IBM Demos Rapid On/Off Energy-saving Optical Receiver

Created March 2, 2018
Alessandro CevreroApplications and Research

Based on Complementary Metal-Oxide-Semiconductor (COMS) technology, a group of researchers from IBM Research in Zurich have demonstrated a novel optical receiver (RX) that can achieve an aggregate bandwidth of 160 Gbits/s through four optical fibres. The team, partnered by a consortium working under the EU-funded project “ADDAPT”, say that this is not only the fastest data transmission speed to date, but the RX also features link power-on/off functionality, and can wake-up and achieve phase-lock in eight nanoseconds, the shortest switch time on record.

According to the researchers, the rapid power-on/off feature will enhance link utilisation and greatly reduce energy consumption on a chip or in an optical interconnect system. Unlike many commercial optical transceivers that are always powered on, regardless of transmission activity, the power here would only be used when data packets are transmitted through the optical link. The novel design, packaged with an 850 nm photodiode array, targets low-cost VCSEL-based optical links for datacentre interconnects.

“This is the first optical receiver that combines high-speed data transmission rate and rapid power-on and off functionality while being extremely low lower in the ‘power-on’ state – about 88 mW,” said Alessandro Cevrero, the primary author of a paper describing the RX and a scientist of IBM Research Lab, Switzerland.

Today, link utilisation in datacentres is less than 10% for 99% of the links. This means only 10% of the links’ work time is actually used for transmitting user data, while the rest of the time is wasted by sending idle data packets that are missing information. To improve power efficiency in optical interconnect system, the researchers developed the rapid on/off functionality for the receiver, so that links can be powered off during idle time and powered back on when the data is ready to be transmitted.

“Our design, for the first time, allows for the on/off switching of and optical link on a per-packet basis,” added Cevrero.

The switch-on time of eight nanoseconds is shorter than the average length of time for an individual data packet in a typical network protocol transmitted at a speed of 160 Gbits/s. “There were previous scientific attempts to turn off the links when there is no data; however the timescale to switch on and off the link was orders of magnitude longer than that of an individual data packet. To achieve shorter power-on, time at a very high data transmission speed is the key challenge.”

To address this, Cevrero’s team designed an optical receiver with four identical channels associated with a proposed link protocol. The link protocol is equipped with self-developed smart analogue circuits that can rapidly align the receiver’s clock with the arrival of the incoming data, and detect the optical signal sequences to rapidly turn the link system on and off.

The innovation will be presented at OFC 2018, 11-15 March, San Diego, California, USA.


This article was written
by John Williamson

John Williamson is a freelance telecommunications, IT and military communications journalist. He has also written for national and international media, and been a telecoms advisor to the World Bank.