Hi All.
It appears we're discussing theoretical limits of silica-based glass
here. The Press Release assertion talks about what a trader might
experience. Hm. I would ask Rob Beck to clarify this point and inform
whether the stated objective in the release accounts for the many o-e
and e-o conversions on the overland part of the end-to-end trader
connection, including the handoffs that occur in the NY and London
metros. I know that terrestrially, i.e., here in the US, some
brokerage firms and large banks (is there any longer a distinction
between those two today?
have used their clout to secure links that
are virtually entirely optical in nature on routes that are under a
thousand miles, but this is not an option on a submarine system
that's intrinsically populated with electronics, never mind the tail
sections that assume multiple service providers getting into the act.
Rob? Anyone?
FAC
Hi Frank,
Yes it does include all the O-E conversions. By the way, my recollection is the undersea regenerators do purely optical regeneration. There is no O-E conversions undersea, only at the landing stations and terrestrial components.
Since the system is just in the planning stage, the latency estimate is conversative. It is better to surprise than disappoint ...
Hi All.
It appears we're discussing theoretical limits of silica-based glass
here. The Press Release assertion talks about what a trader might
experience. Hm. I would ask Rob Beck to clarify this point and inform
whether the stated objective in the release accounts for the many o-e
and e-o conversions on the overland part of the end-to-end trader
connection, including the handoffs that occur in the NY and London
metros. I know that terrestrially, i.e., here in the US, some
brokerage firms and large banks (is there any longer a distinction
between those two today? have used their clout to secure links that
are virtually entirely optical in nature on routes that are under a
thousand miles, but this is not an option on a submarine system
that's intrinsically populated with electronics, never mind the tail
sections that assume multiple service providers getting into the act.
Rob? Anyone?
FAC
By the way, my recollection is the undersea regenerators do purely optical regeneration.
There is no O-E conversions undersea, only at the landing stations and terrestrial components.
I'm not clever enough to know of some way that you could do optical
regeneration without converting the signal to electrical and
retransmitting back as optical.. How is that done?
amplifiers for one possibility.
One has to grok laser fundamentals to get what's going on, but it's not an
especially complex topic.
-Nick
A halfway-decent description of the physics of how this is done, is
covered in Neal Stephenson's excellent article on Wired:
http://www.wired.com/wired/archive/4.12/ffglass.html
The specific page covering optical regeneration:
http://www.wired.com/wired/archive/4.12/ffglass.html?pg=6&topic=
quote:
By the way, my recollection is the undersea regenerators do purely optical regeneration.
There is no O-E conversions undersea, only at the landing stations and terrestrial components.
I'm not clever enough to know of some way that you could do optical
regeneration without converting the signal to electrical and
retransmitting back as optical.. How is that done?
Erbium doped fibers.
What's that quote again...?
Oh, that's it: "The more you know, the more you know you don't."
It feels very appropriate now
Cheers Patrick for that great info & to everyone who contacted me off-list also!
With regards to the Wired Article, I still have my copy of that issue and
would consider that article perhaps my favorite magazine article of all
time.
With regards to the Wired Article, I still have my copy of that issue
and would consider that article perhaps my favorite magazine article
of all time.
i too thought that a great article and often point folk to it. sadly,
the copy on the wired web site does not have the figures 
randy
With regards to the Wired Article, I still have my copy of that issue
and
would consider that article perhaps my favorite magazine article of all
time.
Same here. A classic.
What's that quote again...?
Oh, that's it: "The more you know, the more you know you don't."
It feels very appropriate now
I was wondering for quite some time if there was a scientific term for that
effect, since many of us seem to run into the opposite quite often. It turns
out that it's the Dunning-Kruger effect:
Dunning–Kruger effect - Wikipedia
Ignorant bliss! 
Heath,
By the way, my recollection is the undersea regenerators do purely optical regeneration.
There is no O-E conversions undersea, only at the landing stations and terrestrial components.I'm not clever enough to know of some way that you could do optical
regeneration without converting the signal to electrical and
retransmitting back as optical.. How is that done?
Erbium Doped Fiber Amplifiers (EDFAs) do not re-shape or re-time the signals (the last 2 R's in 3R -- re-amplification, re-shaping, and re-timing). Raman is another popular amplification technology, widely used in long-haul WDM. Some systems have the flexibility of using EDFA and Raman amps on the same spans.
