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Register a new userNonlinear power dependence of the spectral properties of an optical parametric oscillator below threshold in the quantum regime
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Photon pairs and heralded single photons, obtained from cavity-assisted parametric down-conversion (PDC), play an important role in quantum communications and technology. This motivated a thorough study of the spectral and temporal properties of parametric light, both above the Optical Parametric Oscillator (OPO) threshold, where the semiclassical approach is justified, and deeply below it, where the linear cavity approximation is applicable. The pursuit of a higher two-photon emission rate leads into an interesting intermediate regime where the OPO still operates considerably below the threshold but the nonlinear cavity phenomena cannot be neglected anymore. Here, we investigate this intermediate regime and show that the spectral and temporal properties of the photon pairs, as well as their emission rate, may significantly differ from the widely accepted linear model. The observed phenomena include frequency pulling and broadening in the temporal correlation for the down-converted optical fields. These factors need to be taken into account when devising practical applications of the high-rate cavity-assisted SPDC sources.
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Materials with strong $chi^{(2)}$ optical nonlinearity, especially lithium niobate, play a critical role in building optical parametric oscillators (OPOs). However, chip-scale integration of low-loss $chi^{(2)}$ materials remains challenging and limits the threshold power of on-chip $chi^{(2)}$ OPO. Here we report the first on-chip lithium niobate optical parametric oscillator at the telecom wavelengths using a quasi-phase matched, high-quality microring resonator, whose threshold power ($sim$30 $mu$W) is 400 times lower than that in previous $chi^{(2)}$ integrated photonics platforms. An on-chip power conversion efficiency of 11% is obtained at a pump power of 93 $mu$W. The OPO wavelength tuning is achieved by varying the pump frequency and chip temperature. With the lowest power threshold among all on-chip OPOs demonstrated so far, as well as advantages including high conversion efficiency, flexibility in quasi-phase matching and device scalability, the thin-film lithium niobate OPO opens new opportunities for chip-based tunable classical and quantum light sources and provides an potential platform for realizing photonic neural networks.
The dependence of quantum correlation of twin beams on the pump finesse of an optical parametric oscillator is studied with a semi-classical analysis. It is found that the phase-sum correlation of the output signal and idler beams from an optical parametric oscillator operating above threshold depends on the finesse of the pump field when the spurious pump phase noise generated inside the optical cavity and the excess noise of the input pump field are involved in the Langevin equations. The theoretical calculations can explain the previously experimental results, quantitatively.
We present a quantum-theoretical treatment of biphoton generation in single-resonant type-II parametric down-conversion. The nonlinear medium is continuously pumped and is placed inside a cavity which is resonant for the signal field, but nonresonant for the idler deflected by an intra-cavity polarizing beam splitter. The intensity of the classical pump is assumed to be sufficiently low in order to yield a biphoton production rate that is small compared to the cavity loss rate. Explicit expressions are derived for the rate of biphoton generation and for the biphoton wave function. The output spectra of the signal and idler field are determined, as well as the second-order signal-idler cross-correlation function which is shown to be asymmetric with respect to the time delay. Due to frequency entanglement in the signal-idler photon pair, the idler spectrum is found to reveal the longitudinal mode structure of the cavity, even though the idler field is not resonant.
Efficient, on-chip optical nonlinear processes are of great interest for the development of compact, robust, low-power consuming systems for applications in spectroscopy, metrology, sensing and classical and quantum optical information processing. Diamond holds promise for these applications, owing to its exceptional properties. However, although significant progress has been made in the development of an integrated diamond photonics platform, optical nonlinearities in diamond have not been explored much apart from Raman processes in bulk samples. Here, we demonstrate optical parametric oscillations (OPO) via four wave mixing (FWM) in single crystal diamond (SCD) optical networks on-chip consisting of waveguide-coupled microring resonators. Threshold powers as low as 20mW are enabled by ultra-high quality factor (1*10^6) diamond ring resonators operating at telecom wavelengths, and up to 20 new wavelengths are generated from a single-frequency pump laser. We also report the inferred nonlinear refractive index due to the third-order nonlinearity in diamond at telecom wavelengths.
Superfluidity, the ability of a liquid or gas to flow with zero viscosity, is one of the most remarkable implications of collective quantum coherence. In equilibrium systems like liquid 4He and ultracold atomic gases, superfluid behaviour conjugates diverse yet related phenomena, such as persistency of metastable flow in multiply connected geometries and the existence of a critical velocity for frictionless flow when hitting a static defect. The link between these different aspects of superfluid behaviour is far less clear in driven-dissipative systems displaying collective coherence, such as microcavity polaritons, which raises important questions about their concurrency. With a joint theoretical and experimental study, we show that the scenario is particularly rich for polaritons driven in a three-fluid collective coherent regime so-called optical parametric oscillator. On the one hand, the spontaneous macroscopic coherence following the phase locking of the signal and idler fluids has been shown to be responsible for their simultaneous quantized flow metastability. On the other hand, we show here that pump, signal and idler have distinct responses when hitting a static defect; while the signal displays hardly appreciable modulations, the ones appearing in pump and idler are determined by their mutual coupling due to nonlinear and parametric processes.
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