#1
Old 05-11-2017, 04:45 PM
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Fiber Optic question

Silly really, but if you where to cut an active FiOS cable, would you see light coming out of it?

Would you have to stare directly into it? Would it glow?

Don't think transmission would immediately end.
#2
Old 05-11-2017, 04:58 PM
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No, the wavelengths of light used by FiOS are infrared. You wouldn't see them for the same reason you can't see the light emitted by the TV's remote control.

Verizon FiOS and visible spectrum: The shortest wavelength FiOS uses is 1310 nm (upstream Internet), and the longest wavelength humans can see is 750 nm (deep red).

And transmission would end pretty damned quick, as the equipment at both ends detected a complete loss of all the framing data meant to keep them synchronized.
#3
Old 05-11-2017, 05:06 PM
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Thanks. We are having some fiber re-routed in my county (affecting some of my systems) and I was just wondering
#4
Old 05-11-2017, 05:21 PM
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I don't know about FiOS at all, but looking at the light through the fiber is a standard step for troubleshooting fiber Ethernet and serial connection issues. If you see the light, you know the transmitter and fiber itself aren't your issue. It's not a laser, and eye safety hasn't been an issue in my experience.

That's using shorter multimode fibers within buildings, though. Single-mode long distance stuff is usually going to be IR.
#5
Old 05-11-2017, 05:51 PM
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Quote:
Originally Posted by DrCube View Post
I don't know about FiOS at all, but looking at the light through the fiber is a standard step for troubleshooting fiber Ethernet and serial connection issues. If you see the light, you know the transmitter and fiber itself aren't your issue. It's not a laser, and eye safety hasn't been an issue in my experience.

That's using shorter multimode fibers within buildings, though. Single-mode long distance stuff is usually going to be IR.
And even that is tough to see in a bright room. You really need to shade it with your hand and get in close to see the faint red glow.
#6
Old 05-12-2017, 02:16 PM
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Originally Posted by Derleth View Post
No, the wavelengths of light used by FiOS are infrared. You wouldn't see them for the same reason you can't see the light emitted by the TV's remote control.

Verizon FiOS and visible spectrum: The shortest wavelength FiOS uses is 1310 nm (upstream Internet), and the longest wavelength humans can see is 750 nm (deep red).

And transmission would end pretty damned quick, as the equipment at both ends detected a complete loss of all the framing data meant to keep them synchronized.
Can you use your cell phone camera to see it, the way they can see infrared TV remotes?
#7
Old 05-12-2017, 02:26 PM
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Originally Posted by Reply View Post
Can you use your cell phone camera to see it, the way they can see infrared TV remotes?
I don't know about FiOS light, but I use my cell phone camera to detect it my remotes need new batteries.
#8
Old 05-12-2017, 02:47 PM
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Originally Posted by Reply View Post
Can you use your cell phone camera to see it, the way they can see infrared TV remotes?
I'm gonna guess no: A common value I'm seeing for TV remote control wavelength online is around 980 nm, which is still quite a bit shorter than the shortest FiOS uses, so unless the phone camera has a wide bandwidth (and there's no reason it should, really) it would be just as blind to FiOS light as humans are.

This PDF from the ARRL is very informative about how TV remote controls work.
#9
Old 05-12-2017, 03:39 PM
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Originally Posted by Reply View Post
Can you use your cell phone camera to see it, the way they can see infrared TV remotes?
As already observed, probably not. Fiberoptic cables are often operated near 1.5 microns (1500 nm), which is the vicinity of the minimum loss and zero dispersion wavelengths for optical fibers (that is, it's most transparent there, and pulses of light sent at that wavelength won't spread out in distance/time and decrease in height. Overall the best way to do it). Silicon detectors like you have in cell phones won't pick up light past about 1.2 microns. If you had germanium detectors, they'd see it, since germanium works out to about 1.,8 microns.
#10
Old 05-14-2017, 10:22 AM
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Quote:
Originally Posted by DrCube View Post
I don't know about FiOS at all, but looking at the light through the fiber is a standard step for troubleshooting fiber Ethernet and serial connection issues. If you see the light, you know the transmitter and fiber itself aren't your issue. It's not a laser, and eye safety hasn't been an issue in my experience.

