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We present a detailed study of the generation of photon pairs by spontaneous four-wave mixing in a structure composed of two linearly uncoupled resonators, where energy can be transferred from one resonator to another only through a nonlinear interaction. Specifically, we consider the case of two racetrack-shaped resonators connected by a coupler designed to guarantee that the resonance comb of each resonator can be tuned independently, and to allow the nonlinear interaction between modes that belong to different combs. We show that such a coupler can be realized in at least two ways: a directional coupler or a Mach-Zehnder interferometer. For these two scenarios, we derive analytic expressions for the pair generation rate via single-pump spontaneous four-wave mixing, and compare these results with that achievable in a single ring resonator.

International audience; Composite optical systems can show compelling collective dynamics. For instance, the cooperative decay of quantum emitters into a common radiation mode can lead to super-radiance, where the emission rate of the ensemble is larger than the sum of the rates of the individual emitters. Here, we report experimental evidence of super spontaneous four-wave mixing, an analogous effect for the generation of photon pairs in a parametric nonlinear process on an integrated photonic device. We study this phenomenon in an array of microring resonators on a silicon photonic chip coupled to bus waveguides. We measure a cooperative pair-generation rate that always exceeds the incoherent sum of the rates of the individual resonators. We investigate the physical mechanisms underlying this collective behavior, clarify the impact of loss, and address the aspects of fundamental and technological relevance of our results.

Third order parametric down-conversion describes a class of nonlinear processes in which a pump photon can be down-converted into triplets of photons. It has been identified as a source of non-classical light, with capabilities beyond those offered by better-established processes such as spontaneous four-wave mixing. Here we discuss the implementation of TOPDC in integrated photonic systems. We derive equations for the rates of TOPDC in a non-resonant (waveguide) and resonant (microring) platform, such that the scaling with experimental parameters can be plainly seen. We find that generally non-resonant platforms should be pursued for spontaneous TOPDC (SpTOPDC), whereas resonant platforms are more suitable for stimulated TOPDC (StTOPDC). We present a sample calculation for TOPDC rates in sample systems with conservative and accessible parameters. We find that StTOPDC should be observable with the current fabrication technology, and that with some progress in the design of TOPDC platforms, integrated SpTOPDC too could be demonstrated in the near term.

Third-order parametric down-conversion (TOPDC) describes a class of nonlinear interactions in which a pump photon is converted into a photon triplet. This process can occur spontaneously, or it can be stimulated by seeding fields. In the former case, one typically has the generation of non-Gaussian states of light. In the latter, the situation is more variegated, for stimulated TOPDC (StTOPDC) can be implemented in many ways, depending on the number and properties of the seeding fields. Here we show that StTOPDC can be exploited for the generation of quantum correlated photon pairs. We examine the peculiar features of this approach when compared with second-order spontaneous parametric down-conversion and spontaneous four-wave mixing. We model StTOPDC in a microring resonator, predicting observable generation rates in a microring engineered for third-harmonic generation. We conclude that if the experimental difficulties associated with implementing StTOPDC can be overcome, it may soon be possible to demonstrate this process in resonant integrated devices.

Undetected photon imaging based on four-wave mixing is demonstrated in silicon core fibers. Both amplitude and phase images are presented for a low-power telecom pump, with the potential for imaging at longer wavelengths discussed.

We study the generation of photon pairs via spontaneous four-wave mixing in a resonant integrated system with scattering loss. We study the effect of loss on the pair generation rates and the biphoton wavefunctions.

This publisher’s note contains corrections to Opt. Lett. 47, 6201 (2022)10.1364/OL.471241.

Photonic crystal ridge waveguides supporting guided Bloch surface waves (GBSWs) are a valuable and flexible platform for the development of integrated optical devices. However, coupling light into a GBSW from a single-mode optical fiber remains challenging. In this work, we study the main issues preventing the efficient excitation of GBSWs using grating couplers, and we present some solutions to increase the coupling efficiency. Our approaches do not require any additional fabrication step and can lead to a significant improvement compared to previous implementations. Further optimization along the lines illustrated in this work may allow one to achieve even larger coupling efficiency.

