  The quantum characteristics of sum-frequency process in an optical cavity
with an input signal optical beam, which is a half of entangled optical beams,
are analyzed. The calculated results show that the quantum properties of the
signal beam can be maintained after its frequency is conversed during the
intracavity nonlinear optical interaction. The frequency-conversed output
signal beam is still in an entangled state with the retained other half of
initial entangled beams. The resultant quantum correlation spectra and the
parametric dependences of the correlations on the initial squeezing factor, the
optical losses and the pump power of the sum-frequency cavity are calculated.
The proposed system for the frequency conversion of entangled state can be used
in quantum communication network and the calculated results can provide direct
references for the design of experimental systems.
