We theoretically investigate the power efficiency of hyperparametric oscillation in a nonlinear microcavity pumped by two coherent fields in a regime where only two frequency harmonics are produced. We show numerically that complete transfer of the dichromatic pump energy into the generated harmonics can be achieved when the pump power reaches the optimal value approaching two times the oscillation threshold. This result identifies a highly efficient regime of nonlinear frequency conversion, with significant potential for realization of dichromatic optical fields that are simultaneously frequency- and spatially separable, enabling new approaches to the generation of quantum-correlated light.
We theoretically investigate the power efficiency of hyperparametric oscillation in a nonlinear microcavity pumped by two coherent fields in a regime where only two frequency harmonics are produced. We show numerically that complete transfer of the dichromatic pump energy into the generated harmonics can be achieved when the pump power reaches the optimal value approaching two times the oscillation threshold. This result identifies a highly efficient regime of nonlinear frequency conversion, with significant potential for realization of dichromatic optical fields that are simultaneously frequency- and spatially separable, enabling new approaches to the generation of quantum-correlated light.
Integrated microring resonators have a broad range of applications in diverse fields with the potential to design compact, robust, energy-efficient devices crucial for quantum applications. Degenerate optical parametric oscillations (DOPOs) realized in dual-pumped microring resonator with third-order optical nonlinearity are of special interest. They demonstrate both bistability of the phase of the excited signal mode and generation of nonclassical light, which can be used for coherent photonic computing. Using coupled mode equations, we perform a comprehensive numerical analysis of DOPO conditions with normal group velocity dispersion and with bichromatic pumping. Through analytical and numerical approaches, we identify optimal setup parameter values that minimize the threshold power, highlighting the importance of considering the full spectrum of mode interactions. Additionally, we show that dispersion engineering, achievable in photonic molecules or photonic crystal microresonators, may provide a targeted frequency shift of specific microresonator modes resulting in pump power threshold reduction.
We analyze an optical parametric oscillator (OPO) in which cascaded down-conversion occurs inside a cavity resonant for all modes but the initial pump. Due to the resonant cascade design, the OPO present two χ^2 level oscillation thresholds that are therefore remarkably lower than for a χ^3 OPO. This is promising for reaching the regime of an effective third-order nonlinearity well above both thresholds. Such a χ^2 cascaded device also has potential applications in frequency conversion to far infra-red regimes. But, most importantly, it can generate novel multi-partite quantum correlations in the output radiation, which represent a step beyond squeezed or entangled light. The output can be highly non-Gaussian, and therefore not describable by any semi-classical model.
Production of entangled photon pairs is important in secure communication systems, quantum computing, and fundamental physics experiments. Achieving efficient generation of such photon pairs with low-loss parametric oscillators is a key objective in advancing integrated quantum technologies. However, spatially separating the generated photons while preserving their entanglement represents a significant technical challenge. In this work, we demonstrate nonlinear generation of correlated optical harmonics based on non-degenerate four-wave mixing with an optimally pumped optical microcavity with Kerr nonlinearity. The phase matching of the process is achieved with self-injection locked lasers producing parametric oscillation while locked to two different modes of the microresonator. This condition is reminiscent of slow-light technique developed for coherent atomic systems. The experimental design, utilizing counterpropagating light from two self-injection locked lasers, also effectively addresses the challenge of spatial separation of the generated harmonics. We validate the theoretical predictions using two self-injection locked semiconductor lasers integrated with a crystalline whispering gallery mode resonator with optimized spectral structure.
The effect of the quantum properties of light on nonlinear processes has been well studied theoretically. It has been shown that the efficiency of n-photon nonlinear processes in many cases scales as the normalized n-th order correlation function. For light with high intensity correlation function, the efficiency of the n-th harmonic generation will be considerably higher than for coherent light. The experimental observation of this effect remained difficult until recently, because of the absence of bright sources with strong and fast intensity fluctuations. For the experimental demonstration of statistical effects in optical harmonic generation we use as a pump the radiation of high-gain parametric down conversion. Such light shows quantum properties (e.g. quadrature or two-mode squeezing) and has large number of photons in one mode. The normalized n-th order correlation function for this light is (2n - 1)!!, which makes it more attractive for nonlinear processes than both coherent and thermal light. For the generation of optical harmonics we used broadband parametric down conversion around frequency-degeneracy (1600 nm) produced in 1cm BBO crystal from Ti:Sapphire laser (800 nm, 1.6ps, 5kHz, 3W mean intensity). Due to spectral filtering and post-selection technique we could vary the statistics of light from coherent to super-bunched, which allowed us to demonstrate the efficiency enhancement for second-, third-, and fourth-harmonic generation. The obtained experimental results show a good agreement with the theory.
In this paper, we reveal that some kinds of optical nonlinearities are further enhanced when incoherent light, instead of a laser, is used as a pump light. This idea was confirmed both theoretically and experimentally in the case of sum-frequency generation (SFG) using the optical second nonlinearity. The conversion efficiency of the SFG with incoherent light pumping increased as the bandwidth of the incoherent pump light decreased, finally reaching twice the conversion efficiency of conventional second harmonic generation (SHG) by laser pumping. This method dramatically relaxes the severe requirements of phase matching in the nonlinear optical process. The conversion efficiency became less sensitive to misalignment of the wavelength of pump light and also of device operation temperature when the bandwidth of the incoherent pump light was sufficiently broad, although the improvement of the conversion efficiency had an inverse relationship with the insensitivity to the phase-matching condition. The temperature tuning range was enhanced by more than two orders of magnitude in comparison with the conventional SHG method. As an example of a promising application of this new idea, we performed the generation of quantum entangled photon-pairs using cascaded optical nonlinearities (SFG and the subsequent spontaneous parametric down conversion) in a single periodically poled LiNbO3 waveguide device, in which the incoherent light was used as the pump source for both the parametric processes. We have achieved high fidelity exceeding 99% in quantum-state tomography experiments.