High speed, low driving voltage vertical cavity germanium-silicon modulators for optical

Chapter 1 Introduction 
1.1 Interconnects 
Interconnects are the communication system that provides channels to transmit data. 
In conventional data networks and intra-/interchip data links, interconnects have 
continued to scale in complexity and bandwidth for the past fifty years. The limitation 
of metal interconnects in terms of loss, dispersion, crosstalk and fundamental speed 
limits are becoming increasingly obvious as interconnect density increases. This 
naturally leads to the development of optical interconnects, especially based on a Si 
photonics technology platform. This is because of the low cost, high performance and 
CMOS compatible processes of electronic-photonic integration. A gradual transition 
of electrical to optical technology in the interconnect field is taking place. This trend 
started with longer links and is expanding to short range applications. These 
applications areas for optical interconnects include high-performance computing, data 
centers, mobile-to-server interconnects and desktop computers. 
Transistor densities that can be achieved inexpensively on an integrated circuit will 
continue to double every two years for some time into the future [1]. This trend has 
continued for more than half a century and is still dominating the semiconductor 
industry today. As it appears on the ITRS roadmap, electrical interconnects are 
increasingly becoming the bottleneck for today’s integrated circuit operation. Among 
a number of possible solutions to overcome the challenge, optical interconnects are a 
very viable candidate to be the next generation of interconnect technology for 
integrated circuits. Their advantages and limitations have been carefully examined in 
the past few years [2-7]. 

---

 
 
 
2 
We can divide the interconnects into two different levels, depending on 
architecture: inter-chip (off-chip) interconnects and intra-chip (on-chip) interconnects.