Phase-change Material Ge2Sb2Te5 Research Articles

Design of Low-loss Non-volatile Optical Phase Shifter based on Lossy Phase Change Material Ge2Sb2Te5

Design of Low-loss Non-volatile Optical Phase Shifter based on Lossy Phase Change Material Ge2Sb2Te5

Reconfigurable wide-angle broadband terahertz wave antireflection using a non-volatile phase-change material.

Actively wide-angle broadband terahertz (THz) antireflection (AR) coatings with a flexible reconfigurability have a great potential for the development of next-generation versatile THz components and systems with high performance. Here, we present a reconfigurable wide-angle broadband THz AR coating using a phase change material Ge2Sb2Te5 (GST) film, which is based on the impedance matching method. The performance of GST-based AR coating can be effectively achieved by a thermal excitation, exhibiting the complete suppression of unwanted THz-wave reflections for incidence angles from 0∘ to 50∘ in the broad frequency range of 0.1-3.0 THz. Simulation and experimental results show that the GST-based AR coating can efficiently eliminate Fabry-Perot interference caused by unwanted THz-wave reflections from the substrate, thereby significantly improving the performances of THz devices. Moreover, the active AR mechanism of the GST-based coating is investigated, which elucidates the essential role of the phase transition between the amorphous and crystalline phases in changing the conductivity of the film to achieve an impedance matching condition under thermal excitation. Additionally, the non-volatile properties of GST can enable the AR coating to retain a long-term stability for optimal wave-impedance matching without power holding requirements. Our work provides a new, to the best of our knowledge, and promising way for realizing high-performance integrated THz components and systems in the future.

Toward tailored light absorption manipulation by Kerr nonlinear nanoslits within a grating Fabry-Perot cavity coupled with reconfigurable GST225 material

In this paper, we investigate the absorption tunability of a silver plasmonic grating incorporating Kerr-type nonlinear graphene-oxide (GO) nanoslits and Ge2Sb2Te5 (GST225) phase-change material at telecom wavelengths. The linear absorption spectra reveal that the amorphous GST225 grating exhibits two distinct absorption peaks, while half-crystallization leads to a single pronounced peak, and full crystallization results in a redshifted peak with a slightly decreased value. These findings confirm that the crystalline degree of GST225 significantly modulates the absorption characteristics. Upon exposure to a nanosecond Gaussian pulse laser irradiation with appropriate fluences, the electric field confinement within the nanoslits intensifies, particularly at the center of the pulse, leading to a pronounced absorption adjustment due to Kerr nonlinearity. Temporal examination at the L-band wavelength of 1591.5 nm reveals a U-shaped absorption response for both amorphous and crystalline GST225, with a pronounced dip at the pulse’s peak. In the half-crystallized state, the weak linear absorption can be substantially enhanced at both the leading and trailing edges of the pulse, with a dip at the center, illustrating the Kerr nonlinearity within the GO nanoslits. The dynamic behavior of absorption under different laser fluences underscores the potential of this system for high-contrast optical switching. Our results offer insights into the development of reconfigurable optical switches utilizing nonlinear Kerr effects, paving the way for advancements in tunable optical communication technologies.

The effects of Sb/Te ratio on crystallization kinetics in Ge-rich GeSbTe phase-change materials

The effects of Sb/Te ratio on crystallization kinetics in Ge-rich GeSbTe phase-change materials

Giant and reconfigurable vortical dichroism with multi-layer spiral metamaterials

In the photonics orbital angular momentum dimension, the vortical dichroism (VD) of artificial metamaterials at fixed wavelengths has been extensively investigated. However, the challenges of weak and unregulated VD magnitude still limit the development of chiral optics. Herein, we propose multi-layer spiral metamaterials with phase change material Ge2Sb2Te5 (GST), which support giant VD magnitude of −176% in the optical communication band around 1550 nm. Meanwhile, by changing the temperature to control the GST from crystalline to amorphous states, the VD magnitude rapidly decreases to −1%. This large change from extremely giant magnitude to weak magnitude indicates the advantages of reconfigurable VD response. The maximum modulation depth reaches almost 100%. The GST based metamaterials possess excellent switchable capability for VD magnitude without refabricating structures, which is promising in applications for the next generation of chiral optical communication devices.

