Plasmonics Integrates Photonics and Electronics

In the last year we have seen a marked increase in activity around the integrated photonics space, especially around silicon-based photonics. Last year the American Institute for Manufacturing of Photonics (better known as AIM Photonics) was started to boot-strap U.S. efforts in integrated photonics. We also saw multiple announcements by all three major Electronic Design Automation (EDA) players and a host of smaller Photonic Design Automation (PDA) players who are feverishly working to enter the market as photonics takes off. Pushing all of this is the insatiable demand for greater bandwidth density required by mega data centers who are quickly running out of rack front-panel space needed to satisfy the ever increasing data loads of an ever expanding internet of things (IoT) universe(s). Integrated photonics promises to accelerate us to the next level of bandwidth density and data communication speeds but the move into the data centers means much higher chip volumes and the need to push manufacturing costs down.

While silicon-based photonics is moving forward at a rapid pace, one sticking point for getting better cost-reduction has been that photonics does not scale or shrink in size at the same rate as its electronic counterparts. State-of-the-art electronic transistors are now in the sub 10nm range whereas photonic components are up in the 100’s of microns. Although integrated photonics are thousands of times smaller than using discreet photonic components, the photonics are still too large. Most silicon-based photonic integrated circuits (PICs) require waveguides with cross-sectional dimensions comparable in size to the wavelength of the transmitted light. That translates to waveguides with widths in 100’s of nano-meters.

Last year a new effort called PLASMOfab was started in Europe to tackle the photonics size problem. PLASMOfab is working on new structures known as Surface Plasmon Polariton (SPP) waveguides. These SPP waveguides are capable of guiding light at sub-wavelength scales as they can confine light into a width of a few nano-meters. They do this by using plasmonics which taking advantage of electron plasma oscillations near the metal interface. Plasmonics provides the capability to guide the optical field on a metal surface or between two metal surfaces or dielectric surfaces. This is remarkable on several fronts. First it provides for ultra-fine sensing capabilities that could be using for sensing applications and second, it enhances non-linearity’s such as Pockel’s effects used for polarization control in data communications applications. Additionally, SPP waveguides are unique in that they can be used to send both electronic and photonics signals along the same waveguide at the same time using geometries similar to those of electronic IC interconnect. If the work PLASMOfab is doing is successful they will indeed shrink the photonics down to the size of the electronics. Obviously it’s not that easy else it would have already been done but the jest is that there is a path to get there.

PLASMOfab is actually a 3-year collaborative project that brings together ten leading academic and research institutions and companies. The project was launched in January 2016 and it is funded by the European Union’s Horizon 2020 ICT research and innovation program. PLASMOfab’s goal is to develop CMOS compatible planer processes to shrink photonics and integrate it with electronics using plasmonics. Wafer scale integration will be used to demonstrate low cost, volume manufacturing and high yielding powerful photonic ICs. If successful, this new technology could produce a number of innovations in enhanced light-matter interaction for optical transmitters and biosensors.

In 2016 PLASMOfab worked to advance CMOS-compatible metals for the fabrication of plasmonic structures in commercially available foundries. TiN, Al and Cu were targeted for investigation as an alternative to gold or silver. Additionally, they were to generate a number of low-loss plasmonic waveguides on co-planar photonic substrates including SOI, SiO2 and Si3N4 using CMOS compatible metals. This work included interfacing the plasmonic waveguides to photonic waveguides.

In 2017 PLASMOfab is to work with PhoeniX Software to develop a plasmonic/photonic design automation flow and then use this flow to first, develop functional prototypes of an optical modulator and a biosensor with superior performance and then second, to then integrate the modular with 100 Gb/s SiGe electronics in a monolithic 100 Gb/s serial NRZ transmitter. Lastly in the bio-sensing arena, they are to integrate Si3N4-plasmonic biosensors with micro-fluidics and high-speed techniques in a multi-channel, ultra-sensitive lab-on-chip for medical diagnostics.

In 2018 their goal is to then demonstrate volume manufacturing and cost reduction by complying with large wafer-scale CMOS fabs and establishing a plasmonics/photonics/electronics fab-less integration service eco-system that can be adopted by commercial silicon and silicon nitride foundry services.

These are bold goals to be sure, but the potential is more than exciting as this could be a way to push photonics into the really low cost arena of silicon ICs.

For more information, see:
PLASMOfab website http://www.plasmofab.eu/
PLASMOfab write up in PIC Magazine http://www.publishing.ninja/V2/page/2416/143/168/1
PLASMOfab YouTube video https://youtu.be/0bAszCXUOag