Switchable Multi-format Linearly Frequency-Modulated Signal Generator Based on a Sagnac Loop

A compact method to generate switchable multi-format linearly frequency-modulated (LFM) signal is proposed and investigated. The core components are two phase modulators inside a Sagnac loop, which respectively driven by a linearly chirped waveform and a coding signal. By controlling the amplitudes of the coding signal, we can obtain the LFM signals with different formats, including frequency shift keying (FSK), phase shift keying (PSK), dual-band PSK and FSK/PSK modulation formats. A theoretical analysis and a simulation work are performed to demonstrate the system feasibility. The scheme exhibits switchable formats, high tunability, compact structure, and no DC bias drifts, which may find applications in modern multifunctional system.