That's using shorter multimode fibers within buildings, though. Single-mode long distance stuff is usually going to be IR.
I can't believe you said this. This is extremely dangerous as one can cause permanent damage to the retina. Unlike visible light which we can perceive and will blink or wince to disrupt the emission, with IR we don't perceive anything until after the retina begins to burn and then we blink or wince. This will at the very least cause temporary pain and at worst can cause blindness.

Using a cell phone works fine, as well as, Radio Shack used to sell these locally, but they had these business size cards that you could hold a remote up to or a fiber optic too and would turn dark to indicate that IR was present.

Never, ever, look into fiber optics, ever.
#11
Old 05-14-2017, 02:13 PM
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Originally Posted by electronbee View Post
I can't believe you said this. This is extremely dangerous as one can cause permanent damage to the retina. Unlike visible light which we can perceive and will blink or wince to disrupt the emission, with IR we don't perceive anything until after the retina begins to burn and then we blink or wince. This will at the very least cause temporary pain and at worst can cause blindness.

Using a cell phone works fine, as well as, Radio Shack used to sell these locally, but they had these business size cards that you could hold a remote up to or a fiber optic too and would turn dark to indicate that IR was present.

Never, ever, look into fiber optics, ever.
Thanks for the important correction.

It's not really part of my job anymore, but I'll keep that in mind for the future. I gotta say, it's a widespread misconception in my experience. I saw a lot of people do that over the years. I'm sure all transmitters are different, but I've seen some cheap optical transmitters which only used those red 5¢ LEDs they used to sell at Radioshack.

And to reiterate, I've only done this for <100ft fiber cables, within control buildings, using 650nm light. Long distance single mode fiber, on the data sheets I'm seeing, use 1310nm and 1550nm wavelengths (not to mention laser transmitters), which are invisible, and this "trick" would never work (or gain any traction) in the first place.

From here:
http://thefoa.org/tech/wavelength.htm
Quote:
A Note on Safety
The final note is on safety. Look closely at the first drawing above. The visible spectrum is well below the wavelengths used in fiber optics. That means you generally cannot see the light in fiber systems, so there is no reason to look into the end of a fiber to see if there is a signal. Some fiber optic systems like CATV and DWDM do have enough power to be potentially dangerous, so you should never look at the end of a fiber.
But on that page it even mentions 650nm plastic optical fiber, which is visible and harmless. Which explains where the idea comes from.

But yes, if you don't know for sure that's what you're working with, DON'T look into the fiber. It's probably pointless and very possibly dangerous.
#12
Old 05-14-2017, 03:37 PM
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Quote:
Originally Posted by electronbee View Post
I can't believe you said this. This is extremely dangerous as one can cause permanent damage to the retina. Unlike visible light which we can perceive and will blink or wince to disrupt the emission, with IR we don't perceive anything until after the retina begins to burn and then we blink or wince. This will at the very least cause temporary pain and at worst can cause blindness.

Using a cell phone works fine, as well as, Radio Shack used to sell these locally, but they had these business size cards that you could hold a remote up to or a fiber optic too and would turn dark to indicate that IR was present.

Never, ever, look into fiber optics, ever.
So what about fibre optic ceilings which produce the lovely stringy mess of squid wires where the ends are fitted into the ceiling to create pinpricks of light?

There is a reddit DIY post on someone making a squid of fibre optic for deco lighting in a bedroom.

https://reddit.com/r/DIY/comments/68egzs/i_built_a_fibre_optic_star_field_ceiling_in_the/
#13
Old 05-14-2017, 05:06 PM
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Originally Posted by dude robert View Post
So what about fibre optic ceilings which produce the lovely stringy mess of squid wires where the ends are fitted into the ceiling to create pinpricks of light?

There is a reddit DIY post on someone making a squid of fibre optic for deco lighting in a bedroom.

https://reddit.com/r/DIY/comments/68egzs/i_built_a_fibre_optic_star_field_ceiling_in_the/
Cool, but I sure wouldn't want to paint that ceiling...
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