Highly Efficient Spectral Calibration Methods for Swept-Source Optical Coherence Tomography

Abstract

Recent techniques in optical coherence tomography (OCT) make use of specialized light sources that sweep across a broad optical bandwidth, allowing for longer depth ranges at higher resolutions. The produced light source signal can be described as a gaussian damped sinusoid that non-uniformly sweeps across a narrow frequency band. When sampling this interferometric signal uniformly, the generated images present considerable distortion, because the spectral information is a function of wavenumber "k", not time. To solve this problem a "calibration" step needs to be performed; in this process, the acquired interferogram signal is linearized into k-space. The process usually involves estimating the phase-frequency change profile of the SS-OCT system via Hilbert transformation, inverse tangent and phase unwrapping.

In this thesis, a multitude of low complexity, computationally efficient methods for the real-time calibration of Swept Source Optical Coherence Tomography (SS-OCT) systems are implemented and results are evaluated against commonly performed calibration techniques such as Hilbert transformation. Simulation shows execution times decisively improved by up to a factor of ten, depending on the used technique. Axial resolution was also slightly improved across all the tested techniques. Moreover, the inverse tangent and phase unwrapping steps necessary for Hilbert transform calibration techniques are eliminated, vastly reducing circuit implementation complexity and making the system suitable for future inexpensive, power efficient, on-chip solutions in SS-OCT post-processing.