RU2634492C1 - Infrared lightguide with large mode field diameter - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: infrared lightguide with a large mode field diameter contains a core and a shell consisting of rods arranged in a hexagonal order. Herewith the core with a diameter of 92.5-97.5 mcm contains a central rod with a diameter of 10.6-11.7 mcm, the shell is made with a diameter of 0.3-0.5 mm, and the rods in the shell of the same diameter as the central rod are located at the distance of 52.7-58.3 mcm between their centers, in addition, the central rod is made of crystals of solid solutions of silver chloride-bromide.

EFFECT: minimizing the aperture of the emerging laser radiation and ensuring a stable and controlled operation mode of the medical laser.

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Description

The invention relates to photonic crystal fibers for fiber optics of the mid-infrared range of the spectrum, specifically to medical CO ₂ lasers equipped with a fiber cable for transmitting electromagnetic radiation at a wavelength of 10.6 μm.

Under the influence of laser radiation on organic tissues, important parameters are: the power density of the laser radiation, its penetration depth, numerical aperture (NA) in single-mode operation. Of particular importance are these parameters when performing invasive operations. The sparing mode of exposure of tissues to the radiation of a carbon dioxide laser, the penetration depth of which is from 20 to 50 microns, makes its use preferable when performing complex surgical operations, compared with other lasers operating in the visible and near infrared spectral range. The radiation from these lasers is transmitted through quartz fiber and penetrates much deeper into organic tissue, including healthy tissue, injuring it. For example, the penetration depth into organic tissues of radiation from a holmium YAG laser with a wavelength of 2.09 μm is 0.5 mm, the radiation of diode lasers with a wavelength of 0.81 μm penetrates to a depth of 4 to 6 mm [A.M. Shulutko, A.A. Ovchinnikov, et al. Laser endosurgical operations. http://medbe.ru/materials/khirurgiya-trakhei-i-bronkhov/lazernye-endokhirurgicheskie-operatsii/ MTmedbe.ru].

Known single-mode two-layer crystalline infrared fiber (IR) [RF Patent 2340920 from 12/10/2008 / Zhukova LV, Zhukov VV, Examples NV, Chazov AI, Korsakov AS] based solid solutions of silver chloride-bromide doped with monovalent thallium iodide, which has a core with a diameter of 15-45 microns and contains ingredients in the following ratio in wt. %: silver chloride 19.5-15.0; silver bromide 80.0-82.0; monovalent iodide waist 0.5-3.0. The shell with a diameter of 700-1000 microns is made of solid solutions of silver chloride-bromide in the following ratio in wt. %: silver chloride 19.0-21.0; silver bromide 81.0-79.0. The fiber is designed to operate in the spectral range from 5 to 30 microns.

The disadvantage of the fiber is the content of toxic thallium halides, which is unacceptable for medical use.

Known single-mode crystalline infrared fiber [RF Patent No. 2340921 from 10.12.2008. Bull. No. 34 // Zhukova LV, Zhukov VV, Examples NV, Chazov AI, Korsakov AS] based on solid solutions of silver chloride-bromide, which has a core with a diameter of 20-110 microns and contains the ingredients in the following ratio in wt. %: silver chloride 19.0-21.0; silver bromide 81.0-79.0. The shell with a diameter of 700-900 microns contains the same ingredients in a ratio in wt. %: silver chloride 25.0-35.0; silver bromide 75.0-65.0. The fiber is designed to operate in the spectral range of 3-30 microns.

The disadvantage of the fiber is the small diameter of the core of the fiber - from 20 to 39 μm when operating at a wavelength of 10.6 μm (CO ₂ laser), which makes it difficult for the laser to interface with the fiber in the manufacture of interchangeable optical components. The replacement of optical fibers is associated with the procedure for their sterilization and disinfection after use.

