Andrey Medvedev

Abstract: In the current article an advanced method of EFPI baseline measurement by use of spectral function approximation is proposed. The method provides an increase in EFPI baseline measurement precision and computational acceleration. The method bases on two foundations provided by analysis of low-finesse Fabry-Perot interferometer model: reduction of search domain and taking into account the most informative spectral intervals, providing a greater impact on the residual of measured and theoretical EFPI spectral functions. Proposed signal processing method resulted in the EFPI baseline measurement resolution less than 50 pm for the cavity length values between 20 and 700 μm.

Abstract: In this article we discuss a special operation regime of mode-mode interferometer under selective coherent and continuous excitation of multimode fiber in which number of modes increases along the waveguide. Experimental investigations which demonstrated signal dependencies from number of mode groups propagating at the point of perturbation were carried out. Theoretical model was also developed. The results of the work can be fundamental for a new solution of localization task for distributed optical fiber sensors based on mode-mode interference in multimode optical fiber.

Abstract: In this paper, we present a new design of the interferometer, intended for high-precision measurements of electric fields. We combined both arms of the interferometer in one segment of the fiber and the electric field sensor. The interferometer made using this scheme has a high resistance to mechanical and thermal fluctuations.

Abstract: One of the most important elements of the optical scheme of the fiber-optic current sensor is a quarter-wave plate, which converts two orthogonal linearly polarized modes into circularly polarized modes, which propagate further in the sensitive element of the sensor. To maintain the integrity of the system and ensure high-precision measurements, it is important that the plate is made of fiber, and its length is equal to a quarter of the beat length with an accuracy of a hundredth of a millimeter, which is technically very difficult to achieve. This article discusses a model of an electronically adjusted quarter-wave plate, which made it possible to check the operability of the fiber-optic current sensor circuit. The article also describes a method for manufacturing of quarter-wave plate, presents the results of temperature tests of plates of different lengths in the current sensor circuit, and estimates the effect of the quarter-wave plate temperature on the measurement error.

Abstract: The paper describes the problem of fiber quarter-wave plate temperature dependency, its influence on the fiber optic current sensors (FOCS) output error, the method of this error compensation, and the results of this method implementation.

Abstract: Course Description This is an advanced course in which we explore the field of Statistical Optics. Topics covered include such subjects as the statistical properties of natural (thermal) and laser light, spatial and temporal coherence, effects of partial coherence on optical imaging instruments, effects on imaging due to randomly inhomogeneous media, and a statistical treatment of the detection of light. Development of this more comprehensive model of the behavior of light draws upon the use of tools traditionally available to the electrical engineer, such as linear system theory and the theory of stochastic processes.

Abstract: A sourceless sapphire fiber extrinsic Fabry–Perot interferometer for ultrahigh temperature sensing is developed. A sapphire wafer is mounted on the tip of a sapphire fiber as the Fabry–Perot cavity. The interference signal is generated by the thermal radiation that transmits through the wafer and is guided to a spectrometer by a sapphire and then a silica fiber. The entire sensor system is compact and low cost. The sensor was experimentally tested up to 1593°C, and a resolution around 1°C was achieved.

Abstract: The factors limiting the resolution of displacement sensors based on the extrinsic Fabry–Perot interferometer were studied. An analytical model giving the dependency of extrinsic Fabry–Perot interferometric (EFPI) resolution on the parameters of an optical setup and a sensor interrogator was developed. The proposed model enables one to either estimate the limit of possible resolution achievable with a given setup, or derive the requirements for optical elements and/or a sensor interrogator necessary for attaining the desired sensor resolution. An experiment supporting the analytical derivations was performed, demonstrating a large dynamic measurement range (with cavity length from tens of microns to 5 mm), a high baseline resolution (from 14 pm), and good agreement with the model.

Abstract: Resolution investigation of multiplexed displacement sensors based on extrinsic fiber Fabry–Perot interferometers (EFPI) was carried out. The cases of serial and parallel configurations were considered; the analysis of the problems and the advantages of the both was performed. An analytical model describing the resolution limits for the both configurations was developed. Serial and parallel multiplexing schemes have been experimentally implemented with three and four sensing elements, respectively. For both configurations, the achieved optical path difference standard deviations were between 30 and 80 pm, which is, to the best of our knowledge, more than an order better than any other multiplexed EFPI resolution ever reported. A good correspondence between experimental results and analytical predictions was demonstrated. A mathematical apparatus relating the attained sensors resolutions with the number of multiplexed sensors and the optical setup parameters was developed, also demonstrating good correspondence with the experimental results. The main origins of possible sensors cross-talk are described, with the supporting experiments, proving an importance of its consideration. Some recommendations, based on the theoretical analysis and experimental studies, dedicated to optimization of sensors resolution and elimination of the cross-talk influence are provided.