Photonic technology has pushed the limits of astronomy ever more in recent years. Especially, integrated optics (IO) has led to new standards in accuracy and stability in the field of astronomical interferometry where several beams need to be coherently and simultaneously combined. We follow and extend the IO concept by writing mid-IR waveguides in gallium lanthanum sulfide (GLS) using Ultrafast Laser Writing (ULI). Here, we report on the monochromatic and broadband interferometric capabilities in the mid-IR of such combiners. Finally, we outline the way to a fiber-fed IO 4-telescope instrument for next-generation astronomical interferometers.