An improved surface-plasmonic nanobeam cavity for higher Q and smaller V

Abstract

We demonstrate a high-Q hybrid surface-plasmon-polariton-photonic crystal (SP3C) nanobeam cavity. The proposed cavities are analyzed numerically using the three-dimensional finite difference time domain (3D-FDTD) method. The results show that a Q-factor of 2076 and a modal volume V of 0.16(/2n) 3 can be achieved in a 50 nm silica-gap hybrid SP3C nanobeam cavity when it operates at telecommunications wavelengths and at room temperature. V can be further reduced to 0.02(/2n) 3 when the silica thickness decreases to 10 nm, which leads to a Q/V ratio that is 11 times that of the corresponding plasmonic-photonic nanobeam cavity (without silica). The ultrahigh Q/V ratio originates from the low-loss nature and deep sub-wavelength confinement of the hybrid plasmonic waveguide, as well as the mode gap effect used to reduce the radiation loss. The proposed structure is fully compatible with semiconductor fabrication techniques and could lead to a wide range of applications. Considerable efforts are currently focused on exploring ways to increase the quality factor Q and decrease the modal volume V of optical microcavities, because of their significant roles in many fundamental physics studies, including light-matter interactions and device physics [1]. A higher Q value indicates a very long photon lifetime, while a small V means that the cavity can localize the photon in a small spatial volume. Over the last decade, various types of optical microcavities were proposed and investigated, including whispering-gallery microcavities, Fabry-Perot microcavities, and photonic crystal microcavities [2]. Among these cavities, the nanobeam photonic crystal microcavity [3-11] provides not only a very high Q value, but also an ultrasmall V and an ultracompact footprint. Nanobeam photonic crystal microcavities with Q values even higher than 10 9 were demonstrated [12]. Although Q values have been raised considerably by sophisticated designs, the smallest achievable V in a conventional dielectric cavity is bound to the diffraction limit, i.e. it is of the order of several times (/2n) 3 [13]. However, in some cases, an ultrasmall V is more important than a higher Q. For example, when the cavity's resonance linewidth is smaller than the emission linewidth of the emitter, decreasing the effective modal volume is the only way to increase the spontaneous emission rate [14].New microcavity schemes were designed to further decrease V. For example, microcavities based on slot waveguides were proposed [14][15][16][17][18]. Microcavities using surface plasmon polaritons (SPPs) were also studied extensively [19,20]. SPPs are electron density waves excited at and propagating along metal-dielectric interfaces [21,22]. Because of their sub-wavelength confinement of optical fields, they are promising candidates for realization of ultrasmall-V nanocavities. However, the reported Q values of SPP cavities thus far are very small and high Q values were only predicted at cryogenic temperatures [23]. The intrinsic high loss caused by metallic absorption ...

On the developments and applications of optical microcavities: an overview

“…For example, the coupling of NV centers in diamond to SC qubits [35]. The coherent coupling between different physical systems or between the optical cavity and other kinds of cavities, such as superconducting cavity [157] and surface-plasmonic nanobeam cavity [158][159][160][161], and becomes an active area of research for years to come. However, the material properties between these quantum systems are quite different, and experiments on hybrid devices are just starting to demonstrate [35].…”

Silicon hybrid nanoplasmonics for ultra-dense photonic integration

“…The temperature-dependence of a silicon hybrid nanoplasmonic waveguide resonator has been analyzed [73] and an athermal resonator is achieved with the assistance of TiO 2 which has a negative thermal-optical coefficient [74]. Silicon hybrid nanoplasmonic waveguides have also been used to realize photonic-crystal cavities [78][79][80]. The cavity designed in Ref.…”

“…Since the hybrid plasmonic waveguide enables a submicron bending radius [53,64,70,71], one can realize ultra-compact resonators, including submicron rings/donuts [65,66,[71][72][73][74][75], disks [76,77] and photonic-crystal cavities [78][79][80], as the well-known versatile elements in photonic integrated circuits. Such resonators have ultra-compact footprint as well as good performances (e.g., acceptable quality factor and large Purcell efficiency [77]).…”

SOI (silicon-on-insulator)-compatible hybrid nanoplasmonics: waveguiding, polarization-handling, and thermal-tuning

“…The ability for sharp bending and tight optical confinement makes silicon hybrid nanoplasmonic waveguides very promising to realize ultra-dense devices (e.g., with a sub-μm 2 footprint) for photonic integration, including power splitters [74]- [77], directional couplers [78]- [82], grating reflectors [83], submicron rings/donuts [84]- [86], disks [87]- [88] and photonic-crystal cavities [89]- [91]. Particularly, these ultra-compact resonators also have good performances (e.g., acceptable quality factor and large Purcell efficiency [88]) and are very useful as the well-known versatile elements in photonic integrated circuits.…”