Optical Coherence Tomography: Technical Aspects - Biomedical Optical Imaging Technologies: Design and Applications - page 186

Fig. 5.12 Typical full-field OCT configurations. ( a ) Michelson geometry for wide-field OCT
(WF-OCT) and ( b ) Linnik geometry for full-field OCT (FF-OCT)
This can be achieved by controlling the degree of spatial coherence of full-
field illumination. FF-OCT utilizing spatially incoherent sources such as thermal
sources can effectively suppress the effect of coherent cross talk [ 71 ]. Moreover,
thermal sources may provide high axial resolution due to their broad spectral
bandwidth. However, the brightness per spatial mode of thermal sources often
remains insufficient, requiring a trade-off between sensitivity and imaging speed.
The major interest of spatially coherent illumination in FF-OCT resides in the
possibility to use powerful pulsed lasers such as femtosecond lasers, allowing
higher sensitivity and acquisition speed than with thermal light sources. In contrast,
spatially coherent source can generate considerable amount of coherent cross talk
that degrades the image quality.
However, the temporal phase-stepping method employed in FF-OCT for recon-
struction of en face image degrades the time resolution of the system. Over
the last several years, different techniques have been reported for improving the
time resolution of FF-OCT. Single-shot FF-OCT (SS FF-OCT) is a relatively
new concept which aims to improve the time resolution of FF-OCT and extend
the feasibility of FF-OCT for fast imaging application in biological application.
The basic principle of SS FF-OCT is similar to the simultaneous phase-shifting
interferometric method, which has been developed over the years for high-speed
vibration-insensitive optical testing. Nevertheless, the optical configuration of the
four-channel phase stepper optics is quite complex and limits this system's perfor-
mance for practical implementation. Any differences caused by image projections,
optical aberration, and response uniformity will directly influence the reconstruction
accuracy. Recently, the feasibility of SS FF-OCT was reported for dynamic imaging
of biological specimens [ 72 ]andmaterials[ 73 , 74 ].