How many lamps does a passive beam splitter typically have

Beam splitters are sometimes used to recombine beams of light, as in a. In this case there are two incoming beams, and potentially two outgoing beams. But the amplitudes of the two outgoing beams are the sums of the (complex) amplitudes calculated from each of the incoming beams, and it may result that one of the two outgoing beams has amplitude zero. In order for ener. [pdf]