Abstract
Optical diode-like effect has sparked growing interest in recent years due to its potential applications in integrated photonic systems. In this paper, we propose and numerically demonstrate a new type of easy-processing metal/dielectric cylinder composite grating on semi-sphere substrate, which can achieve high-contrast asymmetric transmission of unpolarized light for the sum of all diffraction modes in the entire visible region, and effectively guide the diffraction light transmitting out the substrate. The asymmetric light transmission (ALT) ratio is larger than 2 dB in the waveband from 380 nm to 780 nm and the maximum ALT ratio can reach to 13 dB at specified wavelengths. The thorough theoretical research reveals that the proposed metal/dielectric pillar composite grating structure, together with the substrate, can effectively excite localized surface plasmonic resonance (LSPR) effect and waveguide mode (WGM), and enlarge the diffraction difference between forward and backward transmission spaces, including both number of diffraction orders and diffraction efficiency, thus resulting in high-contrast broadband ALT phenomenon. In particular, lowering the symmetry of the grating can achieve polarization-dependent ALT. Such a type of easy-processing ALT device with high performance for both polarized and unpolarized light can be regarded as suitable candidates in practical applications.
Highlights
Reciprocity scheme has been demonstrated to be the other effective method to achieve asymmetric light transmission (ALT)
The maximum asymmetric subtraction and ratio can reach to 0.8 and 13 dB, indicating our designed metal/dielectric cylinder composite grating (MDCG) exhibits high asymmetric performance. We find that this excellent ALT effect is originated from specific diffraction effect, localized surface plasmonic resonance (LSPR) and waveguide mode (WGM) excited in MDCG, which will be systematically discussed later
We propose and numerically demonstrate a high performance optical diode-like device based on MDCG placed on a semi-sphere substrate
Summary
Optical diode-like effect has sparked growing interest in recent years due to its potential applications in integrated photonic systems. We propose and numerically demonstrate a new type of easy-processing metal/dielectric cylinder composite grating on semi-sphere substrate, which can achieve high-contrast asymmetric transmission of unpolarized light for the sum of all diffraction modes in the entire visible region, and effectively guide the diffraction light transmitting out the substrate. The thorough theoretical research reveals that the proposed metal/dielectric pillar composite grating structure, together with the substrate, can effectively excite localized surface plasmonic resonance (LSPR) effect and waveguide mode (WGM), and enlarge the diffraction difference between forward and backward transmission spaces, including both number of diffraction orders and diffraction efficiency, resulting in highcontrast broadband ALT phenomenon. Through breaking the spatial symmetry of device, a specific asymmetric mode conversion can be excited, and result in light transmission difference between forward and backward directions This scheme tactfully bypasses the Lorentz restricted conditions[14]. The diffraction effect, localized surface plasmonic resonance (LSPR) and weak WGM, which are responsible for the high contrast-ratio broadband ALT, have been systematically investigated
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