Optical coherence microscopy for the in-depth study of biological structures: System based on a parallel detection scheme

We present a new microscopy system based on the OCT principle, that uses a multiplexed lock-in detection scheme to generate a 2D head-on image in parallel without lateral scanning. Our "full-field optical coherence microscope" comprises a Michelson interferometer built with a polarizing beam splitter, and uses a photoelastic birefringence modulator to modulate the optical path difference between the two orthogonal polarizations. A novel signal processing method is used to achieve a demodulation in parallel on every pixel of a 256×256 CCD camera. A 840 nm electroluminescent diode with 20 μm coherence length is used to illuminate the field of view through the microscope objective lens. In-depth exploration of the sample is realized by changing the plane of focus. The lateral resolution of the images is limited by the camera pixel size and is 2 μm. The axial sectioning ability is approximately 8 μm. Having validated our setup on model samples, we now evaluate its performance on biological structures. As an example, images of onion cells from 50-400 μm below the surface are obtained in 1 s with 100 dB sensitivity.