OFC: Integrated silicon photonic switch offers lowest signal loss in high-speed data nets

Applications and Research

Experimental photonic switches tested by researchers at the University of California, Berkeley, US, could enable fully optical, high-capacity switching for future high-speed data transmission networks, say the developers. The switch developed and tested for this research demonstrated capabilities not seen before in photonic switches.

In a paper presented at OFC, researchers Tae Joon Seok and colleagues reported the successful scale-up of a 240×240 input/output integrated silicon photonic switch. Using experimental photonic switches manufactured at the Marvell Nanofabrication Laboratory at UC Berkeley, the research team demonstrated signal loss lower than any previously reported, said Seok, who is both assistant professor at the Gwangju Institute of Science and Technology in South Korea and a visiting scholar at UC Berkeley.

The telecommunications industry long ago embraced fibre-optic technology as a better solution to meet exploding demand for higher speeds and greater capacity data transmission over the electrical copper wires of old.

Now, says Seok, a similar revolution is occurring at the points where the messages transmitted over long-haul fibres are sent and received. Seok said, “Instead of power-hungry electrical switches that require optical-electrical-optical conversions and cause signal loss, researchers are developing and deploying photonic switches to improve transmission quality and link a single transmission to tens and sometimes thousands of servers.”

In particular, silicon-based photonic switches using advanced CMOS technology are drawing a lot of attention from researchers as a powerful platform due to their low cost and high capacity. They have the potential to replace electrical switches, which will soon face scalability limits in performance and energy efficiency.

“Recently, many research groups competitively reported silicon photonic switches with large input/output port counts,” added Seok. “However, the physical size of a silicon photonic chip has been limited to 2 to 3 cm because of the limitations of the lithography tools necessary to etch the required geometric patterns on the silicon wafers used as a base for the integrated chips.”

Seok and his colleagues overcame this limitation by using a process known as lithography stitching, creating a wafer-scale 240×240 silicon photonic switch by stitching together nine 80×80 switch blocks in a 3×3 array, with three input and three output coupler blocks.

The switches developed as part of the experiment coupled light coming in and out of the chip through grating couplers. The switch cells were actuated by electrical probes. The resulting switch area was 4 cm x 4 cm—nearly doubling the size of existing silicon photonic switches. “To the best of our knowledge, this is the largest integrated photonic switch ever reported on any platform,” Seok said.

Measured results from the experimental switch also broke records: “This technology can be applied not only to silicon photonic switches but also to any silicon photonics applications that require ultra-large-scale devices such as programmable photonic processors, and so on,” said Seok.

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