EDFAs amplify a band of spectrum (C- and/or L-band, depending on the device) -- signal *and* noise. The amplified noise floor is clearly visible if you connect an optical spectrum analyzer to the output of an EDFA -- you see a big wide bump across the entire amplified band with spikes for each wavelength. An optical signal can only go through so many EDFAs before it becomes too degraded to be accurately converted back to an electrical signal by the receiver -- either due to dispersion (especially if uncompensated) or noise, tolerances of which are different for every device...(EDFAs introduce some amount of noise, so OSNR before EDFA != OSNR after EDFA )
That being said, one can find examples of all-optical regeneration [1], but I do not know of any transport vendors who have integrated this capability into currently shipping products. (Some have developed various tricks like electronic dispersion compensation, but IIRC, these work by pre-distorting the signal.)
Getting back to the original post from this thread -- when I first read it, I immediately wondered whether the vendor might be using coherent optical receivers which have much higher dispersion tolerances, allowing the optical signal to travel much further without OEO conversions (see [2] and [3] for some background). Unfortunately, I could not find any evidence one way or the other about what Hibernia is doing.
In fact, Per Hansen from Ciena just so happens to be talking about coherent receiver technology [DP-QPSK encoding & DSP analysis] as I write this e-mail...
Cheers,
-Chris
[1] 3R optical regeneration: an all-optical solution with BER improvement, Optica Publishing Group
[2] Coherent receivers enable next-generation transport, http://www.lightwaveonline.com/about-us/lightwave-issue-archives/issue/coherent-receivers-enable-next-generation-transport-53426202.html
[3] Optical hybrid, http://en.wikipedia.org/wiki/Optical_hybrid
Erbium Doped Fiber Amplifiers (EDFAs) do not re-shape or re-time the signals (the last 2 R's in 3R -- re-amplification, re-shaping, and re-timing)....
Thanks Chris - even more reading to do It's interesting stuff
that's for sure.
This is also pretty cool:
I just had a thought about EFDA - please forgive my lack of
terminology though, i'll try to explain:
Say you have signal coming in to EFDA, the signal is just amplified
(as you said, also noise - the whole source signal).
Would it be possible to extract via PLL or similar the source clock
and use that to modulate the amplifier power?
Does it work with QPSK / whatever keying is used?
Would that even help with the noise issue at all, or am I waaaaay off?
Cheers
Heath,
I just had a thought about EFDA - please forgive my lack of
terminology though, i'll try to explain:
Say you have signal coming in to EFDA, the signal is just amplified
(as you said, also noise - the whole source signal).
Would it be possible to extract via PLL or similar the source clock
and use that to modulate the amplifier power?
Does it work with QPSK / whatever keying is used?
Would that even help with the noise issue at all, or am I waaaaay off?
Although you can amplify just a single wavelength with an EDFA (has to be in the 1550nm range, not 1310nm), most deployments are using EDFAs in a DWDM environment. The C-band alone consists of ~5THz (5000GHz) of spectrum between 191.00-195.95 Thz. Some systems pack 40 wavelengths into this space at 100GHz spacing, some 80 channels @ 50GHz spacing, others 160 @ 25GHz. Each of these signals is independent, they can each be using different modulation/bitrate/etc. The amplifiers are completely ignorant to what is going on with each channel, only the devices performing conversion back to the electrical domain need to care about these details (after the incoming light has been demultiplexed into individual signals, of course).
Re: amplifier power... Amplifier gain should really stay constant unless new wavelengths are added/removed from the fiber. There are fixed-gain and variable-gain amps. VGAs have the advantage that engineers do not need to manually re-balance power levels whenever a large number of wavelengths are added or removed from a span, they adjust automatically. Newer DWDM systems should all have VGAs whereas a lot of earlier generation DWDM systems still use fixed-gain amps. With the older fixed-gain amps, you had to have the input power just right -- hence the need to re-balance if your aggregate signal changes a lot -- too low and the EDFA would not kick on at all, too high and you'd saturate the amp.
-Chris
Would it be possible to extract via PLL or similar the source clock
and use that to modulate the amplifier power?
Although you can amplify just a single wavelength with an EDFA (has to be in the 1550nm range, not 1310nm), most deployments are using EDFAs in a DWDM environment. The C-band alone consists of ~5THz (5000GHz) of spectrum between 191.00-195.95 Thz. Some systems pack 40 wavelengths into this space at 100GHz spacing, some 80 channels @ 50GHz spacing, others 160 @ 25GHz. Each of these signals is independent, they can each be using different modulation/bitrate/etc. The amplifiers are completely ignorant to what is going on with each channel, only the devices performing conversion back to the electrical domain need to care about these details (after the incoming light has been demultiplexed into individual signals, of course).
I'm wondering if it could be done per wavelength?
I guess that would be pretty ridiculous having demux + 160 * decoder +
160 * efda + mux..
Just wondering if the theory works though?