Micro/nano optics have the ability to emit, direct, modulate, localize, absorb, and detect light in the subwavelength scale range. Compared with traditional optical devices, micro-nano optical devices have smaller size, higher integration and richer optical functions, showing broader application prospects and higher technical value, and have become an indispensable part of modern integrated optical systems. In terms of performance, micro/nano optics exhibit excellent optical properties such as high resolution, high transmission efficiency and high switching ratio. In terms of manufacturing process, micro-nano optical devices adopt advanced processing technology compatible with semiconductor processes, which not only ensures high production efficiency and accuracy, but also reduces production costs. The development of micro-nano optical devices has greatly promoted the progress of integrated optical technology, making many novel optical phenomena and technologies possible, and thus bringing technological innovation in the fields of optical neural networks, photonic integrated circuits, optical quantum technology, optical communication, biosensing and optical imaging.
Fig.1 Three types of phase change materials and their applications in reconfigurable micro-nano optics.
The optical properties of static micro-nano optical devices are fixed after the completion of their preparation, which limits the expansion of the functionality of the devices to a certain extent, and through the introduction of functional materials (such as liquid crystals, semiconductor materials, two-dimensional materials, flexible materials, phase change materials, etc.) or functional devices (such as heterojunctions, microelectromechanical systems, etc.), the reversible dynamic control of the optical response of micro-nano optical devices can be realized, thus forming reconfigurable micro-nano optical devices. Among them, the reconfigurable optical modulation of the corresponding device is realized due to the concomitant optical properties or shape changes of the material during the phase transformation process, which has the advantages of fast phase change response speed, large number of cycles, high optical contrast caused by phase change and diversified phase change excitation methods, which provides a highly competitive solution for the realization of reconfigurable micro-nano optical devices.
Fig.2. Elemental composition and phase change excitation methods of the three types of phase change materials.
In recent years, Junjie Li's research group at the Institute of Physics, Chinese Academy of Sciences/Beijing National Research Center for Condensed Matter Physics has focused on the design, fabrication, and functional integration of micro-nanophotonics devices, and has made a series of important advances in dynamic light field manipulation based on optical metasurfaces of phase change materials (Advanced Functional Materials 2024,34, 2310626;Laser & Photonics Reviews). 2023，17，2200364；Nanoscale 2020，12, 8758；Applied Physics Letters 2018，113, 231103）。 On this basis, with reference to a large number of literature and the latest research reports, the research group wrote a review article on reconfigurable micro-nano optical devices based on phase change materials, and made a detailed introduction and review of their applications in reconfigurable micro-nano optical devices from the perspective of the properties and phase transformation mechanisms of phase change materials (see Fig. 1).
Fig.3 Schematic diagram of electrical and optical control.
There are three main types of phase change materials introduced in this paper, namely Chalcogenides, transition metal oxides, and shape memory alloys. As shown in Figure 2, the phase change excitation modes of materials include thermal, optical, electrical, mechanical, magnetic field and electrochemical. Among them, electrical control and optical control are better than other phase change control methods in terms of convenience and integration, and are the two most valuable phase change control methods (see Fig. 3). Before and after the phase transition, the dielectric properties of chalcogenide phase change materials and transition metal oxides changed significantly, which was due to the degree of electron delocalization and the change of band structure, respectively, while the shape memory alloys exhibited reconfigurable shape changes based on martensitic phase transitions (Fig. 4).
Fig.4 The physical mechanism of phase transition and the change of material properties caused by phase transition.
Table 1 summarizes the reconfigurable micro-nano optical devices based on phase change materials, mainly including: reconfigurable metasurfaces, reconfigurable on-chip optical devices, tunable optical thin film devices, photodetectors, all-optical switches, tunable metasurface absorbers, tunable terahertz and other ionization components, and reconfigurable bistable optical devices, etc., the working bands of these devices cover ultraviolet, visible, infrared and terahertz bands, and the forms of phase change materials include various forms, including thin film forms and patterned structures. The means to achieve phase change control are mainly focused on electrical control and optical control technology. These devices interact with the incident light in an on-demand or adaptive mode of control to achieve specific optical modulation functions, and play an irreplaceable role in the development of a new generation of micro-nano optical devices and integrated optical systems. Finally, this review summarizes the existing challenges and future development directions of reconfigurable micro-nano optical devices based on phase transition mechanism. In the process of promoting the practical application of reconfigurable micro-nano optical devices, the issues of phase change power consumption, regulation convenience, phase change uniformity, optical signal modulation amplitude and transmission efficiency should be fully considered.
Table 1 Summary of reconfigurable micro-nano optics based on phase change materials.
相关研究成果以“Reconfigurable Micro/Nano-Optical Devices Based on Phase Transitions: From Materials, Mechanisms to Applications”为题，在线发表在期刊。 中国科学院物理研究所博士研究生李晨圣为第一作者，李俊杰研究员和郭海明研究员为本文通讯作者。 该工作得到了国家自然科学基金委员会、中国科学院基础研究领域青年团队计划和北京市科技计划等项目的支持。
Edit: Hanamaki