Metamaterial structure design based on genetic algorithm and phase change material GST for multispectral camouflage

This study proposes a multispectral camouflage tunable multilayer film metamaterial (TMFM) with thermal management function based on genetic algorithm (GA), which is composed of ZnS/YbF3/Ge/Ge2Sb2Te5 (GST)/Au multilayer film. Through numerical analysis, we assess its efficacy in visible-infrared compatibility camouflage and radiative heat dissipation. Within the visible light band, different structural colors can be produced by adjusting the thickness of the ZnS film. The average emissivity within the 3–5 μm and 8–14 μm infrared bands is measured at 0.04 and 0.14, respectively. The low emissivity facilitates effective thermal management. Moreover, an average emissivity of 0.52 within the 5–8 μm range is instrumental in achieving efficient radiation heat dissipation. Laser stealth capability is further enhanced, with an emissivity reaching 0.70 at 10.6 μm. Therefore, this metamaterial structure has broad application prospects in both military and civilian industrial fields.

Optically Controlled Fine-Tuning Phase Shift Cell Based on Thin-Film Ge2Sb2Te5 for Light Beam Phase Modulation

We present the experimental study of free-space optical control of the optical beam phase shift caused by the formation of a layered structure in an elementary controllable cell made of phase-change material Ge2Sb2Te5 subjected to the controlling effect of pulsed laser radiation. The phase change of the signal optical beam passing through the controlled cell from phase-change material relative to the control beam in the Jamin interferometer is demonstrated.

Scattering singularities in Fano-resonant multilayer grating structure with phase-change materials

In non-Hermitian systems, the singularities refer to poles or zeros of the scattering and transfer matrices. Here, we investigate the kinds of singularities in a non-parity-time-symmetric multilayer structure which mainly consists of double layers of silver grating and one layer of phase-change material Ge2Sb2Te5 (GST). When the GST is in its crystalline phase, a unidirectional zero-reflection singularity, i.e., exceptional point (EP) is achieved with the aid of Fano resonance. Interestingly, a coherent perfect absorber (CPA)-laser singularity adjacent to the EP is observed in the Fano peak. Meanwhile, a few CPA singularities exist at other wavelengths. By switching the GST from its crystalline to amorphous phase, the CPA-laser singularity will be absent, and the CPA singularity can be switched to a laser singularity. The scattering spectra near the singularities are sensitive to a tiny perturbation of the gain material and the environmental refractive index. The study is beneficial for making switchable active optical implementations.

Tunable third harmonic generation based on high-Q polarization-controlled hybrid phase-change metasurface

Abstract Dielectric metasurfaces have made significant advancements in the past decade for enhancing light–matter interaction at the nanoscale. Particularly, bound states in the continuum (BICs) based on dielectric metasurfaces have been employed to enhance nonlinear harmonic generation. However, conventional nonlinear metasurfaces are typically fixed in their operating wavelength after fabrication. In this work, we numerically demonstrate tunable third harmonic generation (THG) by integrating a dielectric metasurface with the phase-change material Ge2Sb2Te5 (GST). The hybrid phase-change metasurface can support two BICs with different electromagnetic origins, which are transformed into two high-Q quasi-BICs through the introduction of structural asymmetry. The two quasi-BICs are selectively excited by controlling the polarization of incident light, and their wavelengths are tunable due to the phase transition of GST. Notably, the efficiency of THG is significantly enhanced at the fundamental wavelengths corresponding to the two quasi-BICs, and the operating wavelength for THG enhancement can be dynamically tuned through the GST phase transition. Furthermore, the wavelength of THG enhancement can be further tuned by manipulating the polarization of pump light. Additionally, a high-Q analog of electromagnetically induced transparency is numerically achieved through the interaction between a low-Q Mie resonance and a quasi-BIC mode, which also improves the THG efficiency. The high-Q polarization-controlled hybrid phase-change metasurface holds promise for applications in dynamically tunable nonlinear optical devices.

