  We present the innovative macro-slicer optical and opto-mechanical designs
for the third-generation Mid-resolution InfraReD Astronomical Spectrograph
(MIRADAS) instrument for the 10.4m Gran Telescopio Canarias (GTC) in the 1-2.5
$\mu$m bandpass. MIRADAS uses up to 12 cryogenic, fully steerable probes to
select simultaneous targets in a 5 arcminute field of view. The spectrograph
module is a cross-dispersed echelle spectrograph. The macro-slicer is
effectively a stack of six advanced image slicer Integral Field Units (IFUs)
such as FRIDA or FISICA, and like other IFUs designed and built at the
University of Florida by our group, uses a `bolt-and-go' approach to minimize
the difficulty in alignment and maximize robustness. Like other advanced image
slicer IFUs, there are three sets of mirrors that work together to
geometrically rearrange the loosely packed inputs from the probe arms into a
tightly packed pseudo-slit. The macro-slicer also passively keeps the spectral
resolution of MIRADAS fixed at $R>20,000$ in seeing from 1.2 arcseconds down to
0.4 arcseconds, (typical observing conditions at GTC).