We present two complementary strategies for modeling nonlinear quantum optics in realistic integrated optical devices, where scattering loss is present. In the first strategy, we model scattering loss as an attenuation; in the second, we employ a Hamiltonian treatment that includes a mechanism for scattering loss, such as a `phantom waveguide.' These strategies can be applied to a broad range of structures and processes. As an example, we use these two approaches to model spontaneous four-wave mixing in (i) a ring-channel system and (ii) an add-drop system. Even for these well-understood systems, our strategies yield some novel results. We show the rates of photon pairs, broken pairs, and lost pairs and their dependence on system parameters. We show that the properties of lost and broken photon pairs in such structures can be related to those of the un-scattered photon pairs, which are relatively simple to measure.

Optical nonlinear processes in linearly uncoupled resonators are being actively studied as a convenient way to engineer and control the generation of non-classical light. In these structures, one can take advantage of the independent combs of resonances of two linearly uncoupled ring resonators for field enhancement, with the phase-matching condition being significantly relaxed compared to a single resonator. However, previous implementations of this approach have shown a limited operational bandwidth along with a significant reduction of the generation efficiency. Here, we experimentally demonstrate that a Mach–Zehnder interferometer can be used to effectively linearly uncouple two resonators and, at the same time, allows for their efficient nonlinear coupling. We demonstrate that this structure can lead to an unprecedented control over the rings' interaction and can operate over more than 160 nm, covering the S-, C-, and L-telecom bands. In addition, we show that the photon pair generation efficiency is increased by a factor of four with respect to previous implementations.

Integrated micro- and nano-structures allows for the efficient generation of photon pairs via parametric fluorescence, thanks to the enhancement of the light-matter interaction associated with light confinement in small volumes. For instance, the efficiency of spontaneous four wave mixing in a silicon micro ring resonator can range up to 10 orders of magnitude larger than in bulk silicon. Yet the advantages of using integrated devices go well beyond the sole efficiency improvement, for micro structures grant an unprecedented control over the properties of generated non-classical light. For instance, in a single photonic integrated circuit, one can exploit the interferences of many optical elements to construct complex multipartite states in a compact, stable, and scalable system. In this talk I will focus on the generation of photon pairs and show how their spectral properties can be engineered in an integrated device for use as building blocks in the construction of a whole variety of states, from heralded single-photons to multipartite states.

International audience; We report an enhancement of over 10 4 in the signal-to-noise ratio characterizing the generation of identical photon pairs in a ring resonator system. Parasitic noise, associated with single pump spontaneous four-wave mixing, is essentially eliminated by employing a novel system design involving two resonators that are linearly uncoupled but nonlinearly coupled. This opens the way to a new class of integrated devices exploiting the unique properties of identical photon pairs in the same optical mode.

We exploit orthogonally polarized resonant modes to achieve thermal equilibrium for Kerr soliton generation in Si3N4 microrings. The improved thermal stability allows for soliton mode-locking simply by slow wavelength tuning or thermoelectric cooling.

We investigate spontaneous parametric downconversion (SPDC) in a waveguide array supporting two strongly coupled topological guided modes. We show that it is possible to generate photon pairs that are hyper-entangled in energy and path. We study the state robustness against positional disorder of the waveguides, in terms of Schmidt number (SN), fidelity, and density matrix. We show that quantum correlations are in general robust due to the peculiar interplay between structure topology and second-order nonlinear interaction.

We experimentally demonstrate the feasibility of the use of integrated linearly uncoupled resonators, which are coupled solely through the nonlinear interaction, to selectively enhance or suppress nonlinear processes. This is exploited to selectively enhance dual-pump spontaneous four-wave mixing while suppressing the parasitic noise associated with single pump spontaneous four-wave mixing processes. A signal-to-noise ratio characterizing the generation of identical photon pairs of more than four orders of magnitude is reported, opening the way to a new class of integrated devices exploiting the unique properties of identical photon pairs in the same optical mode.

