A package includes a substrate with an attached emitting IC chip and receiving IC chip. The emitting IC chip includes an optical emitter, and the receiving IC chip includes a main optical sensor and a secondary optical sensor. A case is provided with a bottom portion and a peripheral wall portion to cover the IC chips, wherein the edge of the peripheral wall portion is mounted to the substrate. The bottom portion of the case includes a main opening above the main optical sensor and a secondary opening above the optical emitter. An opaque material is interposed between the case and the receiving IC chip to isolate the main optical sensor from the secondary optical sensor and delimiting a chamber containing the secondary optical sensor and the optical emitter. The chamber is optically isolated from the main optical sensor and main opening, and may be filled with a transparent material.