Si Fin Optical Modulator for Low Power Interconnection

Si photonics is achieving a drastic innovation for optical networks in terms of low power, low cost, high bandwidth, and large-scale integration capabilities with smart electronics fabricated in ubiquitous infrastructures of Complementary-Metal-Oxide-Semiconductor (CMOS) foundries.

Optical networks have been already introduced by using III-V compound semiconductors for long-hall communications, which require higher performance over the cost. Si photonics should not compete in this field, since the industries will not grow just by replacing these markets with Si photonics. Si Photonics is more promising in short-reach optical interconnections, which requires lower power consumption and lower fabrication costs. CMOS technologies are ideal in mass production to provide significant numbers of optical components required for short-reach communications such as backplane board-to-board, intra-board chip-to-chip, and intra-chip optical interconnections.

Si optical modulators, which convert the electrical signals to the optical signals on a chip, are the most important building blocks for Si photonics. Here, we will develop the world's best low power Si modulators, which can be driven by the CMOS front-end driver circuitry.

We will introduce the atomically flat Si fin technologies for the first time in optical modulators to develop the MOS-type Mach-Zehnder Interferometer (MZI) with a slot waveguide and the SiGe fin based Electro-Absorption (EA) modulators for short-reach interconnections and chip-to-chip applications, respectively. We anticipate that these devices will be widely used in data centres for cloud computing and network routing, contributing to reduce the power consumptions substantially, while increasing bandwidths.

Our first target of Si fin MZI optical modulators is aiming for the near term application to C form-factor pluggable 100-Gigabit-ethernet (CFP100GE) in multi-source agreement (MSA) at the 1310-nm wavelength region. We think that this is a natural choice of technology, since we have no MSA at the wavelength of 1550-nm, and a MZI has a better technological-readiness-level over an EA modulator.

For the longer term, however, a EA modulator can exceed its performance over MZI. Therefore, the other target for our SiGe fin EA modulator is the energy demanding chip-to-chip interconnection application by using the 1550-nm wavelength range, where no standardization exists at this moment. We will realize truly low power performance including a CMOS driver and laser diodes. Therefore, our project will cover both 1310-nm and 1550-nm wavelength ranges for near-term businesses and leading future technology trends.

In this project, we will reduce the power consumption of Si modulators more than 1 order of magnitude, compared with our previous state-of-the-art Si MZI modulators. Significant impacts are expected in the R&D communities as well as all users of cloud computing and network servers. Now, the global power consumption in servers exceeds the total power generated from solar energy. It is well known that a modern data centre consumes powers comparable to the generation from a nuclear power station. Therefore, the low power Si modulators will substantially contribute to reduce energy consumptions, heats, and CO2 emissions. We believe that we will develop world's best low power Si optical modulators, which will significantly contribute to the growth of UK businesses for future optical interconnections.