RU2709371C1 - Method of producing infrared fiber assemblies based on silver halide light guides - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to production of infrared fiber assemblies of silver-halide light guides intended for transfer of thermal image in middle infrared range (2–20 mcm) and required for use in industrial and medical thermography in order to visualize distribution of thermal field from a remote object. Method of producing infrared fiber assemblies based on silver-halide light guides involves obtaining light guides by extrusion from monocrystals of solid solutions of silver chloride-bromide and packing them into a hexagonal structure. Workpiece with diameter of 14–16 mm and height of 15–20 mm is preliminarily cut from the monocrystal, after which a polycrystalline workpiece with grain size of 500–600 nm, diameter of 3 mm, length of 430±5 mm is produced by extrusion. Then, it is extruded for production of single-layer light guides with diameter of 100 microns with grain size of 50–60 nm, of which a hexagonal structure of light-emitting diodes 19, 37 and 61 is formed by mechanical assembly with subsequent compaction thereof, diameters of the assemblies being equal to 500, 700, 900 mcm and length of 2.7±0.3 m. Light guides contain 25.0–75.0 wt% silver chloride and 75.0–25.0 wt% silver bromide.

EFFECT: higher temperature resolution, reduced optical losses and reduced crosstalk.

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Description

The proposed method relates to the field of obtaining IR fiber assemblies from silver halide fibers obtained by extrusion from crystals of solid solutions of the AgCl-AgBr system. Ordered IR fiber assemblies are designed to transmit thermal images in the mid-infrared range (2-20 microns) and are in demand for use in industrial and medical thermography in order to visualize the distribution of the thermal field from a remote object.

The first papers on IR fiber assemblies (bunches) based on double-layer silver halide fibers were published in [Paiss, I. Properties of silver halide core – clad fibers and the use of fiber bundle for thermal imaging / I. Paiss, F. Moser, A. Katzir // Fiber and Integrated Optics. - 1991. - Vol. 10. - P. 275-290]. The authors obtained a bilayer fiber from single crystals of AgCl _x Br _1-x solid solutions by extrusion using a “stand in tube” method — the composition of the stand (core); the composition of the tube (matrix) is AgCl _y Br _1-y , where y> x. Then, the bilayer fibers were hexagonal laid in a tube, extruded, cut into segments, extruded again and the process was repeated several times to obtain fiber assemblies of 70 fibers with a total assembly diameter of 2 mm and a length of 40 cm. The diameter of the fibers after multi-stage extrusion was 80 μm with a distance between their centers are 160 microns. Using a thermal imager, the possibility of assembling a thermal image at a wavelength of 10.6 μm (CO ₂ laser) to transmission is shown. But the authors do not give the functional properties of the optical fibers: optical losses, chemical compositions, crosstalk, and spatial resolution of the fiber assembly.

A known method of producing IR fiber assemblies with a total diameter of 1-3 mm and a length of 100 cm. Fiber assemblies are made of 70-250 fibers with a diameter of 60-100 μm, which are obtained by triple extrusion of double-layer silver halide fibers, the segments of which were placed in an AgCl tube and extruded again [Paiss, I. Thermal imaging by ordered bundles of silver halide crystalline fibers / I. Paiss, A. Katzir // Applied Physics Letters. - 1992. - Vol. 61. - P. 1384–1386]. In the same work, assemblies with a tight packing of 1000–2000 fibers with a diameter of 20–40 μm and a length of 30 cm are described. The authors note that it was not possible to achieve good assembly regularity, therefore, high optical transmission losses due to absorption peaks in the IR spectra were recorded. Nevertheless it was transferred thermal images of the fiber assemblies in a temperature resolution of ^about 5-10 C.

Also, a modernized method for producing IR fiber assemblies is known and an assembly of 100-2500 silver halide fibers with a diameter of 50-250 μm obtained by multiple extrusion is reported. The optical loss for the assembly of 900 optical fibers at a wavelength of 10.6 μm was 13.7 dB / m; spatial resolution of 4-5 lines per mm [Rave, E. Thermal imaging through ordered bundles of infrared – transmitting silver – halide fibers / E. Rave, D. Shemesh, A. Katzir // Applied Physics Letters. - 2000. - Vol. 76, No. 14. - P. 1795-1797]. Crosstalk between adjacent fibers is 25%, i.e. signal flow from one fiber to another [Rave, E. Ordered bundles of infrared – transmitting AgClBr fibers: optical characterization of individual fibers / E. Rave, L. Nagli, A. Katzir // Optics Letters. - 2000. - Vol. 25, No. 17. - P. 1237-1239]. At the same time, high optical losses of 1.92 dB / cm (192 dB / m) at a wavelength of 10.6 μm for assemblies of 900 fibers with a diameter of 25 μm are associated with excess scattering at the fiber-matrix interface, as well as with IR radiation, which is transmitted sheath of a bilayer fiber. In addition, the assemblies are inflexible.

