Abstract: A common InP semiconductor substrate device includes a laser emitter H1 for emitting waves having a first wavelength such as 1,300 nm, a photodiode H2 for receiving and detecting waves having a second wavelength such as 1,550 nm, and a separator G absorbing the waves having the first wavelength, the separator being interposed between the laser emitter H1 and the photodiode G for protecting the photodiode against the waves having the first wavelength. An absorption measurement mechanism Q delivers a signal iG representative of the power of the waves absorbed by the separator G, to make it possible to regulate operation of the laser emitter H1. The semiconductor substrate device is particularly applicable to implementing end devices to be installed on subscriber premises for subscribers to optical fiber interactive local area networks.