RU2756882C1 - Photon jet shaping device - Google Patents

Abstract

FIELD: dielectric focusing devices.

SUBSTANCE: device can be used as a dielectric focusing device, in particular, for focusing electromagnetic radiation into a local area with subdiffraction dimensions. A device for forming a photonic jet consists of a radiation source and a dielectric particle with a characteristic size comparable to the wavelength λ of the radiation used. The particle is made in the form of a cylinder, and the radiation falls on its flat end, located perpendicular to the incident radiation.

The particle is formed by an array of coaxial and successively located hollow cones at a distance of no more than 0.5λ from each other and with a cone opening angle ranging from about 88 to 112 degrees, and the cones are made of a material that reflects incident radiation.

EFFECT: creation of a device for focusing a photon jet with a constant value of the required relative refractive index at various values ​​of the refractive index of the environment.

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Description

The invention relates to the field of optical instrumentation, and more precisely to dielectric focusing devices designed, in particular, for focusing electromagnetic radiation into a local area with subdiffraction dimensions and can be used for focusing elastic waves into a focal area with transverse dimensions less than the diffraction limit.

A device for the formation of a photon jet with superresolution properties is known, consisting of a radiation source and a weakly absorbing dielectric particle with a diameter comparable to the wavelength of the incident radiation and located along the direction of radiation propagation [Heints Yu.E., Zemlyanoye A.A., Panina E. TO. Comparative analysis of spatial shapes of photonic jets from spherical dielectric microparticles // Optics of the atmosphere and ocean. 2012. T. 25, No. 5, S. 417-424]. In this case, the dielectric particle is made in the form of a spheroid.

A photon jet arises in the area of the shadow surface of dielectric microspherical particles - in the so-called. near diffraction zone - and is characterized by strong spatial localization and high intensity of the optical field in the focusing area. The spatial resolution of the photonic jet reaches a value of the order of λ / 4-λ / 3, where λ is the wavelength of the radiation used. Analogs of a photonic jet are formed in the radio and acoustic ranges. The concept of an acoustojet as an analogue of a photonic jet in optics was first introduced in [I.V. Minin and O.V. Minin, Acoustojet: acoustic analogue of photonic jet phenomenon, arXiv: 1604.08146 (2016); O.V. Minin and I.V. Minin, Acoustic analogue of photonic jet phenomenon based on penetrable 3D particle // Opt. Quant. Electron. 49, 54 (2017); J.H. Lopes, J.P. Leo-Neto, I.V. Minin, O.V. Minin, a & G.T. Silva, A theoretical analysis of acoustic jets // ICA2016, 0943, (2016)].

Acoustically this is an area of increased concentration of acoustic energy with high (subwavelength) spatial resolution, which appears directly on the shadow side of a meso-sized sound-conducting particle.

The known device generates a photon jet along the direction of incidence of radiation in the "pass through" mode (ie, the region of formation of the photon jet is located on the opposite side of the dielectric particle relative to the radiation source).

Later, the possibility of obtaining photonic nanojets was studied for dielectric axisymmetric bodies, for example, elliptical nanoparticles [IV Minin, OV Minin. Quasi-optics: modern development trends - Novosibirsk: SGUGiT, 2015. - 163 p .; T. Jalalia and D. Erni. Highly confined photonic nanojet from elliptical particles // Journal of Modern Optics, Vol. 61, No. 13, 1069-1076 (2014).], As well as hemispheres [Cheng-Yang Liu. Photonic nanojet shaping of dielectric non-spherical microparticles // Physica E 64 (2014), pp. 23-28.], Discs [C-Y. Liu and C-C. Li. Photonic nanojet induced modes generated by a chain of dielectric microdisks. Optik 127, 267-273 (2016).], Cylinder-sphere [Jinlong Zhu and Lynford L. Goddard. Spatial control of photonic nanojets // Optics Express, Vol. 24, No. 26, 2016, 30445].

