Re: Problem with Laser-fiber coupler

I do have some hands-on experience. To me, this instability looks much too
low-frequency for just laser feedback mechanism. I would also suspect the
mechanical stability of the setup. Launching into single -mode fibre is very
sensitive to misalignment.

I would investigate the effects of temperature and vibration on the launch
efficiency. Some HeNes can exhibit pointing instability, although measuring
this is not trivial. I also much prefer the (more expensive) Point Source
couplers to Oz for ease and stability of alignment.

Good luck.

Ron
--
Gibbs Associates
Optical Design Consultant
www.gibbsassociates.co.uk


"Jepessen" <jepessen@xxxxxxxxx> wrote in message
news:586ab7ac-168e-47fc-821a-75ae6118f155@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Thanks for your answer. I also think that the coating or the AFC
connector is the best solution, but I want to be sure that the cause
is back-reflection itself. I'm glad to see that another people thinks
the same thing :-)

I've measured the output power, in an hour, and that's the result.

http://img201.imageshack.us/my.php?image=gruy4.gif

As you see, in this way it's pratically useless...

Do you know any method for decrease backreflection without change the
fiber?

Daniele

On 27 Nov, 23:20, AES <sieg...@xxxxxxxxxxxx> wrote:
In article
<52cbb4aa-f522-4345-bff3-290664a97...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,

Jepessen <jepes...@xxxxxxxxx> wrote:
My problem is that the laser beam at the output of the fiber has a big
casual oscillation, of about 20% of output power. This oscillation is
not present when I measure the output power of the laser beam, without
the fiber coupler.

I don't have hands-on experience with this particular situation, but the
problem is most likely back-reflections from surfaces in the coupler or
fiber going directly back into He-Ne laser and driving it crazy.

If the laser is directly and efficiently coupled into the fiber, any
reflections within the coupler-fiber system are automatically coupled
equally efficiently and directly back into the laser -- and lasers don't
like that at all.

If this is the situation, serious AR-coating of all significant surfaces
may help, but a professional-grade isolator is probably going to be
needed.


.

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