Not an expert in communications.
Would the SerDes be the new bottleneck in the approach? I imagine there is a reason for serial interfaces dominating over the parallel ones, maybe timing skew between lanes, how can this be addressed in this massive parallel optical parallel interface?
TSMC bets on unorthodox optical tech
21–30 of 110 posts
Re: TSMC bets on unorthodox optical tech
#22Forgive the noob question but what stops us from making optical transistors?
I think the most fundamental reason is that there is no efficient enough nonlinearity at optical frequencies. So two beams(or frequencies in some implementation) tends not to affect each other in common materials, unless you have a very strong source (>1 W) so the current demonstrations for all-optical switching are mostly using pulsed sources.
Re: TSMC bets on unorthodox optical tech
#23Forgive the noob question but what stops us from making optical transistors?
Photons are way more difficult to control than electrons. They don't interact with each other.
Re: TSMC bets on unorthodox optical tech
#24Not an expert in communications. Would the SerDes be the new bottleneck in the approach? I imagine there is a reason for serial interfaces dominating over the parallel ones, maybe timing skew between lanes, how can this be addressed in this massive parallel optical parallel interface?
> timing skew between lanes
That's a big part of it. I remember in the Early Pentium 4 days, starting to see a lot more visible 'squiggles' on PCB traces on motherboards; the squiggles essentially being a case of 'these lines need more length to be about as long as the other lines and not skew timing'
In the case of what the article is describing, I'm imagining a sort of 'harness cable' that has a connector on each end for all the fibers, and the fibers in the cable itself are all the same length, there wouldn't be a skew timing issue. (Instead, you worry about bend radius limitations.)
> Would the SerDes be the new bottleneck in the approach
I'd think yes, but at the same time in my head I can't really decide whether it's a harder problem than normal mux/demux.
Re: TSMC bets on unorthodox optical tech
#25Forgive the noob question but what stops us from making optical transistors?
I think the most fundamental reason is that there is no efficient enough nonlinearity at optical frequencies. So two beams(or frequencies in some implementation) tends not to affect each other in common materials, unless you have a very strong source (>1 W) so the current demonstrations for all-optical switching are mostly using pulsed sources.
I wonder if considerably more engineering and research effort will be applied here when we reach the limit of what silicon and electrons can do.
Re: TSMC bets on unorthodox optical tech
#26As I understand it (from designing high-speed electronics), the major limitations to data/clock rates in copper are signal integrity issues. Unwanted electromagnetic interactions all degrade your signal. Optics is definitely a way around this, but I wonder if/when it will ever hit similar limits.
isn't attenuation also an issue with copper? maybe with small electronics it is negligible given the right amps? in other words, with with no interference, electrons will face impedance and start losing information.
Attenuation is going to be an issue for any signal, but in my experience Fiber can go for many miles without a repeater whereas something like Coax you're going one to two orders of magnitude less. [0]
[0] - Mind you, some of that for Coax is due to other issues around CTB and/or the challenge that in Coax, you've got many frequencies running through alongside each frequency having different attenuation per 100 foot...
Re: TSMC bets on unorthodox optical tech
#27If each cable is 10gb/s and uses 1 pixel to convert into electrical signals, would that mean they need a 10 giga frame per second sensor?
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Re: TSMC bets on unorthodox optical tech
#28Not an expert in communications. Would the SerDes be the new bottleneck in the approach? I imagine there is a reason for serial interfaces dominating over the parallel ones, maybe timing skew between lanes, how can this be addressed in this massive parallel optical parallel interface?
SerDes is already frequently parallelised. The difference is you never expect the edges or even the entire bits to arrive at the same time. You design your systems to recover timing per link so the skew doesnt become the constraint on the line rate.
Re: TSMC bets on unorthodox optical tech
#29> The transmitter acts like a miniature display screen and the detector like a camera. So if I'm streaming a movie, it could be that the video is actually literally visible inside the datacenter?
Obviously this is not how video compression and packets work but for the sake of the argument consider the following. The article speaks of a 300 fiber cable. A one bit per pixel square image with approx. 300 pixels is 17x17 in size. Not your typical video resolution.
Not your typical frame rate either.
Re: TSMC bets on unorthodox optical tech
#30As I understand it (from designing high-speed electronics), the major limitations to data/clock rates in copper are signal integrity issues. Unwanted electromagnetic interactions all degrade your signal. Optics is definitely a way around this, but I wonder if/when it will ever hit similar limits.
isn't attenuation also an issue with copper? maybe with small electronics it is negligible given the right amps? in other words, with with no interference, electrons will face impedance and start losing information.
This is the main mechanism of interference anyhow, called inter-symbol-interference.