A LP free-space Laser source's MFD, waist and other factors (e.g. z, x-y and rotation offsets) get well aligned with a PM fiber coupler (slow axis is in vertical). How and why will the PM fiber coupling ratio (%) be varying with the different polarization incidence angles, e.g. Vertical, Horizontal and Diagonal?
The follow up question of mine in this regard will be:
What will be their output characteristics at the PM fiber output end in terms of the polarization states?
as far as I know in fiber optics
mode excitation in fiber depends on the entrance angle and this might affect coupling ration
The coupling does not depend on the polarization state. The mode matching requirements are the same for both eigenpolarizations and therefore for any linear combination.
The output polarization will vary depending on circumstance. “Polarization maintaining” is a bit of a misnomer. They work by having such a huge retardation between the two eigenpolarizations that one cannot couple to the other. So the fiber will maintain either linear polarization. However any mixture of the two has a gigantic, arbitrary, and easily variable phase retardation. The amplitude in each component will be preserved but the phase between them at the output can be anything and it will vary if you bend the fiber, shake the table, change the temperature, etc.
Hi Hassan S. Ashour and Mike Albert, I am so grateful for your teachings. Now it makes more sense for me to understand the PM fiber working theory and reality beyond that misnomer.
I am sure that your teachings can help other RG colleagues who are puzzled with the same.
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