The construction of directional couplers according to the invention with the
aid of integrated optical waveguides makes it possible to produce such directional
couplers in series very compactly and relatively easily. In this connection, the
integrated optical waveguides in the coupling region have a smaller cross section
than the cross section outside the coupling region. Consequently, it is possible
to keep the spacing of the waveguide segments in the coupling region of a directional
coupler according to the invention sufficiently far away from one another to minimize
the error tolerance conditions in the manufacturing process. This is particularly
advantageous if the difference in the refractive indices between the core of the
integrated optical waveguide and its surroundings is very large.