On-chip guided wave THz photonic switching with a phase change material on a dielectric waveguide encompassed with a novel micro-fins heater

On-chip photonic components, particularly for switching applications, are becoming more and more in demand to create high-density photonic integrated circuits in the THz regime. The nonvolatile switching can meet the requirement of power saving when the complexity of integrated circuits grows in the near future. Here, we propose and analyse the THz wave switching using a nonvolatile phase change material (PCM) Ge2Sb2Te5 (GST) integrated on a broadband THz dielectric waveguide that is encompassed by a novel micro-fins heater. In the proposed device, a small patch of GST of length 1500μm integrated on top of the HRFZ-Si waveguide provides an acceptable insertion loss and high extinction ratio for its broadband operation in the frequency span of 0.5–1.0 THz. Using a novel micro-fins heater, the phase transformation of the GST is carried out through Joule heating. Short electrical pulses of 11 ms and 4μs are found to be capable of raising the temperature of the GST region above its crystallization and re-amorphization temperature, respectively. The corresponding energy consumption for crystallization and re-amorphization is found to be 61.73 mJ and 19.84 mJ, respectively. The switching speed of our reported device is 100 times better than the previously reported metamaterial-based THz photonic switches using PCMs. Since GST is nonvolatile in nature, no continuous pump power is needed to maintain the particular switching state of the proposed device. The work reported here is a step forward for enabling THz photonic switching, and further THz circuits, in guided wave photonic platform using CMOS-compatible materials.

Coordinated multi-band stealth based on phase change materials

With the integrated application of multiple detection technologies, multi-band compatible stealth is crucial to improve the counter-detection capability of targets. However, there are still significant challenges in achieving stealth that is compatible with different bands. This paper presents a wavelength-selective emitter with a structure consisting of a layer composed of a high-temperature-resistant material and a phase change material Ge2Sb2Te5 (GST), and an upper truncated pyramid array composed of TiO2. The structure can transition between “stealthy” and “non-stealthy” states by controlling the phase transition process of the GST. The structure in stealth mode has low reflectivity in the visible (VIS) region, low emissivity in the mid-wave infrared and long-wave infrared region. In addition, it has laser stealth at 1.06 μm and 1.54 μm, and provides radiative cooling in the non-atmospheric window (5–8 μm). The dipole resonance formed by TiO2 on the side gives the structure lower reflectivity in the VIS band and at two laser wavelengths. The high emission in the non-atmospheric window is mainly attributed to the Fabry-Perot resonance supported in the structure. In addition, the effects of incidence angle and temperature on the stealth performance of the structure are investigated. This research has promising applications in the field of multi-band compatible stealth.

Ultra-low loss compact active TM mode pass polarizer using phase change material in silicon waveguide

An active low-loss transverse magnetic (TM) pass polarizer, based on the phase change material (Ge2Sb2Te5), is proposed. The proposed polarizer is based on silicon-on-insulator technology that consists of a silicon waveguide that incorporates a thin layer of Si3N4 placed in-between GST. Enhancing the interaction between light and GST is achieved by strategically placing a double-layer GST adjacent to the slot waveguide. The polarizer’s tunability, on the other hand, depends on the shift in the refractive index (RI) of GST as it transitions between its crystalline and amorphous phases. By optimizing the structure, the polarizer exhibits negligible loss for both modes in the amorphous phase, and with the change of phase to crystalline, the loss of TE mode is more than 8 dB. In contrast, the loss of TM is less than 0.05 dB with a high ER of 21.82 dB, propagation length of 79.89 µm and Figure of merit reaches up to 108 at 1550 nm. Due to the combination of these performance parameters, the suggested active TM pass polarizer is an appealing and effective device for various photonic applications. In addition, the fabrication technique of the proposed active TM pass polarizer is explained.

