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A Look at Photonic Clocking
zymano writes "In an article on the Electronic Engineering Times site James Siepmann shares a few thoughts about Photonic Clocking. Siepmann states: 'Copper interconnects are reaching their limit as data-transmission bandwidth and processor speed continue to rise. [..] Photonic clocking not only solves the limitations of electronic clocking, but also reduces jitter, skew, delay, crosstalk and power consumption while maintaining clock signal integrity for longer distances.'" Are Photonic Processors the next logical step, or will the almighty buck shuffle them aside because of cost?
The article didn't say a whole lot, did it? It just said, "Gee, wouldn't photonic clocking be nice". It didn't say a whole lot about how, and whether it's feasible.
So, I'll quickly fill in what I know. To do clock distribution you need two types of components: waveguides and detectors. Let's assume you are going to work in silicon...
Waveguides function as the optical wiring, and includes things like bends and splitters. Although perhaps not trivial, it is relative straight-forward to make waveguides in or on silicon. Detectors, on the other hand, are not so easy, at least at the wavelength most people are interested in, 1550 nm. There's a number of people researching Ge growth for detectors on Si, and this does have promise, but it's not ready yet. Another option would be bonding InGaAs, but that might always be too expensive.
Now, if you want to do full up optical communication, on chip, you'll want modulators, too. These have been demonstrated by Intel and Cornell in silicon, but only at speeds around 1 Ghz. Optical amplifiers would be nice, too, and this has been demonstrated (using Raman amplification) by Intel and UCLA. (I'm not sure Raman amplification can give you the sorts of amplification and efficiency you really need, though).
(Sorry, I won't be able to respond to any replies; at least not until Monday. I'm off to bed and I'm not planning to be near a computer tomorrow).
Distributing your clock with photons imples you have a photon wave guide. If you are going to build a photon wave guide then why not build an electrical wave guide. Electrical wave guides, like for example coax cable, have wave velocities that are faster than light in glass, so they would logically be even better. And you dont' need any special materials like you would for optical wave guides.
The problem might be that usually wave guides have to be the size of the wavelength to work right. ghz wavelength are larger than the chip. Thus you get forced towards the optical region by this considerarion.
But you can beat this two ways.
1) use negative index of refraction materials. Then the waveguide can be smaller than the wave length
2) use near field waveguides with amplification. When the wavelength is a lot larger than the waveguide then the wave becomes evanscent (decaying). So it can't propagate very far. But hey, that's okay because the chip is not very wide either, so we can tolerate some loss of signal. And we could toss in some amplification to offset it.
Some drink at the fountain of knowledge. Others just gargle.
Transistors don't need clocks, logic gates don't need clocks, but flip-flops do. The reason you need a clock is because the outputs of a bit of logic will be 'unstable' for a while the result is computed. The clock tells the next piece of the system when to read. In place of that, you'd need a 'done' signal, which would rase transistor counts quite a bit. Not to mention it would be very hard to find people who would know how to design these things. I think the future of the CPU involves different parts of the system operating on separate clocks, transferring data via a 'networking' type system. Computers connected via Ethernet don't need to have their clocks synched in order to work. Think of a simple instruction decoder. The decoder reads the instructions, and opens the right 'gates' in the CPU so that there is an electrical connection between the two registers and the ALU, and inside the ALU to the adder or subtractor, or whatever depending on what instruction you're trying to run. Then, the clock signals and tells the ALU that the registers are ready. Without the clock, the ALU might try to add the wrong things. (the ALU doesn't need a clock to work) In the future you could have some sort of system where the decoder just sends a message to the ALU telling it to setup the adder, and to the registry file to access these two registers. Then the register file will send the data to the ALU whenever it's ready.
autopr0n is like, down and stuff.
Not a credible player.
Back in the day, "real" computer manufacturers scoffed at Intel. IBM would only let them produce the chips for the PC after Intel found another manufacturer willing to produce the part in case Intel tanked. The PC was nothing to boast about compared to the mainframes of the day.
Slowly but surely, Intel grew to become the monster they are today. The turning point was somewhere near the Pentium II, when Intel machines were beginning to be used as engineering workstations. Profits truly are the source of competition and progress. Back then, the PC market was small, and improvements came quickly only because things were relatively simple. Now, everyone wants a piece of a growing pie, and companies are innovating as fast as possible.
less heat, less energy consumption, potential for smaller pathways, and higher speed (by definition thanks to the tidbit of information you shared with us just there.)
to name a few...
