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Before submitting a formal comment, we wanted to run this by the reflector for comment. Regarding the upstream wavelength action reflected below, from the September meeting in Seoul, we have a good bit of concern over cost and performance, and would like to propose a return to the originally-planned wavelength of 1590 +/-10 nm for PR(X)10 and 20 downstream data.
Cost and power dissipation: The use of a tight wavelength band (e.g., 1577 +/-3 nm) at any wavelength is going to significantly increase the cost of the laser, both due to the manufacturing tolerance imposed and by the need for heating the laser. Any DFB laser so far as we know, has a temperature drift of about 0.1 nm/deg. C. If one were to provide for a normal indoor temperature range, which can cover 60 degrees, then one will have a 6 nm wavelength shift due to drift. We have found that there is market demand for wider temperature range OLTs, which can easily have a wavelength drift of 10 nm over their operating temperature range. Of course, the answer is to temperature-stabilize the laser, but this requires an added heater/cooler and control, and the best estimate we can make right now is that it will add 2-4 watts per PON to the OLT power dissipation when operated at room temperature. Granted, this is small compared with the total power dissipated by the OLT, but in an age in which we are trying to minimize the power draw of all equipment, it is going in the wrong direction. And it will cost money, not to mention that the laser will have to be specified to a tight wavelength tolerance (or the wavelength tuned by the cooler), adding more cost.
Concerning the availability of devices, we expect that this application will drive adequate volume to get the cost down at whatever wavelength we choose. We’ve been told by one laser manufacturer that the wavelength specified has little bearing on cost, though of course, tolerance and volume play a big part in determining the cost.
Specification: We question the statement that fiber and couplers are not fully specified beyond 1580 nm. Some people are using 1610 nm for OTDRs. A check with a couple of major manufacturers of fiber and couplers indicates that specifications are controlled out to 1625 nm. See, for example, http://www.corning.com/WorkArea/showcontent.aspx?id=15535, and http://www.ofsoptics.com/resources/AllWaveFLEX136web.pdf. As for couplers, I understand that planar couplers are fine over this wavelength range, though fused biconic couplers may not be as good.
Yet another concern we have with the 1577 nm selection is the filtering when a 1550 nm video carrier is used. The video optical carrier can be as high as 1560 nm. For a 1577 nm downstream data carrier, which can go as low as 1574 nm by specification, the WDM to separate the wavelengths has a 14 nm transition region. If we use 1590 +/-10 nm for data, the transition region expands 43%, to 20 nm. This can help reduce ONT cost, as well as the cost of the WDM at the OLT.
For these reasons, we seek reconsideration of the decision to abandon 1590 nm. We would like to receive comments from the reflector, then we are planning to submit a formal comment before the deadline.
Thanks,
Jim Farmer
Alan Brown
Enablence Technologies (Wave7 Optics)
================
From September meeting:
IEEE 802.3av Draft 2.0 IEEE 802.3av d2.0 10G-EPON comments Intermediate Responses
Cl 75 SC 75.1.4 P 51 L 16 # 2158
Comment Type T
This comment concerns the downstream wavelength for the PR10, PR20, PRX10, and
PRX20 PMDs, which is currently specified at 1580 to 1600nm. When this was selected, it
was thought that it would enable cheaper transmitters. However, there are a couple of
issues that argue against this wavelength choice:
1. The 1590nm sources seem to be less available than the 1577nm sources, so any cost
savings due to the wider window will be cancelled out by this effect.
2. The use of wavelengths beyond 1580nm has become increasingly uncertain, since the
fibers and couplers are not fully specified at those wavelengths.
We should also consider that if we use a single downstream wavelength for all PMD types,
then early volumes will be increased and the manufacturing community will be given a
clearer message on what wavelength sources to build.
SuggestedRemedy
Change the downstream wavelength range for all PMD types to 1574 to 1580nm.
This occurs in Table 75-1, 75-5, 75-11, 75-12, 75-13, and 75-20, and throughout section
75.6.1.1.
ACCEPT.
I approve the resolution suggested in the comment:
Yes: 10
No: 0
Abstain: 15
[Accepted]
[COME BACK, review ad-hoc material and revisit]
If accepted, this change will affect Clause 75 draft in a number of places: Table 75-1, 75-5,
75-11, 75-12, 75-13, and 75-20, and throughout section 75.6.1.1. Align figures where
necessary e.g. Figure 75-8.
Jim Farmer, K4BSE
Chief Network Architect,
Enablence Technology
FTTx Networks Division.
1075 Windward Ridge Parkway
Alpharetta, GA 30005 USA
678-339-1045
678-640-0860 (cell)
jim.farmer@xxxxxxxxxxxxx
www.enablence.com