Two-mode squeezing in Raman couplers

We investigate two-mode squeezing of compound Stokes-anti-Stokes modes propagating in a Raman coupler with a broad reservoir phonon system. Three types of squeezing: principal squeezing, generalized squeezing and sum squeezing are examined and their relations are identified. The definition of generalized squeezing is extended to an arbitrary number of modes, and a multimode uncertainty product is introduced. The quantum statistical properties of the optical fields propagating in the coupler are treated within the framework of the generalized superposition of the coherent signal and quantum noise. According to this model, generalized squeezing appears whenever the Glauber-Sudarshan quasidistribution does not exist as an ordinary function.