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On today’s MM ad-hoc call I suggested that there could be a way of assessing the actual chromatic dispersion of a transmitter in the proposed TxVEC measurement rather than the current approach of building into the fixture a filter that always included a worst-case value for chromatic dispersion based on the widest spectral width permitted. The alternative would be to use a length of MMF chosen to have very high modal bandwidth (> ~10,000 MHz*km) at 850 nm. This approach is already used in the measurement of single-mode transmitters. The advantage2 of the approach include: 1. not leaving margin on the table for transmitters having narrower than the maximum permitted spectral width, 2. possibility of including MPN in the Tx test. Disadvantages include: 1. requiring a “specialty” MMF, 2. the impact on measurement uncertainty due to variability of specimens of such fiber. Contributions on this topic were previously presented to 802.3ba. See kolesar_01_0309, kolesar_01_0509, kolesar_02_0509, and others. At the time, these proposals were aimed at enabling extended-reach for 40G and 100G multimode solutions. Now the purpose would be simply to improve yield of transmitters and accuracy/comprehensiveness of test. The proposals were rejected by P802.3ba. But it was suggested that I float the concept to 802.3bm to see if there was interest in pursuing it once more. Your feedback will determine if I dust off the previous material for 802.3bm. If there is a groundswell of support I will make the effort. If the feedback is mostly negative I will not. Regards, Paul |