SS-OCT System Base Unit
Chapter 5: Imaging Artifacts
Page 38
MTN013142-D02
5.3.
Phase Wrapping and Fringe Washout
The A-scan data created by the SD-OCT system is produced from spectral information of an optical interference.
Depending on the system setting, a certain integration time is applied for acquisition of each A-scan. Certain
movement of the sample or parts of it can well be detected by comparing the phase information of adjacent A-
scans. This Doppler Imaging mode is provided by the SD-OCT Software (please refer to the SD-OCT Software
Manual for details). Sample movements of more than ¼ of the detected wavelength
(from A-scan to A-scan)
lead to misleading results. The maximum detectable speed (in direction of the A-scan axis) is
4
max
f
v
For an A-scan rate of f = 1.25 kHz at 930nm, the maximum detectable speed v (in the direction of the A-scan
axis) is 290µm/s. When the direction of the movement occurs at an angle with respect to the A-scan axis, larger
speeds can be imaged.
For larger movements within the integration time of the detector, a complete washout of the interference will
occur.
Figure 51 Sample Image Showing Fringe Washout and Phase Wrapping
To illustrate these effects, a sample has been moved quickly while slowly acquiring a B-scan. Figure 51 shows
the result. The intensity data is shown in black and white, while the Doppler information is displayed red to blue.
When the movement starts, the Doppler information is displayed red which means that the sample moves down.
Now at increasing speed, the Doppler information turns blue. This means that the phases of the signal have
wrapped and an inverse speed is shown. In the middle of the movement where the speed is at its maximum
almost no OCT data is displayed (fringe washout).