It was also found that photonic jets can be formed by asymmetric mesoscale dielectric particles, for example, a cube, a truncated ball, a pyramid, a truncated pyramid, a prism, a three-dimensional hexagon, etc. [I.V. Minin and O.V. Minin. Diffractive optics and nanophotonics: Resolution below the diffraction limit, Springer, 2016 http://www.springer.com/us/book/9783319242514#aboutBook; V. Pacheco-Pena, M. Beruete, I.V. Minin and O.V. Minin. Terajets produced by 3D dielectric cuboids. Appl. Phys. Lett. 105, 084102 (2014); I.V. Minin, O.V. Minin and Geintz Y.E. Localized EM and photonic jets from non-spherical and non-symmetrical dielectric mesoscale objects: brief review. Annalen der Physik (AdP), May 2015 DOI: 10.1002 / andp.201500132; Yu. E. Geintz, A.A. Zemlyanov and E. K. Panina. Photonic Nanonanojets from Nonspherical Dielectric Microparticles. Russian Physics Journal 58, 904-910 (2015); Yu. E. Geints, A.A. Zemlyanov and E.K. Panina. Characteristics of photonic jets from microcones. Optics and Spectroscopy 119,849-854 (2015); I.V. Minin, O.V. Minin. Photonics of isolated dielectric particles of arbitrary three-dimensional shape - a new direction of optical information technologies // Vestnik NSU. Series: Information technologies. 2014, No. 4, S. 4-10.]. A homogeneous dielectric is used as a material for focusing particles.

Photonic (acoustic) jet occurs only for certain values of the relative refractive index in the material of the particle (lens) and the environment, not exceeding 2 [Z. G. Chen, A. Taflove, and V. Backman. Photonic nanojet enhancement of backscattering of light by nanoparticles: a potential novel visible-light ultramicroscopy technique // Optics Express, vol. 12, pp. 1214-1220, Apr 2004. Igor V. Minin, Oleg V. Minin, and Yuri E. Geints. Localized EM and photonic jets from non-spherical and non-symmetrical dielectric mesoscale objects: Brief review // Ann. Phys. (Berlin), 1-7 (2015), Boris S. Luk'yanchuk, Ramón Paniagua-Domínguez, Igor Minin, Oleg Minin, and Zengbo Wang Refractive index less than two: photonic nanojets yesterday, today and tomorrow // Optical Materials Express Vol. 7, Issue 6, pp. 1820-1847 (2017), Minin I.V., Minin O.V. Photonic jets in science and technology // Bulletin of SGUGIT, vol. 22, no. 2, 2017, p. 212-234., J. H. Lopes, M. A. B. Andrade, J. P. Leão-Neto, J. C. Adamowski, I. V. Minin, and G. T. Silva. Focusing Acoustic Beams with a Ball-Shaped Lens beyond the Diffraction Limit // Phys. Rev. Applied 8, 024013 (2017), DOI: 10.1103 / PhysRevApplied 8.024013; Minin I.V., Minin O.V. Superresolution in acoustic focusing devices // Bulletin of SGUGIT, Volume 23, No. 2, 2018, p. 231-244.].

It is believed that when focusing waves of any nature, the wave energy is concentrated in a region with a transverse size not less than half the wavelength [Gorelik G.S. Oscillations and waves. Moscow: State Publishing House. Phys.-Mat.Lit., 1959, p. 377]. The magnitude of the transverse resolution of the lens is determined by the Rayleigh criterion (diffraction limit) [Born M., Wolf E. Fundamentals of optics. M .: Nauka, 1973, 720 p.]:

δ≈1.22λ / D,

where λ is the acoustic wavelength, D is the lens diameter. To achieve high spatial resolution, it is necessary to use lenses with a high NA.

A common disadvantage of devices for the formation of a photonic jet is the impossibility of using them when changing the refractive index of the material of the environment while maintaining the required relative refractive index.

A device according to RF patent No. 178616 was selected as a prototype. A device for forming a photon jet, consisting of a radiation source and a dielectric particle with a characteristic size comparable to the wavelength of the incident radiation, while the particle is made in the form of a cylinder, and the radiation falls on its flat end located perpendicular to the incident radiation.

The disadvantage of the device is the impossibility of using it when the value of the refractive index of the material of the environment changes while maintaining the required relative refractive index.

The objective of the present invention is to eliminate these disadvantages, namely to develop a device for forming a photonic jet with a constant value of the required relative refractive index at various values of the refractive index of the environment in which the particle forming the photonic jet is located.

This task is achieved by the fact that a device for the formation of a photon jet, consisting of a radiation source and a dielectric particle with a characteristic size comparable to the wavelength of the incident radiation, while the particle is made in the form of a cylinder, and the radiation falls on its flat end, located perpendicular to the incident radiation , new is that the particle is formed by an array of coaxial and successively located hollow cones at a distance of no more than 0.5λ from each other, where λ is the wavelength of the radiation used and with a cone opening angle lying in the range from about 88 to 112 degrees, and the cones made of material that reflects incident radiation.

