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I enjoy it so please go ahead ... How can be physically explained the cross talk between the fibers (photon vs. electronic)?
Thanks, Dorin [email protected] wrote: > ---------------------- Forwarded by Don Borowski/SEL on 01/10/2003 10:37 AM > --------------------------- > > Don Borowski > 01/10/2003 10:35 AM > > To: "Chris Maxwell" <[email protected]> > cc: > Subject: RE: Fiber optic cable testing per EN 55022:1998 ? (Document > link: Database 'Don Borowski', View '($Sent)') > > OK, some comments. > > The radiated and conducted emissions of concern are there due to the > possibility of the modulation signal sent to the light source getting > coupled onto the metalic coating of the fiber. > > There are seperate standards covering light leakage that are there for eye > protection. > > We conventionally think about current flow in a pair of wires carrying > energy. The energy is indeed guided by the wires, but is carried by the > transverse electromagnetic (TEM) field around the wires. The energy is not > flowing in the conductors, but in the space around the conductors. > > Even at DC where there is electron flow through the bulk of a > (non-superconductor) material, the energy is transmitted in the electric > and magnetic field outside the wires. There is indeed a magnetic field > inside the wire. However, the only electric field inside the wire is along > the direction of electron flow, and is due to resistance. If you do the > Poynting vector E×H, the direction of the vector is radial into the wire. > There is energy flow into the wire, which causes the wire to produce heat. > This heat production is better known as I²R loss. > > Light certainly can be guided by metal, just as lower frequencies. Take a > cylinder with a nice shiney mirrored surface on the inside, and shine light > into it. You will see light come out at the other end, even if there is a > bend so that there is not a straight shot through. > > It is possible to guide light with two conductors in TEM mode, though it is > quite lossy. Fiber is nice because of its low loss. > > There certainly can be light emissions from fiber - a sharp bend can cause > it. Conversely, bend a fiber sharply and shine a light on the bend, and the > light will go into the fiber. So there is possible emission and > susceptibility. But put a jacket over the fiber, or a metalic coating, and > this problem is solved for any practical source or victim. > > A system with a light source and light receiver is certainly still subject > to problems with RF emissions and RF susceptibility, even if the fiber > itself is not for all practical purposes. The optical components are good > enought the there is no significant susceptibility to or emissions of > light, assuming nothing is broken. Similarly, a GPS receiver may be > susceptible to or radiated emissions that are not at the GPS frequency. > > There are certainly photons at 1 GHz. However, due to the low frequency > (compared to light), an individual photon does not carry much energy - not > enough energy to free an electron as can be done by a single light photon > on a sensitive surface (and then usually multiplied using an electron > multiplier). Due to the difficulty in detecting single photons at 1 GHz, > photons are not part of the normal vocabulary when discussing RF. > > Enough cranial smoke yet? > > Don Borowski > Schweitzer Engineering Labs > Pullman, WA > > "Chris Maxwell" <[email protected]>@majordomo.ieee.org on > 01/10/2003 07:23:40 AM > > Please respond to "Chris Maxwell" <[email protected]> > > Sent by: [email protected] > > To: <[email protected]> > cc: > Subject: RE: Fiber optic cable testing per EN 55022:1998 ? > > OK, > > Enough of this regulatory blah, blah, blah...(although that's what we get > paid for). How about a hypothetical question... > > Typical radiated emissions measure a time varying electric field produced > by the acceleration of electrons. When electrons accelerate back and forth > at a given frequency; then you get EM (ElectroMagnetic) radiation at that > frequency. At these frequencies, we have electron flow in conductors. The > electron acceleration in one conductor (say your computer backplane) gives > off an EM field which will cause a similar electron flow in another > conductor placed some distance away (the measurement antenna). Notice that > in this case, we don't have electrons changing energy states, we just have > free electrons flowing and accelerating. > > Fiber optic cables carry light, which is modeled as photons produced by > electrons changing energy states. We still can model this with similar > wave equations as used for any old EM radiation; but here we have radiation > flow in an insulator. We also throw in the concept of "photons" whereby we > try to quantize the radiation. Light won't (appreciably) flow at all in a > conductor. So, we don't consider fiber optic cables to be susceptable to > "EMI"; and