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 >30 dB Broadcast (extended services) 1550 V-OLT Downstream data WDM l down Passive optical network (PON) OLT Upstream data Upstream Optical subassembly ONT

3. Wavelength Establishing View (Wavelength is to Scale) Today’s 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 Today’s 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.

5. 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)

7. 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