  Exceptional points (EPs) are special singularities of non-Hermitian
Hamiltonians. At an EP, two or more eigenvalues and the corresponding
eigenstates coalesce. Recently, EP-based optical gyroscope near an EP was
extensively investigated to improve the response to rotation. However, the
highly resultant dimensionality in the eigenstate space causing from the
EP-based system is sensitivity to more external perturbations, that is, the
great response at EPs requires strict implementation conditions. To solve this
problem, a new non-Hermitian structure was proposed that realizes an
exceptional surface (EP surface) constructed of numerous EPs embedded in a
high-dimensional parameter space. With respect to the isolated EPs,
non-Hermitian EP surface provides additional degrees of freedom to permit the
undesired perturbations (such as fabrication errors) shifts along the EP
surface which corresponds to the robustness. On the other hand, the rotation
will force the system away from these EPs obtaining a sensitivity enhancement
of three orders of magnitude, compared to the traditional Sagnac effect
rotation detecting. The EP surface system has a potential to combine robustness
with enhanced sensitivity of the rotation.