Known single-mode two-layer crystalline infrared fiber [RF Patent No. 2413257 from 02.27.2011. Bull. No. 6 // Zhukova LV, Zhukov VV, Chazov AI, Korsakov AS] whose core, with a diameter of 10 to 130 μm, is made of solid solutions of silver bromide doped with monovalent thallium iodide at the following ratio of ingredients in wt. %: silver bromide 97.0-90.0; monovalent thallium iodide 3.0-10.0, and the shell is made of two layers, while the first layer of the shell with a diameter of 100 to 300 microns is made of solid solutions of silver bromide - monovalent thallium iodide in the following ratio of ingredients in wt. %: silver bromide 99.5-97.0; monovalent thallium iodide 0.5-3.0, and the second layer of the shell with a diameter of 0.9 to 1.15 mm is made of solid solutions of silver bromide - monovalent thallium iodide in the following ratio of ingredients in wt. %: silver bromide 94.0-98.0; monovalent thallium iodide 6.0-2.0.

The disadvantage of the fiber is the content of thallium halides in the toxic ingredients, which is unacceptable for medical use.

Also known is a single-mode two-layer crystalline infrared fiber [RF Patent No. 2504806 from 01.20.2014 // Korsakov A.S., Zhukova L.V., Kortov CB, Vrublevsky D.S.], including a core and cladding with a diameter of 10-250 μm with the content of the monovalent thallium bromide iodide solid solution (TlBr _0.46 I _0.54 ).

The disadvantage of this fiber, despite a satisfactory mode field diameter of 100 μm at a wavelength of 10.6 μm, is also the content of toxic thallium halides in the composition, which is unacceptable for medical use.

Known single-mode photonic crystal fiber [Arno Millo, Lilya Lobachinsky, Abraham Katzir Single-mode octagonal photonic crystal fibers for the middle infrared. Appliede physics letters vol. 92 021112 (2008)] with a shell diameter of 0.9 mm, made from solid solutions of silver chloride-bromide in the following ratio of ingredients in wt. %: silver chloride 30%, silver bromide 70%; and containing 80 inserts with a diameter of 25 μm composition of silver chloride 70%; silver bromide 30%. arranged in four rows in an octagonal order with a step within a row of 42 microns and a pitch between rows of 55 microns. The diameter of the effective core, providing a single-mode propagation of electromagnetic radiation at a wavelength of 10.6 μm, is 110 μm.

The disadvantage of this fiber is the difficulty in manufacturing the microstructure profile, i.e. manufacturing an infrared fiber with a large diameter field mode. In addition, the fiber has a large sheath diameter, i.e. 0.9 mm, which limits its use for intracavitary operations.

The closest technical solution is an infrared optical fiber with a large mode field diameter [RF patent No. 2506615 dated 02/10/2014 // Korsakov AS, Zhukova LV, Zhukov VV, Vrublevsky DS]. The optical fiber includes a core and a sheath consisting of rods arranged in hexagonal order. The core with a diameter of 98-112 μm is made of crystals based on silver bromide containing a solid solution of monovalent thallium bromide-iodide (ТlВr _0.46 I _0.54 ), in the following ratio of components, wt. %: silver bromide 91.0-61.0; solid solution (TlBr _0.46 I _0.54 ). 9.0-39.0. In the shell are rods with a diameter of 42-48 microns at a distance of 70-80 microns between their centers in the following ratio of components of their composition, wt. %: silver bromide 92.0-64.5; solid solution (TlBr _0.46 I _0.54 ) 8.0-35.5.

A disadvantage of the infrared fiber is the content of toxic monovalent thallium halides (TlBr _0.46 I _0.54 ) in its composition, which is unacceptable for medical use.

The objective of the invention is to obtain an infrared fiber with a large diameter field of the mode, operating at a wavelength of 10.6 μm, containing a core with a central rod (in the figure, the border is dotted), and a sheath with a diameter of 0.3-0.5 mm, separated from the core by a ring of six rods. The core, shell, central core in the core and six rods in the shell are made of crystals based on solid solutions of the chloride – silver bromide system, but having different compositions (see drawing). IR fiber for medical _CO2 lasers.

