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Technology Stocks : LAST MILE TECHNOLOGIES - Let's Discuss Them Here -- Ignore unavailable to you. Want to Upgrade?

To: Frank A. Coluccio who wrote (6635)	3/12/2000 6:07:00 PM
From: wonk	Read Replies (1) \| Respond to of 12823

... Perhaps once I've finished reading their patents later on this afternoon I'll know more about how they plan to address this matter. I read the European patent app last evening. It read like a patent for AMPS cellular of 1982 substituting 'light' for 'RF.' What I don't think I saw was any technology breakthrough. But what I know of optics would maybe fill a thimble. I am looking forward to your opinion. ww p.s. I did note that they are using - it appears - 1/2 kilometer cell sizes in Seattle. Also, the user 'antenna' is roughly analagous in form factor to a DBS dish.

To: Frank A. Coluccio who wrote (6635)	3/13/2000 1:23:00 AM
From: gpowell	Read Replies (2) \| Respond to of 12823

Somewhere else on these boards, I don't recall where exactly, someone made a blanket statement about the safety of 1.4 to 1.5 um wavelengths. I'm sure that this was innocent enough, but the fact is that safety can only be assessed after power levels and beam concentrations have been fully understood, along with other parameters such as which wavelengths are used, filters on viewfinders and other aids, etc. That may have been me. The absorption data should tell you that 1.55um is strongly absorbed by water, therefore, I should have listed one caveat regarding eye safety. The major danger, of a 1.55um laser, is the heating of water contained in the eye. In practice the dangers are minimal, unless we get very high powers to the eye. Obviously, a full assessment of the danger would be a function of beam power and beam spread at the point of likely contact with an eye. I would imagine that it is quite a trivial exercise for a designer to create a safe communication system operating at 1.55um. The real problem is not eye safety, it is getting a signal reliably through rain and fog. Especially since the LASERS being used in these newer systems are said to be rated in terms of actual watts Frank, this is nothing. How many grams of water are contained in the eye? How long will it take to raise the temperature 1 deg C? I would not be surprised to hear that 10mJ/20ns pulses at 1.55um have been used around unprotected personnel. Of course, I don't imagine that these guys were sticking their eye in the beam 2 feet from the laser. I surmise you have little or no experience with 1.55um lasers, which is too bad, I was hoping you could tell me if you had experience with these in rainy conditions. Your concerns over general eye safety are well founded, given that you probably were using systems at .860um or 1.06um. [edit] just read more of this thread.... Message 13183879 Permit me to shed some light on the inclement weather issue, if I may. The tolerance of an infrared system such as the one being discussed here is indirectly proportional to the distance of its end points, AND the bit rate being supported over it. Frank, permit me to be a bit cranky here. If it is true that you do not have any experience with 1.55um laser communications systems, then your statement, which I have italicized, is an overstatement of your direct experience. Therefore, the subsequent text should be retracted vis-…-vis the applicability to terabeam's communication system. You far understate the problems of inclement weather.