OPTICAL DEVICE

PURPOSE:To prevent the leakage of light by using an ink resist that contains a light-absorbing substance and a light-reflecting substance. CONSTITUTION:Ink resist 3 is applied to the upper surface of a case substrate; the ink resist is made of a mixture of one part of an opaque substance like carbon and five parts of a substance, such as TiO2, which reflects visible light. The major part of the light impinging on the surface of the ink resist is reflected and scattered at the reflecting substance, TiO2. The rest of the light passes through the ink resist and is absorbed in the opaque substance, carbon. Therefore, the property of opaqueness is maintained, and this prevents the leakage of light between a light-emitting device and a photodetector.