What is the unit of power of lens?

The unit of power of the lens is Dioptre.

The power of a lens is defined as the reciprocal of the focal length. 1 dioptre is equal to the reciprocal of focal length in the meter. 2 dioptre lens brings || rays of light to focus at 1/2 m. we can’t see any refraction in flat window pains because their optical power of the lens is zero, and it cannot diverge light.