We have proposed a DFG-based optical modulation signal detection device using the second order nonlinear optical effect. The device consists of a periodic poling structure in LiTaO3 crystal and a microwave resonator composed of a straight microwave waveguide [5]. This device has the following advantages; it is possible to detect high-speech opticalmodulation signals with any modulation format (ASK/PSK/APSK), which are hard to detect directly using conventional photo-current based detectors. Additionally, the device has a simple structure, and target frequency can be designed by tuning the polarization reversal period and resonance condition. Therefore, a microwave signal is generated when the frequency of the optical modulation signal coincides with the target frequency, but other optical signals including an optical carrier can pass through the
device without any disturbance.