TSMC bets on unorthodox optical tech

>serial interfaces dominating over the parallel ones

Semi-accurate. For example, PCIe remains dominant in computing. PCIe is technically a serial protocol, as new versions of PCIe (7.0 is releasing soon) increase the serial transmission rate. However, PCIe is also parallel-wise scalable based on performance needs through "lanes", where one lane is a total of four wires, arranged as two differential pairs, with one pair for receiving (RX) and one for transmitting (TX).

PCIe scales up to 16 lanes, so a PCIe x16 interface will have 64 wires forming 32 differential pairs. When routing PCIe traces, the length of all differential pairs must be within >how can this be addressed in this massive parallel optical parallel interface?

From a hardware perspective, reserve a few "pixels" of the story's MicroLED transmitter array for link control, not for data transfer. Examples might be a clock or a data frame synchronization signal. From the software side, design a communication protocol which negotiates a stable connection between the endpoints and incorporates checksums.

Abstractly, the serial vs. parallel dynamic shifts as technology advances. Raising clock rates to shove more data down the line faster (serial improvement) works to a point, but you'll eventually hit the limits of your current technology. Still need more bandwidth? Just add more lines to meet your needs (parallel improvement). Eventually the technology improves, and the dynamic continues. A perfect example of that is PCIe.

That article is really low on details and mixes up a lot of things. It compares microleds to traditional WDM fiber transmission systems with edge emitting DFB lasers and ECLs, but in datacentre interconnects there's plenty of optical links already and they use VCSELs (vertical cavity surface emitting lasers), which are much cheaper to manufacture. People also have been putting these into arrays and coupling to multi-core fiber. The difficulty here is almost always packaging, i.e. coupling the laser. I'm not sure why microleds would be better.

Also transmitting 10 Gb/s with a led seems challenging. The bandwidth of an incoherent led is large, so are they doing significant DSP (which costs money and energy and introduces latency) or are they restricting themselves to very short (10s of m) links?

Phase variations will not introduce any issues here, they most certainly are talking about intensity modulation. You can't really (easily) do coherent modulation using incoherent light sources like leds.

SNR is obviously an issue for any communication system, however fiber attenuation is orders of magnitude lower than coax.

The bigger issues in this case would be mode-dispersion, considering that they are going through "imaging" fibres, i.e. different spatial components of the light walking off to each other causing temporal spread of the pulses until they overlap and you can't distinguish 1's and 0's.

short links it’s in the article

They are doing 10 Gb/s over each fibre, to get to 10 Gb/s you have already undergone a parallel -> serial conversion in electronics (clock rates of your asics/fpgas are much lower), to increase the serial rate is in fact the bottleneck. Where the actual optimum serial rate is highly depends on the cost of each transceiver, e.g. long haul optical links operate at up to 1 Tb/s serial rates while datacenter interconnects are 10-25G serial AFAIK.