we don't consider them to give off "EMI". I think that we all > agree that trying to measure the "conducted" or "radiated" emisions from > fiber optic cables is not required by any standard. They do "conduct" > light; but it is a conduction of photons; not the conduction of free > electrons that the standards try to measure. > > However, I can think of some lower frequencies (lower than light, that is) > that use dielectric waveguides similar to fiber optics; yet they produce > and are susceptable to EMI. For example, many GPS antennas us dielectric > waveguides at the GPS frequency (about 1.5GHz, if I recall correctly) > > So where is the "crossover point"? Does it have to do with skin depth? > Maybe the photoelectric effect? Why don't we talk about photons at 1Ghz? > Is it just because we don't have a material with the correct band gap to > produce a 1Ghz photon? On the other hand, can free electrons be > "conducted" at light frequencies; or isn't there a material with enough of > a skin depth at such frequencies? Anybody want to take a stab at > enlightening(no pun intended) us all on this one? I guess I'm just too > lazy to brush up on my quantum mechanics. It's too bad that Einstein died > before we came up with listservers. I have about a million questions for > him. He probably would have taken a job as an EMC guy just to pay the > bills while he was working on relativity. > > Sure, its a hypothetical question; but it may provide a deeper > understanding of why we don't throw fiber optic cables in the coupling > clamp. > > I can smell the collective cranial smoke from the group already. That's > good. > > Inquizzitively and antagonistically, > > Chris Maxwell | Design Engineer - Optical Division > email [email protected] | dir +1 315 266 5128 | fax +1 315 797 8024 > > NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA > web www.nettest.com | tel +1 315 797 4449 | > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > http://ieeepstc.mindcruiser.com/ > Click on "browse" and then "emc-pstc mailing list"Title: Re: Fiber optic cable testing per EN 55022:1998 ?
I enjoy it so please go ahead ...
How can be physically explained the cross talk between the fibers (photon vs.
electronic)?
Thanks,
Dorin
[email protected] wrote:
> ---------------------- Forwarded by Don Borowski/SEL on 01/10/2003 10:37 AM
> ---------------------------
>
> Don Borowski
> 01/10/2003 10:35 AM
>
> To: "Chris Maxwell" <[email protected]>
> cc:
> Subject: RE: Fiber optic cable testing per EN 55022:1998 ? (Document
> link: Database 'Don Borowski', View '($Sent)')
>
> OK, some comments.
>
> The radiated and conducted emissions of concern are there due to the
> possibility of the modulation signal sent to the light source getting
> coupled onto the metalic coating of the fiber.
>
> There are seperate standards covering light leakage that are there for eye
> protection.
>
> We conventionally think about current flow in a pair of wires carrying
> energy. The energy is indeed guided by the wires, but is carried by the
> transverse electromagnetic (TEM) field around the wires. The energy is not
> flowing in the conductors, but in the space around the conductors.
>
> Even at DC where there is electron flow through the bulk of a
> (non-superconductor) material, the energy is transmitted in the electric
> and magnetic field outside the wires. There is indeed a magnetic field
> inside the wire. However, the only electric field inside the wire is along
> the direction of electron flow, and is due to resistance. If you do the
> Poynting vector E×H, the direction of the vector is radial into the wire.
> There is energy flow into the wire, which causes the wire to produce heat.
> This heat production is better known as I²R loss.
>
> Light certainly can be guided by metal, just as lower frequencies. Take a
> cylinder with a nice shiney mirrored surface on the inside, and shine light
> into it. You will see light come out at the other end, even if there is a
> bend so that there is not a straight shot through.
>
> It is possible to guide light with two conductors in TEM mode, though it is
> quite lossy. Fiber is nice because of its low loss.
>
> There certainly can be light emissions from fiber - a sharp bend can cause
> it. Conversely, bend a fiber sharply and shine a light on the bend, and the
> light will go into the fiber. So there is possible emission and
> susceptibility. But put a jacket over the fiber, or a metalic coating, and
> this problem is solved for any practical source or victim.
>
> A system with a light source and light receiver is certainly still subject
> to problems with RF emissions and RF susceptibility, even if the fiber
> itself is not for all practical purposes. The optical components are good
> enought the there is no significant susceptibility to or emissions of
> light, assuming nothing is broken. Similarly, a GPS receiver may be
> susceptible to or radiated emissions that are not at the GPS frequency.