Tunable high-order harmonic generation in GeSbTe nano-films

Abstract High-order harmonic generation (HHG) in solids opens new frontiers in ultrafast spectroscopy of carrier and field dynamics in condensed matter, picometer resolution structural lattice characterization and designing compact platforms for attosecond pulse sources. Nanoscale structuring of solid surfaces provides a powerful tool for controlling the spatial characteristics and efficiency of the harmonic emission. Here we study HHG in a prototypical phase-change material Ge2Sb2Te5 (GST). In this material the crystal phase can be reversibly changed between a crystalline and amorphous phase by light or electric current mediated methods. We show that optical phase-switching is fully reversible and allows for dynamic control of harmonic emission. This introduces GST as new addition to materials that enable flexible metasurfaces and photonic structures that can be integrated in devices and allow for ultrafast optical control.

Thermally Controlled Broadband Ge2Sb2Te5-Based Metamaterial Absorber for Imaging Applications

In this paper, we theoretically and numerically demonstrate a thermally controlled broadband absorber based on the phase change material Ge2Sb2Te5 (GST). When GST operates in the amorphous state, the proposed metamaterial acts as a broadband nearly perfect absorber. The absorption can reach more than 90% in the wavelength range from 0.9 to 1.41 μm. As an application of the GST-based metamaterial absorber, the near-field imaging effect is achieved by using the intensity difference of optical absorption. Moreover, the thermally controlled switchable imaging can be performed by changing the phase transition characteristics of GST, and the imaging quality and contrast can be adjusted by changing the geometrical parameters. This designed metamaterial may have potential applications in near-infrared temperature control imaging, optical encryption, and information hiding.

Metasurface with all-optical tunability for spatially-resolved and multilevel thermal radiation

Abstract Manipulating the thermal emission in the infrared (IR) range significantly impacts both fundamental scientific research and various technological applications, including IR thermal camouflage, information encryption, and radiative cooling. While prior research has put forth numerous materials and structures for these objectives, the significant challenge lies in attaining spatially resolved and dynamically multilevel control over their thermal emissions. In this study, a one-step ultrafast laser writing technique is experimentally demonstrated to achieve position-selective control over thermal emission based on the phase-change material Ge2Sb2Te5 (GST). Ultrafast laser writing technique enables direct fabrication and manipulation of laser-induced crystalline micro/nano-structures on GST films. Thermal emission can be precisely controlled by adjusting the pulse energy of the ultrafast laser, achieving a high thermal emissivity modulation precision of 0.0014. By controlling thermal emission, the ultrafast laser writing technique enables multilevel patterned processing. This provides a promising approach for multilevel IR thermal camouflage, which is demonstrated with emissivity-modulated GST emitters. Remarkably, ultrafast laser-induced crystalline micro/nano-structures display geometric grating features, resulting in a diffraction-based structural color effect. This study demonstrates the effective use of laser-printed patterns for storing information in both visible and infrared spectrum.

Design and validate a wide-bandwidth, high-performance tunable metamaterial based on cultural-innovation shell materials and its sensing applications

The application of metamaterials in controllable thermal emission devices is an interesting field. However, most of the demonstrated thermal emitters required continuous consumption of external energy (electrical or thermal) to provide an effective thermal emissivity. Here, a metamaterial containing phase change materials Ge2Sb2Te5 (GST) and shell materials with controllable thermal emission power was proposed and measured. Based on the completely amorphous state of the GST layer, an emissivity of 0.212 at wavelength 7.11 μm was achieved by this this metamaterial, while a thermal emission band (with an average amplitude of 0.857 and a bandwidth of 6.16 μm) was excited for the crystalline state. Moreover, numerous thermal emission states were excited by this metamaterial based on the intermediate states between completely amorphous and crystalline states of the GST layer. Tunability of the thermal emission window was obtained by this metamaterial sample. The temperature sensitivity of this metamaterial thermal emitter was 341 nm °C−1. By increasing the thickness of the GST or shell layers, the thermal emission performance of the metamaterial was enhanced. Since the phase transition of GST does not require the continuous consumption of external energy, the metamaterial has the potential to be used in the development of low-power heat emitters, as well as temperature sensors.

