Illusion optics

Last updated February 16, 2024

Illusion optics is an electromagnetic theory that can change the optical appearance of an object to be exactly like that of another virtual object, i.e. an illusion, such as turning the look of an apple into that of a banana. Invisibility is a special case of illusion optics, which turns objects into illusions of free space. The concept and numerical proof of illusion optics was proposed in 2009 based on transformation optics in the field of metamaterials.^[1] It is a scientific disproof of the idiom 'Seeing is Believing'.^[2]

Illusion optics proves that the optical responses or properties of a space containing any objects can be changed to be exactly those of a virtual space but containing arbitrary virtual objects (illusions) by using a passive illusion optics device composed of materials or metamaterials with specific parameters and shape. For example, a dielectric spoon was numerically shown to exhibit the scattering properties of a metallic cup by using an illusion optics device in the seminal paper.^[1] Such illusion effects do not rely on the direction and form of incident waves. However, due to dispersion limitation of specific material parameters, the functionality of illusion optics device only works in a narrow band of frequency.

Difference with optical illusions

Unlike optical illusions that utilize the misinterpretation of the human brain to create illusionary perception different from the physical measurement, illusion optics changes the optical response or properties of objects. Illusion optic devices make these changes happen. Although both these terms deal with illusions, Illusion optics deal with the refraction and reflection of light, whereas while optical illusions are basically mind tricks.

History

Illusion optics was recorded in 1968 when Soviet physicist Victor Veselago discovered that he can make objects appear in different areas through negatively refracting flat slab.^[2] When light is negatively refracted, the light is directed towards the direction it entered and deflected away from the line of refraction. Normal refraction occurs when light passes through the line of refraction. Veselago used this theory to work the slab into a lens, which he recorded in his experiments. He discovered that unlike a normal lens, the objects resolution does not depend on the limits of the wavelengths passing through the lens. Veselago's work has been more prominent in recent years due to the advancement in metamaterials, which are engineered materials that have special internal physical properties and have the ability to negatively refract light.

Devices

An illusion device is how illusion optics works—without a device there is no way to define how light is refracted and deflected. Based on a study on circular objects with illusion optic properties, (i.e. negative refraction indexes) there are three basics of an illusion device: the invisibility cloak, real object, and illusion object.^[3] The invisibility cloak is basically the medium on which light waves refract. Invisibility cloaks allow for an object to be undetected while confined in the area of the cloak. In other words, the viewer does not see the real object. In illusion optics, devices are not limited to only invisibility cloaks. For example, in Veselago's experiments, and lens was used to steer eyes away from the real object and direct them towards the illusion object. The real object refers to any object that is being refracted upon. In this case, while the real object is under the invisibility cloak, light waves are directed around it so the viewer only sees past the cloak. In Veselago's experiments, the real object is being refracted so the viewer sees a mirrored view of it. The illusion object is how the light waves come together and produces what the viewer sees as “normal.” The invisibility cloak refracts the reflected background light around the object and directs it into the viewer. The viewer only perceives there to be a background. With Veselago's experiments, the illusion object is displayed, but is only an image and is not the real object.

Metamaterials

Artificial metamaterials are important to how illusion optic devices are created. The properties of these materials allow it to bend light waves negatively, so as to have negative permittivity and negative permeability.^[4] There are two pieces of metamaterials which hold different properties: the complementary medium and the restoring medium. The complementary medium is the illusion media used to scatter wavelengths away from the object that is being refracted. The restoring medium focuses waves and directs scattered waves together. Transformation optics is an important to creating metamaterials. The intermolecular geometry used in this field is crucial to creating the material properties.

Related Research Articles

<span class="mw-page-title-main">Optics</span> Branch of physics that studies light

Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light. Light is a type of electromagnetic radiation, and other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.

A cloaking device is a hypothetical or fictional stealth technology that can cause objects, such as spaceships or individuals, to be partially or wholly invisible to parts of the electromagnetic (EM) spectrum. Fictional cloaking devices have been used as plot devices in various media for many years.

Invisibility is the state of an object that cannot be seen. An object in this state is said to be invisible. The phenomenon is studied by physics and perceptual psychology.

Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.

A metamaterial is any material engineered to have a property that is rarely observed in naturally occurring materials. They are made from assemblies of multiple elements fashioned from composite materials such as metals and plastics. These materials are usually arranged in repeating patterns, at scales that are smaller than the wavelengths of the phenomena they influence. Metamaterials derive their properties not from the properties of the base materials, but from their newly designed structures. Their precise shape, geometry, size, orientation and arrangement gives them their smart properties capable of manipulating electromagnetic waves: by blocking, absorbing, enhancing, or bending waves, to achieve benefits that go beyond what is possible with conventional materials.

Negative refraction is the electromagnetic phenomenon where light rays become refracted at an interface that is opposite to their more commonly observed positive refractive properties. Negative refraction can be obtained by using a metamaterial which has been designed to achieve a negative value for (electric) permittivity (ε) and (magnetic) permeability (μ); in such cases the material can be assigned a negative refractive index. Such materials are sometimes called "double negative" materials.

A superlens, or super lens, is a lens which uses metamaterials to go beyond the diffraction limit. The diffraction limit is a feature of conventional lenses and microscopes that limits the fineness of their resolution depending on the illumination wavelength and the numerical aperture (NA) of the objective lens. Many lens designs have been proposed that go beyond the diffraction limit in some way, but constraints and obstacles face each of them.

A cloak of invisibility is an item that prevents the wearer from being seen. In folklore, mythology and fairy tales, a cloak of invisibility appears either as a magical item used by duplicitous characters or an item worn by a hero to fulfill a quest. It is a common theme in Welsh and Germanic folklore, and may originate with the cap of invisibility seen in ancient Greek myths. The motif falls under "D1361.12 magic cloak of invisibility" in the Stith Thompson motif index scheme.

$<span class="mw-page-title-main">Negative-index metamaterial</span> Material with a negative refractive index$

Negative-index metamaterial or negative-index material (NIM) is a metamaterial whose refractive index for an electromagnetic wave has a negative value over some frequency range.

A terahertz metamaterial is a class of composite metamaterials designed to interact at terahertz (THz) frequencies. The terahertz frequency range used in materials research is usually defined as 0.1 to 10 THz.

An acoustic metamaterial, sonic crystal, or phononic crystal is a material designed to control, direct, and manipulate sound waves or phonons in gases, liquids, and solids. Sound wave control is accomplished through manipulating parameters such as the bulk modulus β, density ρ, and chirality. They can be engineered to either transmit, or trap and amplify sound waves at certain frequencies. In the latter case, the material is an acoustic resonator.

A photonic metamaterial (PM), also known as an optical metamaterial, is a type of electromagnetic metamaterial, that interacts with light, covering terahertz (THz), infrared (IR) or visible wavelengths. The materials employ a periodic, cellular structure.

A nonlinear metamaterial is an artificially constructed material that can exhibit properties not yet found in nature. Its response to electromagnetic radiation can be characterized by its permittivity and material permeability. The product of the permittivity and permeability results in the refractive index. Unlike natural materials, nonlinear metamaterials can produce a negative refractive index. These can also produce a more pronounced nonlinear response than naturally occurring materials.

Metamaterial cloaking is the usage of metamaterials in an invisibility cloak. This is accomplished by manipulating the paths traversed by light through a novel optical material. Metamaterials direct and control the propagation and transmission of specified parts of the light spectrum and demonstrate the potential to render an object seemingly invisible. Metamaterial cloaking, based on transformation optics, describes the process of shielding something from view by controlling electromagnetic radiation. Objects in the defined location are still present, but incident waves are guided around them without being affected by the object itself.

The history of metamaterials begins with artificial dielectrics in microwave engineering as it developed just after World War II. Yet, there are seminal explorations of artificial materials for manipulating electromagnetic waves at the end of the 19th century. Hence, the history of metamaterials is essentially a history of developing certain types of manufactured materials, which interact at radio frequency, microwave, and later optical frequencies.

Theories of cloaking discusses various theories based on science and research, for producing an electromagnetic cloaking device. Theories presented employ transformation optics, event cloaking, dipolar scattering cancellation, tunneling light transmittance, sensors and active sources, and acoustic cloaking.

