2nd IFU prototype nearly spot-on! #

After the promising performance of the 3D printed IFU prototype in early 2023, we moved forward with a 2nd IFU prototype. Some design adjustments were made to ease the work of Keynote Photonics and make the 2nd IFU even better. We mostly reduced the pitch to 125 microns, so that fibers are now in contact. We cannot do less, unless using more exotic fibers.

[A] Font view of the fiber bundle surface, on which the 7 micro-lens array has been printed. One sees here the 7 fiber cores in the center of each fiber; [B] & [C]: front and side views of the IFU, with side illumination. [D] three-quarter view, where one sees a laser beam emitted from one of the fiber and diffused by the lenslet material.

Like its predecessor, this IFU has been tested on our small coronagraphic bench. Ideally when the star is best coupled into the central fiber, we expect to see little to no flux into the 6 surrounding fibers thanks to the nulling effect. This can only happen if 1) the bench has a top optical quality (it has!); and 2) the microlens array is built properly on top of the fibers (it is!). As a result, we could effectively measure excellent nulls at the expected positions (marked by the white circles in the figure below; blacker is better). So here we are, our first bench demonstration of nulling at 2lbd/D over 6 fibers!

And what’s more: 5 of the 7 fibers have a transmission > 80% from what it should be! The two others, are at only 65%. Not so bad, but still room for improvement before we are absolutely happy, because exoplanet photons are expensive!

So-called coupling maps for the 7 fibers of the IFU, at the focus of the bench. The maps are obtained by a 2-dimensionnal scan of the focus. In practice, the only point of interest is at the center of each imagelet, sympbolized by the white circles. The rest of the maps helps us apprehend the global performance of the IFU and understand how to work with it and eventually improve it.