The closest technical solution as the choice of a prototype for the “Method for producing infrared fiber assemblies based on silver halide fibers” includes the production of double layer optical fibers from single crystals of solid solutions of the AgCl-AgBr system by extrusion using the “tube in tube” method, packing them in a hexagonal structure with subsequent extrusion, cutting segments that are extruded again.

The result is a flexible fiber assembly with a length of up to 2 m, an outer diameter of 0.7 mm, containing 36 fibers with a diameter of 40 microns. The optical loss of the assembly (attenuation coefficient) at a wavelength of 10.6 μm was 0.5 dB / cm (50 dB / m), the spatial resolution of 4.3 lines per mm, crosstalk - 30% [Rave, E. Ordered bundles of infrared transmitting silver halide fibers: attenuation, resolution and crosstalk in long and flexible bundles / E. Rave, A. Katzir // Optical Engineering. - 2002. - Vol. 41, No. 7. - P. 1467-1468]. The same work presents a fiber assembly up to 2 m long, 0.9 mm in diameter, containing 100 fibers with a diameter of 70 microns. The optical loss of the assembly at a wavelength of 10.6 μm is 0.7 dB / cm (70 dB / m), a resolution of 6.5 lines per mm, crosstalk - 45%. At the same time, the authors note that the initial bilayer fiber had an optical loss of 0.2 dB / m in the wavelength range of 9-11 μm, but the transparency range of the fiber assemblies in the mid-IR range, their bending radius, and also the chemical composition were not indicated fibers.

Thus, the developed IR fiber assemblies of the composition of solid solutions of the AgCl-AgBr system have optical properties unsatisfactory for practical use. Specifically, high optical losses at a wavelength of 10.6 μm, high crosstalk and low temperature resolution.

There is a problem of obtaining long and flexible fiber assemblies for industrial and medical thermography based on silver halide optical fibers of a certain chemical composition, transparent in the mid-IR range, having low optical losses, crosstalk, and high spatial and temperature resolution.

The solution to the problem is achieved in that in a method for producing infrared fiber assemblies based on silver halide fibers, including obtaining optical fibers by extruding silver chloride-bromide solid solutions from single crystals, packing them in a hexagonal structure, characterized in that a blank of diameter 14-16 is cut from a single crystal first mm, a height of 15-20 mm, after which a polycrystalline preform with a grain size of 500-600 nm, a diameter of 3 mm, a length of 430 ± 5 mm is obtained by extrusion and then extruded for for producing single-layer fibers with a diameter of 100 μm, grain sizes of 50-60 nm, of which a hexagonal structure of 19, 37 and 61 fibers is formed by mechanical assembly with their subsequent densification, while the diameters of the assemblies are 500, 700, 900 μm and a length of 2.7 ± 0 , 3 m, moreover, the optical fibers contain ingredients in the following ratio in wt. %:

silver chloride 25.0–75.0; silver bromide 75.0–25.0.

The essence of the invention lies in the fact that a preform is cut out of single crystals of a certain composition of the AgCl-AgBr system, extruded to obtain a nanoscale polycrystalline structure (500-600 nm). Then, the polycrystalline preform is again extruded to create a nanocrystalline grain size (50-60 nm) in single-layer fibers with a diameter of 100 μm, which are mechanically assembled in a certain amount into a hexagonal structure, compacted, and regular fiber assemblies are obtained for remote transmission of a thermal image in the infrared spectral range.

The existing problem is solved due to the fact that a method has been developed for producing fiber assemblies that are transparent in the mid-infrared range from 2.0 to 20.0 μm, having low optical losses at a wavelength of 10.6 μm - 0.4-0.5 dB / m and low crosstalk between adjacent fibers - 4.5-5%. The spatial resolution in the assembly is 5 lines per mm. Due to the nanocrystalline structure obtained by extrusion of optical fibers from plastic single crystals of solid solutions of the AgCl-AgBr system, fiber assemblies are flexible.

Example 1

From a single crystal of 25.0% silver chloride, 75.0% silver bromide (in wt.%), A preform is cut out with a diameter of 14 mm, a height of 20 mm and extruded to obtain a polycrystalline preform with a grain size of 500 nm with a diameter of 3 mm and a length of 425 mm . Then, the preform is extruded again through a specially made die and a fiber d = 100 μm, 50 m long, is obtained.

