Abstract
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.
Highlights
The proposed optical escalators made by birefringent material cannot only restore the angle and the position of the reflected light, and preserve the phase since the optical path length is preserved by transformation optics
The range of controllable height is from −3 mm to 3 mm for a device of 21 mm thickness within the visible spectrum, which is far beyond the current capability of metamaterials in terms of that the metamorphosis distance is at the order of 104 wavelength
The conventional method based on natural calcite crystals requires new fabrications of the calcite piece and corresponding change of background refractive index, when there is any change of cloaking size. This schematic can even go beyond dynamic fabless cloak. These features ensure the escalator suffer from no detectable lateral shift during and after the metamorphosis
Summary
Transformation optics has offered an important approach to control electromagnetic fields [1, 2], which can be used to design various amazing optical devices, including invisibility cloaks [3,4,5,6,7,8,9,10,11,12,13,14], beam shifters and splitters [15], wave adapters [16], deep-subwavelength transformers [17] and light concentrators [18, 19]. One can obtain desired birefringence by varying the strength and direction of external forces without changing the device’s configuration (see Fig. 1) This is not attainable even in the use of natural calcite crystals, since the thickness of calcite will require new fabrications and corresponding alteration of the refractive index of the background medium [30]. Our schematic eliminates the use of artificially structured metamaterials, it is of broadband operation and the metamorphosis from elevator to cloak is only completed via the control of external mechanical force. This demonstration of force-loaded transformation offers new perspective in optical manipulation
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