Experimental set-up for the measurement of the optical signal detection is shown in Fig. 5. The input signal of the DFG device was an intensity modulated lightwave generated from an EO-intensity modulator, in which the optical carrier was a 1550nm CW lightwave from a DFB laser diode, and the optical modulation signal was a microwave with a tunable frequency range of 13GHz-19GHz from a microwave source. The intensity modulated lightwave was amplified up to ~ 60mW by an Er-doped optical fiber amplifier. After that, it