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I work in a photonics lab and for all of the new fancy techniques you see show up in popular science publications for slowing and stopping light... they're all

I work in a photonics lab and for all of the new fancy techniques you see show up in popular science publications for slowing and stopping light... they're all impractical. In the real world when we need to slow down light we still just use delay coils. Wrap tens to hundreds of kilometers of fiber into a coil (using a pump laser amplifier at some point if it gets too long) and just letting the light spin around in circles for the desired amount of time.

jberryman 13y ago
> when we need to slow down light Why do you need to do that? I'd never heard of "photonics" before now.
- cmiller1 13y ago
  Delaying light is sometimes used for a buffer in optical networks and signal processing, it is also used in the internal workings of certain opto-electronic devices such as optical oscillators; sometimes also used for testing and calibration of optical systems, making sure things are coming out as clean and at the same time as they do through the 'test' delay coil.
cheapsteak 13y ago
Could you give an example of a real world application for stopping/delaying light?
- theorique 13y ago
  Optical switching? The trouble is that the power levels required for a nonlinear optical material are often much higher than the light beam being switched. So you might need to use a 1000W beam to switch a 1W beam (for example).
  - cmiller1 13y ago
    Most of the switches we use are still opto-mechanical, just mechanically change the connection.
lifeformed 13y ago
How big do 100km bundles of fiber get?
- cmiller1 13y ago
  The dimensions would vary depending on the form factor needed for the particular application, but a spool with a 9 inch by 9 inch spool with a 2 inch hub (which works for 1310nm applications) would hold about 120km
  - lifeformed 13y ago
    Wow. That's pretty impressive. I was imagining massive cylinders the size of refrigerators.
    - cmiller1 13y ago
      The fiber we're talking about has an outer diameter of 250µm (standard single mode) so it packs pretty densely; we can actually do a bit better using some more exotic (expensive) fibers and some of our proprietary tricks to packing a bit more in there, but the size I gave is pretty typical. The largest ones we have made fit in a 5U rack enclosure, but I can't remember the length we had on those offhand and some of the internal space was used for amplifiers.
vacri 13y ago
Wouldn't that impart an improper spin on the light? -cough-

jberryman 13y ago

> when we need to slow down light Why do you need to do that? I'd never heard of "photonics" before now.

cmiller1 13y ago
Delaying light is sometimes used for a buffer in optical networks and signal processing, it is also used in the internal workings of certain opto-electronic devices such as optical oscillators; sometimes also used for testing and calibration of optical systems, making sure things are coming out as clean and at the same time as they do through the 'test' delay coil.

cheapsteak 13y ago

Could you give an example of a real world application for stopping/delaying light?

theorique 13y ago
Optical switching? The trouble is that the power levels required for a nonlinear optical material are often much higher than the light beam being switched. So you might need to use a 1000W beam to switch a 1W beam (for example).
- cmiller1 13y ago
  Most of the switches we use are still opto-mechanical, just mechanically change the connection.

lifeformed 13y ago

How big do 100km bundles of fiber get?

cmiller1 13y ago
The dimensions would vary depending on the form factor needed for the particular application, but a spool with a 9 inch by 9 inch spool with a 2 inch hub (which works for 1310nm applications) would hold about 120km
- lifeformed 13y ago
  Wow. That's pretty impressive. I was imagining massive cylinders the size of refrigerators.
  - cmiller1 13y ago
    The fiber we're talking about has an outer diameter of 250µm (standard single mode) so it packs pretty densely; we can actually do a bit better using some more exotic (expensive) fibers and some of our proprietary tricks to packing a bit more in there, but the size I gave is pretty typical. The largest ones we have made fit in a 5U rack enclosure, but I can't remember the length we had on those offhand and some of the internal space was used for amplifiers.

vacri 13y ago

Wouldn't that impart an improper spin on the light? -cough-