RU2744027C1 - Quasi-optical waveguide - Google Patents

Abstract

FIELD: wave transmission.SUBSTANCE: quasi-optical waveguide contains a set of dielectric lenses made in the form of spheres and located coaxially close to each other in the direction of radiation spread. According to the invention, the lenses are made of a material with a relative refractive index that is approximately in the range of more than 1.01 to 1.05.EFFECT: technical result is providing possibility of creating a quasi-optical waveguide characterized by low radiation losses on reflection at the "lens-free space" boundary.1 cl, 3 dwg

Description

The invention relates to microwave and terahertz quasi-optical devices for transmitting waves, in particular to devices for quasi-optical transmission lines - waveguides, and can be used to transfer energy in various sensors for non-destructive testing, biomedical research with spatial superresolution and high energy density.

From the technical literature it is known that for the channeling of microwave radiation are used: metal hollow waveguides; surface wave lines - dielectric waveguides; quasi-optical lines consisting of transmitting and receiving apertures [Submillimeter wave technique. Ed. R.A. Valitova. Sov. Radio, 1969, 480 p., P. 249-298].

In metal hollow waveguides, with an increase in the frequency of radiation of an electromagnetic wave, linear losses rapidly increase. For example, at a wavelength of λ = 0.2 mm, losses increase to 120 dB / m [Submillimeter technique The attenuation in metal waveguides increases in proportion to the frequency to the power of three seconds, which makes it impossible to use them in the terahertz range. In dielectric waveguides, the attenuation increases in proportion to the frequency of radiation of the electromagnetic wave [Technique of submillimeter waves. Ed. R.A. Valitova. Sov. Radio, 1969, 480 p., P. 257].

The total loss of a dielectric waveguide includes losses in the dielectric and in the medium surrounding the waveguide. The most significant are losses in the dielectric material. In contrast to the optical wavelength range in the microwave range, even the best materials have significant losses, the loss tangent is 10 ^-3 -10 ^-4 , which makes it impossible to use them in the terahertz range. Quasi-optical lines - lens ray waveguides [Submillimeter wave technique. Ed. R.A. Valitova. Sov. Radio, 1969, 480 p., P. 274-296] consist of a set of lenses installed in the direction of radiation propagation.

Known is the device of an optical transmission line of millimeter and submillimeter waves [USSR Patent No. 171453, IPC N01R 3/20. Optical transmission line of millimeter and submillimeter waves], consisting of a set of dielectric lenses of an elliptical shape with a quadratic law of thickness, spatially spaced apart at equal distances and located along the direction of wave propagation. The quasi-optical transmission line uses lenses with a diameter of 10-40λ.

It is well known from the technical literature that in the simplest case, with a perpendicular incidence on the interface of an electromagnetic wave, the ratio of the reflected energy to the incident energy is determined:

where n _1,2 represent the refractive indices of the environment and the lens material of the quasi-optical waveguide. Thus, the reflectivity R depends only on the difference in the refractive indices of both media.

The disadvantages of such a device are the complexity of dielectric lenses and the need to accurately maintain the distances between the lenses, large losses in reflection of radiation at the border of the lens - free space, due to the high value of the refractive index of the lens material.

Known device quasi-optical waveguide [RF Patent 163231, IPC N01R], consisting of a set of dielectric half-lenses, spatially spaced between each other at equal distances and located along the direction of wave propagation on a metal substrate.

The disadvantages of this quasi-optical waveguide are the complexity of the device and large losses for reflection of radiation at the boundary of the lens - free space, due to the high value of the refractive index of the lens material of the device.

