Si Fin Optical Modulator for Low Power Interconnection

Lead Research Organisation: University of Southampton
Department Name: Electronics and Computer Science


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.

Planned Impact

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.
Description We have developed the patterning technologies to make the silicon waveguide with the atomically flat surface roughness. We have achieve the record low propagation loss of 0.8 dB/cm with the refined process technology. This proves the validity of our ideas to use silicon-on-insulator wafers with a special crystallographic orientation.
We have successfully fabricated a slot waveguide with the record propagation loss of 4.0 dB/cm with a slot width as narrow as 100nm. We have also established the processes to fabricate sub-10nm slot waveguide, which is quite suitable to optical modulators. Recently, we have confirmed the proof of the principle of our optical modulator, which successfully operated at 20 Gbps with low power consumption.
Exploitation Route By using this patterning technology, we can fabricate the optical modulator. We have started to fabricate the device.
Sectors Electronics


including Industrial Biotechology

Description We have developed a new IP based on our research. We have filed a patent. Several industries are interested in the patent. The US patent application was successfully granted on 22/02/2022: United States Patent Number 11,256,113 from Application Number 16/324,748 Crystalline Silicon Slot Waveguide Another patent was also successfully granted: The US patent application was successfully granted on 16/01/2024: United States Patent Number 11874540 from Application Number 17/587679 A CAPACITOR RESONATOR MODULATOR
First Year Of Impact 2022
Sector Digital/Communication/Information Technologies (including Software)
Impact Types Economic

Description Platform Grant (CoI)
Amount £1,477,730 (GBP)
Funding ID EP/N013247/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 01/2016 
End 12/2020
Description Collaboration with Hitachi for Si Photonics 
Organisation Hitachi
Country Japan 
Sector Private 
PI Contribution We are developing Si photonics modulators with the industrial partner, Hitachi. They are interested in using high-speed optical modulators for their data centres and Si photonics will contribute to reduce the cost substantially due to the massive fabrication capabilities. We are contributing to designs, fabrications, and testing of these optical modulators. In particular, we have developed a novel design to use ultra-thin gate oxide to reduce the power consumption of the optical modulators. This will contribute to reduce the power consumption in data centres.
Collaborator Contribution Hitachi provided cash contributions of £50k for consumables and provided Si-On-Insulator wafers. Hitachi also contributed to support the design of the optical modulator by sending a senior research scientist to the University of Southampton as a visiting researcher for 1 year.
Impact We have several joined journal publications. Recently, we have confirmed the high speed operation of the designed optical modulator, which was accepted for publication in Photonics Research. We have also filed a patent for the optical modulator.
Start Year 2015
Description This patent covers the novel silicon optical modulator with thin insulating slot at the middle of the waveguide. By using the atomically flat Si (111) surfaces, we have realized low propagation loss, and low power consumption. 
IP Reference GB1613791.1 
Protection Patent application published
Year Protection Granted 2016
Licensed No
Impact The invented modulators would be a standard for the optical modulators in Si photonics to enable short reach optical communications in a data centre.