Real time active aiming?( was Re: [Laser] Laser comm stuff)

[J. Forster]

Derek Weston wrote:

> All points taken.
>
> However, the retroreflector route seems to me inefficient (more
> hi-precision HW req'd) if the link is inherently capable of data
> transfer. Why add "stuff" when you don't need to? Some microcontroller
> code is much easier (for me) and cheaper than precision optics and
> mechanical (including thermal movement) difficulties.

One reason is if you loose lock either way, you have to start from scratch. With the retro
scheme, you can reacquire automatically. You maintain lock by a very small dther in
pointing, and re-acquire by a raster or conical scan, looking for a maximum return signal.
Each end re-acquires stand alone.

> I guess also that my thinking is colored by my experience with a
> neighbourhood laser-linked network I set up a few years back. It worked
> well when aligned, but frequent realignment was necessary. To get the
> necessary range the beams were narrow, typically less than an inch
> diameter at the target, so a retroreflector offset by an inch from the
> photodetector would not have been be useful.

Clearly, beam size is an issue. For max. received power, the beam should under fill the
receive aperture. For retros, it needs to be a bit larger.

-John