METHODS OF HOT WIRE CREATION FOR FIBER-OPTICAL THERMAL ANEMOMETER

Subject of Research. The paper presents the study of various methods of optical radiation coupling from the fiber core into its cladding with the aim of creating a fiber-optic anemometer hot wire. The effectiveness of the described methods is evaluated by analyzing the obtained dependencies. Method. The structures of two optical fibers were studied, one of which was used to transmit an information signal, and the other — to create a hot wire. A Bragg grating was formed in the core of the first fiber, and a radiation coupling region was created in the second fiber. These fiber sections were aligned with each other and fixed by a tin-lead alloy. The temperature was measured by monitoring the spectral characteristics of fiber Bragg gratings inscribed by the phase mask method. The areas of radiation coupling were formed either by changing the fiber geometry using custom modes of the arc fusion splicer, or by creating a SMF-MMF-SMF transition. Main Results. Structures are developed which can be used as a hot wire of a fiber-optic anemometer sensitive element. The dependencies of the Bragg resonance wavelength shift on the pump laser power are obtained; the Bragg wavelength shift varies in the range from 0.15 nm to 3 nm as a result of a hot wire creation. The resulting curves are constructed after three experiments for each type of structure, taking into account the standard deviation. They make it possible to judge the effectiveness of various methods of radiation coupling. Comparative analysis of the studied methods is presented. Practical Relevance. The study describes the capabilities of fiber-optic anemometry when creating point and distributed sensors. The results of this work can be used in the areas where the creation of quasi-distributed and point diffusers is necessary, as well as partial or complete coupling of radiation from a fiber core.