Three possible ways for the perfect squeezing of quantum noise of electro-magneti field in the detuned degenerate four-wave mixing are discussed in this paper.
It is found that the field of the combined mode of the probe wave and the phase-conjugate wave in the process of degenerate four-wave mixing exhibits higher-order squeezing to all even orders. The degree of squeezing increases with the order N, and the higher-order squeeze parameter qN may approach -1.