Problems Collimating 1550nm light

[djhon]

Hello,

I'm trying to obtain a collimated beam from my 1550 nm light source.

I have a fibered mono-mode source and when I analyze its profile with an IR camera at one end of the fiber, it appears clean.

But when I put an IR coated microscope objective or an IR coated lens between the end of the fiber and the camera to start to build my collimation system, interference rings appear.

I know that, for reflection, when you use a thin glass slide (for example) you obtain interferences but here, I can't explain why I obtain this phenomenon in transmission.

I tried to change my fiber, to put the end of the fiber at the focus length of the microscope objective, then closer to the optic or further, to use a lens with small focus length (2.5 mm) and bigger focus length (20 mm) ... I obtain these rings all the time.

I'm sure I missed something simple.
Does anybody know how to deal with these rings ?

 

[djhon]

up :)

 

[y33t]

Hello,

I'm trying to obtain a collimated beam from my 1550 nm light source.

I have a fibered mono-mode source and when I analyze its profile with an IR camera at one end of the fiber, it appears clean.

But when I put an IR coated microscope objective or an IR coated lens between the end of the fiber and the camera to start to build my collimation system, interference rings appear.

I know that, for reflection, when you use a thin glass slide (for example) you obtain interferences but here, I can't explain why I obtain this phenomenon in transmission.

I tried to change my fiber, to put the end of the fiber at the focus length of the microscope objective, then closer to the optic or further, to use a lens with small focus length (2.5 mm) and bigger focus length (20 mm) ... I obtain these rings all the time.

I'm sure I missed something simple.
Does anybody know how to deal with these rings ?

Can you confirm that the fringes appearing in IR coated lens case is the true fringes ? Is your system fully functional with IR lens ? Are you certain that the fringes are not due to interference of the reflected part of your IR beam and the IR source ?