With the ever-increasing prevalence of minimally invasive procedures (MIP) in the medical world, the designing of
endoscopes, essential in MIP, becomes more and more challenging. As the continuous and ubiquitous need for
miniaturization is starting to outmatch the possibilities offered by the combination of conventional fibre optics and
micro-optics, novel approaches are necessary in order to ensure the advancement of endoscopy and consequently of MIP.
In conventional fibre bundles the phase-relation between cores is not conserved during the propagation of an electrical
field and as such extra micro-optics at the distal end are necessary in order to be able to focus or scan the exiting light or
achieve a certain field of view (FOV). In this paper we analyze the requirements and constraints for a multi-core optical
fibre (MCF) which conserves the phase relationship between the cores. With such a phase conserving MCF, focusing
and scanning light at the distal end could be done by shaping the wavefront through adaptive optics before coupling the
light into the fibre therefore making extra micro-optics superfluous.
Using numerical and mode solving simulations we investigate the relationship between the size, the period and the
numerical aperture of the cores on the one hand and the focal point and field of view on the other hand. We show that
there is a non-circumventable trade-off between intercore crosstalk and the FOV. In addition, we determine the effects
on the focusing ability and on the FOV of deviations of core size and period, due to fabrication errors. Using this
knowledge, we propose two designs for the phase conserving MCF. The first design allows for focusing and scanning the
exiting light but is sensitive to deviations in core size and separation. The second design is less sensitive to fabrication
errors but can only focus and not sweep.