The signal and noise properties of standard time domain optical coherence tomography system are analyzed in
near-infrared region based on extended Huygens-Fresnel principle. The signal-to-noise ratio and maximum probing
depth are estimated for scattering media with discontinuity plane inside. In numerical simulation, the relationship
between coherent signal and scattering coefficients, and depth dependence SNR are calculated. The difference between
specular and diffuse reflection is given out and analyzed. Numerical result is verified by well established experiment
with different concentration mixture solution of IntralipidTM, from 1% to 15%. The OCT system consists of fiber
Michelson interferometer and 1550 nm ASE optical source with coherent length of 14μm. Both numerical and
experimental results show that multiple scattering events are the main reason for decreasing of signal-to-noise ratio.
According to the research, wavelength at 1550 nm is also suitable for imaging of biomedical tissue because of lower
scattering coefficients. More than 2 mm penetration depth is obtained in experiment for 10% IntralipidTM which has
scattering coefficient similar to skin tissue.
A new optical fiber Fabry-Perot (F-P) cavity sensor for liquid level detection was developed. The end of a flexible metal bellows, which can sustain a large strain displacement, is suggested to be one surface of the F-P cavity. Both electronic hardware and demodulation scheme in software were developed for fringes counting and direction discrimination of the liquid level. A scheme for temperature compensation was proposed. A prototype of the liquid level sensor was fabricated and the experiments for air pressure and water level measurement were carried out. Because the interference fringe counting technique was used for signal demodulation, the noise resistance capability of the sensor against optical power fluctuation and other disturbances is greatly improved.
1. There have been many methods to fabricate microlens arrays, such as, the ion-exchanging, molding. plasma CVD, interfacial-gel copolymerising, photolytic, and monolithic techniques. Among them, the ion- exchange process has achieved the better improvements and results in theory and practice. The authors obtained analytic solutions of the diffusion equations for window and disc mask processes in fabricating ion-exchanged planar microlens array, derived the optimum index distribution for disc-mask microlens (DM lens), gave the image matrix of microlens, fabricated the divergent disc- mask planar microlens array and show the parameters and the picture taken with the array.