  Nonlinear SU(1,1) interferometers are fruitful and promising tools for
spectral engineering and precise measurements with phase sensitivity below the
classical bound. Such interferometers have been successfully realized in bulk
and fiber-based configurations. However, rapidly developing integrated
technologies provide higher efficiencies, smaller footprints, and pave the way
to quantum-enhanced on-chip interferometry. In this work, we theoretically
realised an integrated architecture of the multimode SU(1,1) interferometer
which can be applied to various integrated platforms. The presented
interferometer includes a polarization converter between two photon sources and
utilizes a continuous-wave (CW) pump. Based on the potassium titanyl phosphate
(KTP) platform, we show that this configuration results in almost perfect
destructive interference at the output and supersensitivity regions below the
classical limit. In addition, we discuss the fundamental difference between
single-mode and highly multimode SU(1,1) interferometers in the properties of
phase sensitivity and its limits. Finally, we explore how to improve the phase
sensitivity by filtering the output radiation and using different seeding
states in different modes with various detection strategies.
