Inverse Vernier effect in coupled lasers

In this report we study the Vernier effect in coupled laser systems consisting of two cavities. We show that depending on the nature of their coupling, not only can the "supermodes" formed at overlapping resonances of these two cavities have the lowest thresholds as previously found, leading to lasing at these overlapping resonances and a manifestation of the typical Vernier effect, but also they can have increased thresholds and are hence suppressed, which can be viewed as an inverse Vernier effect. The inverse Vernier effect can also lead to an increased free spectrum range and possibly single-mode lasing, which may explain the experimental findings in several previous studies. We illustrate this effect using two coupled micro-ring cavities and a micro-ring cavity coupled to a slab cavity, and we discuss its relation to the existence of exceptional points in coupled lasers.