These look cool, they're supposed to oscillate to the several 10's of gigahertz.
http://physicsweb.org/articles/news/9/9/9/1
Physicists in the US have shown that two nano-scale magnets can be made to oscillate in phase when they are positioned close to one another. The phenomenon, which is similar to the way two pendulum clocks mounted on the same wall become synchronized via the weak coupling of acoustic signals, produces a stable microwave output. It could therefore replace bulky and expensive components which operate on the same "phase-locking" principle in devices such as portable phones and radar systems. The magnets may also serve as tiny receivers that would enable microchips to communicate with each other without being in contact, dramatically increasing the processing power of computers (Nature 437 389 & 393).
Ethernet does rely on synchronised clocks. You might be misstating that Ethernet doesn't have a clock line, meaning there is no dedicated wire with a clock signal on it.
There is a high-precision clock on every Ethernet card. An Ethernet frame has a 64-bit preamble with Manchester encoding. That preamble adjusts the skew of the receiver clock so that it's synchronised with the transmitter clock. If the synchronisation didn't occur, you wouldn't know when to latch the data on the line and you couldn't receive a frame. The synchronisation occurs on every Ethernet frame and the precision of the clock must be high enough that the synchronisation lasts for the length of a frame.
Async architectures will likely use a similar technique. The subsystems won't be driven by a system-wide clock line, as in the existing synchronous architectures, but the various clocks in subsystems will certainly be synchronised.
erm ... a waveguide is a waveguide, no matter what kind of terminators you use. The pertinent condition is to support propagation modes.
>>Sorry to parent, but people seem to be taking this seriously so I gotta point out that this is BS so hopefully noone takes this seriously...
Oh? Read on.
>"Consider the semiconductor."
>>Ok, here is the parent posts first fundamental misconception. Digital doesn't necessarily mean semiconductor. Say, for example CDs which encode digital data using light.
No, you misconstrue it. Transistor logic is what's used to do state changes that amount to the various relationships that form what a CPU does. Go back to your basics. We need the equivalent of optical accumulators in dense forms to make photonic processors feasible.
>"By adding information, you can blend things together, then demodulate them to see what happened as the change in information."
>>that isn't how light works, the waves superpose ontop of each other, just like every other kind of wave...
>"This modulation mimics how ALUs/accumulators/CPUs work"
>>No, no it doesn't.
Yes, it can. When you modulate, endowing information, and sum the modulations, you do the same thing as changing states in the lowly semiconductor when merged modulations are seen by an optical accumulator or reflective accumulator like your own eye. Yes, you've changed the information to create new states that accumulate information. Then it needs to be stored or moved on to be changed again to suit the calculative ends of the program.
>>There is a difference between storing and transmitting information and actual computation. You need some kind of devices which emit light depending on light inputs implementing AND OR and NOT logic.
Yes, we agree that to satisfy Boole's needs, this must be done.
>>Not helping is that this guy sounds like an idiot:
>>WTF does "mosh" mean anyway?
Sum, integrate, push together to form a meta value. I can tell you've never had a good punk rock experience.
>>"integer algebraic"?
How much about processor theory do you understand? Is integer algebra via binary summation foreign to you? Perhaps you're not familiar with integer algebra as the root method to obtain the basics of microprocessors.
>>"the electromagnetic spectra" (I guess theres more than one of the electromagnetic spectrum)
I can see that you're on a tangent, here. Yes, there are all sorts of subsections of the spectrum. Consider these spectra as finite sections of frequency ranges. There is one total spectrum. But Ethernet, a baseband technology, starts at 0hz and goes to varying heights of frequency; it's not modulated onto another carrier.
>>"your basic light switch is your basic computer" see above, a SWITCH is one bit of memory -- computation means implementing AND OR or NOT, at a minimum.
An SPST switch is either zero, or one. It's the most elemental binary calculator there is. Run your program and the switch closes, or it doesn't-- it's a computer and you control the logic state. But because it has either state, it isn't a static value. You can add logic onto multiple switches in numerous ways. You can then build truth tables, and so on. This is how the first computational devices were built via binary logic accumulators.
So, mod me down if you'd like. Moderation isn't the point-- photonic CPUs are the point. Building dense arrays of photonic sensors that can have state changes as a result of merging light sources (think loosely of colors, like red and yellow merging to orange, with orange as the new piece of information) can have future application. We can modulate light, change its frequency, make it do tricks by interrupting it in various modulations, then pushing them onto an observeration point to discern changes.
The modulations and summations can be programmed. The result of these inputs are an output. That's what we do in computing--> have inputs, process them, and do something with the outputs, now on a grand scale with the evolution of microprocessor integration capabilities and the surrounding chipsets that make use of I/O.
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