Breaking optical data transmission speed records

Read an article this week about records being made in optical transmission speeds (see IEEE Spectrum, Optical labs set terabit records). Although these are all lab based records, the (data center) single mode optical transmission speed shown below is not far behind the single mode fibre speed commercially available today. But the multi-mode long haul (undersea transmission) speed record below will probably take a while longer until it’s ready for prime time.

First up, data center optical transmission speeds

Not sure what your data center transmission rates are but it seems pretty typical to see 100Gbps these days and inter switch at 200Gbps are commercially available. Last year at their annual Optical Fiber Communications (OFC) conference, the industry was releasing commercial availability of 400Gbps and pushing to achieve 800Gbps soon.

Since then, the researchers at Nokia Bell Labs have been able to transmit 1.52Tbps through a single mode fiber over 80 km distance. (Unclear, why a data center needs an 80km single mode fibre link but maybe this is more for a metro area than just a datacenter.

Diagram of a single mode (SM) optical fiber: 1.- Core 8-10 µm; 2.- Cladding 125 µm; 3.- Buffer 250 µm; & 4.- Jacket 400 µm

The key to transmitting data faster across single mode fibre, is how quickly one can encode/decode data (symbols) both on the digital to analog encoding (transmitting) end and the analog to digital decoding (receiving) end.

The team at Nokia used a new generation silicon-germanium chip (55nm CMOS process) able to generate 128 gigabaud symbol transmission (encoding/decoding) with 6.2 bits per symbol across single mode fiber.

Using optical erbium amplifiers, the team at Nokia was able to achieve 1.4Tbps over 240km of single mode fibre.

A wall-mount cabinet containing optical fiber interconnects. The yellow cables are single mode fibers; the orange and aqua cables are multi-mode fibers: 50/125 µm OM2 and 50/125 µm OM3 fibers respectively.

Used to be that transmitting data across single mode fibre was all about how quickly one could turn laser/light on and off. These days, with coherent transmission, data is being encoded/decoded in amplitude modulation, phase modulation and polarization (see Coherent data transmission defined article).

Nokia Lab’s is attempting to double the current 800Gbps data transmission speed or reach 1.6Tbps. At 1.52Tbps, they’re not far off that mark.

It’s somewhat surprising that optical single mode fibre technology is advancing so rapidly and yet, at the same time, commercially available technology is not that far behind.

Long haul optical transmission speed

Undersea or long haul optical transmission uses multi-core/mode fibre to transmit data across continents or an ocean. With multi-core/multi-mode fibre researchers and the Japan National Institute for Communications Technology (NICT) have demonstrated a 3 core, 125 micrometer wide long haul optical fibre transmission system that is able to transmit 172Tbps.

The new technology utilizes close-coupled multi-core fibre where signals in each individual core end up intentionally coupled with one another creating a sort of optical MIMO (Multi-input/Multi-output) transmission mechanism which can be disentangled with less complex electronics.

Although the technology is not ready for prime time, the closest competing technology is a 6-core fiber transmission cable which can transmit 144Tbps. Deployments of that cable are said to be starting soon.

Shouldn’t there be a Moore’s law for optical transmission speeds

Ran across this chart in a LightTalk Blog discussing how Moore’s law and optical transmission speeds are tracking one another. It seems to me that there’s a need for a Moore’s law for optical cable bandwidth. The blog post suggests that there’s a high correlation between Moore’s law and optical fiber bandwidth.

Indeed, any digital to analog optical encoding/decoding would involve TTL, by definition so there’s at least a high correlation between speed of electronic switching/processing and bandwidth. But number of transistors (as the chart shows) and optical bandwidth doesn’t seem to make as much sense probably makes the correlation evident. With the possible exception that processing speed is highly correlated with transistor counts these days.

But seeing the chart above shows that optical bandwidth and transistor counts are following each very closely.

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So, we all thought 100Gbps was great, 200Gbps was extraordinary and anything over that was wishful thinking. With, 400Gbps, 800 Gbps and 1.6Tbps all rolling out soon, data center transmission bottlenecks will become a thing in the past.

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