Ultra-low-loss on-chip resonators with sub-milliwatt parametric oscillation threshold

Ji, Xingchen; Barbosa, F. A. S.; Roberts, Samantha P.; Dutt, Avik; Cárdenas, Jaime; Okawachi, Yoshitomo; Bryant, Alex; Gaeta, Alexander L.; Lipson, Michal

doi:10.1364/optica.4.000619

Cited by 470 publications

(331 citation statements)

References 59 publications

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“…All listed applications benefit from small V eff and most benefit from high Q. Moreover, because Q factors are often practically limited (by material losses, scattering [29], or application-specific bandwidth constraints), reducing V eff is particularly beneficial for many applications.…”

Section: Prl 118 223605 (2017) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

Self-Similar Nanocavity Design with Ultrasmall Mode Volume for Single-Photon Nonlinearities

2017

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We propose a photonic crystal nanocavity design with self-similar electromagnetic boundary conditions, achieving ultrasmall mode volume (V eff ). The electric energy density of a cavity mode can be maximized in the air or dielectric region, depending on the choice of boundary conditions. We illustrate the design concept with a silicon-air one-dimensional photon crystal cavity that reaches an ultrasmall mode volume of V eff ∼ 7.01 × 10 −5 λ 3 at λ ∼ 1550 nm. We show that the extreme light concentration in our design can enable ultrastrong Kerr nonlinearities, even at the single-photon level. These features open new directions in cavity quantum electrodynamics, spectroscopy, and quantum nonlinear optics. DOI: 10.1103/PhysRevLett.118.223605 Optical nanocavities with small mode volume (V eff ) and high quality factor (Q) can greatly increase light-matter interaction [1] and have a wide range of applications including nanocavity lasers [2-4], cavity quantum electrodynamics [5,6], single-molecule spectroscopy [7], and nonlinear optics [8][9][10]. Planar photonic crystal cavities can enable high Q factors, exceeding 10 6 [11], together with mode volumes that are typically on the order of a qubic wavelength. However, it was shown that by introducing an air slot into a photonic crystal (PhC) cavity, it is possible to achieve the electromagnetic (EM) mode with small V eff on the order of 0.01λ 3 [12], where λ is the freespace wavelength. This field concentration results from the boundary condition on the normal component of the electric displacement ( ⃗ D). Here, we propose a method to further reduce V eff by making use of the second EM boundary condition, the conservation of the parallel component of the electric field. Furthermore, these field concentration methods can be concatenated to reduce V eff even further, limited only by practical considerations such as fabrication resolution. The extreme field concentration of our cavity design opens new possibilities in nonlinear optics. In particular, we show that Kerr nonlinearities, which are normally weak, would be substantially enhanced so that even a single photon may shift the cavity resonance by a full linewidth, under realistic assumptions of materials and fabrication tolerances.The mode volume of a dielectric cavity [described by the spatially varying permittivity ϵð ⃗rÞ] is given by the ratio of the total electric energy to the maximum electric energy density [13],In typical PhC cavity designs, the minimum cavity mode volume is given by a half-wavelength bounding box, or3 [14], agreeing with the diffraction limit. However, as is clear from Eq. (1), the mode volume is determined by the electric energy density at the position where it is maximized. Thus, it is not strictly restricted by the diffraction limit. A strong local inhomogeneity in ϵð ⃗rÞ can greatly increase this electric energy density and correspondingly shrink the mode volume. Figure 1(a) plots the fundamental mode of a silicon-air one-dimensional PhC cavity produced by three-dimensional FDTD simulati...

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Section: Prl 118 223605 (2017) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

Self-Similar Nanocavity Design with Ultrasmall Mode Volume for Single-Photon Nonlinearities

2017

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“…The possible contributing factors are ionimplantation damage introduced during the LN thin-film production process, top-surface roughness due to LN polishing, and finite PECVD SiO 2 cladding absorption. Importantly, these loss mechanisms could be mitigated by a combination of defects annealing and finer top-surface polishing [8]. We expected that the these loss contributions of the monolithic LN platform could be further reduced towards its material intrinsic loss limit of < 0.1 dB/m [1].…”

