An optical device is provided. The optical device includes a time-of-flight (TOF) sensor array, a photon conversion thin film, and a light source. The photon conversion thin film is disposed above the time-of-flight sensor array. The light source emits light with a first wavelength towards the photon conversion thin film to be converted into light with a second wavelength received by the time-of-flight sensor array. The second wavelength is longer than the first wavelength.