Integral Imaging Microscope for measurements in near wall fluid flow

Plenoptic cameras are a cost-effective and fast method to capture a 3D scene. Multiple views of a scene can be captured at different angles using a number of positioned cameras or with the use of a microlens array. This later technique is called Fourier Integral Microscopy (FIMic) or Integral Microscopy (IMic). In both IMic and FIMic, a micro lens array (MLA) is placed in front of an image sensor to capture several elemental images (EI) that provide different perspectives of a 3D scene. This integral image contains spatial and angular information that can be used to reconstruct the image at various depths. IMic is simply a variation of the very compact FIMic, where the lenslets are placed at the Fourier plane of the objective, whereas in IMic, the lenslets are placed at the image plane of the objective.

The system’s performance is characterized in terms of lateral resolution, FOV, Depth of field (DOF) and 3D reconstructions of the images. The axial and lateral resolution of the system at focus is determined by the size of the diffraction-limited spot beneath a single microlens. The computation of the PSF (Point Spread Function) and MTF (Modulation Transfer Function) allows us to determine the most advantageous imager in term of resolution and compactness. By playing both with the distances and the optical elements (focal length, quantity of elements, …), the change in the MTF, is immediate and this can be used to improve our imager. A Zemax model of the microscope, a powerful and versatile optical software that offers ray optics visualization as well as wave optics computation, is depicted along with its calculated performance and comparison to the final design.

This instrument allows for compact stereoscopic measurements for different laboratory scenarios, mainly for biological samples. Because of its compactness and flexibility, we want to adapt this imaging technique for measurements in near wall fluid flow.