Another candidate for the detection of an optical modulation signal is DFG based on the second order nonlinear optical effect [1]. Several studies on the signal generation/detection based on DFG from the second order nonlinear optical effect have been reported [1], [2], however, output signal of the DFG-based optical modulation signal detection device is rather weak. One of the main reasons is the small conversion efficiency due to difficulties of phase matching over a long interaction length and the limitation of the Manley-Rowe relation [3].