A plasmonic refractive index (RI) sensor based on metal-insulator-metal (MIM) waveguide coupled with concentric double rings resonator (CDRR) is proposed and investigated numerically. Utilizing the novel supermodes of the CDRR, the FWHM of the resonant wavelength can be modulated, and a sensitivity of 1060 nm/RIU with high figure of merit (FOM) 203.8 is realized in the near-infrared region. The unordinary modes, as well as the influence of structure parameters on the sensing performance, are also discussed. Such plasmonic sensor with simple framework and high optical resolution could be applied to on-chip sensing systems and integrated optical circuits. Besides, the special cases of bio-sensing and triple rings are also discussed.

Infrared camouflage is an effective technique to avoid many kinds of target detection by detectors in the infrared band. For a high‐temperature environment, thermal management of selective emission is crucial to dissipate heat in the mid‐infrared non‐atmospheric window (5–8 μm). However, it still remains challenges for balancing infrared camouflage and thermal management. Here, we experimentally demonstrate a multilayer film structure (MFS) for infrared camouflage with thermal management. Combining the ideal emission spectrum and genetic algorithm (GA), the inverse‐design MFS containing 7 layers of five materials (SiO ₂ , Ge, ZnS, Pt and Au) has been designed. Based on the hierarchical metamaterial, the optimized MFS has high performance of infrared camouflage to against the lidar detection in the near‐infrared band. The experimental results reveal the high compatible efficiency among thermal camouflage ( ε _3–5μm = 0.21, ε _8–14μm = 0.16), laser stealth ( ε _1.06μm = 0.64, ε _1.55μm = 0.90, ε _10.6μm = 0.76) and thermal management ( ε _5–8μm = 0.54). Therefore, the proposed MFSs are attractive as basic building block of selective emitter, for the application of advanced photonics such as radiative cooling, infrared camouflage, and thermal emission.

Metasurfaces draw everyone’s attention because they can precisely control the phase, amplitude and polarization of emergent light to achieve light field control in recent years. As one of the most practicable devices among the many applications of metasurface, metalens can extremely reduce the size as well as complexity of optical systems and realizes the higher optical quality compared with conventional lens. So it will be very potential to use metalens in integration systems to reaching higher integration and efficiency. In addition, dynamic control is always desirable in optical systems. In this work, we firstly design a near-infrared tunable metalens treating phase change materials as the meta-atoms which makes the tunable metalens become more compact. At designed wavelength of 1.55 μm, the focusing efficiency of our amorphous metalens is more than 16 times of the efficiency when it works at crystalline state, and its focal length can stay almost unchanged when the GST state is switched. The broadband performance of the metalens is also confirmed. This work may bring some good opportunities for the revolution of the next generation tunable integrated optics.

Adiabatic waveguide taper and on‐chip wavelength demultiplexer are the key components of photonic integrated circuits. However, these two kinds of devices which were designed by the traditional semi‐analytic methods or the brute‐force search methods usually have large size. Here, based on the regularized digital metamaterials, a two‐channel focused wavelength demultiplexer with a footprint of 2.4 × 10 μm ² has been proposed. The designed demultiplexer can directly connect to a grating coupler under the absence of a long adiabatic waveguide taper. The objective first method and the modified steepest descent method are used to design the demultiplexer which splits 1520 nm and 1580 nm light. Experimental results show that the insertion loss of the upper (lower) channel of the demultiplexer is −1.77 dB (−2.10 dB) and the crosstalk is −25.17 dB (−12.14 dB). Besides, the simulation results indicate that the fabrication tolerance of the device can reach ±20 nm in etching depth and ±10 nm in plane size changing. Benefitted from the extensibility of the design method, other types of ultra‐compact “focused” devices, like mode splitters, mode converters, and power splitters can also be designed. Most importantly, this design method can be used to design devices with more complicated functionalities, such as multi‐channel focused wavelength demultiplexers.

Infrared (IR) stealth with thermal management is highly desirable in military applications and astronomy. However, developing selective IR emitters with properties suitable for IR stealth and thermal management is challenging. In this study, we present the theoretical framework for a selective emitter based on an inverse-designed metasurface for IR stealth with thermal management. The emitter comprises an inverse-designed gold grating, a Ge₂Sb₂Te₅ (GST) dielectric layer, and a gold reflective layer. The hat-like function, which describes an ideal thermal selective emitter, is involved in the inverse design algorithm. The emitter exhibits high performance in IR stealth with thermal management, with the low emissivity (ɛ_{3–5 µm} =0.17; ɛ_{8–14 µm} =0.16) for dual-band atmospheric transmission windows and high emissivity (ɛ_{5–8 µm} =0.85) for non-atmospheric windows. Moreover, the proposed selective emitter can realize tunable control of thermal radiation in the wavelength range of 3–14 µm by changing the crystallization fraction of GST. In addition, the polarization-insensitive structure supports strong selective emission at large angles (60°). Thus, the selective emitter has potential for IR stealth, thermal imaging, and mid-infrared multifunctional equipment.