Ref: Laser Metrology/ Encoders

Its Friday :) Good time for a silly idea. Laser light is a fixed and stable
wavelength, right? Can polorised glass filter these waves, as in if a wave is
rising and hits the glass it will be blocked and if it is falling it will
pass through?
If that would work does that mean a beam source moved towards and away from a
sensor would cause a pulse from the sensor every 800nm (or whatever it is)?

BTW, cheers for the info for the rotary encoders, they look well worth
getting.