We review recent developments in directly modulated lasers (DMLs) with low operating energy for datacom and computercom applications. Key issues are their operating energy and the cost for employing them in these applications. To decrease the operating energy, it is important to reduce the active volume of the laser while maintaining the cavity $Q$-factor or photon lifetime in the cavity. Therefore, how to achieve high-reflectivity mirrors has been the main challenge in reducing the operating energy. In terms of the required output power from the lasers, the required input power into the photodetector and the transmission distance determine the lower limit of laser active volume. Therefore, the operating energy and output power are in a trade-off relationship. In designing the lasers, the cavity volume, quantum well number, and optical confinement factor are critical parameters. For reducing the cost, it is important to fabricate a large-scale photonic integrated circuit (PIC) comprising DMLs, an optical multiplexer, and monitor photodetectors because the lower assembly cost reduces the overall cost. In this context, silicon (Si) photonics technology plays a key role in fabricating large-scale PICs with low cost, and heterogeneous integration of DMLs and Si photonics devices has attracted much attention. We will describe fabrication technologies for heterogeneous integration and experimental results for DMLs on a Si substrate.

中文翻译：

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用于短距离光学互连的低工作能量直接调制激光器

我们回顾了在数据通信和计算机通信应用中具有低工作能量的直接调制激光器（DML）的最新发展。关键问题是它们的工作能量以及在这些应用中使用它们的成本。为了降低工作能量，重要的是在保持腔体的同时减小激光器的有效体积$问$系数或腔中的光子寿命。因此，如何实现高反射镜一直是降低工作能量的主要挑战。根据激光器所需的输出功率，进入光电检测器的所需输入功率和传输距离决定了激光器有效体积的下限。因此，工作能量和输出功率处于折衷关系。在设计激光器时，腔体积，量子阱数和光学限制因子是关键参数。为了降低成本，重要的是制造包括DML，光学多路复用器和监控光电探测器的大规模光子集成电路（PIC），因为较低的组装成本降低了总成本。在这种情况下，硅（Si）光子技术在低成本制造大型PIC中起着关键作用，而DML和Si光子器件的异构集成引起了广泛关注。我们将描述用于在Si衬底上进行DML异构集成的制造技术和实验结果。