A method is presented to measure refractive index of a plane parallel plate of optical glass. We have applied focal
displacement method to measure refractive index of a plane parallel plate of an optical glass having thickness of the
order of millimeters. The best focus position is found by applying edge detection algorithm. We have measured LAF2
optical glass using focal displacement method and obtained the value 1.746, which is within 0.1% of the standard value
1.747 at 555 nm. In comparison to Abbe refractometer, this method is simple in terms of sample preparation,
experimental set up and for measuring high refractive index of Zinc Sulfide. Using this method, refractive indices of
other optical glasses are also measured.