3 research outputs found
Microwave Photonic Imaging Radar with a Millimeter-level Resolution
Microwave photonic radars enable fast or even real-time high-resolution
imaging thanks to its broad bandwidth. Nevertheless, the frequency range of the
radars usually overlaps with other existed radio-frequency (RF) applications,
and only a centimeter-level imaging resolution has been reported, making them
insufficient for civilian applications. Here, we propose a microwave photonic
imaging radar with a millimeter-level resolution by introducing a
frequency-stepped chirp signal based on an optical frequency shifting loop. As
compared with the conventional linear-frequency modulated (LFM) signal, the
frequency-stepped chirp signal can bring the system excellent capability of
anti-interference. In an experiment, a frequency-stepped chirp signal with a
total bandwidth of 18.2 GHz (16.9 to 35.1 GHz) is generated. Postprocessing the
radar echo, radar imaging with a two-dimensional imaging resolution of ~8.5
mm~8.3 mm is achieved. An auto-regressive algorithm is used to
reconstruct the disturbed signal when a frequency interference exists, and the
high-resolution imaging is sustained
Stepped-Frequency THz-wave Signal Generation From a Kerr Microresonator Soliton Comb
Optically generated terahertz (THz) oscillators have garnered considerable
attention in recent years due to their potential for wide tunability and low
phase noise. Here, for the first time, a dissipative Kerr microresonator
soliton comb (DKS), which is inherently in a low noise state, is utilized to
produce a stepped-frequency THz signal ( 280 GHz). The frequency of
one comb mode from a DKS is scanned through an optical-recirculating
frequency-shifting loop (ORFSL) which induces a predetermined frequency step
onto the carrier frequency. The scanned signal is subsequently heterodyned with
an adjacent comb mode, generating a THz signal in a frequency range that is
determined by the repetition frequency of the DKS. The proposed method is
proved by proof-of-concept experiments with MHz level electronics, showing a
bandwidth of 4.15 GHz with a frequency step of 83 MHz and a period of 16
s
Millimetre-Resolution Photonics-Assisted Radar
Radar is essential in applications such as anti-collision systems for driving, airport security screening,
and contactless vital sign detection. The demand for high-resolution and real-time recognition in
radar applications is growing, driving the development of electronic radars with increased bandwidth,
higher frequency, and improved reconfigurability. However, conventional electronic approaches are
challenging due to limitations in synthesising radar signals, limiting performance.
In contrast, microwave photonics-enabled radars have gained interest because they offer numerous
benefits compared to traditional electronic methods. Photonics-assisted techniques provide a broad
fractional bandwidth at the optical carrier frequency and enable spectrum manipulation, producing
wideband and high-resolution radar signals in various formats. However, photonic-based methods
face limitations like low time-frequency linearity due to the inherent nonlinearity of lasers, restricted RF bandwidth, limited stability of the photonic frequency multipliers, and difficulties in achieving
extended sensing with dispersion-based techniques.
In response to these challenges, this thesis presents approaches for generating broadband radar
signals with high time-frequency linearity using recirculated unidirectional optical frequency-shifted
modulation. The photonics-assisted system allows flexible bandwidth tuning from sub-GHz to over 30
GHz and requires only MHz-level electronics. Such a system offers millimetre-level range resolution
and a high imaging refresh rate, detecting fast-moving objects using the ISAR technique. With
millimetre-level resolution and micrometre accuracy, this system supports contactless vital sign
detection, capturing precise respiratory patterns from simulators and a living body using a cane toad.
In the end, we highlight the promise of merging radar and LiDAR, foreshadowing future
advancements in sensor fusion for enhanced sensing performance and resilience