Photonic Generation of Multi-Featured Chirp Microwave Signal With a Phase Tunable Mechanism for Chirp Rate Variation

Abstract

A tunable chirp microwave signal having center frequency in microwave frequency spectrum is tremendously required in remote sensing applications. This study demonstrates a photonic method for producing chirp signals with multiple features and a phase tuning mechanism for controlling the pace at which chirps occur. The digital technique has many advantages over the analogue one, such as being more repeatable, adaptable, and performable. Discrete multi-frequency microwave signals with frequency doubling characteristics are photonically generated via a digital approach. The multiple frequencies are generated concurrently by cascading two Mach-Zehnder modulators (MZMs), with one of the modulating signals given by M-ARY Quadrature Amplitude Modulation (QAM). The multiple frequency window of chirp signals is used to drive second MZM, while microwave chirp signals are generated in nonconstant envelope forms with center frequency at 2 GHz. In the proposed technique center frequency can be increased to higher frequencies by increasing the frequency of modulating signal at first MZM. Further, a baseband chirp signal of up, down, and dual chirp signals is electronically generated and used as a modulating signal to achieve continuous frequency sweeps in the chirp microwave signal at center frequency of 4 GHz. Additionally, the generation of discrete chirp signals is demonstrated. In the final part of the paper, a phase-tunable chirp signal is generated with chirp variation in a single configuration. A wide range of chirp variation is obtained between 23.7 THz/s and 99 THz/s with single to dual chirp variation by changing the phase angles between $-90^{o}$ and $90^{o}$ .