Trapping and releasing light by mechanical implementation in metamaterial waveguides

Experimental demonstration of broadband light trapping by exciting surface modes of an all-dielectric taper

We design an all-dielectric taper and then excite its surface modes by illuminating a plane wave upon the taper to achieve broadband light trapping spanning from 20 to 100 GHz. Via Lewin’s theory, such excitation of surface modes could be analogous to “trapped rainbow”, i.e., activation of negative Goos-Hänchen effect within a negative refractive waveguide. To further reinforce this statement, the corresponding power flow distributions within the all-dielectric taper are recorded in finite-integration time domain simulation and suggest that a chromatic incident pulse is indeed trapped at different critical thicknesses of the taper, a character of the negative refractive waveguide. Finally, the transmittance is measured and compared to the simulated ones. The two followed the similar trend.

On-chip sub-terahertz surface plasmon polariton transmission lines with mode converter in CMOS

An on-chip low-loss and high conversion efficiency plasmonic waveguide converter is demonstrated at sub-THz in CMOS. By introducing a subwavelength periodic corrugated structure onto the transmission line (T-line) implemented by a top-layer metal, surface plasmon polaritons (SPP) are established to propagate signals with strongly localized surface-wave. To match both impedance and momentum of other on-chip components with TEM-wave propagation, a mode converter structure featured by a smooth bridge between the Ground coplanar waveguide (GCPW) with 50 Ω impedance and SPP T-line is proposed. To further reduce area, the converter is ultimately simplified to a gradual increment of groove with smooth gradient. The proposed SPP T-lines with the converter is designed and fabricated in the standard 65 nm CMOS process. Both near-field simulation and measurement results show excellent conversion efficiency from quasi-TEM to SPP modes in a broadband frequency range. The converter achieves wideband impedance matching (<-9 dB) with excellent transmission efficiency (averagely -1.9 dB) from 110 GHz-325 GHz. The demonstrated compact and wideband SPP T-lines with mode converter have shown great potentials to replace existing waveguides as future on-chip THz interconnects. To the best of the author's knowledge, this is the first time to demonstrate the (sub)-THz surface mode conversion on-chip in CMOS technology.

Detuned Plasmonic Bragg Grating Sensor Based on a Defect Metal-Insulator-Metal Waveguide

A nanoscale Bragg grating reflector based on the defect metal-insulator-metal (MIM) waveguide is developed and numerically simulated by using the finite element method (FEM). The MIM-based structure promises a highly tunable broad stop-band in transmission spectra. The narrow transmission window is shown to appear in the previous stop-band by changing the certain geometrical parameters. The central wavelengths can be controlled easily by altering the geographical parameters. The development of surface plasmon polarition (SPP) technology in metallic waveguide structures leads to more possibilities of controlling light at deep sub-wavelengths. Its attractive ability of breaking the diffraction limit contributes to the design of optical sensors.

Acoustic rainbow trapping by coiling up space

We numerically realize the acoustic rainbow trapping effect by tapping an air waveguide with space-coiling metamaterials. Due to the high refractive-index of the space-coiling metamaterials, our device is more compact compared to the reported trapped-rainbow devices. A numerical model utilizing effective parameters is also calculated, whose results are consistent well with the direct numerical simulation of space-coiling structure. Moreover, such device with the capability of dropping different frequency components of a broadband incident temporal acoustic signal into different channels can function as an acoustic wavelength division de-multiplexer. These results may have potential applications in acoustic device design such as an acoustic filter and an artificial cochlea.

A 4-way wavelength demultiplexer based on the plasmonic broadband slow wave system

We propose a broadband slow wave system based on the thin metal-insulator-metal (MIM) graded grating structure composed of two corrugated metal strips with periodic array of grooves on a thin dielectric substrate. The guided spoof surface plasmon polaritons (SSPPs) at different frequencies can be localized at different positions along the ultrathin MIM grating. By introducing specially designed non-corrugated MIM branches with specific lengths at the locations where the EM waves are trapped, the trapped EM waves can be released and propagate along these branches. A 4-way wavelength demultiplexer based on such plasmonic broadband slow wave system is then demonstrated and fabricated. To improve the isolations between different branches at lower frequencies, band-reject filters are inserted at the front of some MIM branches. The measurements and the simulation results have shown very good agreements, which validate the feasibility of the 4-way wavelength demultiplexer.