We present spectra evolution of photonic molecules upon individual or collective coupling of supermodes in one resonator with single mode in the other one by tuning the coupling strength and spectral overlap of the modes.
In this paper, we analyze a chain-linked triple-cavity photonic molecule (TCPM) with controllable coupling strengths between the cavities on their spectral properties and field (energy) distributions by solving eigenvalues and eigenvectors of the Hamiltonian matrix based on coupled-mode theory. Phase transition is extended from double-cavity photonic molecules (DCPMs) to TCPMs, and evolutions of the supermode frequencies and linewidths are analyzed, which have synchronous relations with the degree of coherence between adjacent optical microcavities and energy distributions in the three cavities, respectively. We develop a superposition picture for the three supermodes of the TCPM, as interferences between supermodes of sub-DCPMs. In particular, we demonstrate the abnormal properties of the central supermode in TCPMs, such as the dark state in the middle cavity and phase shift when energy is flowing between the side cavities; these are promising for information processing and remote control of energy. General properties of TCPMs are summarized and limitations on linewidths are given. Finally, we make an interesting analog to intracavity electromagnetically induced transparency in multilevel atomic systems using the flexible TCPM platform under appropriate conditions.
We implement permanent spectral tuning to bring lifetime-limited emitters into collective resonance within an integrated photonic cavity. This addresses a fundamental challenge in solid-state cavity QED: combining multiple coherent quantum emitters with scalable nanophotonics. Our hybrid approach decouples emitter synthesis from nanophotonic fabrication using straightforward techniques that make cavity QED broadly accessible. High doping densities allow us to couple several coherent emitters to a single cavity mode, while optically-induced frequency shifting provides long-lived spectral control. By tuning two molecules into resonance, we demonstrate controlled formation of collective quantum states, establishing a scalable platform for many-body cavity QED. This opens pathways toward chemically-designed quantum systems where optical properties are engineered through synthetic chemistry.
Photonic molecules are systems of coupled optical resonators, or of deliberately coupled modes within one resonator, whose collective states have engineered frequencies, lifetimes and optical access. Integration on silicon, silicon nitride, thin-film lithium niobate and hybrid platforms has turned them from spectroscopic objects into circuit elements for filtering, frequency conversion, nonlinear light generation, lasing and sensing. This review covers the physics and the state of the art of integrated photonic molecules. We first introduce the temporal coupled-mode description of a two-resonator molecule and the quantities used to characterize it: mode splitting, linewidth and their ratio. We then review each platform: thermally tuned and photonic-crystal molecules in silicon for compact spectral processing, spectrometry and sensing; low-loss silicon nitride molecules for soliton and parametric generation, squeezed light and narrow-linewidth Brillouin lasing; and electro-optic molecules in lithium niobate and hybrid stacks for programmable two-level dynamics, frequency shifting, comb generation and transduction. Non-Hermitian and active molecules, including exceptional-point devices and coupled lasers, are treated separately. Comparison tables collect the reported metrics together with their operating conditions. We close with the open problems of calibration, stability and packaging and with prospects in microwave photonics and quantum technologies.