Optical Data Transmission Li-Fi System Transmits 1 GBit/s With A Latency of Less Than 100 ns

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Optical data transmission is ideal wherever wireless networks reach their EMC limits or cables wear out quickly. With Li-Fi-Grathus, a Fraunhofer has presented a real-time-capable full-duplex system that delivers gigabit rates.

Reliable, broadband and wireless communication is essential in factory automation. Physical cables are often a mechanical weak point for moving machine parts, robots or large rotating systems. Conventional wireless solutions such as Wi-Fi or 5G, on the other hand, suffer from reflections in highly metallic environments and are susceptible to electromagnetic interference (EMC).

With the Li-Fi Grathus system, the Fraunhofer Institute for Photonic Microsystems IPMS is addressing precisely this gap. It uses light for data transmission (light fidelity) and enables a wireless point-to-point connection over distances of up to 33 feet. As the transmission is purely optical, it is by definition immune to any EMC influences in the workshop environment.

Deterministic Real-Time for Motion Control

From a system integration perspective, latency is the decisive factor. The IPMS specifies a deterministic, predictable latency of less than 100 nanoseconds for Li-Fi Grathus. The system operates in full-duplex mode, i.e. it transmits and receives simultaneously without any loss of time. These extremely short runtimes make the module suitable for demanding closed-loop control systems (motion control) and it fits seamlessly into clock-synchronous networks.

On the hardware side, the system supports common Industrial Ethernet standards such as Profinet, EtherCAT, EtherCAT G, SERCOS III and Time Sensitive Networking (TSN). In addition to standard Gigabit Ethernet, USB 3.0/3.1 interfaces are also available. A separate side channel with 1 Mbit/s is also available for management, diagnostics and safety signals.

A Multi-Path Lens Replaces Beam Steering

The classic disadvantage of many free space optics (FSO) communication systems is the high line-of-sight requirement and the usually high-precision mechanical alignment. Systems with active beam steering or adaptive optics also drive up system costs.

Fraunhofer IPMS overcomes this problem with Li-Fi Grathus using a patented multi-directional lens. On the one hand, this optical design enables higher transmission powers without exceeding the eye safety limits (laser class 1). On the other hand, the radiation and reception profile is widened so that manual alignment of the modules is sufficient. No complex optical adjustment is required, making the system a plug-and-play solution in a robust metal housing.

Typical Application Scenarios And Evaluation

The range of applications extends from retrofitting existing systems to backhaul connections for wireless access points and automated guided vehicles (AGVs). The latter can use the high bandwidth to upload or download large amounts of collected sensor data at charging stations within seconds. The optical path is also a wear-free replacement for slip rings in large rotating machines.

To make it easier for developers to get started, Fraunhofer IPMS is now offering the technology as an evaluation kit. The kit contains two Grathus transceiver modules, which can be used to replace a wired 1 Gbps Ethernet connection directly with the optical link for testing purposes. (heh)

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