Multimode Squeezing of frequency combs

The novel aspect of this study is grounded on the fact that squeezing spectrum of a finite set of super-modes operators can be below the standard quantum limit, giving a clear image that the system is a highly quantum multi-mode system. In fact, not only the super-mode of minimum threshold is perfectly squeezed at threshold but, further, all the other super-modes have nonclassical character and are significantly squeezed provided that their threshold is sufficiently close to the minimum one. It is concluded that synchronously pumped OPOs reveal to be very interesting devices for studying frequency combs at the quantum level. Their quantum multi-modal behavior could be exploited for generation of nonclassical states of the light used for implement optical time measurement of great sensitivity or quantum information protocols.