All-optical RAM to clear comms bottleneck
NTT shows off nanowatt optical memory
Japanese researchers are claiming a breakthrough in all-optical memory, one of the key bottlenecks remaining in the optical communications world.
The high throughput of optical communications systems brings its own problem: any function that can’t be performed in the optical domain demands an opto-electric conversion, creating a bottleneck in the system. This has put a premium on research into optical switching, amplification and signal regeneration.
Memory is a tough nut to crack, however: it demands that a photon’s state be captured, retained and read out – all without converting the signal back to electrons, and in a repeatable and cheap fashion.
The NTT researchers say they have created an ultra-low-power optical RAM using optical cavities that represent a 1 or 0 by either passing or blocking light. The memory cell uses a material based on an indium gallium arsenide strip buried in gallium arsenide.
It acts as a memory because the indium-gallium arsenide strip changes its refractive index when exposed to a laser. The light beam it’s trying to “remember” will be blocked or passed depending on the state of the strip. A second pulse of laser on the “control” strip reverses its state.
While it only retains state for about a microsecond, the researchers say that’s long enough for other system components to use the stored information (and four times the previous record for an all-optical memory). Importantly, they also say the optical cavity approach consumes very low power – according to the Nature Photonics abstract, 30 nW, which is “more than 300 times lower than the previous record”. ®
Bootnote: Proposals for optical memory have existed for a surprisingly long time. For example, this Wikipedia entry describes an approach using a loop of photo-emissive and photo-sensitive materials from the 1950s, as an attempt to solve the problems of memory speed in early computers. ®
Re: 30 nanowatts you say?
Doesn't really stop it being useable, it just puts an upper limit on the amount of RAM you can have if you've only got a domestic mains connection. Personally I think the more important "orders of magnitude short of a useable system" element is that they've only got four bits of optical RAM at the moment...
30 nanowatts you say?
Since the article also mentions a refresh time of a microsecond or so, I assume that's the ongoing cost of maintaining 1 bit of data with this new scheme. That's several hundred watts per gigabyte and a few kilowatts for a half-decent server. (Come back Pentium 4! All is forgiven!)
I know this is research and things will improve. I just though someone ought to flag up that we are several orders of magnitude short of a usable system.
Re: Re: Re: Oh dear, oh dear - you don't remember your history do you
also, its definitely write only