Extended focus optical coherence tomography with Fresnel lens

We report a Fresnel lens based spectral domain optical coherence tomography (SDOCT) setup to overcome the trade-off between lateral resolution and focusing depth which is one of the main problems for OCT system. We demonstrated the feasibility of the Fresnel lens based SDOCT system by measuring the lateral resolution at different depth positions and compared these results with that obtained by conventional SDOCT illuminated with a light source of a central wavelength of 840 nm and a bandwidth of 50 nm. These results indicated that the Fresnel lens based SDOCT can maintain a constant lateral resolution (~ 6.2 μm or better in our system) over a depth of ~ 2 mm which is nearly 1.2 mm larger than conventional SDOCT. This advantage of the proposed method is very useful for SDOCT based imaging technique applied in the clinical application.