Wavelength Issues in the Downstream Direction

1
Wavelength Issues in the Downstream Direction

• James O. Jim Farmer
• Alan M. Brown
• Enablence Technologies (Wave7 Optics)

IEEE 802.3av meeting, November 2008
2
Wavelength Issues in the Downstream Direction
Must attenuate opposite signal gt30 dB
Broadcast (extended services)
1550
V-OLT
Downstream data
WDM
l down
Passive optical network (PON)
OLT
Upstream data
Upstream
Optical subassembly
ONT
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Wavelength Establishing View
(Wavelength is to Scale)
Todays 1 Gb/s downstream (1490 nm)
1 Gb/s upstream
Broadcast 1550 nm
1577 /-3 nm downstream
10 Gb/s upstream
1590 nm down- stream
Todays 50 nm nominal transition (comfortable)
1270
1320
1370
1420
1470
1520
1570
20 nm nominal transition
14 nm nominal transition
Wavelength (nm)
4
But Wait! It Gets Worse
Those messy, practical details

• When we take tolerances and temperature drift
  into account, the situation gets worse
• So we will make certain concessions to the real
  world
• Broadcast (extended services) band
• Was 1550 - 1560 nm (existing transmitters)
• Make it 1550 - 1555 nm
• 1577 nm data down
• Was and is 1577 /-3 nm
• 1590 nm data down (currently not in standard)
• Was 1590 /-10 nm
• Make it 1590 /-3 nm
• Makes OLT somewhat more expensive, but maybe not
  prohibitively so. Makes ONT easier
• We shall make these assumptions and look at the
  implication for using broadcast with downstream
  data. We will not look at upstream data
  transmission at this time.

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Assume we try to use 1577 nm with broadcast
2. Practical filter bandwidth after taking into
account temperature drift and initial center
frequency tolerance
Reduced broadcast wavelength
1. Specified 1577 nm data wavelength
1540
1550
1560
1570
1580
1590
1600
1610
Wavelength (nm)
6
Assume we try to use 1577 nm with broadcast
Practical filter
Reduced broadcast wavelength
Filter center frequency is low, and temperature
forces it even lower
1 nm transition - Impossible!!!
1540
1550
1560
1570
1580
1590
1600
1610
Wavelength (nm)
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Now try it with a downstream wavelength of 1590 nm
2. Practical filter bandwidth after taking into
account temperature drift and initial center
frequency
Reduced broadcast wavelength
1. Specified 1590 nm data wavelength (reduced
bandwidth)
1540
1550
1560
1570
1580
1590
1600
1610
Wavelength (nm)
8
Now try it with a downstream wavelength of 1590 nm
Reduced broadcast wavelength
Practical filter
14 nm transition. Tight, but much better than 1
nm
Filter center frequency is low, and temperature
forces it even lower
1540
1550
1560
1570
1580
1590
1600
1610
Wavelength (nm)
9
Conclusion

• Use of the broadcast overlay with a 1577 nm data
  carrier is impossible
• Use of the broadcast overlay with a 1590 nm data
  carrier is difficult, but should be feasible
• We do not object to use of 1577 nm for PR(X)30
• We seek reinstatement of the 1590 nm wavelength
  in order to preserve use of the broadcast
  overlay, which we have agreed is still important