Abstract
A flexible curled optical cord is useful for a common-path optical coherence tomography (OCT) system because a bending-insensitive arbitrary length can be chosen for the endoscopic imaging probe. However, there has been a critical problem that the partial reflector needs to be placed in between the sample and the objective lens. It limits the structure design of optical probe and leads to a low transverse resolution OCT imaging. Instead of a conventional single common-path interferometer, we propose a novel double common-path interferometer configuration in order to generate an interference signal that is independent of the optical distance between the partial reflector and sample. Due to the limitless tuning of the objective distance, an objective lens with a high numerical aperture (NA) up to 0.85 can be successfully used for phase-sensitive optical coherence tomography to achieve a 3-dimensional profile image of a transverse resolution of 0.7 μm. The intensity and phase terms of the interference signal can be obtained simultaneously from a Fourier-domain mode locked swept laser source for fast data acquisition with a phase stability of 979 pm.
Highlights
Optical coherence tomography (OCT) is useful for various sensing applications, including medical imaging diagnostics as well as industrial surface profilometry [1, 2]
The transverse resolution cannot be reduced below one micrometer because it is difficult to use an objective lens with a high numerical aperture (NA) due to the limited path-length difference between the partial reflector and sample in a conventional common-path interferometer
To illustrate the usefulness of an arbitrary distance between the sample and partial reflector due to the proposed double common-path interferometer, we demonstrate a phase-sensitive OCT experiment with an enhanced performance achieved by using an objective lens with a high NA over 0.85
Summary
Optical coherence tomography (OCT) is useful for various sensing applications, including medical imaging diagnostics as well as industrial surface profilometry [1, 2]. It is critical to overcome this limitation in order to achieve the flexibility of sample positioning in front of the optical probe There has been another problem of the fixed path-length difference in a common-path interferometer configuration, especially for the phase-sensitive OCT applications [8,9,10,11,12,13,14,15]. When a curled optical cord is used in the sample arm as the flexible optical probe, we can clearly see that the OCT image quality varies considerably, depending on the relative polarization state of the two separate arms. In conclusion of this section, we showed the problems in using MZI for a flexible optical probe OCT
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