A review of tunable photonics: Optically active materials and applications from visible to terahertz

Abstract

The next frontier of photonics is evolving into reconfigurable platforms with tunable functions to realize the ubiquitous application. The dynamic control of optical properties of photonics is highly desirable for a plethora of applications, including optical communication, dynamic display, self-adaptive photonics, and multi-spectral camouflage. Recently, to meet the dynamic response over broad optical bands, optically active materials have been integrated with the diverse photonic platforms, typically in the dimension of micro/nanometer scales. Here, we review recent advances in tunable photonics with controlling optical properties from visible to terahertz (THz) spectral range. We propose guidelines for designing tunable photonics in conjunction with optically active materials, inherent in wavelength characteristics. In particular, we devote our review to their potential uses for five different applications: structural coloration, metasurface for flat optics, photonic memory, thermal radiation, and terahertz plasmonics. Finally, we conclude with an outlook on the challenges and prospects of tunable photonics.

Keywords: Applied physics; Materials science; Photonics.

Graphical abstract

Figure 1

Operation mechanisms of tunable photonics and refractive index variation (A) Tunable photonics with optically active material and key operation mechanisms. (B) Refractive indices variation comparison of optically active materials corresponding to each spectral range. (C) Schematic of common types of photonic structures and light-matter interaction divided in photonic quasiparticles and electromagnetic waves, respectively. R, T, and A represent reflection, transmission, and absorption, respectively.

Figure 2

Overview of tunable photonics from visible to THz (A) Frequency and wavelength range and corresponding spectral range from visible to THz. (B) Representative tunable photonics applications corresponding to each spectral range. (ⅰ) Structural color using visible spectral range including tunable color filter, Reproduced with permission from (He et al., 2020), Copyright@2020 The Optical Society, dynamic display, Reproduced with permission from (Hosseini et al., 2014), Copyright@2014 Springer Nature, and adaptive camouflage, Reproduced with permission from (Wang et al., 2016a), Copyright@2016 American Chemical Society. (ⅱ) Metasurface for flat optics based on all of the represented spectral range (i.e., visible to THz) showing the applications of hologram, Reproduced with permission from (Li et al., 2017), Copyright@2017 Springer Nature, metalens, Reproduced with permission from (Shalaginov et al., 2021), Copyright@2021 Springer Nature, and wavefront engineering, Reproduced with permission from (Huang et al., 2016), Copyright@2016 American Chemical Society. (ⅲ) Photonic memory based on NIR and MIR including applications of photonic synapse, Reproduced with permission from (Cheng et al., 2017), Copyright@2017 AAAS and in-memory computing, Reproduced with permission from and (Ríos et al., 2019), Copyright@2019 AAAS. (ⅳ) Thermal radiation based on MIR and FIR spectral range showing applications in infrared regulator, Reproduced with permission from (Gu et al., 2022), Copyright@2022 American Chemical Society, thermal camouflage, Reproduced with permission from (Qu et al., 2018). Copyright@2018 Springer Nature, and self-adaptive radiative cooling, Reproduced with permission from (Tang et al., 2021), Copyright@2021 AAAS. (ⅴ) Terahertz plasmonic-based applications of phase/amplitude modulator, Reproduced with permission from (Gu et al., 2012), Copyright@2012 Springer Nature, and multidimensional manipulation, Reproduced with permission from (Pitchappa et al., 2019), Copyright@2019 John Wiley and Sons.

Figure 3

Structural coloration and dynamic functions (A) Schematic of tunable photonics with optically active materials and dynamic color change. (B) Schematic of GST-225-based tunable color filter shows a crystallinity change between the amorphous and crystalline states (left). Optical image of GST-225-based color filter (right). Reproduced with permission from (Hosseini et al., 2014), Copyright@2014 Springer Nature. (C) Dynamic color display based on polyaniline (PANI) and optical scattering (solid lines) and absorption spectra (dashed lines) for different redox states. Reproduced with permission from (Peng et al., 2019), Copyright@2019 AAAS. (D) Dynamic color display based on IGZO activated by H₂ doping and transmittance spectra. Reproduced with permission from (Kim et al., 2020b), Copyright@2020 The Optical Society. (E) Pixelized addressable color display based on liquid crystal (LCs) with resonance shift. Reproduced with permission from (Franklin et al., 2015), Copyright@2015 Springer Nature. (F) Adaptive coloration with camouflage function based on metal ion deposition using electrodeposition/stripping method. Reproduced with permission from (Wang et al., 2016a), Copyright@2016 American Chemical Society.

