A plurality of semiconductor devices are disposed in a line on the surface of
a
supporting substrate. Each semiconductor device is adapted to generate an electric
signal depending on the intensity of incident light. Adjacent semiconductor devices
are optically coupled by an interconnecting optical waveguide so that light can
pass through the semiconductor device one by one in a direction from a first stage
closest to an input end to a last stage. An electric signal transmission line is
formed of a pair of conductors connected to the semiconductor devices so that the
electric signal generated by the semiconductor devices can propagate. One conductor
of the pair of conductors of the electric signal transmission line is formed so
as to extend in the air above the supporting substrate between adjacent semiconductor devices.
