I understand that a quarter wave plate converts linearly polarised light (single axis) to circularly polarised light (two axes) with one wave delayed by quarter of a wave length. I understand that this result can be achieved by linear light being polarised through a lens angled at 45 degrees:
It makes sense that linearly polarised light can be formed by light of multiple axes being "filtered", converting it into to a single axis, however I do not understand how an axis can be "added back" through another filter/plate. How does this work (slow axis, fast axis, etc.) and what is the importance of 45 degrees? I would like to simply understand the process and logic behind how this occurs, rather than the math.
I have read this post on Stack Exchange, but the reasoning is fairly complicated.
I've had a look at a visualisation of what's happening when a light wave passes through the plate, but it, nor it's accompanying article seem to clearly explain how the spinning transformation is occurring for someone without experience with the concept: