Question

Is a process that modifies light waves so they vibrate in a single plane

Answer 1

The process you're fishing for is "polarization", but that's a

misleading description.

Polarization doesn't do anything to change the light waves. 

It simply filters out (absorbs, as with a polarizing filter) the

light waves that aren't vibrating in the desired plane, and

allows only those that are to pass.

The intensity of a light beam is always reduced after

polarizing it, because much (most) of the original light

has been removed.

A laser light source may be thought of as an exception,

since everything coming out of the laser is polarized.