An analysis of fibre optic interferometer configurations for optical coherence tomography applications

Abstract

The Michelson Interferometer has been the principal interferometer configuration for Optical Coherence Tomography (OCT) imaging. For OCT applications, in particular endoscopy, there may be polarisation induced signal fading due to environmental changes within the sample arm. The most significant cause of polarisation induced fading within OCT systems is suggested to be due to changes within the optical fibres. The Fizeau interferometer has been shown to eliminate this polarisation induced fading as the sample and reference arm experience the same environmental effects. However the Signal to Noise Ratio (SNR) o f the Fizeau configuration is lower than that o f the Michelson because a second processing interferometer is required. An investigation into suitable interferometer configurations for OCT was carried out in order to increase the performance o f the Fizeau interferometer compared with Michelson configuration. It was shown theoretically that by using a circulator and balanced detection, a standard Fizeau interferometer could achieve a signal to noise ratio (SNR) up to I8dB greater than the conventional Michelson interferometer and a comparable SNR to the Michelson interferometer optimised for power conservation. An analysis into the optical components used in OCT systems was carried out and the optimal Fizeau interferometer design was constructed. The Optimal design was shown to give an increase o f 26dB compared to the standard Fizeau interferometer relative to theoretical results using the same optical components. It was experimentally shown that the use o f an optical circulator within the Fizeau interferometer improves the SNR compared to the standard configuration.