Disclosed is a loop-back optical network terminal using a Febry-Perot laser diode as an active type optical modulator in a wavelength division multiplexing based optical network. In a first mode, signals from a first line sensor L1 group are written in a first line memory L1 group while signals from a second line sensor L2 group are written in a second line memory L2 group. A drain unit is adapted to be connected to a door drain hole in the door sill for drainage of liquid therethrough. A receiver is disposed in the craft to make it possible to determine the position of the craft with respect to the antenna radiation patterns, and hence its position with respect to the axis of the antenna, the determination of this position being performed by demodulating the signals captured by the receiver. The detector furthermore produces a first and a second alignment signal, respectively, associated with said first and second range of wavelengths, respectively.