>
> There are certainly photons at 1 GHz. However, due to the low frequency
> (compared to light), an individual photon does not carry much energy - not
> enough energy to free an electron as can be done by a single light photon
> on a sensitive surface (and then usually multiplied using an electron
> multiplier). Due to the difficulty in detecting single photons at 1 GHz,
> photons are not part of the normal vocabulary when discussing RF.
>
> Enough cranial smoke yet?
>
> Don Borowski
> Schweitzer Engineering Labs
> Pullman, WA
>
> "Chris Maxwell" <[email protected]>@majordomo.ieee.org on
> 01/10/2003 07:23:40 AM
>
> Please respond to "Chris Maxwell" <[email protected]>
>
> Sent by: [email protected]
>
> To: <[email protected]>
> cc:
> Subject: RE: Fiber optic cable testing per EN 55022:1998 ?
>
> OK,
>
> Enough of this regulatory blah, blah, blah...(although that's what we get
> paid for). How about a hypothetical question...
>
> Typical radiated emissions measure a time varying electric field produced
> by the acceleration of electrons. When electrons accelerate back and forth
> at a given frequency; then you get EM (ElectroMagnetic) radiation at that
> frequency. At these frequencies, we have electron flow in conductors. The
> electron acceleration in one conductor (say your computer backplane) gives
> off an EM field which will cause a similar electron flow in another
> conductor placed some distance away (the measurement antenna). Notice that
> in this case, we don't have electrons changing energy states, we just have
> free electrons flowing and accelerating.
>
> Fiber optic cables carry light, which is modeled as photons produced by
> electrons changing energy states. We still can model this with similar
> wave equations as used for any old EM radiation; but here we have radiation
> flow in an insulator. We also throw in the concept of "photons" whereby we
> try to quantize the radiation. Light won't (appreciably) flow at all in a
> conductor. So, we don't consider fiber optic cables to be susceptable to
> "EMI"; and we don't consider them to give off "EMI". I think that we all
> agree that trying to measure the "conducted" or "radiated" emisions from
> fiber optic cables is not required by any standard. They do "conduct"
> light; but it is a conduction of photons; not the conduction of free
> electrons that the standards try to measure.
>
> However, I can think of some lower frequencies (lower than light, that is)
> that use dielectric waveguides similar to fiber optics; yet they produce
> and are susceptable to EMI. For example, many GPS antennas us dielectric
> waveguides at the GPS frequency (about 1.5GHz, if I recall correctly)
>
> So where is the "crossover point"? Does it have to do with skin depth?
> Maybe the photoelectric effect? Why don't we talk about photons at 1Ghz?
> Is it just because we don't have a material with the correct band gap to
> produce a 1Ghz photon? On the other hand, can free electrons be
> "conducted" at light frequencies; or isn't there a material with enough of
> a skin depth at such frequencies? Anybody want to take a stab at
> enlightening(no pun intended) us all on this one? I guess I'm just too
> lazy to brush up on my quantum mechanics. It's too bad that Einstein died
> before we came up with listservers. I have about a million questions for
> him. He probably would have taken a job as an EMC guy just to pay the
> bills while he was working on relativity.
>
> Sure, its a hypothetical question; but it may provide a deeper
> understanding of why we don't throw fiber optic cables in the coupling
> clamp.
>
> I can smell the collective cranial smoke from the group already. That's
> good.
>
> Inquizzitively and antagonistically,
>
> Chris Maxwell | Design Engineer - Optical Division
> email [email protected] | dir +1 315 266 5128 | fax +1 315 797 8024
>
> NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA
> web www.nettest.com | tel +1 315 797 4449 |
>
> -------------------------------------------
> This message is from the IEEE EMC Society Product Safety
> Technical Committee emc-pstc discussion list.
>
> Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/
>
> To cancel your subscription, send mail to:
> [email protected]
> with the single line:
> unsubscribe emc-pstc
>
> For help, send mail to the list administrators:
> Ron Pickard: [email protected]
> Dave Heald: [email protected]
>
> For policy questions, send mail to:
> Richard Nute: [email protected]
> Jim Bacher: [email protected]
>
> All emc-pstc postings are archived and searchable on the web at:
> http://ieeepstc.mindcruiser.com/
> Click on "browse" and then "emc-pstc mailing list"
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