High-resolution imaging of a high-speed target based on a reconfigurable photonic fractional Fourier transformer.

The previously reported photonics-based radar working with a large bandwidth has the advantages of realizing high-resolution imaging of targets with low velocity. However, the high velocity of a target will introduce Doppler dispersion to the echo signals, which severely deteriorates the imaging resolution. This problem becomes more noticeable as the bandwidth increases. In this paper, we propose a radar receiver based on a reconfigurable photonic fractional Fourier transformer (PFrFTer). The order of the PFrFTer can be reconstructed flexibly by changing the optical transform kernel. When the transform order matches the velocity of the target, the chirp echo signals behave as narrow impulses in the fractional Fourier domain, showing the range information with a high resolution. In the experiment, a PFrFTer is established and applied to process the echo signals with a bandwidth of 12 GHz. A lossless range resolution of 1.4 cm is obtained in range profiles and inverse synthetic aperture radar imaging for high-speed targets. This range resolution is much higher than that in the classical optical de-chirping receiver. These results demonstrate the PFrFTer is immune to the Doppler dispersion effect and is excellent for high-resolution imaging of high-speed target. The introduced technique would be of practical interest in the detection and recognition of targets.

Photonics-based simultaneous distance and velocity measurement of multiple targets utilizing dual-band symmetrical triangular linear frequency-modulated waveforms.

The distance and velocity measurement can be obtained by the round-trip time and Doppler effect on the down-chirp and the up-chirp of the linear frequency-modulated waveform (LFMW), but false targets will appear in a multi-target situation, resulting in erroneous detection. Here, we report a photonics-assisted approach to realize unambiguous simultaneous distance and velocity measurement in multi-target situations utilizing a dual-band symmetrical triangular LFMW. Dual-band observation invariance is proposed, to effectively resolve the false targets. The de-chirped signals can be obtained from parallel de-chirping processing to the dual-band echoes. By measuring and calculating the beat frequencies of the de-chirped signals in the two frequency bands, the actual parameter measurements can be acquired according to the authenticity criterion. In the experiments, detections to three targets are performed, and the distance and velocities are acquired without false targets. The absolute measurement errors of the distance and the velocity are less than 9 mm and 0.16 m/s, respectively. These results show the feasibility of the proposed approach.

Photonics based microwave dynamic 3D reconstruction of moving targets.

In this paper, a photonics based microwave dynamic 3D reconstruction of moving targets is proposed for the first time. The system is based on optical arbitrary waveform generation and photonics assisted 3D imaging processing. An X-band system is established experimentally. A 3D reconstruction of two pairs of cross-placement rotary balls is demonstrated to prove the effectiveness of the proposed system. Experimental results show that the proposed system can provide information on the stereoscopic physical structure of the targets dynamically, being favorable to identification and surveillance of the complex targets.

High-resolution W-band ISAR imaging system utilizing a logic-operation-based photonic digital-to-analog converter.

W-band inverse synthetic aperture radar (ISAR) imaging systems are very useful for automatic target recognition and classification due to their high spatial resolution, high penetration and small antenna size. Broadband linear frequency modulated wave (LFMW) is usually applied to this system for its de-chirping characteristic. However, nearly all of the LFMW generated in electronic W-band ISAR system are based on multipliers and mixers, suffering seriously from electromagnetic interference (EMI) and timing jitter. And photonic-assisted LFMW generator reported before is always limited by bandwidth or time aperture. In this paper, for the first time, we propose and experimentally demonstrate a high-resolution W-band ISAR imaging system utilizing a novel logic-operation-based photonic digital-to-analog converter (LOPDAC). The equivalent sampling rate of the LOPDAC is twice as large as the rate of the digital driving signal. Thus, a broadband LFMW with a large time aperture can be generated by the LOPDAC. This LFMW is up-converted to W band with an optical frequency comb. After photonic-assisted de-chirping processing and data processing to the echo, a high-resolution two-dimension image can be obtained. Experimentally, W-band radar with a time-bandwidth product (TBWP) as large as 79200 (bandwidth 8 GHz; temporal duration 9.9 us) is established and investigated. Results show that the two-dimension (range and cross-range) imaging resolution is ~1.9 cm × ~1.6 cm with a sampling rate of 100 MSa/s in the receiver.

Photonics-based wideband distributed coherent aperture radar system.

A photonics-based wideband distributed coherent aperture radar (DCAR) system is proposed and experimentally demonstrated. In the proposed system, the central controlling system and several spatially dispersed remote transceivers are connected by the optical fiber-based time synchronization network. In the central controlling system, the optical-carried orthogonal/coherent linear frequency modulated waveforms (LFMWs) are generated by a reconfigurable multi-channel optical arbitrary waveform generator (RMOAWG), and the signal processing for the echo waves is also implemented there. While in the remote transceivers, only the optical/RF and RF/optical conversions are carried out. Benefitting from the use of photonics-based methods, bandwidths of the generated radar signals can be large, improving the detection resolution of the system. Due to the centralized signal generation and processing, the remote transceivers can be simplified, reducing the system complexity. Moreover, the fiber-based distribution ensures low loss, good transportability, and great flexibility. Experimentally, a two-unit DCAR system operating in X-band with a bandwidth of 3 GHz is presented. When full coherence is achieved, signal-to-noise ratio (SNR) gains of 8.3 dB and 8.33 dB are obtained over a single radar for radar 1 and radar 2, respectively. Results are in good agreement with theoretical prediction. Theoretically, with such SNR gain, the range detection precision can be improved to about 2.6 times that of a single radar.

Curcumin suppresses TGF-ß signaling by inhibition of TGIF degradation in scleroderma fibroblasts.

The transforming growth factor-ß (TGF-ß) signaling pathway plays a key role in the fibrotic process in systemic scleroderma (SSc). Curcumin, a Turmeric root extract, has been demonstrated to exert antifibrotic activity. In the present study, we carefully investigated the effect of curcumin on TGF-ß signaling and its potential mechanism in SSc fibroblasts. We demonstrated a potent inhibitory effect of curcumin on TGF-ß signaling. Curcumin counteracted TGF-ß-induced phosphorylation of Smad2 but not Smad3. Further study revealed curcumin induced upregulation of TGF-ß-induced factor (TGIF), a negative regulator of TGF-ß signaling. The TGIF silencing results evidenced the essential role of TGIF in curcumin-mediated TGF-ß/Smad2 suppression. Moreover, our data indicated that the upregulation of TGIF by curcumin might result from decreased ubiquitination of TGIF, which blocks its proteasome-mediated degradation. Collectively, our data provide a novel mechanism of curcumin-mediated suppression of fibrotic process in scleroderma.