We present a conguration of two coupled parametric oscillators that generates two-mode oscillation and squeezing with fully tuned frequency separation from degeneracy up to the repetition rate. We verify our concept with an experiment in the radio-frequency (RF) domain, that serves as a physical simulator of op-tical parametric squeezing.

An optical parametric oscillator (OPO) is the standard source of squeezed light. Unfortunately, generation of well controlled two-mode squeezing with a low (tuned) frequency separation as required for many applications, is difficult in an OPO since the frequency separation between modes of the OPO is by deffinition equal to the repetition rate of the hosting cavity (and multiples of). Thus, to obtain two-mode squeezing with low frequency separation a physically long cavity is necessary, which is physically inconvenient to tune and requires special measures to select only the wanted frequency-pair and suppress other modes. Here, we present a simple method for generating fully-tuned two-mode squeezed light using a pair of coupled parametric oscillators with a variable coupling strength. The coupling between the two OPOs defines the frequency separation between the two oscillation modes (beat), analogous to the beat frequency of two mechnical coupled pendula.

While coupling of laser oscillators was extensively researched in the past, coupled OPOs were far less explored. Generally speaking, coupling of two oscillators splits the cavity modes of each oscillator by lifting the degeneracy between the symmetric and anti-symmetric mode combinations. Due to mode competition, lasers will tend to oscillate in only one mode of the coupled cavity (the one with the highest net-gain). Parametric oscillators however are different. An OPO can only amplify waves that are in-phase with the pump wave, which indicates that an OPO must oscillate in a symmetric set of the split modes, creating beats. When operating above threshold, these coupled OPOs emit a pair (or more) of high-power two-mode squeezed frequencies, where the frequency separation is controlled by the coupling strength, fully tunable with a fixed cavity-configuration of fixed repetition rate.

Using standard RF components, such as frequency mixers, ampliers, couplers, etc., we simulate the semi-classical behavior of such OPOs the in RF domain. We couple the oscillators with a variable coupling mechanism, and demonstrate the dynamics of the coupled OPOs for weak and intermediate coupling. Specifically, we show the tuned transition from steady-state to irregular to regular beats as the coupling strength is increased.