Optical interconnects
With the exponential growth of compute power and memory capacity comes a commensurate need for I/O bandwidth – which can only be met by further improving optical links.
The current evolution in computing points to an exponential demand for bandwidth, far into the future. This will require developing new interconnect solutions between all levels of computer systems: optical solutions that allow for a denser and faster data connection than purely electrical interconnects.
In its optical I/O program, imec develops the technology to enable these future optical interconnects. In the first place, they’re meant for high-performance and data center systems, and for rack-to-rack, within-rack, and within-board connections. One of the key challenges is making cost-efficient packages. To do so, imec is looking at wafer-scale solutions leveraging the methods developed in its 3D system integration program.
- a) Vision for a wafer-level, optically interconnected multi-XPU compute system
- b) Demonstrated test system comprising PIC dies with embedded SiN waveguides and evanescent couplers bonded to a bottom PIC wafer with complementary SiN evanescent couplers.
Optimizing optical interconnects: more than bandwidth alone
Imec’s scientists tackle the challenge along three dimensions at the same time. In addition to bandwidth scaling, an equally impressive reduction in power consumption (10x) and cost per bit (10-100x) are essential to drive a sustained improvement.
- To further scale the bandwidth, imec develops a silicon photonics integrated platform with electro-optical transceiver bandwidths beyond 1 Tbps/mm2.
- The second focus is improving the power efficiency, which involves looking at new designs for lasers, modulators, drivers, photodetectors and amplifiers. In addition, to remove bandwidth bottlenecks in the chips, the optical transceivers will need an increasingly tighter integration with the silicon electronics.
- Thirdly, cost reduction is also key. To achieve it, we’re looking amongst others to realize low-cost parallel fiber packaging and low-cost multi-wavelength laser sources.
Optical I/O program: targeted components
These are some of imec’s innovations to enable the next generation of optical interconnects.
- optical modulators – advancing the state-of-the-art in optical phase and/or amplitude waveguide modulators integrated on silicon
- waveguide photodetectors – integrated on silicon through advanced process and device simulation, modeling, characterization and optimization
- wavelength-division multiplexing filters (WDM) both thermally tuned silicon designs and a-thermal silicon-nitride designs with channel counts scaling from 8 to 32
- multi-wavelength lasers for the WDM – first with hybrid flip-chip III-V integration and later with monolithic III-V approaches
- electro-optical co-packaging – with fiber-array coupling interfaces and packaging solutions scaling to 32 fibers and more
- electro-optical wafer-scale testing – developing solutions for process-control monitoring and known-good-die testing, and evaluating the reliability of new optical devices
- studies on system level – including proof-of-concept prototypes
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