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We propose an all-optical phase-shifting method using Yb-doped optical fibers and demonstrate its potential in on-axis digital holography microscopy (DHM) system. The Yb-doped optical fiber induces a phase change under optical pumping conditions. The induced phase shift shows a good linear response to applied pumping currents, and N-step phase-shifting up to 2p can be properly performed. Four-, six-, and eight-step phase-shifting methods are performed, and the phase retrievals from their phase-shifted interferograms are achieved using an interframe correlation matrix method. An 8-step phase shifting-based reconstruction, which is effective for background noise reduction, is used for 3D imaging of an indium tin oxide (ITO) thin film and an organic light-emitting diode (OLED) thin film. The reconstructed surface profile was in agreement with the step structure of the samples. The proposed all-optical phase-shifting method is expected to be applied to various optical imaging systems using fiber-based phase-shifting interferometers.

We proposed novel phase-shifting interferometry using a fiber-optic vibration sensor. The Doppler shift in the coiled fiber caused by vibrations can be used to detect the vibrations by using a fiber-optic interferometer. The principle can be applied to induce phase shifts. While applying vibrations to the coiled fiber at various vibration frequencies, we recorded the variations in the interference fringes. The interference fringe moved to longer wavelengths when a vibration frequency was increased from 38.00 to 38.40 kHz. Phase variations of 3.59 rad/kHz were obtained. The ability to accurately control the phase by using the vibrations in the coiled fiber was demonstrated by the elimination of the depth degeneracy using the complex signal generated by the phase-shifted interference fringes. Using vibrations to control phase shifting can be an acceptable alternative to conventional methods and can be applied to resolve the depth ambiguity in Fourier domain optical coherence tomography.

We demonstrated the performance of a fiber sensor based on a photonic crystal fiber (PCF) for the detection of high temperatures. The proposed fiber sensor was implemented by collapsing the air holes of the PCF with an arc discharge and forming an in-fiber Mach-Zehnder interferometer. The intentionally collapsed parts in the PCF cause coupling between the core mode and the cladding modes, which produces interference fringes in the transmission spectrum. The spectral response was observed while changing the ambient temperature. The fiber sensor operated properly at high temperatures up to 1000 C. The proposed fiber sensor presented good reliability after repeated temperature variation cycles and showed low hysteresis over wide temperature range. We expect this compact fiber sensor to be applied to monitoring the high-temperature distribution around a thin film sensor and to be an alternative for a strain/pressure thin film sensor under high temperatures in harsh conditions.

We propose the application of high-resolution Optical Coherence Tomography (OCT) in nonbiomedical and biomedical elds. OCT imaging is performed in the biomedical eld for anterior chamber and a tooth, and in the non-biomedical eld for an air-gap imaging, multilayer-thin-lm imaging, and laser-spot-mark monitoring. Our results suggest that OCT is a potential method, with a few microns resolution, for non-destructive investigations in material science and biological research.