All dielectric macroscopic cloaks for hiding objects and creating illusions at visible frequencies

Integration of Hybrid Plasmonic Au-BaTiO3 Metamaterial on Silicon Substrates

Silicon integration of nanoscale metamaterials is a crucial step toward low-cost and scalable optical-based integrated circuits. Here, a self-assembled epitaxial Au-BaTiO₃ (Au-BTO) hybrid metamaterial with highly anisotropic optical properties has been integrated on Si substrates. A thin buffer layer stack (<20 nm) of TiN and SrTiO₃ (STO) was applied on Si substrates to ensure the epitaxial growth of the Au-BTO hybrid films. Detailed phase composition and microstructural analyses show excellent crystallinity and epitaxial quality of the Au-BTO films. By varying the film growth conditions, the density and dimension of the Au nanopillars can be tuned effectively, leading to highly tailorable optical properties including tunable localized surface plasmon resonance (LSPR) peak and hyperbolic dispersion shift in the visible and near-infrared regimes. The work highlights the feasibility of integrating epitaxial hybrid oxide-metal plasmonic metamaterials on Si toward future complex Si-based integrated photonics.

Long distance invisibility system to hide dynamic objects with high selectivity

With the development of invisibility technology, invisibility devices have now become more practical, with properties such as working at visible wavelengths, using natural materials, and hiding macroscopic objects. Recently, the cloaking of dynamic objects was experimentally realized using ray-optics. Here, based on a phase retrieval algorithm and phase conjugation technology, we design and fabricate a system to hide dynamic objects that changes at speeds faster than 8 seconds per frame. Different from shell cloaks and carpet-like cloaks, which conceal the entire region covered by the cloak, our system works when the object is at a distance and hides only the selected part of an object when the entire object is within the working area of the system. We experimentally demonstrate the concealment of a millimeter-scale object at different wavelengths. We believe that our work may provide a new approach to hiding objects in real life and may also be applicable in biological imaging and atmospheric imaging.

Directionally hiding objects and creating illusions above a carpet-like device by reflection holography

Realization of a perfect invisibility cloak still challenges the current fabricating technologies. Most experiments, if not all, are hence focused on carpet cloaks because of their relatively low requirements to material properties. Nevertheless, present invisibility carpets are used to hide beneath objects. Here, we report a carpet-like device to directionally conceal objects and further to create illusions above it. The device is fabricated through recording a reflection hologram of objects and is used to produce a time-reversed signal to compensate for the information of the objects and further to create light field of another object so as to realize both functions of hiding the objects and creating illusions, respectively. The carpet-like device can work for macroscopic objects at visible wavelength as the distance between objects and device is at decimeter scale. Our carpet-like device to realizing invisibility and creating illusions may provide a robust way for crucial applications of magic camouflaging and anti-detection etc.

Directionally hiding objects and creating illusions at visible wavelengths by holography

Invisibility devices have attracted considerable attentions in the last decade. In addition to invisibility cloaks, unidirectional invisibility systems such as carpet-like cloaks and parity-time symmetric structures are also inspiring some specific researching interests due to their relatively simplifying design. However, unidirectional invisibility systems worked generally in just one certain illumination direction. Here, based on time-reversal principle, we present the design and fabrication of a kind of all-dielectric device that could directionally cancel objects and create illusions as the illuminating light was from different directions. Our devices were experimentally realized through holographic technology and could work for macroscopic objects with any reasonable size at visible wavelengths, and hence may take directional invisibility technology a big step towards interesting applications ranging from magic camouflaging, directional detection to super-resolution biomedical imaging.

Macroscopic broadband optical escalator with force-loaded transformation optics

Transformation optics enables one to guide and control light at will using metamaterials. However the designed device is deterministic and not flexible for different objects. Based on force-loaded transformation optics we propose a force-induced transformational device, which can realize dynamic escalator metamorphosing continuously between optical elevator and invisibility cloak. This escalator can visually lift up and down the perceived height of a plane fixed in space by controlling the forces loaded in different directions. Or conversely, the escalator can physically lift up and down a plane while visually maintaining the same height to an outside observer. One can quickly adjust this device to the required demand without changing the background index, while the usual transformation cloak will be detectable due to the lateral shift from mismatched background. The schematic is self-adaptive, multi-functional, and free of metamaterial or nanofabrication. Our work opens a new perspective in controlling light dynamically and continuously, empowering unprecedented applications in military cloak, optic communication, holographic imaging, and phase-involved microtechnique.

Design and demonstration of temporal cloaks with and without the time gap

We introduce a Fourier analysis method to design temporal cloaks for hiding events in time domain. The cloaks are constructed with two linear time-invariant filters with different transfer functions, which can create a temporal gap and then closed it orderly, making any events occurring during the gap not detectable outside. We further reveal that even a no-gap temporal cloak can also hide events. All the analytical results are verified by fast Fourier transformation simulations.