Being invisible ad libitum has long captivated the popular imagination, particularly in terms of safeguarding modern high-end instruments from potential threats. Decades ago, the advent of metamaterials and transformation optics sparked considerable interest in invisibility cloaks, which have been mainly demonstrated in ground and waveguide modalities. However, an omnidirectional flying cloak has not been achieved, primarily due to the challenges associated with dynamic synthesis of metasurface dispersion. We demonstrate an autonomous aeroamphibious invisibility cloak that incorporates a suite of perception, decision, and execution modules, capable of maintaining invisibility amidst kaleidoscopic backgrounds and neutralizing external stimuli. The physical breakthrough lies in the spatiotemporal modulation imparted on tunable metasurfaces to sculpt the scattering field in both space and frequency domains. To intelligently control the spatiotemporal metasurfaces, we introduce a stochastic-evolution learning that automatically aligns with the optimal solution through maximum probabilistic inference. In a fully self-driving experiment, we implement this concept on an unmanned drone and showcase adaptive invisibility in three canonical landscapes—sea, land, and air—with a similarity rate of up to 95%. Our work extends the family of invisibility cloaks to flying modality and inspires other research on material discoveries and homeostatic meta-devices.
Chromatic aberration-free meta-devices (e.g., achromatic meta-devices and abnormal chromatic meta-devices) play an essential role in modern science and technology. However, current efforts suffer the issues of low efficiency, narrow operating band, and limited wavefront manipulation capability. We propose a general strategy to design chromatic aberration-free meta-devices with high-efficiency and ultrabroadband properties, which is realized by satisfying the key criteria of desirable phase dispersion and high reflection amplitudes at the target frequency interval. The phase dispersion is tuned successfully based on a multiresonant Lorentz model, and high reflection is guaranteed by the presence of the metallic ground. As proof of the concept, two microwave meta-devices are designed, fabricated, and experimentally characterized. An achromatic meta-mirror is proposed within 8 to 12 GHz, and another abnormal chromatic meta-mirror can tune the reflection angle as a linear function. Both meta-mirrors exhibit very high efficiencies (85% to 94% in the frequency band). Our findings open a door to realize chromatic aberration-free meta-devices with high efficiency and wideband properties and stimulate the realizations of chromatic aberration-free meta-devices with other functionalities or working at higher frequency.
InP-based back-illuminated modified uni-traveling-carrier photodiodes (MUTC-PDs) with high-speed and highresponsivity are demonstrated using flip-chip technology in this letter. The partially depleted absorption layer with gradual doping and cliff layer are utilized to realize large 3-dB bandwidth. A high responsivity of 0.54 A/W with over 40 GHz large 3-dB bandwidth from a 7-μm-diameter back-illuminated MUTC-PD is achieved. The results demonstrate that the modified design can effectively enhance the internal electric field and concentration gradient, so as to optimize the response speed of the device.
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