IMEC Aims to Strengthen Next-gen Optical Networks With TIA Chip
With their transimpedance amplifier (TIA) chip, IMEC researchers offer a key technology for ensuring high reliability in 100G passive optical networks (PONs).
A major goal in the telecommunications industry today is to provide connectivity to people even in the most remote of areas. However, as telecom networks continually grow in physical scale and distance to accommodate this, there are a number of technical challenges that arise.
In an effort for greater reliability in these networks, last week IMEC researchers at Ghent University and Nokia Bell Labs have debuted a new transimpedance amplifier (TIA) chip for passive optical networks. In this article, we’ll discuss passive optical networks, challenges with scaling, and the new amplifier from IMEC.
Passive Optical Networks
One of the most standard types of networks used by telecommunications network providers is the passive optical network (PON). A PON can be defined as an optical network in which the desired signal is carried all the way to the user through fiber optic cabling.
Example of a passive optical network. Image used courtesy of TechTarget
Unlike active optical networks, a distinguishing feature of passive optical networks is the use of optical beam splitters which serve to distribute a single signal through multiple upstream branches.
In this architecture, an optical line terminal (OLT) is placed at the head of a network and a single fiber optical cable runs from the OLT to the beam splitter. Here, the beam splitter passively multiplies and relays the signal to many optical network terminals, where end-users eventually receive the signal. In these networks, downstream signals are transmitted continuously, while upstream packets are sent in bursts.
One of the primary benefits of PONs is that it reduces the number of fiber runs needed to reach multiple end-users. On top of this, it eliminates the need to power transmission devices through its passive nature.
A challenge with the design of passive optical networks is in terms of reliability as networks advance. Specifically, it has been well documented that upstream packets arriving at an OLT receiver may exhibit a wide range of received optical power.
One reason for this has to do with the differential path loss that the signal experiences throughout the PON. This is caused by many issues, including the fiber optics cables as well as the signal frequency.
Both of these variables have a direct impact on path loss: as length and/or frequency increases, path loss will also increase. Because of this, the chance of a bit error increases and network reliability decreases.
Path loss increases with increased distance. Image used courtesy from Fiber Transceiver Solution
Unfortunately, these challenges are only expected to become worse as networks strive for higher data rates. Further, the aim of connecting people in remote locations means that future PONs will be physically longer than current solutions.
Together, both of these factors are expected to challenge reliability as networks advance.
IMEC’s Transimpedance Amplifier
The new amplifier chip for passive optical networks that researchers at IMEC unveiled last week aims to improve network performance and reliability.
From a performance perspective, the new chip is being called the industry’s first upstream linear burst-mode transimpedance amplifier (TIA) with the ability to support 50 Gbit/s NRX and 100 Gbit/s PAM-4 modulation. Fabricated in a 0.13 μm SiGe process, the chip is said to exhibit a power consumption of 275 mW at 2.5 V, while offering a settling time under 150 ns.
Burst mode receiver (top view). Here, it is wirebonded with photodiode onto a PCB. Image used courtesy of IMEC
Overall, the idea of the new transimpedance amplifier is to mitigate the effects of upstream signal degradation by amplifying upstream signals such that upstream bursts all have a uniform and high received signal strength. According to IMEC, tests have shown that their amplifier is able to amplify each packet with an overhead in the tens of nanoseconds, allowing for maximum speed and reliability.
Moving forward, IMEC hopes that the International Telecommunication Union (ITU), which is currently defining 50G upstream PON standard G.9804, will adopt their chip into their standardization efforts.