Re: back reflection from fiber collimator

On Aug 21, 10:52 am, DM <d...@xxxxxxxxxxx> wrote:
Helpful person wrote:
On Aug 21, 8:26 am, DM <d...@xxxxxxxxxxx> wrote:
Helpful person wrote:
On Aug 21, 5:07 am, DM <d...@xxxxxxxxxxx> wrote:
In the case of single mode fibre collimators this is not the approach that
is adopted. The fibre ends are never, to my knowledge, AR coated. The end
of the fibre and the collimating lens are typically polished at 8 degrees
(similar to APC connectors). This has less to do with Brewsters angle and
more to do with the NA of the fibre. The output end of the collimator is
however AR coated.
cheers
David- Hide quoted text -
Could you please explain why the fiber NA makes an 8 degree angle
desirable?
www.richardfisher.com
You simply want the angle to be greater than the acceptance angle of the
fibre, such that any back reflected light will not be guided. Exact same
principle as an APC connector

cheers

David- Hide quoted text -

- Show quoted text -

Any back reflections by a surface square to any ray will go back into
the fiber. If the lens is tilted to reduce this, why does the fiber
exit face need to be tilted?

www.richardfisher.com

If the fibre exit face is not tilted (and not AR coated) then you get a
reflection from that face.- Hide quoted text -

- Show quoted text -

Thanks.

www.richardfisher.com

.

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    ... The fibre ends are never, to my knowledge, AR coated. ... of the fibre and the collimating lens are typically polished at 8 degrees ... Could you please explain why the fiber NA makes an 8 degree angle ... If the fibre exit face is not tilted then you get a reflection from that face. ...
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