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The work is devoted to the study and development of a non-toxic and non-hygroscopic system of AgBr - AgI crystals. Crystals of this system are non-toxic, non-hygroscopic, flexible, safe for organic tissues and media, which makes them promising for use in medical technologies. During the development of crystals, the phase diagram of this system was refined. On the basis of the phase diagram, the modes of high-purity raw materials' synthesis and single crystals growth are selected. Using the selected modes, single crystals of various compositions were grown and their optical properties were determined, such as the spectral transmission range and refractive indices at the short-wavelength absorption edge and at the wavelength of the CO 2 laser (10.6 µm), The work results are the basis for the technology development for the production of optical products (infrared fibers, lenses, windows, prisms) for use in laser, endoscopic and diagnostic medicine, including in systems for early diagnosis of cancer.

Infrared photonic-crystal fibers (IR PCF) based on AgClxBr l-x and AgBrxIl-x crystals have been developed for operation at a CO 2 laser wavelength (10.6 µm). The prospects of using fiber optics, including those with a photonic structure, in medical technologies as a conductor of laser radiation are considered. The advantages and disadvantages of unjacket and two-layer fibers, as well as the versatility and uniqueness of photonic crystal fibers are shown. The process of designing optical fibers with a photonic structure is presented, from the stages of mathematical and computer modeling to seven-stage extrusion and properties study. In computer simulations, plane wave and finite element methods were used to analyze the band structure and mode analysis, respectively. In the properties' study, a CO 2 laser and a Spiricon Pyrocam III camera were used. The model was verified with a real fiber by measuring the radiation distribution in the far zone. High convergence of simulation results with the fabricated fiber is obtained. Thus, infrared fibers with an increased mode field diameter were obtained, which are flexible, easy to sterilize and safe for humans for medical applications.

The article is devoted to the manufacture of fiber bundle for the mid-infrared range by extrusion from crystals of the AgBr - TlBr0.46I0.54 system. The fabricated bundle have improved spectral transmittance, optical loss, and spatial resolution characteristics - the main fiber bundle performance indicators. The basic optical properties of the developed bundles have been studied, allowing us to talk about their applicability in various industries, including as channels for delivering laser radiation.

The article discusses infrared polycrystalline fibers based on the AgCl-AgBr crystals system, which are promising for use in medicine, since they are non-hygroscopic, non-toxic, and easy to sterilize. Mid-Infrared radiation (MIR) is interesting for medical applications, since numerous organic molecules and compounds are absorbed in the wavelength range from 2.0 to 15.0 $\mu$ m. To date, various sources of MIR radiation have been developed, such as IR lasers and IR spectrometers. These devices require fiber optic channels to output an optical signal to provide a non-invasive and safe examination of biological tissues and organic substances. Fibers made on the basis of AgCl-AgBr crystals can be used as such channels, since they have a wide transparency range from 2.0 to 20.0 $\mu$ m without absorption windows, have high mechanical strength and flexibility, and low optical loss. Uncladded and cladded polycrystalline infrared fibers are convenient for use in IR spectroscopy for the study of biological tissues. Photonic crystal fibers are convenient for use as fiber radiation leads, since they provide a small aperture and high transmission power of radiation.

This paper presents the results of a study of the refractive-index dispersion for the AgBr–TlI, AgBr–TiBr0.46I0.54, and AgCl–AgBr crystal systems in the spectral range from 0.4 to 56 µm, along with the results of the development and fabrication of single-mode microstructured IR fibers by extrusion from solid solutions of metal halides. The fibers had a central insert 16 µm in diameter of composition 2.6 mol% TlI in AgBr, located in a matrix of composition 2.3 mol% TlI in AgBr with external diameter 525 µm. Inserts with diameter 16 µm of composition 2.0 mol% TlI in AgB were placed in the matrix in hexagonal order. The distribution of the radiation emitted from the fibers in the far field at wavelength 10.6 µm was studied, along with the influence of local heating of a section of the fiber on the transport of the IR radiation. The mode-field diameter was experimentally estimated as 120±30µm. The fibers were suitable for transporting both laser and thermal radiation from heated objects to a thermal viewer.

The presented work is devoted to the study and development of the technology for obtaining the AgBr – AgI crystals system. Studies have been carried out to study the phase diagram in order to clarify the region of stable solid solutions' existence. Based on the data obtained, the modes were selected and single crystals of various compositions were synthesized. Their main optical properties, such as the spectral transmission range, were investigated and the refractive indices were determined at the wavelength of the short-wave absorption edge and the CO2 laser (10.6 μm). The work’ results are necessary for the manufacture of various structures IR fibers, windows, lenses, and other optical products, which are widely used in different fields of science and technology, including laser, endoscopic, and diagnostic medicine.

The article presents temperature measurement experiments using the infrared thermography method utilizing nanopolycrystalline (PIR) fibers. The authors designed an experimental setup that allows temperature measurement of both reference temperature sources, which were used as liquid and dry-block calibrators, and bodies with known properties, such as transformer oil and Peltier element. The research was carried out on individual PIR fibers with a diameter of 1120 μm and a length of 0.2 and 1.0 m, as well as on a fiber bundle of 16 fibers, each with a diameter of 525 μm and a length of 0.3 m. According to the experiments, linear dependences of the measured temperature of these bodies on the actual values were obtained. The physical sense of the obtained linear dependencies coefficients has been described and equations for calibration of fiber-optic temperature sensors have been presented. Additionally, we considered the thermal images transmission over a fiber bundle, which research has shown a high spatial resolution and confirmed the possibility of conducting fiber thermal flaw detection.

This article presents a fiber-optic channel for delivering infrared (IR) radiation within the range from 2.5 to 25.0 μm. It comprises AgBr – TlBr0.46I0.54 uncladded fibers with an extremely small diameter of 90 μm. In the framework of this study, the infrared crystals of AgBr – TlBr0.46I0.54 system and optical fibers based on them, as well as their properties, are described. The stages of the fiber bundle development are also described: the mathematical evaluation of crosstalk is carried out; the computer simulation of the mode field distribution across the bundle is performed. Based on the numerical results, the geometric parameters of the bundle, enabling the efficient transmission of IR radiation, were selected. The fiber bundle with low crosstalk and high spatial resolution was manufactured.

In this paper, we modeled and fabricated a single-mode microstructured fibre (MOF) based on the solid solution crystals of AgBr–TlI and AgBr–TlBr0.46I0.54 systems. For this purpose, we gained the refractive index dispersion of the given systems in the wavelength range of 19–25 μm. It served as a basis for fibre simulations. The obtained MOF model was 700 μm in diameter; it included 200-μm central insert and 40 quasi-square peripheral inserts with the cross-section of 20 × 20 μm and the pitch of 80 μm and operated in a single-mode regime within the wavelength range of 22–25 μm, while the transmitting range was 2.5–25 μm. It possessed an enlarged mode field when compared to a corresponding single-mode step-index fibre (SIF). This MOF was fabricated using a method, which combines hot pressing and extruding. It was shown that the fundamental mode is tightly confined in the fibre core region. The developed MOF structure may be suitable for producing outputs, splitters, and couplers for various types of solid-state lasers based on semiconductors and gas steam lasers, including ones deployed in a harsh environment.