The Frequency Detection Of Low-Power Signals Based On Optoelectronic Oscillator

In modern electronic warfare (EW) receivers, discriminating the intercepted microwave signal from the contaminating noise is of critical importance. The microwave measurement methods have narrow bandwidth which can’t meet the needs of electronic warfare (EW). Photonic techniques have many advantages, such as broad bandwidth, low loss and immunity to electromagnetic interference. Thus many microwave signal detection systems based on photonic techniques have been.proposed, including using dispersive elements, monitoring and comparing two optical powers or two microwave powers. However, these techniques cannot be used to amplify very low power radio-frequency (RF) signals while suppressing the other ones.Recently, P. S. Devgan et al. proposed a system that can be used to amplify and detect low power RF signals using multi-frequency optoelectronic oscillator (MF-OEO). Compare with traditional single-frequency OEO, the MF-OEO don’t have band-pass filter. The MF-OEO can be injection-locked to any incoming frequency that matches the free-running modes of the cavity. In order to detect two sets of interleaved low power signals, the modes have to be switched by switching between one or two lasers. The system is difficult to control and cost high.To solve the problem mentioned above, we propose a novel mode switching method of MF-OEO. The two sets of interleaved modes can be switched by adjusting the bias voltage of Mach-Zehnder modulator (MZM). It can be quickly switched. Moreover, the system is cost-effective compare with a two laser MF-OEO. The experiment results show that the system can detect two sets of interleaved RF signals by switching the bias voltage of the MZM. The injection signal can be amplified and the system has a high input sensitivity of-78dBm. The operating bandwidth is4-9GHz.