  Image slicing is a powerful technique in astronomy. It allows the instrument
designer to reduce the slit width of the spectrograph, increasing spectral
resolving power whilst retaining throughput. Conventionally this is done using
bulk optics, such as mirrors and prisms, however more recently astrophotonic
components known as photonic lanterns (PLs) and photonic reformatters have also
been used. These devices reformat the multi-mode (MM) input light from a
telescope into single-mode (SM) outputs, which can then be re-arranged to suit
the spectrograph. The photonic dicer (PD) is one such device, designed to
reduce the dependence of spectrograph size on telescope aperture and eliminate
modal noise. We simulate the PD, by optimising the throughput and geometrical
design using Soapy and BeamProp. The simulated device shows a transmission
between 8 and 20 %, depending upon the type of adaptive optics (AO) correction
applied, matching the experimental results well. We also investigate our
idealised model of the PD and show that the barycentre of the slit varies only
slightly with time, meaning that the modal noise contribution is very low when
compared to conventional fibre systems. We further optimise our model device
for both higher throughput and reduced modal noise. This device improves
throughput by 6.4 % and reduces the movement of the slit output by 50%, further
improving stability. This shows the importance of properly simulating such
devices, including atmospheric effects. Our work complements recent work in the
field and is essential for optimising future photonic reformatters.
