Photonic Generation of 30 GHz Bandwidth Stepped-Frequency Signals for Radar Applications

Abstract

Wideband microwave signals with high timefrequency linearity for high-resolution radar applications can be optically generated using high-speed electronic waveform generators. Frequency-shifting modulation in an optical cavity provides an attractive approach to generate broadband microwave signals with reduced complexity requiring only MHz-level electronics. However, the in-loop signal instability and inter-pulse interference usually cause amplitude fluctuations, leading to limited signal-to-noise ratio and signal bandwidth. Here, we overcome these challenges and demonstrate, for the first time, the photonic generation of 30-GHz-wide stepped-frequency (SF) signals with 100 MHz frequency steps defined by an MHz-level electrical oscillator. We achieved this performance by mitigating the in-loop polarization scrambling and inter-pulse interference using a polarization-maintaining cavity and a high-extinction optical switch. This allows stable consecutive acousto-optic frequency-shifting modulation that significantly improves the signal-to-noise ratio. While achieving a bandwidth surpassing the state-of-the-art demonstrations based on wideband electronics, our approach alleviates the necessity for high-speed signal generators or wideband tunable lasers. To exemplify the utility, we systematically evaluate the signal quality and show its applications in radar imaging compared to those using electrical waveform generators.

Photonic radar for contactless vital sign detection

“…https://doi.org/10.1038/s41566-023-01245-6 frequency multiplication 30,31 and digital-to-analogue converters 32 provide a substantial bandwidth and high time-frequency linearity for accurate radar sensing. Photonic radar can generate different types of radar signal, including linear-frequency modulated (LFM) 33,34 and stepped-frequency (SF) signals [35][36][37][38][39] . Moreover, it can operate in multiple frequency bands across the millimetre-wave region, optimizing the performance based on operating conditions 40 .…”

“…A total synthesized 25-GHz SF signal can be generated after the first injected pulse finishes 250 roundtrips in the frequency-shifting cavity. High time-frequency linearity is inherited from the constant and stable AOFS-enabled frequency-time shifting 38 , which is challenging to achieve using other photonics-based approaches 43,44 .…”

A new approach to contactless probing of vital signs

“…In summary, this methodology could potentially facilitate continuous surveillance of uncooperative targets, including those facing away or to the side, in contrast to the limitations of relying on a singular radar access point. [1][2][3][4][5][6]…”

“…Despite advancements in user experience, wearable sensors are not prescribed for individuals with burn wounds or skin irritations, as well as with limited surface area specially for infants. [1][2][3][4][5][6] Non-contact methods utilizing optical sensors have been investigated, such as employing cameras to monitor specific areas of interest. Nevertheless, camera-based systems, such as infrared and conventional cameras, exhibit sensitivity to variations in skin color and lighting conditions.…”