According to the invention, a first band-pass multidielectric filter (F1) receives optical signals, transmits at least one of them and reflects the untransmitted signals. An adding means (F2) inserts among them at least one other optical signal. A photoinduced Bragg grating filter (R) receives the signals reflected by the first filter and transmits them to the adding means and reflects any optical signal of the same wavelength as the signal transmitted by the first filter and which is liable to exist among the signals reflected by it. Application to optical telecommunications.