Biomedical Engineering Reference
In-Depth Information
Scanning the
mirror axially
Mirror
Reference
arm
Magnitude
Sample
Beam
splitter
λ
Broadband
source
Magnitude
Photodiode
detector
Time
Figure 13.2
TD-OCM.
using a scanning mirror and an internal reflectivity profile of the sample is constructed as
illustrated in Figure 13.2 .
In FD-OCM, a stationary mirror is used, the spectral density of the interference pattern is
captured, and a Fourier analysis is used to reconstruct the internal sample reflectivity
profile. There are two types of implementations of FD-OCM systems: spectral-domain
OCM (SD-OCM) and swept-source OCM (SS-OCM). In SD-OCM, a broadband light
source with constant spectrum is used in combination with a spectrometer allowing for
all the depth information to be acquired in a single exposure. SS-OCM uses a swept light
source with adjustable wavelength which is scanned over time and is detected using a
photodiode, allowing higher control of the wavelength intervals. Implementations of the
two systems are shown in Figures 13.3 and 13.4 .
The major advantage of TD-OCM over FD-OCM is that the length of the reference arm can
be synchronized with the position of the sample arm giving a high axial resolution along
the penetration depth. However, because TD-OCM implements a mechanically moving
mirror in the separate reference arm, these systems cannot measure fast dynamic processes
and suffer from high phase noise. On the other hand, FD-OCM can have no mechanical
moving parts, which decreases the phase noise and as so, it is more adequate for phase
measurements of dynamic objects. Both of these concepts can be used to obtain either
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