Time domain OCT measures the interference between sample and reference radiation as a function of the reference arm length. In full-field-OCT (FF-OCT) a camera is used instead of a scanned beam for a parallel detection of the interference pattern and thus acquiring a complete en face image. Because multiple images have to be acquired to resolve the phase ambiguity, this method is prone to motion artifacts.
We present a novel motion-insensitive approach to FF-OCT. Spatially coherent illumination and an off-axis reference beam is used to introduce path-length differences between reference and sample light in neighboring pixels. This spatial carrier frequency replaces the temporal carrier frequency in scanned TD-OCT.
The setup is based on a Mach-Zehnder interferometer with a super-luminescent diode and a CMOS area camera. The Sensitivity of the system was determined to be 75 dB. The field of view was 1.42 x 1.42 mm. Each frame had 237x237 lateral channels at an axial resolution of 9 µm in tissue. By step-wise changing the length of the reference arm between the en face scans, volumetric in vivo FF-OCT measurements of the human retina have been acquired within 1.3 s.
OCT with a spatially coherent off-axis reference beam is suitable for in vivo imaging of human retina. The quality of the images is sufficient to discriminate the different tissue layers.