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We demonstrate an optical planar waveguide sensor that can be used to measure the direction and intensity of physical force. The interferometric structure, on which the proposed sensor is based, introduces an interference pattern in wavelength. Its phase is shifted by the external force. On the other hand, since the cross-sectional effective refractive index profile is asymmetric because of the core formed on one side of silica substrate, the phase shift appears with respect to the direction of the external force against the surface. Therefore, we can measure the direction and intensity of the applied force by monitoring the phase change.

We present and optical methane sensor that employs a Mach-Zehnder interferometer formed on a planar waveguide. The overclad of only one arm of interferometer is partially etched up to the boundary between the core and clad. Then, the etched region is coated by SnO2 thin layer and the sensor module is annealed at high temperature. When the fabricated sensor module is exposed to methane gas, the interferogram is changed and quickly saturated in 10 seconds.

A novel linearized interrogation method is presented for Fourier-domain mode locked (FDML) fiber Bragg grating (FBG) sensor system. In the ultra high-speed regime over 10 kHz modulation, only sine wave is available to scan a center wavelength of FDML wavelength-swept laser instead of conventional triangular wave. However, sine wave modulation has been suffered an exaggerated nonlinear filter response in demodulating the time-encoded parameter into the absolute wavelength. The linearized demodulation is demonstrated by the third order polynomial conversion of filter between the time-encoded parameter and wavelength-encoded parameter based on the spectral information of polarization maintaining fiber (PMF) Sagnac interferometer.

We demonstrate a high speed fiber Bragg grating sensor array interrogation using 1.3 μm Fourier-domain modelocked (FDML) wavelength-swept laser. The slope coefficients for measured relative wavelength difference and relative time delay from the static strain are 1.02 pm/μstrain and 0.16 ns/μstrain, respectively. We demonstrate the dynamic response of the FBG sensor array with 100 Hz modulation strain based on the FDML wavelength swept laser at 25.3 kHz scanning rate. The FBG sensor interrogation system using FDML wavelength swept laser can be realized for the high speed and high sensitivity monitoring systems.

Novel wavelength-swept Raman laser is newly demonstrated to implement an arbitrary gain band for a swept-source optical coherence tomography (SS-OCT). Instead of conventional semiconductor optical amplifier, we adapt optical fiber Raman amplification, which can easily generate an instant femto-second optical gain at arbitrary wavelength region from 1.1 to 1.6 micrometer using a high-power optical pump power. We also experimentally demonstrate OCT images using the novel wavelength-swept Raman laser source.

Ultra-fast 31.3 kHz interrogation is newly demonstrated for fiber Bragg grating (FBG) sensor system using Fourierdomain mode-locked (FDML) wavelength-swept laser. Higher speed interrogations are useful for the real-time monitoring of dynamic sloshing pressure and strain.

We demonstrate a novel implementation of spectral domain OCT by using a proposed sweeping detector at 1320 nm wavelength range. A fiber pigtailed Fabry-Perot tunable filter is newly adapted to receive spectral interferometer information using a photo-receiver instead of using charged couple detector arrays. In order to show a possibility of the scheme in other view point, we have changed the position of the Fabry-Perot tunable filter of the interferometer. The combination of a super luminescent LED and a semiconductor optical amplifier was used as an optical source. Its output power is about 10 mW and the spectral bandwidth is about 60 nm. The filtered light after passing thorough the Fabry- Perot tunable filter has 0.15 nm instantaneous spectral linewidth with 1.3 mW average output power. The system with an axial resolution of 12 μm performed OCT imaging of a cornea of a rat eye proving potential about the application of the proposed sweeping detector OCT.

There have been several technologies to enable high resolution cross-sectional images of biological tissues in optical coherence tomography (OCT) method. Optical frequency comb (OFC) source has been proposed to overcome the crosstalk problem among the CCD detector pixels of the continuous spectrum of light source. Recently, a passive-type OFC is demonstrated simply placing a Fabry-Perot interferometer filter right after the broadband light source, but it shows a high loss of output light power and limited tenability of channel spacing of multi-wavelength. In this work, we experimentally demonstrate a spectral comparison of a novel multi-wavelength source based on a fiber Sagnac interferometer. The channel spacing is flexibly tuned by the effective length control of polarization-maintaining fiber (PMF). The uniform and stable multi-wavelength spectral distribution is also helpful to obtain the higher sensitivity from the lower exposure intensity source to get a better quality spectral OCT image.