An optical device is provided. The optical device includes: a light source; a pinhole plate arranged on a path of input light between the light source and an objective lens; an image sensor configured to detect a reflected light generated by the input light being reflected by a sample; and a noise filter arranged on the path of the reflected light between the image sensor and the objective lens, and the noise filter may remove a part of the reflected light generated by underlying layers below a measurement target layer of the sample.