Dear all,
I have an optical setup for cleaning up the laser diode beam, which includes coupling the laser light into a polarization-maintaining single mode FC/APC fiber.
I have a technical question on coupling the laser light into an FC/APC connector. Should I introduce any tilt on the fiber holder for that? Or should the angled end be tilted with 8 degrees from the optical axis by simply pluging the fiber into the holder?
I understand that with tilting I will lose the advantages of reducing the back reflections into the source. However, the proper adjustment of such fiber is not clear to me.
Thank you in advance for your help!
Marta
Dear Marta,
you do not need to add more tilt on the fiber tip, the easiest way is to use the fiber cnonnectorizing kit from Thorlabs and follow the manual instructions. they have a buck that introduces this tilt angle (8 degrees) which gives a big advantage to minimize the back reflection into the fiber towards the laser diode. You will find this kit in the url:
https://www.thorlabs.com/thorproduct.cfm?partnumber=CK05
Good Luck!
Dear Marta, i do agree with Mohammed on the recommendations because the kit will expose u to the available options. But note that u cannot eliminate the back-scatter completely. You can only minimize it
I would recommend buying a collimator matching to your prefered beam diameter:
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1696
and a kinematic tilt mount like
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=219&pn=KAD11F
maybe also an x/y-shift stage. Precise angle adjustment is much more sensitive and important than sideways shift.
It depends how much power loss you can accept. It is for sure possible to use an appropriate lens such that the focal waist corresponds to the mode diameter of the fibre and use a til of approximately 4º as stated above. However, if you want the maximum coupling possible buy a collimator as suggested by Alexander Dräbenstedt.
To easily couple the light to the fiber, I agree with Alexander that the collimator that you can directly screw on the FC or APC connectorized fiber is great in combination to mounting it onto optomechanical mounts.
On top, I would suggest to use an "alignment laser" plugged from the other end of the fiber. With that you can easily see and overlap the incoming beam with the out-coming beam from the fiber. For this you can use a red laser that you can plug to the fiber connector; it is sometimes called fiber checker:
http://www.all4fiber.com/Inspection/Inspection-and-Microscopes/VFL-250.htm?shop=palden_e&SessionId=&a=article&ProdNr=A13401&t=27&c=1779&p=1779
The easier way is to use a collimator linked to an APC connector (Thorlabs or else) mounted on a x/y-shift stage. You also need to have the possibility to control the angle but generally it's included on the collimator mount. You finally optimise the ouptut optical power using a power meter when playing with the geometrical degrees of freedom.
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