[Laser] Is a typical laser pointer (635nm) fast enough for 10Mbps ethernet link?

[Glenn Thomas]

Another consideration is that raw ethernet, without some kind of bridge, is 
limited in range. This is due to timing (signal propagation speed) issues 
that a laser will not fix.

73 de Glenn

At 08:44 AM 5/8/2005, you wrote:
>Yes and maybe......
>
>The speed (generally) is not an issue with the stock laser pointer driver 
>or the diode itself.....although laser diodes built into fiber optic 
>transmitter modules can be driven much faster.
>
>To use your laser pointer at high speeds, turn it on. After the output 
>settles, use a fast current sink to steal current from the laser diode 
>during times you do not want any output.
>
>This can provide medium turn on and turn off times, probably allowing 10 Mbps.
>
>Regarding range...you have left quite a few questions unanswered..... Are 
>you asking about fiber optic or free space links? Are you willing to use 
>an APD, photomultiplier tube or garden variety photodiode? Do you need a 
>24/7 link, or will it only operate when it's dark outside? Do you want a 
>simple inexpensive solution, or do you have a big budget? What are your 
>size limitations on the transmitter/receiver pair? Can you build your own 
>gear, or do you need to use building block assemblies that you can buy 
>already built? Do you really need a laser, or will an LED provide enough 
>range---LED's can give great performance over fiber if the distances 
>aren't to great.
>
>I think Ethernet slows down automatically if the link becomes marginal, is 
>this acceptable or do you need a bone crushing signal strength so that the 
>highest speed is always used?
>
>There are some ready built free space data laser home built projects on 
>the web, look them up.
>
>If you want to modify ready built transceiver modules, you can buy them 
>dirt cheap these days and convert them from fiber to free space fairly 
>easier-this gives you the receiver and transmitter that is already 
>assembled. These transceivers usually use some sort of FM, which has the 
>advantage of a constant duty cycle to the laser..which is much easier to 
>control from the laser driver aspect.
>
>For free space, there is no amount of laser power and receiver sensitivity 
>that will guarantee a 24/7 link....it rains, snows and gets foggy. If you 
>want to go over a half mile with any reliability, you probably want an rf 
>solution rather than laser.
>
>Laser transmitters and receivers that transmit video are becoming very 
>inexpensive to purchase as well. EBAY has several video LED links, which 
>can be modified for longer range by converting to laser and/or putting a 
>lens in front of the receiver for additional range.
>
>Perhaps others will comment.........
>
>After you get a better idea of the issues above, let us know so the group 
>and make suggestions regarding whether your project is likely to succeed 
>and give you some general guidance so that you don't end up with a design 
>that has no chance at all to function.
>
>Unless you really need ethernet, a USB link is easier to implement. Some 
>IRDA hardware is easily modifiable in order to extend the range.
>
>Regards,
>
>Art
>
>
>
>
>
>
>At 10:12 AM 5/8/2005, you wrote:
>>Hello there,
>>
>>Is a typical laser pointer (635nm) fast enough for 10Mbps ethernet
>>link? What is the expected longest link range achieved by such
>>pointer?
>>
>>Thanks,
>>
>>Don
>>_______________________________________________
>>Laser mailing list
>>Laser at mailman.qth.net
>>http://mailman.qth.net/mailman/listinfo/laser
>
>
>_______________________________________________
>Laser mailing list
>Laser at mailman.qth.net
>http://mailman.qth.net/mailman/listinfo/laser