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Korea Advanced Institute of Science and Technology

Wang Joo Lee

Byoung Yoon Kim

Bong Kyu Kim

Ki Ho Han

This invention relates to optical devices such as a fiber-optic frequency shifter and an optical interferometer. This invention also relates to a method of generating optical interference signals to obtain reliable sensor signals independent of polarization fluctuations of the optical waves in the fiber. Fiber-optic interferometers have many advantages such as high sensitivity and convenient way of using even in poor surrounding environments. These interferometer, however, exhibit polarization dependent signal degradation since the polarization of a light wave passing through an optical fiber irregularly changes depending on the birefringence of the fiber. This invention is characterized in that the frequencies of two orthogonal eigen polarizations of a light wave are shifted to different frequency values at one optical path of the interferometer. They produce two beat interference signals after interfering with the light wave passed through the other optical paht of the interferometer. The two beat interference signals have amplitudes varying complementarily. Selecting the larger one from the two beat signals can prevent polarization dependent signal degradation. Moreover, the beat signals from the optical interferometer according to the invention requires simpler signal processing compared to the output of conventional fiber-optic interferometer.

Fiber-optic frequency shifter, optical interferometer and method of generating two complementary optical interference signals using the same

The present invention relates to a Sagnac interferometric sensor array for acoustic sensing and method of sensing acoustic signal that is able to observe acoustic signals coming from several sources simultaneously. The acoustic sensor of the present invention is a Sagnac interferometric sensor array employing a depolarizer. Unlike a single Sagnac interferometric sensor, two light signals traveling in the opposite directions from each other pass through the off-center position of the loop at different times in the Sagnac loop when they are pulses, and thus, it is possible for the light pulses to be maintained at a constant phase difference by giving arbitrarily a certain amount of phase to them. By using the fact, the interferometer is constructed in such a way that the interference light output coincides with the applied acoustic signals in waveform. This invention suggests a way of fabricating an array of fiber-optic acoustic sensors that is easy to be made and is highly sensitive at some frequency band.

Growing community of inventors

Taejon, South Korea

Wang Joo Lee