The problem is solved due to the fact that the infrared fiber with a large diameter of the mode field, including the core and the sheath, consisting of rods arranged in hexagonal order, characterized in that the core with a diameter of 92.5-97.5 μm contains a central rod with a diameter of 10, 6-11.7 μm, the shell is made with a diameter of 0.3-0.5 mm, and the rods in the shell of the same diameter as the central rod are located at a distance of 52.7-58.3 μm between their centers, with the central the core is made of crystals of solid solutions chloride-bromine silver and at following component ratio, wt. %:

Silver chloride 13.1-12.3 Silver bromide 86.9-87.7

the core and shell are made of crystals of solid solutions in the following ratio of components, wt. %:

Silver chloride 14.8-13.9 Silver bromide 85.2-86.1

the rods in the shell have a composition in the following ratio of components, wt. %:

Silver chloride 20.7-19.8 Silver bromide 79.3-80.2

In infrared optical fibers having such a structure and composition, a maximum of electromagnetic radiation propagates in the core, i.e. only one lower-order mode, within the fundamental forbidden zone, such as a shell, where electromagnetic radiation does not propagate (see drawing). The drawing shows a diagram of infrared light with a large mode field diameter (MFD) = 95.0 ± 2.5 μm. The central rod and six rods in the shell have a diameter (d) = 11.1 ± 0.6 μm, the rods in the shell are located at a distance Δ = 55.5 ± 2.8 μm between their centers. The shell has a diameter (D) = 0.4 ± 0.1 μm.

New optical fiber with a large mode field diameter is mainly intended for medical a CO ₂ laser manufactured by extrusion from nontoxic crystals of silver chloride-bromide, as in prior art optical fiber contains toxic thallium halides (TlVr _0.46 I _0.54).

The new photonic structure of the fiber is made by extrusion of crystals based on solid solutions of silver chloride-bromide and consists of a core of a certain composition with a central rod with a diameter from 10.6 to 11.7 μm of a different composition having a higher refractive index than the composition of the core, shell and six rods in the shell. In the shell with a diameter of 0.3 to 0.5 mm, six rods of the same diameter as the central rod are located in a hexagonal order, at a distance between their centers of 52.7 to 58.3 μm, which makes it possible to obtain a large mode field diameter from 92.5 to 97.5 microns, while maintaining a single-mode operation at a wavelength of 10.6 microns (CO ₂ laser).

Due to the combination of distinctive features, namely, the complex structure of infrared optical fibers and certain chemical compositions of the core and cladding, as well as the central rod located in the core, and the presence of six rods in the cladding, the operation mode of the infrared fiber is single-mode within the fundamental forbidden zone.

Example 1

Fiber optics with a core diameter of 95.0 μm, in which a central rod with a diameter of 11.1 μm, were made from crystals based on solid solutions of silver chloride-bromide, were made by extrusion. The composition of the core in wt. %:

Silver chloride - 14.4;

Silver bromide - 85.6.

The composition of the Central rod in wt. %:

Silver chloride - 12.7;

Silver bromide - 87.3.

The fiber cladding with a diameter of 0.4 mm has a core composition. Six rods with a diameter of 11.1 μm are placed in a hexagonal order at a distance of 55.0 μm between their centers, having a composition in wt. %:

Silver Chloride - 20.3

Silver bromide 79.7.

With this structure of the fiber, the ratio of the diameter of the rods in the cladding to the distance between their centers is 11.1 / 55.0 = 0.2. A fiber end was surveyed at an output radiation power of 0.5 W, which corresponds to a power density of 7.05 kW / cm ² at a wavelength of 10.6 μm. Radiation has the form of a Gaussian function. It propagates at an angle of 7.7 ° with a numerical aperture NA = 0.134, which indicates the existence of one fundamental mode of a lower order, i.e. The single-mode operation of the infrared fiber is confirmed.

Example 2

A single-mode fiber was obtained for operation at a wavelength of 10.6 μm (CO ₂ laser). The core of the fiber has a diameter of 92.5 μm and is made of crystals of the composition in wt. %:

Silver chloride - 14.8;

Silver bromide - 85.2,

in which the central rod with a diameter of 10.6 μm of the composition in wt. %:

Silver chloride - 13.1;

Silver bromide 86.9.

The shell with a diameter of 0.3 mm of the composition of the core in wt. %:

Silver chloride - 14.8;

Silver bromide - 85.2.

includes six rods with a diameter of 10.6 μm, located at a distance of 52.7 μm between their centers. The rods are made of crystals of the composition in wt. %:

Silver chloride - 20.7;

Silver bromide - 79.3.

The ratio of the diameter of the rods in the shell to the distance between their centers is 10.6 / 52.7 = 0.2. When the power of the laser radiation emerging from the fiber is 0.5 W at an angle of 8.1 ° and with NA = 0.143, the power density is 8.17 kW / cm ² for the operation of a CO ₂ laser. A single lower-order mode propagates in a fiber.

