FEMTO-ST-Franche Comté Electronique Mécanique Thermique et Optique - Sciences et Technologies
Video de présentationFrom basic research to industrial partnership
Depth dependant dispersion correction
The dispersion problem in OCT is a highly sensitive point when speaking about high resolution OCT. Indeed a high axial resolution in OCT means a broad spectral range and then a higher sensitivity to group velocity dispersion problem (second order of the dispersion term). A second point to notice is that the dispersion is depth dependant and increases linearly with the penetrating depth into the sample under test. This further means that in an A-Scan the dispersion is not the same for the first reflected interface than for the last one: this is what is called ‘depth dependant dispersion’. Dispersion and its correction have been investigated since people does interferometry and especially in OCT. Main techniques are based on numerical or hardware correction. Depending on the kind of method (rather numerical) depth dependant dispersion correction has been successfully proposed by several authors…but often at a price of time consuming algorithm.
We have just demonstrated that our grating based correlation system could also allows optical depth dependant dispersion correction. The principle is close from this already demonstrated for pulse compression in Femto second laser sources. This correction uses the higher order dispersion terms of diffraction gratings when enlightened under special conditions. This effect is combined with the fact that the grating transverse direction is directly correlated to the depth observation into the sample. Both properties lead to this useful effect of ‘depth dependant dispersion compensation’. For a bit more detailed analysis you may consult this presentation (ppt, 861 Ko) that we recently proposed in a French conference on Biomedical Optics (OptDiag)…unfortunately this presentation is in French but there is now an English version that we have presented in ECBO 2007 (ppt, 1047 Ko) (Munich June 2007). We just published a more detailed analysis for OPtics Communications. And if you would like to have more details please feel free to contact me.
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