4 ms·

>higher sample rate ADCs and DACs becoming more viable Question, on optical networks doesn't this make dispersion more of a problem?

ArkyBeagle 11y ago
80 GHz isn't quite optical yet. It's a couple octaves down from infrared. SFAIK, it's still very much radio.
- walrus01 11y ago
  a great deal lower, the optical ITU DWDM grid is around 191.7 THz to 196.1 THz
  - ArkyBeagle 11y ago
    The more general dividing line between microwave and infrared ( outside comms ) is 300 GHz, which was what I meant.
    - walrus01 11y ago
      That is true. One of the fun things illustrating first-hand how microwave/millimeter wave and fiber are the same thing is if you ever get to handle a 120 GHz band waveguide/feed. Some radar and military stuff operates in the 120 band. It's so incredibly tiny and narrow compared to a 11 or 18 GHz microwave waveguide. Then imagine continuing to make it narrower while increasing the frequency, follow that to its logical conclusion and you have imagined a 9/125 fiber.
      - ArkyBeagle 11y ago
        But it's something of an apparently completely different... phenotype from a small waveguide. The seemingly arbitrary 300Ghz line was probably more cultural than essential; the instrumentation was just very different. What's the analog for a prism for microwave?
        detaro 11y ago
        Apparently a block of plastics like Delrin works: http://www.physics.rutgers.edu/ugrad/205/manuals/micro.pdf http://www.physics.rutgers.edu/ugrad/205/manuals/micro.pdf
        walrus01 11y ago
        The key part in physics is it's still a wave... And a singlemode fiber is a type of waveguide. A 120GHz signal is a wave, a 171 THz signal is a wave, the latter just has a much shorter wavelength.
        Sanddancer 11y ago
        300Ghz ends up with a wavelength of 1mm, so it more follows the pattern of bandwidth assignment, which likes nice round numbers given in wavelength.
    - madengr 11y ago
      Back in 60's AT&T make lots and lots of circular waveguide, intending to bury it across the country. One of the circular modes is dispersionless; then fiber was invented; lot's of money lost on circular waveguide. Interesting that mmWavguide is still rectangular. Wonder if one could do a mmWave fiber? Don't see why not.
      - walrus01 11y ago
        millimeter wave waveguide on the rear of a parabolic antenna (30, 60cm dish) is actually circular (cylindrical), supporting dual polarity operation (opposite H and V). Individual radio heads like this russian radio or other 80 GHz radios are still single polarity. In certain scenarios you can mount two radio heads on a T-shaped waveguide on the rear of one dish antenna, one in H, one in V.
        madengr 11y ago
        Thanks for the info. I got to mess with W-band stuff years ago, but I'm mostly Ku and below now. Would love to tear down some 80 GHz hardware. Have you seen anything come of the "angular momentum" polarization discovered a few years ago? Seemed specific for P2P microwave.
        walrus01 11y ago
        I've yet to see a product of any sort I can buy with a credit card or purchase order. Would also like to know if anything comes of it.
        wrigby 11y ago
        I would love to hear more about that - have any links? From a quick google, all I can dig up makes it sound like it's normal circular polarization, which is used quite often in satellite. Not sure why it wouldn't make it into terrestrial, since it has some interesting advantages (no x-pol alignment issues!)
        madengr 11y ago
- cmiller1 11y ago
  Sorry, I work in a photonics lab so in casual conversation more of the spectrum is "optical" to me. I just meant to ask if you just increase your sampling rate doesn't that mean you have to worry more about things like dispersion happening along the path of the signal?
  - ArkyBeagle 11y ago
    Optical and microwave are sort of an arbitrary distinction, so you're also right :) There's even the "millimeter wave" designation, or E(xtremely)HF. Different frequencies scatter differently. This isn't bad: https://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet70/oet70a.pdf https://transition.fcc.gov/Bureaus/Engineering_Technology/Do...

ArkyBeagle 11y ago

80 GHz isn't quite optical yet. It's a couple octaves down from infrared. SFAIK, it's still very much radio.

walrus01 11y ago
a great deal lower, the optical ITU DWDM grid is around 191.7 THz to 196.1 THz
- ArkyBeagle 11y ago
  The more general dividing line between microwave and infrared ( outside comms ) is 300 GHz, which was what I meant.
  - walrus01 11y ago
    That is true. One of the fun things illustrating first-hand how microwave/millimeter wave and fiber are the same thing is if you ever get to handle a 120 GHz band waveguide/feed. Some radar and military stuff operates in the 120 band. It's so incredibly tiny and narrow compared to a 11 or 18 GHz microwave waveguide. Then imagine continuing to make it narrower while increasing the frequency, follow that to its logical conclusion and you have imagined a 9/125 fiber.
    - ArkyBeagle 11y ago
      But it's something of an apparently completely different... phenotype from a small waveguide. The seemingly arbitrary 300Ghz line was probably more cultural than essential; the instrumentation was just very different. What's the analog for a prism for microwave?
      - detaro 11y ago
        Apparently a block of plastics like Delrin works: http://www.physics.rutgers.edu/ugrad/205/manuals/micro.pdf http://www.physics.rutgers.edu/ugrad/205/manuals/micro.pdf
      - walrus01 11y ago
        The key part in physics is it's still a wave... And a singlemode fiber is a type of waveguide. A 120GHz signal is a wave, a 171 THz signal is a wave, the latter just has a much shorter wavelength.
      - Sanddancer 11y ago
        300Ghz ends up with a wavelength of 1mm, so it more follows the pattern of bandwidth assignment, which likes nice round numbers given in wavelength.
  - madengr 11y ago
    Back in 60's AT&T make lots and lots of circular waveguide, intending to bury it across the country. One of the circular modes is dispersionless; then fiber was invented; lot's of money lost on circular waveguide. Interesting that mmWavguide is still rectangular. Wonder if one could do a mmWave fiber? Don't see why not.
    - walrus01 11y ago
      millimeter wave waveguide on the rear of a parabolic antenna (30, 60cm dish) is actually circular (cylindrical), supporting dual polarity operation (opposite H and V). Individual radio heads like this russian radio or other 80 GHz radios are still single polarity. In certain scenarios you can mount two radio heads on a T-shaped waveguide on the rear of one dish antenna, one in H, one in V.
      - madengr 11y ago
        Thanks for the info. I got to mess with W-band stuff years ago, but I'm mostly Ku and below now. Would love to tear down some 80 GHz hardware. Have you seen anything come of the "angular momentum" polarization discovered a few years ago? Seemed specific for P2P microwave.
        walrus01 11y ago
        I've yet to see a product of any sort I can buy with a credit card or purchase order. Would also like to know if anything comes of it.
        wrigby 11y ago
        I would love to hear more about that - have any links? From a quick google, all I can dig up makes it sound like it's normal circular polarization, which is used quite often in satellite. Not sure why it wouldn't make it into terrestrial, since it has some interesting advantages (no x-pol alignment issues!)
        madengr 11y ago
cmiller1 11y ago
Sorry, I work in a photonics lab so in casual conversation more of the spectrum is "optical" to me. I just meant to ask if you just increase your sampling rate doesn't that mean you have to worry more about things like dispersion happening along the path of the signal?
- ArkyBeagle 11y ago
  Optical and microwave are sort of an arbitrary distinction, so you're also right :) There's even the "millimeter wave" designation, or E(xtremely)HF. Different frequencies scatter differently. This isn't bad: https://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet70/oet70a.pdf https://transition.fcc.gov/Bureaus/Engineering_Technology/Do...