Coherent Optical Fiber Sensing Based on a Frequency Shifting Loop

Billault, Vincent; Travers, Pierre; Arpison, Guillaume; Crozatier, V.; Kemlin, Vincent; Morvan, Loïc; Dolfi, Daniel; Chatellus, Hugues Guillet de

doi:10.1364/sensors.2021.stu2b.7

Cited by 1 publication

(1 citation statement)

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“…This limitation can be feasibly overcome by using a minor frequency step (Δf ). One way of achieving the minor frequency step is to cascade two AOMs with the opposite frequency shift (e.g., a frequency shift from −10 to +10 MHz has been demonstrated in [45]) to achieve an unambiguous range over 100 meters, comparable to the 120 meters unambiguous range window (1.25 MHz frequency shift) from the CARABAS system -a very early airborne synthetic aperture radar that employed SF signals -mounted on an aircraft [46]. It should be noted that the radar's maximum detection range is not limited by its unambiguous range [35], [47].…”

Section: Discussionmentioning

confidence: 99%

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

Zhang

Liu

Eggleton

2022

J. Lightwave Technol.

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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.

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