We study degenerate spontaneous parametric down conversion in a structure composed of two linearly uncoupled resonators, in which the linear properties of the fundamental and second harmonic field can be engineered independently.

We study spontaneous and stimulated three photon generation rates in resonant and non-resonant structures. In the stimulated regime, we find that current technology allows for the generation of 105 photons per second in both structures.

We study spontaneous parametric down conversion in a waveguide array supporting two strongly coupled topological guided modes. Quantum correlations in the generated hyper-entangled quantum state are robust due to topological protection.

We report on the design of a novel nanoresonator operating at visible wavelengths, in which light confinement is achieved by a hybrid mechanism based on total internal reflection and photonic band gap. We show that this structure can support resonant nanophotonic modes with mode volumes on the order of one cubic wavelength, and Q factors exceeding several tens of thousands. Its properties make it ideal for controlling and enhancing the light-matter interaction at sub-wavelength scales.

We report on the suppression of nonlinear parasitic processes affecting dual-pump spontaneous four-wave mixing in ring resonators. We measure an enhancement of over 104 in the signal-to-noise ratio with respect to conventional ring resonators.

Integrated micro- and nanostructures allow for the efficient generation of photon pairs via parametric fluorescence, thanks to the enhancement of the light-matter interaction associated with light confinement in small volumes. Yet the advantages of using integrated devices go well-beyond the improvement of generation efficiency, for micro-structures can be designed to enable a precise control over the properties of the generated non-classical light. Particularly interesting are structures composed of more than one micro-resonator. In such systems one can control the spectral properties of the generated light, and suppress unwanted phenomena, with a careful engineering of the linear and nonlinear coupling of the resonant elements. Here we show that we can exploit this structure to generate photon pairs that are highly energy entangled or completely uncorrelated.

We study degenerate spontaneous parametric downconversion in a structure composed of two linearly uncoupled resonators, in which the linear properties of the fundamental and second-harmonic field can be engineered independently. As an example, we show that in this system it is simple to generate photon pairs that are nearly uncorrelated in energy. These results extend the use of linearly uncoupled resonators to the case of second-order nonlinear interactions.

Cooperative photon pair generation by Spontaneous Four-Wave Mixing (SFWM) process in singlechannel and dual-channel side-coupled ring resonator sequences is investigated. Our analysis shows that superlinear growth of generation rate with respect to the number of rings is possible even in presence of loss. Experimental evidence of super-SFWM is provided by comparing individual and collective generation rates obtained from a dual-channel ring resonator sequence. The results are in good agreement with theory and suggest that high photon pair generation rates can be achieved from integrated silicon ring resonator sequences without initiating nonlinear absorption processes.

We experimentally demonstrate stimulated four-wave mixing in two linearly uncoupled integrated S i 3 N 4 micro-resonators. In our structure, the resonance combs of each resonator can be tuned independently, with the energy transfer from one resonator to the other occurring in the presence of a nonlinear interaction. This method allows flexible and efficient on-chip control of the nonlinear interaction, and is readily applicable to other third-order nonlinear phenomena.

We theoretically study light propagation in guided Bloch surface waves (BSWs) supported by photonic crystal ridges. We demonstrate that low propagation losses can be achieved just by a proper design of the multilayer to obtain photonic band gaps for both light polarizations. We present a design strategy based on a Fourier analysis that allows one to obtain intrinsic losses as low as 5 dB/km for a structure operating in the visible spectral range. These results clarify the limiting factors to light propagation in guided BSWs and represent a fundamental step towards the development of BSW-based integrated optical platforms., Comment: v2: figures revised

We demonstrate emission of photon pairs from a Silicon integrated microres onator under electrical self-pumping. By controlling excitation conditions, the photon pairs are time-energy entangled, with fringe visibility in a Franson experiment of 93.9% ± 0.9%.

We report on the generation of photon pairs through dual-pump four-wave-mixing in a system composed of two resonators coupled solely through a third-order nonlinear interaction, which allows for the suppression of parasitic nonlinear phenomena.