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confidence: 99%

Monolithic ultra-high-Q lithium niobate microring resonator

Zhang¹,

Wang²,

Cheng³

et al. 2017

Optica

704

430

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We demonstrate an ultralow loss monolithic integrated lithium niobate photonic platform consisting of dry-etched subwavelength waveguides. We show microring resonators with a quality factor of 10 7 and waveguides with propagation loss as low as 2.7 dB/m.Lithium niobate (LN) is a material with wide range of applications in optical and microwave technologies, owing to its unique properties that include large second order nonlinear susceptibility (χ (2) = 30 pm/V), large piezoelectric response (C 33 ∼ 250 C/m 2 ), wide optical transparency window (350 nm − 5 µm) and high refractive index (∼ 2.2) [1]. Conventional LN components, including fiber-optic modulators and periodically poled frequency converters have been the workhorse of the optoelectronic industry. The performances of these components have the potential to be dramatically improved as optical waveguides in bulk LN crystals are defined by ion-diffusion or proton-exchange methods which result in low index contrast and weak optical confinement. Integrated LN platform, featuring sub-wavelength scale light confinement and dense integration of optical and electrical components, has the potential to revolutionize optical communication and microwave photonics [1][2][3][4][5][6][7].The major road-block for practical applications of integrated LN photonics is the difficulty of fabricating devices that simultaneously achieve low optical propagation loss and high confinement. Recently developed thin-film LN-on-insulator technology makes this possible, and has resulted in the development of two complementary approaches to define nanoscale optical waveguides: hybrid and monolithic. The hybrid approach integrates an easyto-etch material (e.g. silicon or silicon nitride) with LN thin films to guide light [2-4] with a relatively low propagation loss (0.3 dB/cm) [4]. However, the resulting optical modes only partially reside in the active material region (i.e. LN), reducing the nonlinear interaction efficiency. The monolithic approach relies on direct etching of LN to achieve high optical confinement in the active region, but has suffered from a relatively high propagation loss. While freestanding LN microdisk resonators have achieved optical quality factors (Q) of ∼ 10 6 [5, 6], integrated microring resonators typically feature Q ∼ 10 5 with waveguide propagation loss on the order of 3 dB/cm [7]. Since LN is perceived as a difficult-to-etch material, it is commonly accepted that low-loss propagation in a monolithic waveguide is not possible, and that therefore it is not the most promising path forward.Here we challenge the status quo and show that subwavelength scale lithium niobate waveguides can be fabricated with a propagation loss as low as 2.7 ± 0.3 dB/m through an optimized etching process. We also demonstrate ultra-high Q factor optical cavities with intrinsic Q = 10 7 . We fabricate waveguide coupled microring and racetrack resonators with a bending radius r = 80 µm, and various straight arm lengths l and waveguide widths w (Fig. 1). The optical modes in these reso...

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“…For instance, figures 7(b) and 8(c) show that 99% conversion efficiency and spectral purity is possible for Q L /Q i ∼400. If, for instance, the pump, idler, and output modes have coupling Qs of 10 4 the corresponding intrinsic Q must be 4×10 6 , which is well below what has been demonstrated [35]. Electronic feedback control at these short timescales remains to be demonstrated, but since many quantum information processing tasks rely on it, we are optimistic that the field will progress sufficiently.…”

Section: Discussionmentioning

confidence: 90%

Unidirectional frequency conversion in microring resonators for on-chip frequency-multiplexed single-photon sources

et al. 2019

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Microring resonators are attractive for low-power frequency conversion via Bragg-scattering fourwave-mixing due to their comb-like resonance spectrum, which allows resonant enhancement of all four waves while maintaining energy and momentum conservation. However, the symmetry of such mode structures limits the conversion efficiency to 50% due to the equal probability of up-and downconversion. Here, we demonstrate how two coupled microrings enable highly directional conversion between the spectral modes of one of the rings. An extinction between up-and down-conversion of more than 40 dB is experimentally observed. Based on this method, we propose a design for on-chip multiplexed single-photon sources that probabilistically generate photon pairs across many frequency modes of a ring resonator and subsequently convert them to a single frequency-thereby enabling quasi-deterministic photon emission. Our numerical analysis shows that once a photon is generated, it can be converted and emitted into a wave packet having a 90% overlap with a Gaussian with 99% efficiency for a ratio between intrinsic and coupling quality factors of 400.

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Ultra-low-loss on-chip resonators with sub-milliwatt parametric oscillation threshold

Cited by 470 publications

References 59 publications

Self-Similar Nanocavity Design with Ultrasmall Mode Volume for Single-Photon Nonlinearities

Self-Similar Nanocavity Design with Ultrasmall Mode Volume for Single-Photon Nonlinearities

Monolithic ultra-high-Q lithium niobate microring resonator

Unidirectional frequency conversion in microring resonators for on-chip frequency-multiplexed single-photon sources

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