Figure 4

Metasurfaces for flat optics with tunable function (A) Schematic of dynamic metasurface based on active meta-atom with the function of tuning amplitude, phase, and polarization. (B) Schematic of meta-hologram based on metasurface coated with PANI for phase tuning. Reproduced with permission from (Kaissner et al., 2021), Copyright@2021 AAAS. (C) Meta-hologram based on LCs by controlling the polarization state of incident light (i.e., tuning between left and right circularly polarized light). Reproduced with permission from (Kim et al., 2020a), Copyright@2020 John Wiley and Sons. (D) Beam steering based on PEDOT:PSS nanoantenna using the optical constant tunable property by applying electric potential. Reproduced with permission from (Karst et al., 2021), Copyright@2021 AAAS. (E) GST-326-based reversibly tunable nanoantenna by designing the structures on a small area of heating electrode for fast phase change. Reproduced with permission from (Wang et al., 2021b), Copyright@2021 Springer Nature. (F) Active metasurface based on large switching volume ability of GSST-2241 meta-atoms. Reproduced with permission from (Zhang et al., 2021), Copyright@2021 Springer Nature. (G) Tunable meta-lens based on GST-326 with the tunability of focal length. Reproduced with permission from (Yin et al., 2017). Copyright@2017 Springer Nature. (H) Reconfigurable metasurface based on light-induced phase change of GST-225 and dynamically tuning the functionality of the phase-change metasurface with SEM image. The scale bar is 10 μm. Reproduced with permission from (Wang et al., 2016b). Copyright@2015 Springer Nature.

Figure 5

Photonic memory and device system (A) Schematic of ultrashort optical pulse to change the phase of active layer. By applying different power to the pulses, the information can write and erase information. There are several types of photonic structures including waveguide, ring resonator, and nanogap. (B) Illustration of the photonic memory cell with pulse shape and corresponding multilevel transmittance change. Reproduced with permission from (Li et al., 2019), Copyright@2019 The Optical Society. (C) A calculating chip-processor that shows optical abacus ability by applying multiple pulses to PCM cells. Reproduced with permission from (Feldmann et al., 2017), Copyright@2017 Springer Nature. (D) Neuronal circuit system consisting of pre-synaptic input and one post-synaptic output connected via PCM synapse. Reproduced with permission from (Feldmann et al., 2019), Copyright@2019 Springer Nature. (E) Normalized transmission measurement of the PCM synapse with change of coupling between ring and waveguide. Reproduced with permission from (Feldmann et al., 2019), Copyright@2019 Springer Nature. (F) Multi-bit, multi-wavelength non-volatile photonic memory enabled by GST-225 based waveguide with different resonating structures. Reproduced with permission from (Ríos et al., 2015), Copyright@2015 Springer Nature. (G) Multi-wavelength write/erase cycling with wavelength selective readout of individual cells. Reproduced with permission from (Ríos et al., 2015), Copyright@2015 Springer Nature.

Figure 6

Tunable photonics based on thermal radiation effect (A) Schematic of tunable thermal radiation by selective emission control. In the graph, the purple-shaded area represents atmospheric transmittance. (B) Mode-tunable active photonic structure which modulates the function between thermal emitter and solar absorber. Reproduced with permission from (Kort-Kamp et al., 2018), Copyright@2018 American Chemical Society. (C) Temperature-adaptive radiative cooler based on W_xV_1-xO₂ which actively changes the function between keeping warm and radiative cooling. Reproduced with permission from (Tang et al., 2021), Copyright@2021 AAAS. (D) Radiative cooling regulating thermochromic smart window based on VO₂ which actively changes the function between keeping warm and radiative cooling. Reproduced with permission from (Wang et al., 2021a), Copyright@2021 AAAS. (E) Thermal camouflage for different background temperatures based on metal/GST-225 resonator. Reproduced with permission from (Qu et al., 2018), Copyright@2018 Springer Nature. (F) Thermal emission controllable graphene sheet by intercalating of ionic liquids, resulting in Fermi level variation. Reproduced with permission from (Salihoglu et al., 2018), Copyright@2018 American Chemical Society.

Figure 7

Tunable photonics for terahertz plasmonic modulation (A) Schematic of tunable terahertz plasmonic structure. (B) Phase/amplitude modulator based on ring-dumbbell composite resonator using VO₂ (left) and SEM image (right). Reproduced with permission from (Zhao et al., 2018), Copyright@2018 American Chemical Society. (C) Volatile and non-volatile state tunable meta-device based on GST-225 (left) and resonance modulation corresponding to different pumping power (right). Reproduced with permission from (Pitchappa et al., 2021a), Copyright@2021 John Wiley and Sons. (D) Multidimensional manipulation based on thermally switchable multilevel nonvolatile states (left) and optically controllable ultrafast resonance switching (right). Reproduced with permission from (Pitchappa et al., 2019), Copyright@2019 John Wiley and Sons. (E) Terahertz dynamic beam splitter based on Si and Al hybrid structure using optical pumping. Reproduced with permission from (Cong et al., 2018), Copyright@2018 Springer Nature. (F) Active metasurface for terahertz hologram based on phase-transition material (VO₂) by applying thermal energy. Reproduced with permission from (Liu et al., 2019b), Copyright@2019 John Wiley and Sons.