An optical device including a first substrate, a light source, a second substrate, an image capturing device, a microstructure layer, and an infrared pass layer is provided. The light source is disposed on the first substrate. The second substrate is disposed above the first substrate. The second substrate includes a first surface and a second surface opposite to the first surface. The image capturing device is disposed on the first substrate to receive a light beam, which is originated from scattered light beams scattered by an object touching the first surface of the second substrate. The microstructure layer is disposed on the first surface of the second substrate. The microstructure layer is adapted to increase a light beam, which is scattered by the object and transmitted to the image capturing device. The infrared pass layer is adapted to pass the infrared light.