Example 3

For transmitting electromagnetic radiation medical _CO2 laser fiber manufactured from nontoxic crystals AgCl-AgBr system. The fiber consists of a core with a diameter of 97.5 microns and a composition in wt. %:

Silver chloride - 13.9;

Silver bromide 86.1.

In the core is a central rod with a diameter of 11.7 microns and composition in wt. %:

Silver chloride - 12.3;

Silver bromide - 87.7.

A fiber sheath with a diameter of 0.5 mm of the core composition has six rods of the same diameter as the central rod, i.e. 11.7 microns, located in hexagonal order at a distance between their centers of 58.3 microns, having a composition in wt. %:

Silver chloride - 19.8;

Silver bromide - 80.2.

The diameter of the rods in the shell to the distance between their centers is 11.7 / 58.3 = 0.2. When shooting the end of a fiber operating at a wavelength of 10.6 μm, the radiation has a Gaussian function with a radiation power of 0.5 W emerging from the fiber at an angle of 7.4 °, NA = 0.130 and a power density of 6.7 kW / cm ² . A fiber of this structure is single-mode within the fundamental forbidden zone.

In the manufacture of an infrared fiber having a core and cladding composition of less than 85.2 wt. % or more 86.1 wt. % silver bromide in a solid solution of silver chloride-bromide with a core diameter of less than 92.5 microns or more than 97.5 microns, as well as in the manufacture of a central rod and six rods in a shell with a diameter of less than 10.6 microns or more than 11.7 microns and the distance between the centers of the rods in the shell is less than 52.7 microns or more than 58.3 microns with the composition of the central rod less than 86.9 wt. % or more than 87.7 wt. % silver bromide in a solid solution of silver bromide chloride and the composition of the rods in the shell of less than 79.3 wt. % or more than 80.2 wt. % silver bromide in a solid solution, it is not possible to achieve a single-mode mode of operation of an infrared fiber. In addition, the diameter of the shell should not be less than 0.3 and more than 0.5 mm.

Technical result

The structure diagram of the fiber and the distribution of the Z-component of the light vector are presented in the drawing. The main part of the light flux density S in the core satisfies the condition S≤Smax / e ² and accounts for an area of 7088 μm ² , which corresponds to a diameter of 95.0 ± 2.5 μm. Based on the latter, the microstructure parameters are specified: the diameter of the rods in the shell d = 11.1 ± 0.6 μm and the microstructure pitch Δ = 55.5 ± 2.8 μm, i.e. the distance between their centers.

In the center of the core there is a rod with a higher refractive index than the compositions of the core, shell, and six rods in the shell. Due to this, the contribution to mode maintenance is made not only by the mechanism of photonic band gaps, but also by the mechanism of total internal reflection.

The single-mode mode of operation of the fiber when transmitting CO ₂ laser radiation minimizes the aperture of the output laser radiation, and the expansion of the mode field from 92.5 to 97.5 μm allows you to transmit energy density from 6.7 to 8.17 kW / cm ² , which provides stable and controllable operation medical CO ₂ laser. In this case, the depth of penetration of laser radiation into organic tissue is from 20 to 50 microns. In addition, there is the possibility of creating interchangeable, easily matching fiber optic components for laser medical equipment at a wavelength of 10.6 microns.

Claims (6)

An infrared optical fiber with a large mode field diameter, including a core and a sheath, consisting of rods arranged in hexagonal order, characterized in that the core with a diameter of 92.5-97.5 μm contains a central rod with a diameter of 10.6-11.7 μm, the sheath made with a diameter of 0.3-0.5 mm, and the rods in the shell of the same diameter as the central rod are located at a distance of 52.7-58.3 μm between their centers, while the central rod is made of crystals of solid solutions of chloride silver bromide in the following ratio of components comrade, wt. %: Silver chloride 13.1-12.3 Silver bromide 86.9-87.7 the core and shell are made of crystals of solid solutions in the following ratio of components, wt. %: Silver chloride 14.8-13.9 Silver bromide 85.2-86.1 the rods in the shell have a composition in the following ratio of components, wt. %: Silver chloride 20.7-19.8 Silver bromide 79.3-80.2

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