Biomedical Engineering Reference
In-Depth Information
Fig. 5.15
Schematics of a fiber optics-based swept-source OCT setup.
OC
optical circulator,
PC
polarization controller,
RM
reference mirror,
BPD
balanced photodetector,
FC
fiber coupler
Line-Field/Full-Field SS-OCT
The schematics of line-field OCT system using frequency-sweeping source is
similar to that of LF-SD-OCT, which is based on free-space implementation of
Michelson interferometer and, instead of 2D detector array line-field SS-OCT, uses
a 1D linear detector at the spectrometer side. The irradiation is done by an elliptical
beam onto the imaging sample using a cylindrical lens, and then the wavelength-
resolved interference signal is detected by a line CCD camera [
84
]. Since the system
uses the line CCD camera as a detector, the exposure time can be reduced (in the
microsecond range); therefore, the images are influenced to a lesser extent by motion
artifacts.
Instead, the full-field SS-OCT is a full-field version of swept-source optical
coherence tomography. A set of 2D Fourier holograms are recorded at discrete
wavenumbers spanning the swept-source tuning range. The resultant 3D data cube
contains comprehensive information on 3D morphology of the sample that can be
retrieved by software via 3D discrete Fourier transform. This method of recording
of the OCT signal confers signal-to-noise ratio improvement in comparison with
“flying-spot” TD-OCT. The spatial resolution of the 3D reconstructed image,
however, is degraded due to the presence of a phase cross-term, whose origin and
effects are addressed below.
5.5.2.3
Full-Range Complex Fourier Domain OCT
As described in the preceding section, one of the major drawbacks of FD-OCT that
limits its practical application is the complex conjugate ambiguity. This is because
in FD-OCT the detected realvalued spectral interferogram is Fourier transformed
to localize the scatter within the sample. The Fourier transform of a realvalued
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