Optical coherence tomography (OCT) is an optical imaging technique which provides three-dimensional images with micrometer-resolution. OCT has been extensively used for disease diagnostics, treatment planning, and surgical guidance. Currently, most of the OCT systems are based on discrete free-space optical components and optical fibers. These discrete components keep these instruments costly and bulky. The development in integrated optical circuit technology provides the opportunity to develop miniaturized, stable and maintenance-free OCT systems. The goal of this study is developing an OCT chip with external light source and detector. The developed chip is intended to be used in a hand-held OCT probe for skin applications. In this study, a literature survey summarized the achievements and limitations of current chip-based OCT systems. Our common-path design uses the end facet of the waveguide as the reference plane, thus eliminating the need for a space-consuming and dispersive on-chip loop reference arm, thereby reducing the chip size and obviating the need for dispersion compensation. Our on-chip micro-ball lens eliminates the need of external optical elements for coupling the light between the chip and the sample, thereby further reducing the size and the complexity of the system. The signal to noise ratio (SNR) of our system was measured to be 71 dB with 2.6 mW of power on a mirror sample at a distance of 0.3 mm from the waveguide end facet. At this moment, the SNR of our chip system is slightly lower (11 dB lower) than a fiber-based system under the same experimental condition. The suggestions for improving the SNR of our chip system were discussed. Multiple ghost images caused by additional reference planes (originating from the lens surface) could be largely suppressed using a deconvolution scheme. Finally, we presented the design and fabrication results of a common-path parallel SS-OCT (PSS-OCT) chip followed by suggestions for characterization measurements and for possible improvements in the parallel chip design. We believe that by integrating a micro-ball lens onto the chip and using a common-path configuration we have moved a significant step forward in the development of on-chip SS-OCT systems.
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