  Possible squeezed states generated in a three-waveguide nonlinear coupler
operating with second harmonic generation is discussed. This study is carried
out using two well-known techniques; the phase space method (based on positive
P-representation) and the Heisenberg-based analytical perturbative method. The
effect of the key design parameters is analyzed for both codirectional and
contra-directional propagation. The optimal degree of feasible squeezing is
identified. Also, the performance and capacities of both methods are critically
evaluated. For low levels of key design parameters and in the early stages of
evolution, a high level of agreement between the two methods is noticed. In the
new era of quantum-based technology, the proposed system opens a new avenue for
utilising nonlinear couplers in nonclassical light generation.
