European PLAT4M project is speeding industrialization of silicon photonics
CEA-Leti (Grenoble, France) and its partners in the European FP7 project PLAT4M announced that they have built three silicon photonics technology platforms, created by PLAT4M members Leti, Imec, and STMicroelectronics. The four-year project, which launched in 2013, aims at building a European-based supply chain in silicon photonics and speeding industrialization of the technology. PLAT4M is funded by a European Commission grant of 10.2 million euros. This is a long post, because there is a lot going on with PLAT4M.
Imec
Imec's silicon photonics platform is based on 200 mm substrates, has matured thanks to the PLAT4M project. The platform is based on SOI substrates with 220 nm crystalline silicon on a 2000 nm buried oxide. During the project, existing fabrication processes and integration flow have been fine tuned to have stable and repeatable performance for all photonics building blocks (couplers, waveguides, phase shifters, photodetectors). PLAT4M partners Thales, Polytec, and TNO already are using the technology. Beyond the 200 mm platform, Imec has begun exploiting advanced optical lithography with its 193 nm immersion lithography scanner. It also has demonstrated very low propagation loss (~0.6dB/cm) for fully etched waveguides with excellent within-wafer linewidth control (standard deviation <3nm for 450-nm-wide waveguides) and sub-100-nm features. Deep subwavelength features can be made in a manufacturable process, avoiding the use of e-beam lithography with this technology.
Imec and Thales: coherent beam combination
Using the Imec platform, Thales demonstrated coherent beam combination (CBC) of laser light. This application aims at producing high-power, high-energy laser sources for sensing, industry, or fundamental physics. The CBC rationale is to push the limits of single laser emitters (typically fiber amplifiers) by using a large number of amplifiers and coherently adding the output beams. The coherent addition requires locking the phase of all the amplifying channels. With the number of channels—potentially very large (from tens to thousands)—an integrated technology is a major concern in terms of possible industrial products. The first-generation CBC demonstrator of PLAT4M, which was packaged by Tyndall UCC, included a one-to-16 channel splitter tree, plus 16 independent thermal phase modulators. The CBC experiment showed the successful coherent addition of 16 laser beams at 1.55 µm.
Leti
Leti has developed a new photonic platform based on 200 mm SOI wafers. The process offers multilevel silicon patterning that allows the design of various passive and active devices (e.g. modulator and photodiode) with thermal tuning capability. Two AlCu levels are available for routing. A process design kit (PDK) is available for circuit design and an MPW service will be proposed in 2016. Leti says state-of-the-art performances have been demonstrated: insertion losses are below 2 dB/cm for monomode waveguides and below 0.2 dB/cm for multimode devices. Germanium photodiode responsivity is >0.75 A/W for a bandwidth >30 GHz. Mach-Zehnder modulator VpLp is in the 2 V.cm range for 2 V operation with an E/O bandwidth > 25 GHz. Moreover, Leti and III-V Lab have developed integrated hybrid III-V lasers and electro-absorption modulators (EAMs) on silicon using a wafer-bonding technique. The hybrid lasers operate in the single-mode regime and the EAMs exhibit an extinction ratio higher than 20 dB with a drive voltage lower than 2 V. Clear eye diagrams have been achieved at a bit rate of 25 Gbit/s, confirming strong potential for telecom applications.
STMicroelectronics
During the project, ST developed an additional silicon-photonic platform in 300 mm technology to be used as an R&D tool for proof-of-concept purposes. The technology, called DAPHNE (Datacom Advanced PHotonic Nanoscale Environment), is designed for evaluating new devices and subsystems for demonstration. DAPHNE is a flexible platform intended to fit R&D needs. While developing it, ST demonstrated wavelength-division-multiplexing (WDM) solutions using arrayed waveguide gratings, echelle gratings, cascaded Mach-Zehnder interferometers, and side-coupled integrated spaced sequence of resonators. Some of the configurations are designed for the 100GBase-LR4 standard, and the experimental characterization results show insertion losses below 0.5 dB and channel cross-talks above 25 dB for a band flatness of 2 nm. Furthermore, proper operation of receiver-and-transmitter blocks to be interfaced to optical devices above them has been demonstrated at 28 Gbit/s, making use of 65-nm-node technologies.
Others
In addition, Paris-Sud University has studied theoretically the behavior of different phase shifters and photodetectors for time-efficient and precise modeling. Mentor Graphics and PhoeniX Software partners have improved phase-aware routing and tool interoperability. Verification and manufacturability have reached industry-requirement standards as a result of new techniques based upon the Mentor Graphics Calibre platform that delivers layout-versus-schematic comparison, photonic rule checks, and curvilinear-aware design-rule checks. Mask preparation is also improving, with better pattern-density control and mask correction. PLAT4M includes 15 European R&D institutes and CMOS companies, industrial and research organizations in design and packaging, and end users in different application fields, to build the complete supply chain.
For more info, see http://plat4m-fp7.eu/
John Wallace | Senior Technical Editor (1998-2022)
John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.