Abstract
Controlling spontaneous emission at optical scale lies in the heart of ultracompact quantum photonic devices, such as on-chip single photon sources, nanolasers and nanophotonic detectors. However, achiving a large modulation of fluorescence intensity and guiding the emitted photons into low-loss nanophotonic structures remain rather challenging issue. Here, using the liquid crystal-tuned gap surface plasmon, we theoretically demonstrate both a high-contrast switching of the spontaneous emission and high-efficiency extraction of the photons with a specially-designed tunable surface plasmon nanostructures. Through varying the refractive index of liquid crystal, the local electromagnetic field of the gap surface plasmon can be greatly modulated, thereby leading to the swithching of the spontaneous emission of the emitter placed at the nanoscale gap. By optimizing the material and geometrical parameters, the total decay rate can be changed from 103γ0 to 8750γ0, [γ0 is the spontaneous emission rate in vacuum] with the contrast ratio of 85. Further more, in the design also enables propagation of the emitted photons along the low-loss phase-matched nanofibers with a collection efficiency of more than 40%. The proposal provides a novel mechanism for simultaneously switching and extracting the spontaneous emitted photons in hybrid photonic nanostructures, propelling the implementation in on-chip tunable quantum devices.
Highlights
Controlling spontaneous emission (SE) at subwavelength scale is of fundamental and practical importance in nanophotonics, cavity quantum electrodynimics, and quantum information processing, propelling the performance of on-chip quantum devices such as single photon sources[1,2,3], nanolasers[4,5], and nanophotonic detectors[6,7]
The nanoscale gap between metallic nanorod and nanofilm guarantees the existence of the GSP49,50, whose hotspots lead to the large enhancement of the SE19–23
Through varying the refractive index of the liquid crystal (LC) by various means[40,51] to modulate the local electromagnetic field of the gap surface plasmon (GSP), the SE rate of the emitter placed at the nanoscale gap is modulated
Summary
Controlling spontaneous emission (SE) at subwavelength scale is of fundamental and practical importance in nanophotonics, cavity quantum electrodynimics, and quantum information processing, propelling the performance of on-chip quantum devices such as single photon sources[1,2,3], nanolasers[4,5], and nanophotonic detectors[6,7]. By incorporating quantum dots in an electrically control p-i-n dipole maintained at liquid-nitrogen temperature, the energy relaxation into electron-hole pairs can be tuned electrically, thereby the switching of SE is attained[24,25]; by combining neutral nitrogen-vacancy centre with a novel diamond diode[26,27] or through replacing the semiconductor quantum dots with organic molecules[28], room-temperature electrical modulating SE can be realized Another more obvious way of controlling SE is by changing the optical mode density. The SE rate can be tuned by introducing reconfigurable multiscale biological material into quantum dot-nanoparticle system[34], where the distance between quantum dot and nanoparticle can be controlled and in turn influences the lifetime of quantum dot about two folds Besides tunability, another highly desirable feature is efficient coupling of the emitted photons into some waveguide nanostructures[35,36,37]. If the quantum emitter is suited at the hot spots inside the nanoscale gap, its SE rate will be greatly modulated; the emitted photons could be effectively extracted by the phase-matched low-loss nanofibres
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