Sensors and structured beams in optical coherence tomography
Optical coherence tomography (OCT) is an emerging medical imaging technique that provides images of various tissue structures at micrometer scale resolution. A swept source laser which emits time-varying wavelengths light at a high-speed was developed that greatly improves OCT processing speed and image resolution. This dissertation presents system developments for swept source based OCT. I have designed and demonstrated three different OCT systems that can be used for diagnostic applications. First, I present a common-path OCT system with a cleaved optical fiber as a probe. The system is built as a tactile sensor for implementation in surgical robots. A tactile sensor, often referred to as a force sensor, is a device that is sensitive to applied force or pressure. Since the system has a high sensitivity to pressure and a compact size, the sensor is compatible with the surgical robots field which require fine force control. This new sensor may aid in diagnosing diseased tissue or cells by measuring their Young' s modulus. Secondly, an Angular/Longitudinal Doppler OCT system (ALD-OCT) was constructed to sense the rotation of an object. Previous work has shown, it is feasible to detect a linearly moving object by Doppler OCT. However, ALD-OCT, OCT utilizes a helical phase shape beam that, has been studied due to its distinct characteristics. An application of using a vortex beam is sensing a rotating object by measuring the angular Doppler shift from the beam reflected off the object. ALD-OCT can utilize depth resolved analysis and be implemented to detect helical shaped particles or the vorticity of blood flows under the skin or in the retina noninvasively. Lastly, we propose several designs of optical probes for a swept source OCT system. The designs of the GRIN lens bundle probes were presented to demonstrate angled illumination and detection techniques in OCT systems. The beam profiles of the output beams from the probes were analyzed theoretically using ABCD ray matrices. We present a method to measure the beam profile of a sweeping wavelength laser source, which can be applied to measure any optical probes connected to the swept source laser.
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