Patent ID: 8810807
Filing Date: 2014-08-19
Classification: G01B,G02B

Abstract:
1. A displacement detecting device comprising: a light source; an objective lens configured to condense light emitted from the light source toward a surface-to-be-measured; a separation optical system configured to separate an optical path of light reflected from the surface-to-be-measured from an optical path of the light emitted from the light source; a condenser configured to condense the light reflected from the surface-to-be-measured; an astigmatism generator configured to generate astigmatism in light condensed by the condenser; a light receiving section configured to detect an amount of the light output by the astigmatism generator; and a position information generator configured to generate position information of the surface-to-be-measured using a focus error signal obtained based on the amount of light detected by the light receiving section, wherein the condenser, the astigmatism generator, and the light receiving section are configured so that the value of the focus error signal is equal to “0” when a focus of light condensed by the objective lens is located outside of the surface-to-be-measured and displaced from a front side or a back side of the surface-to-be-measured by a predetermined amount.