Silicon Investor (SI) -- The First Internet Community

STOCKTALK

We've detected that you're using an ad content blocking browser plug-in or feature. Ads provide a critical source of revenue to the continued operation of Silicon Investor. We ask that you disable ad blocking while on Silicon Investor in the best interests of our community. If you are not using an ad blocker but are still receiving this message, make sure your browser's tracking protection is set to the 'standard' level.

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

To: Frank A. Coluccio who wrote (6644)	3/13/2000 12:31:00 PM
From: gpowell	Respond to of 12823

Frank, truth always takes a beating as we begin to extrapolate from direct experience or observation. Always. (anywhere in the 0.8 to 1.6 um range), and this covers the region that you are showing expert testimony in. if you use a telescope or pair of binoculars looking into these things Stop right there Frank, These wavelengths and their interaction with matter are not created equal, particularly in regards to water. Do not attempt to lump these wavelengths together. I don't think that you have allowed in your replies (both here and on the tb board) that one should give credence to the potential problems to eye safety when viewing lasers, either directly up front with the naked eye, or more importantly where this model is concerned: through optical aids. Okay, I'll take the heat. For a professional, working around many types of laser systems, prudence demands that you treat all wavelengths as potential hazards. That is more a matter of practice so that one does not develop any bad habits. It's a good thing. Let's focus on the plans to commercially deploy a 1.55um laser communications system and assess the dangers. First, let go of your experience. The absorption data should be your starting point to assess the dangers of 1.55um laser light. If my absorption coefficient is correct then assuming the water in your eye has a depth of 7mm, the attenuation would be roughly 40db. So for 100 watts in you get .01 watts out. Suppose the depth is 11mm, then you get 0.00006 watts out. How much energy would it take to raise the temperature of the eye one degree? It will certainly be many joules (1 watt is 1 Joule per second) - since it takes 4.18 joules to raise the temperature of 1 gram of water 1 degree. If I may extrapolate, the first effect you will feel from staring at 1.55um laser light is heat and that will only occur after many seconds of staring at very high power lasers. What are the conceivable power levels of terabeam's system?

To: Frank A. Coluccio who wrote (6644)	3/13/2000 1:12:00 PM
From: Bill Fischofer	Read Replies (4) \| Respond to of 12823

Re: Eye safety TeraBeam may introduce a new wrinkle into the eye safety question. Because TB is Point to Multipoint (PTMP) this implies that the transmitting laser is swept through an arc. As I understand it, all receivers receive all downstreams in their sector and encryption is used to ensure that customer A doesn't see what customer B is being sent, etc. This necessarily implies that the beam will swathe an entire area whether or not there are receivers "tuned" to it in the path of the beam. Gilder makes reference to "diffusion" as the means of preventing eye problems which is why the receiver is the size of a small satellite dish (presumably to allow it sufficient beam gathering power). I'm sure that this implies that the "diffused beam" is safe to the naked eye but the question remains what about telescopes and binoculars. It's entirely possible that someone may use such devices without even being aware that they are in a TeraBeam "sector". It will be interesting to see if TeraBeam addresses this aspect of their technology.

To: Frank A. Coluccio who wrote (6644)	3/13/2000 5:30:00 PM
From: gpowell	Respond to of 12823

Re: the weather challenges that IR devices face in general, that is exactly what I was overing, their challenges, in general terms. I believe that I gave a well rounded account of my own personal experiences, which should have been useful for others to begin to extrapolate what the factors are in a general sense, when beginning to assess this new model. Am I being too lenient in your opinion, or too forgiving? Unfortunately, I think your experience is too limited to be of much use as a starting point in assessing the reliability of 0.80 ev photon transmission and detection, and the safety issue regarding these systems. I would much rather rely on first principles in this case. Forget the safety issue, this is the least of Terabeam's challenges. 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. Since the attenuation of 0.80 ev photons is depended upon weather, the state of the transmission media will change completely - one state highly absorbing (rain) and the other weakly absorbing (sunny day). On a rainy day, the "proportional factor" may be an exponential decay of the signal. My initial reaction, keeping in mind the absorption data, and other anecdotal evidence, which I am not at liberty to discuss, was to say that this system would simply not work in the rain. I am open to be proved wrong though, and will, over the next several weeks, attempt to test, quantitatively, the effect of rain on 0.80 ev photon transmission and detection.