  We consider coupled waveguide lattices as an architecture that implement a
wide range of multiport transformations. In this architecture, a particular
transfer matrix is obtained through setting the step-wise profiles of the
propagation constants seen by the field evolving in the lattice. To investigate
the transformation capabilities, the implementation of a set of transfer
matrices taken at random and particular cases of discrete Fourier transform,
Hadamard and permutation matrices have been described. Because the waveguide
lattices schemes are more compact than their traditional lumped-parameter
counterparts, our architecture may be beneficial for using in photonic
information processing systems of the future.
