  In this paper we derive the quantum statistical and dynamical properties of
nonlinear optical couplers composed of two nonlinear waveguides operating by
the second subharmonic generation, which are coupled linearly through
evanescent waves and nonlinearly through nondegenerate optical parametric
interaction. Main attention is paid to generation and transmission of
nonclassical light, based on a discussion of squeezing phenomenon, normalized
second-order correlation function, and quasiprobability distribution functions.
Initially coherent, number and thermal states of optical beams are considered.
In particular, results are discussed in dependence on the strength of the
nonlinear coupling relatively to the linear coupling. We show that if the Fock
state $|1>$ enters the first waveguide and the vacuum state $|0>$ enters the
second waveguide, the coupler can serve as a generator of squeezed vacuum state
governed by the coupler parameters. Further, if thermal fields enter initially
the waveguides the coupler plays similar role as a microwave Josephson-junction
parametric amplifier to generate squeezed thermal light.