The fiber has a nanocrystalline structure with a grain size of 50 nm, it is cut into 2.4 m lengths and a fiber assembly with a diameter of 500 μm is mechanically assembled, containing 19 fibers, followed by compaction of the assembly.

The fiber assembly is transparent in the spectral range from 2 to 20 μm, optical loss over a length of 10.6 μm is 0.4 dB / m, crosstalk - 4.5%, spatial resolution - 5 lines per mm, temperature resolution is 0.2 ^about S.

Example 2

From a single crystal of 75.0% silver chloride, 25.0% silver bromide (in wt.%), A preform is cut out with a diameter of 16 mm and a height of 15 mm, extruded to obtain a polycrystalline preform (grain size 600 nm) with a diameter of 3 mm and a length of 435 mm, which is again extruded to obtain a fiber of a nanocrystalline structure (60 nm) with a diameter of 100 μm and a length of 50 m. The fiber is cut into lengths of 3.0 m in an amount of 61 pieces, a regular fiber assembly with an external diameter of 900 μm is assembled and compacted.

Functional properties of the assembly:

• transparency range from 2 to 20 microns;

• optical losses over a length of 10.6 μm are 0.45 dB / m;

• crosstalk - 5%;

• spatial resolution - 5 lines per mm;

• temperature resolution is 0.25 ^o C.

Example 3

The experiments were carried out in the same way as in example 1, but the single crystal billet with a diameter of 15 mm and a height of 17 mm had a composition in wt. %: silver chloride - 50.0, silver bromide - 50.0. After its extrusion, a polycrystalline billet (grain size 550 nm) with a diameter of 3 mm, a length of 430 mm was obtained, and as a result of repeated extrusion, a nanocrystalline fiber with a diameter of 100 μm (grain size 55 nm) of a 50-meter length was produced. The fiber was cut into lengths of 2.7 m and mechanical laying followed by compaction formed a regular fiber assembly of a hexagonal structure with a diameter of 700 μm, containing 37 fibers.

The fiber assembly is transparent in the IR range of 2.0–20.0 μm, has optical losses at a wavelength of 10.6 μm, 0.43 dB / m, crosstalk 4.8%, spatial resolution of 5 lines per mm, temperature resolution 0, 3 ^about S.

In the case of manufacturing IR fiber assemblies under conditions and conditions that do not correspond to the claims and confirmed by examples, it is not possible to obtain assemblies with the required optical properties that are necessary for practical use.

Technical result

The developed method for producing IR fiber assemblies based on silver halide fibers has the following advantages over the prototype:

1. Reduced by 2-3 times in time and labor the process of manufacturing assemblies. In the prototype and analogues carry out multiple extrusion of obtaining double-layer optical fibers, cutting segments and, again, repeating the extrusion process in order to obtain fibers of a certain diameter. In the proposed method, double extrusion is used.

2. A unique tooling was developed and manufactured to create a nanocrystalline structure of single-layer silver halide fibers of small diameter 100 μm and a length of up to 50 m and more.

3. Fiber assemblies are designed to operate in the mid-IR range (from 2.0 to 20.0 microns); in the prototype, the transparency range of the fiber assemblies is not specified.

4. While maintaining a comparable spatial resolution for fiber assemblies at the level of 5 lines per mm (for the prototype - 4.3 - 6.5 lines per mm), the following parameters are improved:

• improved temperature resolution for fiber assemblies to values of 0.2 - 0.3 ^{° C} against prototype - 5 - 10 ^{° C;}

• reduced optical loss at a wavelength of 10.6 μm in assemblies of 0.4-0.5 dB / m, in the prototype - 50-70 dB / m;

• reduced crosstalk in the method of 4.5-5%, in the prototype - 30-45%.

Claims (2)

A method for producing infrared fiber assemblies based on silver halide fibers, including obtaining optical fibers by extrusion of silver chloride-bromide solid solutions from single crystals, packing them in a hexagonal structure, characterized in that a blank with a diameter of 14-16 mm and a height of 15-20 mm is cut from a single crystal first after which a polycrystalline preform is obtained by extrusion with a grain size of 500-600 nm, diameter 3 mm, length 430 ± 5 mm and secondly extruded to obtain single-layer optical fibers with a diameter of rum 100 μm with a grain size of 50-60 nm, of which a hexagonal structure of 19, 37 and 61 fibers is formed by mechanical assembly with their subsequent densification, while the diameter of the assemblies is 500, 700, 900 μm, length 2.7 ± 0.3 m, and the optical fibers contain ingredients in the following ratio, wt. %: silver chloride 25.0–75.0 silver bromide 75.0–25.0