  In this paper, we propose a method for the generation of higher dimensional
modal entanglement through type II spontaneous parametric down conversion
process using a three waveguide directional coupler in a periodically poled
lithium niobate substrate. We show that by a proper design, it is possible to
achieve an output state of two photons occupying three different spatial modes.
The advantage of using such waveguide structure is its flexibility and the
design space availability to achieve desired characteristics of the photon
pairs generated in the down conversion process
