为模型，并最终验证设计的硬件驱动程序，我们打算找到在低于7 pJ/bit的低能耗下高达116 Gb/s的高数据速率的最佳权衡。与目前最先进的基于vcsel的数据传输速度（71 Gb/s）相比，这一速度提高了1.6倍，能效提高了1.9倍。

In the DUET project, we want to develop novel concepts and integrated drivers for the direct modulation of vertical-cavity surface-emitting lasers (VCSELs) with a duobinary signal, which massively improves the performance of optical transmitters and paves the way for next generation optical short-range data communication systems.To accommodate the increasing Internet data traffic, induced by the progress of Internet services and the development of 5G, 6G and the Internet of Things, short-range optical interconnects based on VCSELs have gained huge attention in the last decade. While VCSELs enable low-cost and power-efficient data transmission, with bandwidths of below 30 GHz, they limit the transmitted non-return-to-zero (NRZ) data rate to approximately 40 Gb/s. Therefore, techniques to overcome this limitation have been proposed. Pulse amplitude modulation with four levels (PAM-4) can double the NRZ data rate, but comes along with increased system complexity, power penalty and reduced tolerance to noise and nonlinearity. The fastest VCSEL-based data transmission of 71 Gb/s was achieved by using signal equalization. However, this comes at the cost of high energy consumption of 13.4 pJ/bit. For optical data rates above 71 Gb/s, no integrated VCSEL-drivers exist today.Duobinary is a 3-level modulation, which is twice as spectrally efficient as NRZ. Compared to PAM-4, it offers a simpler as well as a more energy-efficient implementation and is more tolerant to noise and nonlinearities. It has been mainly applied in copper-based links and also in long-range optical links with 100 Gb/s. However, very often laboratory instruments or offline digital signal processing is used to generate the duobinary signal, which is not suitable for a system implementation with low power consumption. For VCSEL-based links almost no works on duobinary modulation are available and only one integrated VCSEL driver at 5 Gb/s was reported. In DUET, we will design novel VCSEL-based transmitters with integrated duobinary drivers in the fastest available SiGe BiCMOS technology, which offers transistors with 500 GHz maximum oscillation frequency. Three VCSEL drivers will be designed incorporating a duobinary pre-/encoder, an equalized duobinary driver and an encoder-less duobinary driver. Furthermore, performance and power adaptivity will be investigated, by using our innovative method of simultaneous tuning of bias currents and load resistances. Starting with intensive system simulations, including behavioral models of current high-speed VCSELs, and finalizing with the verification of designed hardware drivers, we intend to find the best trade-offs for high data rates of up to 116 Gb/s at low energy consumption of below 7 pJ/bit. This is a >1.6X improvement in speed and a >1.9X improvement in energy efficiency compared to the fastest state-of-the-art VCSEL-based data transmission of 71 Gb/s.