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We report what we believe to be a novel and unique approach for achieving high-performance and broadband THz phase shifting based on spatially-resolved photoconductivity modulation (SRPM). By changing the illumination area on a hybrid Au-Ge mesa-array (AGMA) structure in front of an indium tin oxide (ITO) layer for local photoconductivity modulation, the phase difference between the incident- and reflected-waves can be tuned nearly continuously with extremely low reflection loss. For a prototype demonstration, a photonically-driven THz phase shifting device based on the WR-5.1 (140-220 GHz) waveguide configuration was designed, modeled and simulated. To achieve phase tuning in the range of 0° to -180° at 180 GHz (band center frequency), a mesa-array consisting of 12 × 6 unit cells (each 105 μm × 105 μm) was designed, and a distancedof 250 μm between the AGMA and ITO was used. The SRPM is accomplished using computer-generated light patterns from a closely-coupled micro-LED array for through-ITO illumination, without the need for any biasing circuitry. Full wave simulation results have shown that pseudo-continuous and broadband phase shifting can be achieved in the entire WR-5.1 band, and a shifting range of 0° to -180° at 180 GHz can be realized as designed. In addition, by using light patterns of different combinations of vertical strips, a fine phase tuning step as small as ∼0.05° can be demonstrated. For all phase tuning states, the simulated reflection loss is generally less than 1 dB with low loss variation. The proposed technology for high-performance THz phase modulation is promising and powerful, while offering far more design flexibility and frequency scalability than the current state-of-the-art since it requires no biasing wires thus eliminating parasitic-related performance degradation. Therefore, this technology is suitable for the development of large-scale THz phased-arrays, reconfigurable reflectarrays, and tunable metasurfaces for dynamic beam steering/forming required in next generation (6G or beyond) wireless communications.
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Broadband electrically tunable VO 2 ‑Metamaterial terahertz switch with suppressed reflection
Abstract Devices designed to dynamically control the transmission, reflection, and absorption of terahertz (THz) radiation are essential for the development of a broad range of THz technologies. A viable approach utilizes materials which undergo an insulator‐to‐metal transition (IMT), switching from transmissive to reflective upon becoming metallic. However, for many applications, it is undesirable to have spurious reflections that can scatter incident light and induce noise to the system. We present an electrically actuated, broadband THz switch which transitions from a transparent state with low reflectivity, to an absorptive state for which both the reflectivity and transmission are strongly suppressed. Our device consists of a patterned high‐resistivity silicon metamaterial layer that provides broadband reflection suppression by matching the impedance of free space. This is integrated with a VO2ground plane, which undergoes an IMT by means of a DC bias applied to an interdigitated electrode. THz time domain spectroscopy measurements reveal an active bandwidth of 700 GHz with suppressed reflection and more than 90% transmission amplitude modulation with a low insertion loss. We utilize finite‐difference time domain (FDTD) simulations in order to examine the loss mechanisms of the device, as well as the sensitivity to polarization and incident angle. This device validates a general approach toward suppressing unwanted reflections in THz modulators and switches which can be easily adapted to a broad array of applications through straightforward modifications of the structural parameters.
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- Award ID(s):
- 1810252
- PAR ID:
- 10457813
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Microwave and Optical Technology Letters
- Volume:
- 62
- Issue:
- 8
- ISSN:
- 0895-2477
- Page Range / eLocation ID:
- p. 2782-2790
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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