Multi-cavity photonic systems, known as photonic molecules (PMs), are ideal multi-well potential building blocks for advanced quantum and nonlinear optics [1][2][3][4]. A key phenomenon arising in double well potentials is the spontaneous breaking of the inversion symmetry, i.e. a transition from a delocalized to two localized states in the wells, which are mirror images of each other. Although few theoretical studies have addressed mirror-symmetry breaking in micro and nanophotonic systems [5][6][7][8][9], no experimental evidence has been reported to date. Thanks to the potential barrier engineering implemented here, we demonstrate spontaneous mirror-symmetry breaking through a pitchfork bifurcation in a PM composed of two coupled photonic crystal nanolasers. Coexistence of localized states is shown by switching them with short pulses. This offers exciting prospects for the realization of ultra-compact, integrated, scalable optical flip-flops based on spontaneous symmetry breaking. Furthermore, we predict such transitions with few intracavity photons for future devices with strong quantum correlations.Spontaneous symmetry breaking (SSB) unifies diverse physical mechanisms through which a given symmetric system ends up in an asymmetric state [10]. It explains many central questions from particle and atomic physics to nonlinear optics (the Goldstone boson and the Higgs mechanism [11,12], phase transitions in BoseEinstein condensates -BECs- [13,14], metamaterials [15], bifurcations in lasers [16,17], photorrefractive media [18], to mention just a few). A paradigmatic symmetry in this context is given by reflection in a double-well potential (DWP), as it is the case of pyramidal molecules (e.g. ammonia) [19]: SSB dictates whether the state of a system will be delocalized or, in turn, confined within either well. In photonics, such a mechanism is possible provided the third order nonlinearities overcome photon tunneling [20]. In this work we experimentally show SSB in a photonic molecule (PM) given by two evanescently coupled photonic crystal (PhC) nanolasers. Switchable localized modes with broken mirror-symmetry will be demonstrated herein. This can be prospected as a nanoscale version of a laser flip-flop [21]; the memory is pumped incoherently, set and reset can be induced with positive pulses and there is no coherent driving beam to bias the device, as in conventional bistable cavities. This paves the way for the realization of ultra-small flip-flop optical memories based on SSB.We represent the PM as a DWP, symmetric with respect to the inversion plane. We describe the dynamics in terms of the complex amplitudes of the photonic field at the left (ψ L ) and right (ψ R ) sites, |ψ| 2 being photon number. A finite potential barrier leads to a tunneling rate K. We further consider a local (nonlinear) interaction U |ψ L,R | 2 , and a lifetime τ due to losses. SSB instabilities occur as long as K is lower than a critical value K c (|K| < |K c |), with |K c τ | ∼ |U | · |ψ| 2 [22]. In the case of our PM laser, |ψ| 2...
We demonstrate a large tuning of the coupling strength in Photonic Crystal molecules without changing the inter-cavity distance. The key element for the design is the "photonic barrier engineering", where the "potential barrier" is formed by the air-holes in between the two cavities. This consists in changing the hole radius of the central row in the barrier. As a result we show, both numerically and experimentally, that the wavelength splitting in two evanescently-coupled Photonic Crystal L3 cavities (three holes missing in the ΓK direction of the underlying triangular lattice) can be continuously controlled up to 5× the initial value upon ∼ 30% of hole-size modification in the barrier. Moreover, the sign of the splitting can be reversed in such a way that the fundamental mode can be either the symmetric or the anti-symmetric one without altering neither the cavity geometry nor the inter-cavity distance. Coupling sign inversion is explained in the framework of a Fabry-Perot model with underlying propagating Bloch modes in coupled W1 waveguides.
We implement the band-folding approach in coupled photonic crystal L3 (three missing holes) nanocavities and demonstrate a dramatic beaming improvement compatible with high-Q operation. Directional laser effect is achieved. In addition, resonant free-space coupling to the symmetric and anti-symmetric hybrid modes of the photonic molecule is shown. We measure the coupling to each mode as a function of the spatial position of the laser spot, which can be used as a technique to probe the symmetry of coupled cavity modes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.