Reconfigurable Mach–Zehnder interferometer for dynamic modulations of spoof surface plasmon polaritons

Abstract

We propose an ultrathin reconfigurable Mach–Zehnder interferometer (MZI) for realizing dynamic frequency and amplitude modulations of spoof surface plasmon (SSP) signal. Active varactor diodes are integrated in the SSP unit cells on one of the MZI arms to introduce asymmetry to the MZI structure, which can control the interference patterns by varying bias voltages applied on the varactor diodes. We show that the spectral positions of multiple sharp interference dips are very sensitive to the change of diode capacitance, thereby allowing for good frequency modulation. We also demonstrate continuous amplitude modulation by tuning the varactor diodes at multiple selected frequencies. To verify the reconfigurable feature of the proposed SSP MZI, the frequency shift keying (FSK) and amplitude modulations have been experimentally demonstrated on the same structure. The modulation depth of the amplitude modulation can be further improved by designing geometrical parameters of the SSP structure, reaching a significant amplitude change from 0.88 to 0.05 in experiments.

Logic Gates of Terahertz Spoof Surface Plasmons

“…Due to the limitations of the experimental conditions, the proposed SSPP waveguide structure is designed to be similar to the Mach-Zehnder Interferometer (MZI), where the upper and lower arms are regarded as the two input signals, respectively. [44,45] Thus, the phase difference (Δϕ 0 ) between the upper and lower arms determines the output state and can be written as…”

“…Due to the limitations of the experimental conditions, the proposed SSPP waveguide structure is designed to be similar to the Mach–Zehnder Interferometer (MZI), where the upper and lower arms are regarded as the two input signals, respectively. [ 44,45 ] Thus, the phase difference (Δφ 0 ) between the upper and lower arms determines the output state and can be written as $$\[ \begin{array}{*{20}{c}}{\left| {{A_o}} \right| = \left| {{A_{\rm{i}}}\cos \frac{{\Delta {\varphi _0}}}{2}} \right|}\end{array} \]$$where Ao and A i are the output and input amplitudes of the waveguide, respectively. When the phase difference is (2 k + 1) π ( k = 0, ±1, ±2,…), the output signal is zero.…”

Reprogrammable Spoof Plasmonic Modulator

“…[ 7,8 ] Compared to conventional waveguides, such as microstrip in microwave frequencies, the SSPP waveguide can effectively suppress crosstalks between different waveguides when signals are transmitted in parallel. [ 9–12 ] Benefiting from these advantages, some SSPP‐based circuit components have been designed and demonstrated experimentally on the spoof plasmonic platform, [ 13–18 ] such as reconfigurable SSPP parametric amplifier, [ 13 ] nonmagnetic spoof plasmonic isolator, [ 14 ] and wireless body sensor networks. [ 15 ] In general, most research efforts on reconfigurable SSPP devices, usually by integrating active chips, are mainly focused on the physical phenomena and the manipulations of surface EM waves in an analog way, neglecting the digital‐programmable potentials.…”

“…[25][26][27][28][29][30][31][32] In order to expand the promising application of digital coding metamaterials, the concept of digital spoof plasmonic metamaterials loaded with active chips has been reported. [33][34][35][36] For example, by manipulating the dispersion behaviors in real time, the amplitude and phase modulations are achieved on an ultrathin corrugated metallic strip loaded with varactors. [33] After that, the amplitude modulation was experimentally verified by controlling the bias voltage applied to varactors loaded on an ultrathin reconfigurable Mach-Zehnder interferometer.…”

“…[33] After that, the amplitude modulation was experimentally verified by controlling the bias voltage applied to varactors loaded on an ultrathin reconfigurable Mach-Zehnder interferometer. [34] In addition, the amplitude and phase modulations were verified by coding the metal and dielectric states of the SSPP unit loaded with PIN diodes. [35,36] However, the literature mentioned above could only achieve pure phase modulation, amplitude modulation, or joint modulations with a certain correlation between amplitude and phase.…”