Transformation optics is a branch of optics which applies metamaterials to produce spatial variations, derived from coordinate transformations, which can direct chosen bandwidths of electromagnetic radiation. This can allow for the construction of new composite artificial devices, which probably could not exist without metamaterials and coordinate transformation. Computing power that became available in the late 1990s enables prescribed quantitative values for the permittivity and permeability, the constitutive parameters, which produce localized spatial variations. The aggregate value of all the constitutive parameters produces an effective value, which yields the intended or desired results.

A flat lens is a lens whose flat shape allows it to provide distortion-free imaging, potentially with arbitrarily-large apertures. The term is also used to refer to other lenses that provide a negative index of refraction. Flat lenses require a refractive index close to −1 over a broad angular range. In recent years, flat lenses based on metasurfaces were also demonstrated.

A plasmonic metamaterial is a metamaterial that uses surface plasmons to achieve optical properties not seen in nature. Plasmons are produced from the interaction of light with metal-dielectric materials. Under specific conditions, the incident light couples with the surface plasmons to create self-sustaining, propagating electromagnetic waves known as surface plasmon polaritons (SPPs). Once launched, the SPPs ripple along the metal-dielectric interface. Compared with the incident light, the SPPs can be much shorter in wavelength.

Sergei Anatolyevich Tretyakov is a Russian-Finnish scientist, focused in electromagnetic field theory, complex media electromagnetics and microwave engineering. He is currently a professor at Department of Electronics and Nanoengineering, Aalto University, Finland. His main research area in recent years is metamaterials and metasurfaces from fundamentals to applications. He was the president of the European Virtual Institute for Artificial Electromagnetic Materials and Metamaterials and general chair of the Metamaterials Congresses from 2007 to 2013. He is a fellow/member of many scientific associations such as IEEE, URSI, the Electromagnetics Academy, and OSA. He is also an Honorary Doctor of Francisk Skorina Gomel State University.

References

1 2 Lai, Y.; Ng, J.; Chen, H. Y.; Han, D. Z.; Xiao, J. J.; Zhang, Z. Q.; Chan, C. T. (2009). "Illusion Optics: The Optical Transformation of an Object into Another Object". Physical Review Letters 102 (25): 253902. arXiv : 0905.1484. doi : 10.1103/PhysRevLett.102.253902.
1 2 Pendry, J. (2009). "Optics: All smoke and metamaterials". Nature 460: 579. doi : 10.1038/460579a.
↑ Cojocaru, E. (2010). Illusion Devices with Internal or External Circular Objects Designed by the Coordinate Transformation Method. Journal of Electromagnetic Waves & Applications, 24(16), 2309-2317. doi : 10.1163/156939310793699091
↑ Wei Xiang, J., Hui Feng, M., Qiang, C., & Tie Jun, C. (2010). Illusion media: Generating virtual objects using realizable metamaterials. Applied Physics Letters, 96(12), 121910. doi : 10.1063/1.3371716

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[Lai-1] 1 2 Lai, Y.; Ng, J.; Chen, H. Y.; Han, D. Z.; Xiao, J. J.; Zhang, Z. Q.; Chan, C. T. (2009). "Illusion Optics: The Optical Transformation of an Object into Another Object". Physical Review Letters 102 (25): 253902. arXiv : 0905.1484. doi : 10.1103/PhysRevLett.102.253902.

[Pendry-2] 1 2 Pendry, J. (2009). "Optics: All smoke and metamaterials". Nature 460: 579. doi : 10.1038/460579a.

[Coj-3] Cojocaru, E. (2010). Illusion Devices with Internal or External Circular Objects Designed by the Coordinate Transformation Method. Journal of Electromagnetic Waves & Applications, 24(16), 2309-2317. doi : 10.1163/156939310793699091

[4] Wei Xiang, J., Hui Feng, M., Qiang, C., & Tie Jun, C. (2010). Illusion media: Generating virtual objects using realizable metamaterials. Applied Physics Letters, 96(12), 121910. doi : 10.1063/1.3371716

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