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On large ground-based telescopes, the combination of extreme adaptive optics(ExAO) and coronagraphy with high-dispersion spectroscopy (HDS), sometimesreferred to as high-dispersion coronagraphy (HDC), is starting to emerge as apowerful technique for the direct characterisation of giant exoplanets. Thehigh spectral resolution not only brings a major gain in terms of accessiblespectral features but also enables a better separation of the stellar andplanetary signals. Ongoing projects such as Keck/KPIC, Subaru/REACH, andVLT/HiRISE base their observing strategy on the use of a few science fibres,one of which is dedicated to sampling the planet's signal, while the otherssample the residual starlight in the speckle field. The main challenge in thisapproach is to blindly centre the planet's point spread function (PSF)accurately on the science fibre, with an accuracy of less than 0.1 $\lambda/D$to maximise the coupling efficiency. In the context of the HiRISE project,three possible centring strategies are foreseen, either based onretro-injecting calibration fibres to localise the position of the sciencefibre or based on a dedicated centring fibre. We implemented these threeapproaches, and we compared their centring accuracy using an upgraded setup ofthe MITHiC high-contrast imaging testbed, which is similar to the setup thatwill be adopted in HiRISE. Our results demonstrate that reaching aspecification accuracy of 0.1 $\lambda/D$ is extremely challenging regardlessof the chosen centring strategy. It requires a high level of accuracy at everystep of the centring procedure, which can be reached with very stableinstruments. We studied the contributors to the centring error in the case ofMITHiC and we propose a quantification for some of the most impacting terms.

Validation of strategies for coupling exoplanet PSFs into single-mode fibres for high-dispersion coronagraphy