Metasurfaces have found broad applicability in free-space optics, while its potential to tailor guided waves remains barely explored. By synergizing the Jones matrix model with generalized Snell’s law under the phase-matching condition, we propose a universal design strategy for versatile on-chip mode-selective coupling with polarization sensitivity, multiple working wavelengths, and high efficiency concurrently. The coupling direction, operation frequency, and excited mode type can be designed at will for arbitrary incident polarizations, outperforming previous technology that only works for specific polarizations and lacks versatile mode controllability. Here, using silicon-nanoantenna-patterned silicon-nitride photonic waveguides, we numerically demonstrate a set of chip-scale optical couplers around 1.55 μm, including mode-selective directional couplers with high coupling efficiency over 57% and directivity about 23 dB. Polarization and wavelength demultiplexer scenarios are also proposed with 67% maximum efficiency and an extinction ratio of 20 dB. Moreover, a chip-integrated twisted light generator, coupling free-space linear polarization into an optical vortex carrying 1 ℏ orbital angular momentum (OAM), is also reported to validate the mode-control flexibility. This comprehensive method may motivate compact wavelength/polarization (de)multiplexers, multifunctional mode converters, on-chip OAM generators for photonic integrated circuits, and high-speed optical telecommunications.
Sensing technologies based on terahertz (THz) waves have significant application prospects in fast imaging, free label, and non-invasive inspection methods. However, the main drawback limiting the performance of THz-based bio-chemical...
As fundamental elements, optical diodes are required for on-chip optical communications and computing. However, it is still a challenge to realize ultracompact devices working in the terahertz (THz) range. Here an optical diode device with a bandwidth up to 100 GHz that is able to produce a highly asymmetric THz propagation was designed by coupling a gradient metasurface and subwavelength waveguide modes. This system is based on the breaking of the momentum symmetry at the interface with phase discontinuities. The asymmetric transmission process generated by THz mode conversion is detected by employing time-resolved phase contrast imaging. The results agree well with full-wave electromagnetic simulations. Moreover, the performance of the working bandwidth and the ratio of transmission of the device can be optimized by the induced arbitrary scattering phase. These performances indicate that this design provides a very effective method and a versatile platform for on-chip information processing by preventing undesired light interference in the integrated system.
Advanced sensing devices, highly sensitive, and reliable in detecting ultralow concentrations of circulating biomarkers, are extremely desirable and hold great promise for early diagnostics and real‐time progression monitoring of diseases. Nowadays, the most commonly used clinical methods for diagnosing biomarkers suffer from complicated procedures and being time consumption. Here, a chip‐based portable ultra‐sensitive THz metasensor is reported by exploring quasi‐bound states in the continuum (quasi‐BICs) and demonstrate its capability for sensing low‐concentration analytes. The designed metasensor is made of the designed split‐ring resonator metasurface which supports magnetic dipole quasi‐BIC combining functionalized gold nanoparticles (AuNPs) conjugated with the specific antibody. Attributed to the strong near‐field enhancement near the surface of the microstructure enabled by the quasi‐BICs, light‐analyte interactions are greatly enhanced, and thus the device's sensitivity is boosted significantly. The system sensitivity slope is up to 674 GHz/RIU, allowing for repeatable resolving detecting ultralow concentration of C‐reactive protein (CRP) and Serum Amyloid A (SAA), respectively, down to 1 pM. The results touch a range that cannot be achieved by ordinary immunological assays alone, offering a novel non‐destructive and rapid trace measured approach for next‐generation biomedical quantitative detection systems.
Recognizing special molecules is crucial in many biochemical processes, and thus, highly enhanced sensing methods are in high demand. In this work, we designed a microrod array metasurface with a SiO2-loaded subwavelength lithium niobate waveguide as a unique platform for enhanced experimental fingerprint detection of lactose. The metasurface could lead to strong surface wave modes due to the near-field coupling of the spoof localized surface plasmon, which also could provide a stronger interaction length between light and matter. The selectivity was remarkable in the transmission spectrum at an intrinsic characteristic frequency of 0.529 THz with a thin layer of lactose, while it was faint while transmitting terahertz (THz) waves normally through a lactose layer of the same thickness. Together with the ability to freely design the shape of the metasurface and the electromagnetic properties, we believe that this platform can function as an elegant on-chip-scale enhanced THz sensing platform.
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