There is a known device for a quasi-optical transmission line of terahertz waves, containing a set of dielectric lenses, spatially separated from each other and located along the direction of wave propagation, while the lenses are made in the form of a cuboid with a wall size L lying in the range from 0.85λ to 1.3λ, where λ - the wavelength of the terahertz radiation used in the surrounding space, and made of a dielectric with a relative refractive index N / N ₀ (N ₀ is the refractive index of the environment), lying in the range from 1.2 to 1.6, and the distance between the corresponding lenses is chosen in the range from 2L to 3L [RF Patent 2 591282, The device of a quasi-optical transmission line for terahertz waves, ed. Minin I.V., Minin O.V., Publ. 20.07.2016 Bul. No 20].

The disadvantages of a quasi-optical transmission line for terahertz waves are large losses in reflection of radiation at the lens boundary - free space, due to the high refractive index of the lens material of the device, the complexity of the device, due to the need to accurately observe the distances between the lenses and their alignment.

Known quasi-optical planar waveguide containing a set of planar lenses, spatially separated and located along the direction of propagation of radiation and placed on a metal substrate [T. Yoneyama, M. Shimokoriyama, S. Nishida. Lens design for surface wave applications // Electronics Letters, 5th March 1981, V.17, No. 5, p. 210-211].

The disadvantages of a quasi-optical planar waveguide are large losses in reflection of radiation at the lens boundary - free space, due to the high value of the refractive index of the lens material of the device, the complexity of the device, due to the need to accurately observe the distances between the lenses and their alignment.

The closest technical solution chosen as a prototype is an optical radiation channeling device consisting of a radiation source, a plurality of optically transparent spheres located close to each other in the direction of radiation propagation [Patent US N 8554031, G02B 6/00, B01J 19/12. Focusing multimodal optical microprobe devices], while the radiation incident on the sphere forms a "photon jet" with a high spatial resolution, ie. of order or less than λ. Radiation is periodically focused along a chain of spheres, which leads to the appearance of periodic optical modes. To obtain photonic jets, spheres with a diameter from 4λ to 20λ and a high refractive index from 1.4 to 1.71 are used [Seungmoo Yang, V.N. Astratov. Photonic nanojet-induced modes in chains of size disordered microspheres with an attenuation of only 0.08 dB per sphere // Appl. Phys. Lett. 92, 261111 920080].

The disadvantages of such a device are large losses in reflection of radiation at the lens - free space interface.

The objective of the present invention is to create a quasi-optical waveguide characterized by low radiation losses due to reflection at the lens-free space interface.

The technical result is expressed in the fact that the quasi-optical waveguide has a high efficiency of radiation transmission, due to the practically absence of radiation losses due to reflection from the boundaries of the lens - free space.

The task is achieved by the fact that the quasi-optical waveguide contains a set of dielectric lenses made in the form of spheres and located coaxially close to each other in the direction of radiation propagation, according to the invention, the lenses are made of a material with a relative refractive index that is approximately in the range of more than 1.01 up to 1.05. In addition, the lenses can be made in the form of discs and placed on a metal support.

The presence of features that distinguish the invention from the prototype allows us to conclude that it meets the "novelty" criterion.

The applicant has not identified sources of information that would contain information about the influence of the distinctive features of the utility model on the achieved technical result. The specified new properties of the object determine, according to the applicant, the compliance of the utility model with the criterion of "inventive step".

FIG. 1 shows a schematic diagram of a quasi-optical waveguide with spherical lenses.

FIG. 2 shows a schematic diagram of a quasi-optical planar waveguide with disc-shaped lenses.

FIG. 3 shows an example of the result of modeling the propagation of an electromagnetic wave in a quasi-optical waveguide. The lens diameter is 4λ, where λ is the radiation wavelength, the refractive index of the lens material is n = 1.05.

Designations: 1 - incident radiation, 2 - spherical (spherical) lenses, 3 - radiation at the exit of the quasi-optical waveguide, 4 - disc-shaped lenses, 5 - metal substrate.

