Survey of Photonic and Plasmonic Interconnect Technologies for Intra-Datacenter and High-Performance Computing Communications

Large scale data centers (DC) and high performance computing (HPC) systems require more and more computing power at higher energy efficiency. They are already consuming megawatts of power, and a linear extrapolation of trends reveals that they may eventually lead to unrealistic power consumption scenarios in order to satisfy future requirements (e.g., Exascale computing). Conventional complementary metal oxide semiconductor (CMOS)-based electronic interconnects are not expected to keep up with the envisioned future board-to-board and chip-to-chip (within multi-chip-modules) interconnect requirements because of bandwidth-density and power-consumption limitations. However, low-power and high-speed optics-based interconnects are emerging as alternatives for DC and HPC communications; they offer unique opportunities for continued energy-efficiency and bandwidth-density improvements, although cost is a challenge at the shortest length scales. Plasmonics-based interconnects on the other hand, due to their extremely small size, offer another interesting solution for further scaling operational speed and energy efficiency. At the device-level, CMOS compatibility is also an important issue, since ultimately photonics or plasmonics will have to be co-integrated with electronics. In this paper, we survey the available literature and compare the aforementioned interconnect technologies, with respect to their suitability for high-speed and energy-efficient on-chip and offchip communications. This paper refers to relatively short links with potential applications in the following interconnect distance hierarchy: local group of racks, board to board, module to module, chip to chip, and on chip connections. We compare different interconnect device modules, including low-energy output devices (such as lasers, modulators, and LEDs), photodetectors, passive devices (i.e., waveguides and couplers) and electrical circuitry (such as laserdiode drivers, modulator drivers, transimpedance, and limiting amplifiers). We show that photonic technologies have the potential to meet the requirements for selected HPC and DC applications in a shorter term. We also present that plasmonic interconnect modules could offer ultra-compact active areas, leading to high integration bandwidth densities, and low device capacitances allowing for ultra-high bandwidth operation that would satisfy the application requirements further into the future

Flip-chip III-V-to-silicon photonics interfaces for optical sensor

We demonstrate flip-chip solder assembly of InP chips on Silicon-Photonic (Si-Ph) substrates aimed at high volume manufacturing using typical microelectronic lead-free solders. In our show-case application, an InP die is both a light source and a detector in an integrated optical methane gas sensor that operates near 1.6mm. For high-resolution laser absorption spectroscopy sensing, a single-mode tunable laser is desired. We create an external cavity laser with InP as optical gain, butt-coupled to a Si-Ph external cavity, which incorporates the laser's frequency selective elements. For minimal reflection at the InP-Si interface, waveguides are angled to the facet, an index-matching medium is applied between the mating surfaces, and an anti-reflection coating designed for the index-matching medium is applied to the optical coupling facet of InP chip. Sub-micron alignment accuracy is obtained without high-accuracy assembly tooling. Lithographically defined alignment features on both InP and Si components allow reproducible high-accuracy alignment. Interface throughput loss were measured to be as low as 1.4 dB, and interface reflections are more than 30dB smaller than main signal beams

Flip-chip III-V-to-silicon photonics interfaces for optical sensor

\u3cp\u3eWe demonstrate flip-chip solder assembly of InP chips on Silicon-Photonic (Si-Ph) substrates aimed at high volume manufacturing using typical microelectronic lead-free solders. In our show-case application, an InP die is both a light source and a detector in an integrated optical methane gas sensor that operates near 1.6mm. For high-resolution laser absorption spectroscopy sensing, a single-mode tunable laser is desired. We create an external cavity laser with InP as optical gain, butt-coupled to a Si-Ph external cavity, which incorporates the laser's frequency selective elements. For minimal reflection at the InP-Si interface, waveguides are angled to the facet, an index-matching medium is applied between the mating surfaces, and an anti-reflection coating designed for the index-matching medium is applied to the optical coupling facet of InP chip. Sub-micron alignment accuracy is obtained without high-accuracy assembly tooling. Lithographically defined alignment features on both InP and Si components allow reproducible high-accuracy alignment. Interface throughput loss were measured to be as low as 1.4 dB, and interface reflections are more than 30dB smaller than main signal beams.\u3c/p\u3