  Advances in the emerging field of coherent quantum feedback control (CQFC)
have led to the development of new capabilities in the areas of quantum control
and quantum engineering, with a particular impact on the theory and
applications of quantum optical networks. We consider a CQFC network consisting
of two coupled optical parametric oscillators (OPOs) and study the squeezing
spectrum of its output field. The performance of this network as a
squeezed-light source with desired spectral characteristics is optimized by
searching over the space of model parameters with experimentally motivated
bounds. We use the QNET package to model the network's dynamics and the PyGMO
package of global optimization algorithms to maximize the degree of squeezing
at a selected sideband frequency or the average degree of squeezing over a
selected bandwidth. The use of global search methods is critical for
identifying the best possible performance of the CQFC network, especially for
squeezing at higher-frequency sidebands and higher bandwidths. The results
demonstrate that the CQFC network of two coupled OPOs makes it possible to vary
the squeezing spectrum, effectively utilize the available pump power, and
overall significantly outperform a single OPO. Additionally, the Hessian
eigenvalue analysis shows that the squeezing generation performance of the
optimally operated CQFC network is robust to small variations of phase
parameters.