Medium-range structural order in amorphous Ge2Sb2Te5 phase change material

The crystallization rate is an important factor for the application of phase change materials as memory devices, which, thus, motivates a strong interest in the underlying crystallization processes. We analyzed the crystallization kinetics of as-deposited amorphous Ge2Sb2Te5 by differential scanning calorimetry, revealing that the thermal treatment below the crystallization onset temperature effectively enhances the crystallization rate compared to the as-deposited samples. Variable resolution fluctuation electron microscopy was carried out to characterize the corresponding amorphous structure of the as-deposited films and the differently annealed states regarding their medium-range order (MRO). As a result, relatively large MRO correlation lengths in the range of 3–4 nm were observed, whereas the MRO volume fraction doubled after longer annealing treatments, demonstrating the importance of MRO and MRO tuning for optimizing the properties of amorphous phase change materials. The increased volume fraction of the MRO seems to also favor an increased nanoindentation hardness.

Dynamic and Polarization-Independent Wavefront Control Based on Hybrid Topological Metasurfaces.

Exceptional points (EPs), known as non-Hermitian singularities, have been observed and investigated in parity-time symmetric metasurfaces. However, the chirality and tunability in non-Hermitian metasurfaces still need to be explored. Here, we propose a dynamic topological metasurface with the meta-atom consisting of two orthogonally oriented nanorods, which are placed on the phase change material Ge2Sb2Te5 (GST) and SiO2 dielectric layer, respectively. When GST is converted from the amorphous state (a-GST) to the crystalline state (c-GST), an EP can be dynamically switched from the "ON" state to the "OFF" state in a parameter space. Moreover, based on the topologically protected phase and amplitude modulations of the cross-polarization component, the phase-only hologram and amplitude-only hologram are engineered in the a-GST case and concealed in the c-GST case. Finally, we explore the 2D-chiral symmetry of meta-atoms and further propose two spin-selective meta-deflectors and a hybrid meta-deflector operating with arbitrary polarizations. The GST-based hybrid metasurface offers richer possibilities to realize various wavefront controls.

Actively Reconfigurable Valley Topological Edge and Corner States in Photonic Crystals Based on Phase Change Material Ge2Sb2Te5

Actively Reconfigurable Valley Topological Edge and Corner States in Photonic Crystals Based on Phase Change Material Ge2Sb2Te5

Realization of a photoswitchable anapole metasurface based on phase change material Ge2Sb2Te5

The electromagnetic anapole mode originates from the phase cancellation interference between the far-field radiation of an oscillating electric dipole moment and toroidal dipole moment, which presents a radiation-free state of light while enhancing the near-field, and has potential applications in micro- and nanophotonics. The active control of the anapole is crucial for the design and realization of tunable photonic devices. In this paper, we realize dynamic tuning of an anapole metasurface and metasurface optical switching based on the phase change material Ge2Sb2Te5 (GST). By utilizing the destructive interference of the electric dipole moment and ring dipole moment, we design the non-radiative anapole mode. At the same time, we introduce the phase change material GST to dynamically regulate the intensity and position of the far-field scattering, electric field, and transmission spectra, and to realize the transition from anapole mode to electric dipole mode. At the same time, the modulation of the transmission spectrum by the metasurface after the addition of GST film is achieved. A relative transmission modulation of 640.62% is achieved. Our study provides ideas for realizing effective active modulation of active micro- and nanophotonic devices, and promotes active modulation of active micro- and nanophotonic devices in lasers and filters and potential applications in dynamic near-field imaging.