Researchers at Université Grenoble Alpes, STMicroelectronics and Université de Lyon in France have co-integrated a 1.3μm III-V laser source with a silicon-based Mach–Zehnder modulator (MZM), potentially overcoming impediments in the advancement of silicon photonics.
The hybrid III-V/silicon photonics devices, which have shown to be compatible with the wavelength-multiplexing requirements of the 100GBASE-LR4 and other communications standards, were able to transmit information at 25 Gigabits/second at wavelengths of 1303.5 nm and 1315.8 nm, with a 2.5 V peak-to-peak signal.
The primary application for the silicon photonic transmitter would be data communication in data centers.
“The transmitter co-integrates on the same silicon-on-insulator (SOI) wafer a heterogeneously integrated III-V on-silicon laser source emitting at 1.3 µm and a silicon-based Mach-Zehnder modulator offering a 25 Gb/s modulation rate,” says Thomas Ferrotti, lead author of the paper “Co-integrated 1.3µm hybrid III-V/silicon tunable laser and silicon Mach-Zehnder modulator operating at 25Gb/s,” published in Optics Express. Collaborators and co-authors were Dr Badhise Ben Bakir of CEA-LETI and Dr Frederic Boeuf of STMicroelectronics.
The team, whose work was funded by IRT Nanoelec, chose a distributed Bragg reflector (DBR) structure with two grating reflectors located in the silicon layer for the laser to be able to precisely control its emission wavelength by its grating period and by thermal tuning. Thermal heaters are also located in the passive section of the Mach-Zehnder modulator to set it at quadrature during the measurements, and the modulated optical signal at the output of the modulator is coupled into a single-mode fiber, thanks to a silicon surface grating coupler.
First step toward complete integration on chip
“This demonstration is the first step towards a complete integration of a light source into a fully monolithic silicon photonics chip, including a receiver. This has never been demonstrated,” confirms Ferrotti, whose same group also studied the integration of the laser on the backside of the wafer. The results were presented at last year’s International Electron Device Meeting (IEDM). “By combining these two studies, in the near future, we’ll be able to build a fully integrated Si-photonics chip,” the expert projects.
Impact on the future of silicon photonics
“Thanks to the heterogeneous integration of III-V materials on silicon, it is now possible to build completely integrated silicon photonic circuits, without relying on any optical device external to the system,” says Ferrotti, who believes this advance potentially means a reduction in the system cost by simplifying the packaging and could also smoothen the way to efficient chip-to-chip communication for high-performance computing, where several light sources will have to be integrated on a single chip.
Ferrotti reports that while the fabrication of these transmitters started on 8” SOI wafers, downsizing to 3” was necessary to perform the final processing steps. “Therefore, the next step of this work would be to integrate these transmitters on a complete 8” — or even 12” — fabrication platform, combined with the integration of the laser on the back-side of the wafer as shown at the IEDM,” he says. “This will allow us to integrate more complex interconnects and, therefore, design a full-duplex, multi-channel silicon photonics chip containing both transceiver and receiver for future silicon photonics products.”
Written by Sandra Henderson, research editor Novus Light Technologies Today