Known artificial dielectric formed from a lattice of parallel plates set at an angle θ to the incident radiation. The principle of operation of such an artificial environment is to make waves move between inclined plates. In this case, the traversable path increases by 1 / сos times, which corresponds to the effective refractive index in relation to wave propagation in free space n = 1 / сosθ [Kock W. E. Metal-lens antennas // Proc. IRE. 34,828-836 (1946); Winston E. Kock. Metallic Delay Lenses // Bell System Technical Journal, 1948, 27, p. 58-82.].

In such an artificial dielectric, the effective refractive index depends only on the angle of inclination of the grating plates. Table 1 shows the values of the effective refractive index n _eff from the angle of inclination of the plates.

Table 1

Eph. refractive index, n _eff 1.0 1.02 1.06 1.15 1.31 1.56 1.74 2.0 The angle of inclination of the plates 0 ten twenty thirty 40 50 55 60

The invention is illustrated by drawings.

FIG. 1 shows a device for forming a photonic jet.

FIG. 2 shows the results of numerical simulation of the formation of a photon terastruct of a particle in the case of incidence of radiation on a cylinder formed by an array of coaxial and sequentially located hollow cones from the side of their base (a) and top (b).

FIG. 1 denotes: 1 - radiation incident on a particle from a radiation source, 2 - a particle that forms a photonic jet, 3 - an array of coaxial and sequentially located hollow cones, 4 - a photonic jet.

The claimed device operates as follows. Illuminating radiation 1 falls on a particle in the form of a cylinder 2 formed by an array of coaxial and successively located hollow cones 3. An electromagnetic or acoustic wave, passing a larger one along the surface of the cone, has a larger effective refractive index than when radiation propagates along the surface of a cylindrical particle. A feature of the device is that the substance surrounding the particle 2 is located between an array of coaxial and sequentially located hollow cones 3. As a result of the diffraction of an electromagnetic or acoustic illuminating wave on a cylindrical particle and the interference of waves that have passed through the particle, a focusing region 4 (photonic jet) with a subwavelength resolution.

The advantage of the proposed device is the independence of its properties from the parameters of the environment, since the material of the environment is in the structure of the forming device, and its relative refractive index depends only on the physical length of the lateral sides of the cone or on the angle of inclination θ with respect to the incident radiation.

When simulating the operation of the device, the distance between the coaxial cones was chosen less than λ / 2, approximately 0.4λ. As the distance between the plates decreases, the "uniformity" of such a material increases. With an increase in the distance between the coaxial cones more than 0.5 λ, the intensity of the formed focusing area decreased.

The cones can be made of a material that reflects the incident radiation to ensure efficient propagation of radiation between the surfaces of the coaxially located hollow cones. For example, in the electromagnetic wavelength range, these can be various metals or dielectrics with a high refractive index in relation to the refractive index of the medium surrounding the cylindrical particle. In the acoustic range, the cones can be made of a material that creates a contrasting impedance with the environment. They can be made using 3D printing.

The lower limit of the 88 degree cone angle corresponds to a refractive index of approximately 1.4. When the refractive index is less than 1.4, a focusing area is formed with a resolution approximately equal to the diffraction limit. The upper limit of the opening of the 112-degree cone corresponds to a refractive index of about 1.8. When the refractive index is more than 1.8, the focusing area shifts into the body of the cylindrical particle.

The specific value of the size of the opening of the particle cones is determined depending on the purpose of the device and the required optimal parameters of the focusing area.

The claimed device provides an actual expansion of the instrumental arsenal of modern focusing systems with subwavelength dimensions that form photonic jets.

The technical result is to create a device for focusing a photon jet with a constant value of the required relative refractive index at different values of the refractive index of the environment in which the particle forming the photon jet is located.

Claims (1)

A device for forming a photon jet, consisting of a radiation source and a dielectric particle with a characteristic size comparable to the wavelength of the incident radiation, while the particle is made in the form of a cylinder, and the radiation falls on its flat end, located perpendicular to the incident radiation, characterized in that the particle formed by an array of coaxial and sequentially located hollow cones at a distance of no more than 0.5λ from each other, where λ is the wavelength of the radiation used and with a cone opening angle ranging from about 88 to 112 degrees, and the cones are made of a material that reflects incident radiation ...

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