Microwave Photonic System for Generating and De-Hopping a Frequency Hopping Signal

A microwave photonic structure that is capable of generating and de-hopping a frequency hopping signal, is presented. It is based on applying a programmed waveform, which consists of a series of sawtooth waves with time varying periods designed according to the hopping sequence, to an optical phase modulator. This shifts the optical carrier frequency with the amount of frequency shift changing with time. The proposed structure enables an RF signal with many precise and arbitrary hopping frequencies to be generated, which is needed for practical applications but unable to achieve by the reported photonics-based structures. The amplitude of the generated frequency hopping signal remains constant as the frequency changes. The proposed structure can also be used for de-hopping a frequency hopping signal. Proof-of-concept experiments are set up. Frequency hopping signals with precise frequencies within ±1 Hz of the desired values for different RF carrier frequencies are demonstrated. The hopping frequencies are repeatable. The measured hop rate and frequency switching time are 10 MHz and 7.3 ns respectively. De-hopping a frequency hopping signal is also demonstrated experimentally.