beyond the diffraction limit, provide a promising platform for the development of all-optical logic circuits. [12][13][14][15][16][17][18] Recently, several groups have reported that plasmonic microstructures, either nanowires or nanogrooves, could be used to build microscale all-optical logic gates. [19][20][21][22][23] Using different microfabrication techniques, devices with varying scales and output intensity contrast ratios have been demonstrated. In spite of the progress so far, these devices either have a small contrast ratio which affects the signal extraction, or have a big loss which is hard for integration. More importantly, broadband response and multifunctionality have not been demonstrated, which are crucial for high-density data transmission and processing.In this work, we propose and demonstrate broadband (over 100 nm in free-space wavelength) Boolean logic devices, including seven fundamental logic gates, while maintaining their high-contrast-ratio properties. Each device contains a curved grating with a rectangular groove profile for the input port(s) and a subwavelength hole as the output port. Because of its unique geometric property, the curved grating can transduce the input optical signals to propagating surface plasmon polaritons (SPPs), and focus them to the focal point without using any additional guiding structure. Consequently, the SPPs from different input ports can interfere at the focal point, and are coupled out to the far-field by using the hole as the output signal port. Essentially, this configuration is a zero-order interferometer, which naturally has a wide operating bandwidth. Besides, when propagating freely, the SPPs experience minimal losses in comparison with the case propagating in waveguides. [24] The loss is further decreased by using single-crystalline silver, instead of the polycrystalline silver films usually prepared by thermal evaporation. Meanwhile, these logic gates can maintain the high intensity contrast ratio even using front illumination. Here, we obtain a maximum contrast ratio of 29 dB. In addition, we used only one geometric configuration to realize all the fundamental logic gates, making this method easy for device fabrication and system integration.The designed device configuration is illustrated in Figure 1a. The input optical signal is incident on the curved grating and transduced into SPPs, which are focused to the grating focal point. To build a broadband device, two conditions need to be met: the first one is that the grating has a broadband spectral response to the incident signals, and the second one is that the focus of the input signals from different input ports is achromatic, i.e., independent of the operating wavelength.Plasmonic logic gates provide a promising platform to realize diffractionunlimited all-optical logic circuits. However, previous plasmonic logic gates suffer from narrow bandwidth and high loss. Here, broadband plasmonic logic gates are proposed and demonstrated using a unique design based on curved silver gratings. These log...
We present a strong coupling system realized by coupling the localized surface plasmon mode in individual silver nanogrooves and propagating surface plasmon modes launched by periodic nanogroove arrays with varied periodicities on a continuous silver medium. When the propagating modes are in resonance with the localized mode, we observe a √N scaling of Rabi splitting energy, where N is the number of propagating modes coupled to the localized mode. Here, we confirm a giant Rabi splitting on the order of 450–660 meV (N = 2) in the visible spectral range, and the corresponding coupling strength is 160–235 meV. In some of the strong coupling cases studied by us, the coupling strength is about 10% of the mode energy, reaching the ultrastrong coupling regime.
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