A tilt can be detected highly accurately by minimizing the tilt detection error. The bi-directional voltage translator includes a step-up voltage translator for converting signals of a first voltage level to signals of a second voltage level, and a step-down voltage translator for converting signals of the second voltage level to signals of the first voltage level. The shell is attached to the heat shield and includes a shell hot side facing the shield cold side, a shell cold side facing away from the shield cold side, and a row of cooling holes. The semiconductor element is mounted on the insulating substrate. The diffractive gratings may be formed in a silicon substrate using anisotropic etching techniques to produce smooth, flat facets defined by crystallographic planes.