Search

Исследуются непрерывные квантовые измерения в вероятностном представлении квантовой механики. Показано, что для каждого конкретного результата измерения квантовой системы можно ввести парциальный классический пропагатор симплектической томограммы, для чего используется представление непрерывного измерения через ограниченный интеграл по путям. В случае неселективного измерения классический пропагатор системы получается путем суммирования парциальных пропагаторов по множеству результатов измерений. Представленный подход проиллюстрирован на примерах неселективного измерения координаты квантового осциллятора и квантовой частицы.

A comprehensive theoretical study of the light propagation in a bent spun birefringent optical fiber is presented. We consider the wave equation for a birefringent medium with rotation of the principal axes in the presence of additional linear birefringence and then find an approximate solution being reasonable over a wide range of birefringence parameters. Using this solution, the polarization modes of a bent spun fiber are introduced as a generalization of the modes of a straight spun fiber, allowing one to predict the polarization parameters of light throughout the bent spun fiber. Moreover, it is established that the introduced modes are resistant to coupling if the bending radius varies smoothly making it practically easy to convert the modes of the straight spun fiber to the modes of the bent spun fiber. The polarization peculiarities of non-monochromatical light propagating in a spun fiber is also studied.

The response of an interferometric low-coherence fiber-optic electric current sensor (FOCS) to a short current pulse is studied theoretically and experimentally. The main feature of current pulse sensing is analyzed that manifests itself when the duration of the pulse is comparable to or less than the light propagation time in the sensing fiber. An advanced small-radius sensing fiber coil is considered that allows one to improve the characteristics of FOCSs. In addition, the effect of the intensity noise due to the beating of the spectral components of radiation on the FOCS is studied. It is experimentally shown that this intensity noise can be reduced by using a two-channel optical scheme.

A Faraday fiber-optic current sensor with suppression of excess noise produced by a low-coherent light source is presented. The sensor is designed to detect short current pulses and represents an in-line interferometer with a sensing element based on a spun highly birefringent fiber. To suppress the excess noise, a two-channel light detection scheme without an additional delay line is applied. It is established that bending birefringence induced in the spun fiber wound on a coil limits the noise suppression. To minimize this effect, a new geometry of the sensing coil is used. The proposed sensor exhibits a 5-fold improvement of the signal-to-noise ratio and the same enhancement of the sensitivity to a value of 0.8A in the 3.5 MHz bandwidth. The minimum duration of the measured current pulse is 200 ns.

Optical phase modulator on Faraday effect in microstructured spun fiber is suggested for current sensor. It is showed that such modulator has a high effectiveness which is closed to theoretical one if a period of modulation is more than transit time of light through the fiber. A variation of parameters of optical interferometer with incorporated modulator is experimentally studied under mechanical disturbances on modulator fiber ends. It is discovered that a relative variation of interferometer visibility factor is considerably more than a variation of magneto-optical sensitivity under identical disturbances.