With the development of infrared detection, infrared stealth technology is receiving increasing attention. This will require the implementation of multispectral infrared stealth, including infrared laser stealth and thermal stealth. However, the infrared laser stealth with high absorption faces challenges of laser damage. It is still difficult to balance between laser stealth and laser protection. Here, we propose a smart infrared stealth scheme that realizes laser stealth at low energy thresholds and laser protection at high energy thresholds. The conversion ratio between stealth and protection are 0.4 and 0.78, respectively. The proposed smart infrared stealth demonstrates the high performance of infrared stealth (R1.06μm=0.13, R10.6μm=0.03), thermal stealth (ε3-5μm=0.3, ε8-14μm=0.5) and thermal management (ε5-8μm=0.7, ε14-17μm=0.9).
Adaptive thermal camouflage which is bioinspired and used to avoid infrared detection plays a crucial role in the military field. However, compared with mature infrared detection methods, it still has challenges to achieve adaptive thermal camouflage and imaging manipulation of object. In this paper, we experimentally demonstrate a 440-nm-thick Ge2Sb2Te5 (GST) metamaterial with continuous changed average emissivity from 15% to 66% in the wavelength range of 7.5–14 μm. The precise (⪆10 states) and fast (⪅10 ms) manipulation for phase-change character of GST is achieved by laser irradiation. Combining Emissivity Engineering (EE) and Phase Change Materials (PCMs), the proposed metamaterial can be employed to multi-functional thermal camouflage device, which can simultaneously realize some functions including adaptive thermal camouflage, illusion and messaging without changing the structural parameters. The proposed PCM-based thermal camouflage metamaterials have promising potentials for applications in the field of multi-functional thermal camouflage, thermal imaging and thermal management.
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 non-atmospheric window (5–8 μm). However, it still remains challenges for balancing infrared camouflage and thermal management. Here, we theoretically demonstrate inverse design multilayers for infrared camouflage with thermal management. Combining the ideal emission spectrum and genetic algorithm (GA), a multilayer film structure (MFS) containing 9 layers of four materials (SiO2, Ge, ZnS and Au) has been designed. The results reveal the high compatible efficiency (εeff=81%) among thermal camouflage, mid-infrared laser camouflage and thermal management. Therefore, the proposed multilayers are attractive as basic building block of selective emitter, for the development of advanced infrared materials such as radiative cooling, infrared camouflage and thermal emission.
Silicon photonics is becoming the leading technology in photonics for a variety of new applications. However, due to the large volume and high cost of traditional optical devices, they are not suitable for high integration. It is challenging to further improve the integration and performance of silicon photonics. Here, we proposed a power splitter designed by inverse design algorithm has high transmission efficiency and compact structure size, which is helpful to the integration of photonic integrated circuit (PIC). The emergence of inverse design algorithm makes a great breakthrough in the problems existing in optical devices. In recent years, inverse design algorithms have attracted researchers' attention because of their ability to regulate light transmission by changing the refractive index distribution in the subwavelength structure. Direct-binary-search (DBS) algorithm, as the most commonly used inverse design algorithm, is applied to the design of on-chip photonic devices because of its simple working principle and high optimization efficiency. As one of the important components of photonic integrated circuits, on-chip power splitter plays an important role in optical communication system. Power splitters which can achieve any power ratio are widely used in optical interconnect devices. The traditional arbitrary power splitter can achieve different split ratios through different structures, but they can not achieve controllable split ratios in the same device, which is an obstacle to the integration of PIC. Phase change materials have been widely used in controllable photonic devices due to their unique optical properties. We combined the DBS algorithm to program and control the Ge2Sb2Se4Te1 (GSST), divided the whole device into multiple units, and optimized the design of each unit. Finally, the phase distribution in line with the target splitting ratio was obtained, and the high-efficiency and small-size power distributor was realized. A 3D finite-difference time-domain (FDTD) solution was used to simulate the device, and the TE0 mode light from the input waveguide was transmitted through the coupling region to the upper and lower output waveguides. Simulation results show that the device size is only 2.4 × 2.4 um2, and in the wavelength range of 1530 nm-1560 nm, the power split ratio of 1:1.5 and 1:2.5 is achieved. This method is helpful for the development of programmable integrated photonic interconnect devices.
Polarizing beam splitter is designed with a broadband and wide range of incident angle. Polarizing beam splitter designed here is a kind of double periodic subwavelength medium-metal grating, which consisted of silicon dioxide as the substrate, magnesium fluoride (MgF2) as medium material and silver for the grid lines. It has the polarization splitting function of TE reflection and TM transmission. Based on the rigorous coupled-wave analysis(RCWA) and the continuous optimization of the structure parameters, the polarization beam splitter has high polarization conversion efficiency, high extinction ratio and a wide tolerance of incident angle in the near infrared band (1μm − 3μm) .The simulation results show that the reflection efficiency of TE polarized light and the transmission efficiency of TM polarized light are both higher than 96%, and the reflection extinction ratio and transmission extinction ratio are greater than 17dB and 28dB respectively. When the incident angle of incident light is from -80° to 80°, the reflection efficiency of TE polarized light is over 96%; when the incident angle is from -40°to 40°, the transmission efficiency of TM polarized light is over 90%. The reflection extinction ratio exceeds 17dB, and the transmission extinction ratio exceeds 35dB in the incident wavelength of 1550nm.The designed polarizing beam splitter is expected to be used in optical communication, optical storage, optical sensing and other fields for light modulation and control.
Inverse design is one of the most important design methods of nanophotonic devices. In recent years, with the rapid development of deep learning technique and applications, deep learning assisted inverse design method has been introduced into the field of nanophotonic device design. In this work, by combining the direct binary search method with multilayer convolutional neural networks, we present the inverse design of a wavelength demultiplexer which has 1352 design variables. The dropout strategy has been employed to avoid overfitting in training the inverse design model. The simulation results indicate that the trained CNN can both efficiently forward predict the spectrum and inverse design the structure.
Using the principle of Surface Plasmons Polaritons, we propose a graphene broadband terahertz absorption structure that achieves the tunable absorption of electromagnetic waves. In our absorption structure, the method of patterning graphene is used to realize continuous broadband absorption from 0.5THz to 2.1THz. The absorption which is more than 50% reaches 1.1THZ, especially the structure designed here has three plasmonic resonance peaks which above 98% at 0.79THz, 1.18THz and 1.35THz, respectively. In addition, the symmetry in the pattern design consider that our absorption structure is not sensitive to the polarization and incident angle. Due to a series of excellent characteristics of the absorption structure, it may play an important role in the field of aircraft stealth, absorber, and light wave modulation.
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