The device works as follows. When an electromagnetic wave 1 falls on a set of dielectric lenses in the form of spheres 2 or discs 4 located coaxially close to each other in the direction of radiation propagation, the electromagnetic wave penetrates into the dielectric material of the lenses. Since radiation inside lens 2 or lens 4 in the vicinity of their surface propagates with a higher phase velocity than radiation in the center of the lens, the resulting phase incursion between different sections of the incident wave leads to deformation of the radiation wavefront and leads to focusing of radiation (the width of the electromagnetic radiation beam periodically decreases ), which provides the possibility of quasi-optical transmission of electromagnetic energy. In this case, the disc lens 4 can be located on the metal substrate 5.

Such a lens, consisting of at least 2 spherical or disc lenses coaxially located in close proximity to each other, can be considered as an inhomogeneous medium. The refractive index of such a medium n (x) decreases from the axis ( x is the distance to the axis). It was found that the largest (on the axis) refractive index n (0) of the lens should be approximately 1.01-1.05. when the refractive index is less than about 1.01, the focusing of electromagnetic radiation inside the lens material does not occur. With a refractive index greater than about 1.05, radiation losses due to reflection at the lens - free space interface increase and the focusing period in the lens material decreases, which leads to an increase in the radiation path in the lens (equivalent to an increase in lens thickness) and an increase in radiation absorption losses in the material lenses.

It is known from the technical literature that the lens with the minimum refractive index possesses the smallest losses due to reflection of incident electromagnetic radiation. At the indicated refractive indices, the reflection loss is only a few percent.

The materials of the lenses of the quasi-optical waveguide can be used, for example, in the microwave and submillimeter wavelength range: foams, metamaterials, composite materials, for example, expanded polystyrene foam PS-1 with a material density of 0.1 g / cm ³ has a refractive index of 1.05 [Foams Ed. A.A. Moiseeva - M .: Oborongiz, 1960. - 184 pp.], Composites based on fluoroplastic 4 cover the range of n values from 1.05 to 1.40 at a wavelength of 1-2 mm [Measurements on millimeter and submillimeter waves / Ed. R.A. Valitov and B.I. Makarenko - M .: Sov. Radio, 1984. - 296 p.].

In the optical and terahertz wavelength ranges, the refractive index n metamaterials can be more than one, about one, or less than one [Sukhov S.V. Heterogeneous medium with a single refractive index // Bulletin of the Samara Scientific Center. - 2004. -T. 6. - S. 149-154; Sukhov S.V. Nanocomposite material with a single refractive index // Quantum Electronics. - 2005. -T. 35, No. 8. - S. 741-744; Optical cloaking with metamaterials / W. Cai, U. Chettiar, A. Kildishev, V. Shalaev // Nature Photonics. - 2007. - Vol. 7. - P. 224-227; Moiseev SG Active maxwell-garnett composite with the unit refractive index // Physica B: Physics of Condensed Matter. -2010. - Vol. 405. - P. 3042-3045; Moiseev S.G. Optical properties of the Maxwell-Garnett composite medium with nonspherical silver inclusions. Izvestiya VUZov. Physics. - 2009 .-- T. 52, No 11. -S. 7-12; Sergey G. Moiseev Active Maxwell-Garnett composite with the unit refractive index // Physica B 405 (2010) 3042-3045]. For example, a material has been created with a refractive index of 1.025 in the optical wavelength range [Xu A. Zhang, Abhijeet Bagal, Erinn C. Dandley, Junjie Zhao, Christopher J. Oldham, Bae-Ian Wu, Gregory N. Parsons, and Chih-Hao Chang ... Ordered 3D Thin-Shell Nanolattice Materials with Near-Unity Refractive Indices // Adv. Funct. Mater. 2015, 25, 6644-6649].

Thus, the problem of creating a quasi-optical waveguide with minimal radiation losses due to reflection at the lens-0-free space interface is being solved.

Claims (1)

Quasi-optical waveguide, including a set of dielectric lenses made in the form of spheres and located coaxially close to each other in the direction of propagation of radiation, characterized in that the lenses are made of a material with a relative refractive index, which is approximately in the range of more than 1.01 to 1, 05.

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