  We study optomechanically induced transparency (OMIT) in a compound system
consisting of coupled optical resonators and a mechanical mode, focusing on the
unconventional role of loss. We find that optical transparency can emerge at
the otherwise strongly absorptive regime in the OMIT spectrum, by using an
external nanotip to enhance the optical loss. In particular, loss-induced
revival of optical transparency and the associated slow-to-fast light switch
can be identified in the vicinity of an exceptional point. These results open
up a counterintuitive way to engineer micro-mechanical devices with tunable
losses for e.g., coherent optical switch and communications.
