In optical coherence tomography, axial and lateral resolutions are determined by the source coherence length and the numerical aperture of the sampling lens, respectively. Whereas axial resolution can be improved by use of a broadband light source, there is a trade-off between lateral resolution and focusing depth when conventional optical elements are used. We report on the incorporation of an axicon lens into the sample arm of an interferometer to overcome this limitation. Using an axicon lens with a top angle of 160 degrees , we maintained 10-microm or better lateral resolution over a focusing depth of at least 6 mm. In addition to having high lateral resolution, the focusing spot has an intensity that is approximately constant over a greater depth range than when a conventional lens is used.

The Doppler bandwidth extracted from the standard deviation of the frequency shift in phase-resolved functional optical coherence tomography (F-OCT) was used to image the velocity component that is transverse to the optical probing beam. It was found that above a certain threshold level the Doppler bandwidth is a linear function of flow velocity and that the effective numerical aperture of the optical objective in the sample arm determines the slope of this dependence. The Doppler bandwidth permits accurate measurement of flow velocity without the need for precise determination of flow direction when the Doppler flow angle is within +/-15 degrees perpendicular to the probing beam. Such an approach extends the dynamic range of flow velocity measurements obtained with the phase-resolved F-OCT.

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We have developed a novel real-time phase-resolved functional optical coherence tomography system that uses optical Hilbert transformation. When we use a resonant scanner in the reference arm of the interferometer, with an axial scanning speed of 4 kHz, the frame rate of both structural and Doppler blood-flow imaging with a size of 100 by 100 pixels is 10 Hz. The system has high sensitivity and a larger dynamic range for measuring the Doppler frequency shift that is due to moving red blood cells. Real-time images of in vivo blood flow in human skin obtained with this interferometer are presented.

We have developed a novel real-time phase-resolved optical coherence tomography (OCT) and optical Doppler tomography (ODT) system using optical Hilbert transformation. By combining circularly polarized reference and linearly polarized sample signals, in-phase and quadrature interference components are produced in separate channels and treated as the real and imaginary parts of a complex signal to obtain the phase information directly. Using a resonant scanner at an axial scanning speed of 4 kHz in the reference arm of the interferometer, both structure and blood flow velocity images with 200 axial scans can be acquired at 20 frames per second with high sensitivity and large dynamic range. Real-time videos of in vivo blood flow in the chick chorioallantoic membrane using this interferometer are presented.

We describe a phase-resolved functional optical coherence tomography system that can simultaneously yieldin situ images of tissue structure, blood flow velocity, standard deviation, birefringence, and the Stokes vectors in human skin. Multifunctional images were obtained by processing of analytical interference fringe signals derived from two perpendicular polarization-detection channels. The blood flow velocity and standard deviation images were obtained by comparison of the phases from pairs of analytical signals in neighboring A-lines in the same polarization state. The analytical signals from two polarization-diversity detection channels were used to determine the four Stokes vectors for four reference polarization states. From the four Stokes vectors, the birefringence image, which is not sensitive to the orientation of the optical axis in the sample, was obtained. Multifunctional in situ images of a port wine stain birthmark in human skin are presented.

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