Although
injectable hydrogel microsphere has demonstrated tremendous
promise in clinical applications, local overactive inflammation in
degenerative diseases could jeopardize biomaterial implantation’s
therapeutic efficacy. Herein, an injectable “peptide-cell-hydrogel”
microsphere was constructed by covalently coupling of APETx2 and further
loading of nucleus pulposus cells, which could inhibit local inflammatory
cytokine storms to regulate the metabolic balance of ECM in
vitro. The covalent coupling of APETx2 preserved the biocompatibility
of the microspheres and achieved a controlled release of APETx2 for
more than 28 days in an acidic environment. By delivering “peptide-cell-hydrogel”
microspheres to a rat degenerative intervertebral disc at 4 weeks,
the expression of ASIC-3 and IL-1β was significantly decreased
for 3.53-fold and 7.29-fold, respectively. Also, the content of ECM
was significantly recovered at 8 weeks. In summary, the proposed strategy
provides an effective approach for tissue regeneration under overactive
inflammatory responses.
A high resolution optical vector network analyzer (OVNA) implemented based on a wideband and wavelength-tunable optical single-sideband (OSSB) modulator is proposed and experimentally demonstrated. The OSSB modulation is achieved using a phase modulator and a tunable optical filter with a passband having two steep edges and a flat top. Wideband and wavelength-tunable OSSB modulation is achieved. The incorporation of the OSSB modulator into the OVNA is experimentally evaluated. The measurement of the magnitude and phase response of an ultra-narrow-band fiber Bragg grating (FBG) and that of the stimulated Brillouin scattering (SBS) in a single-mode fiber is performed. A measurement resolution as high as 78 kHz is achieved.
Photonics‐based microwave frequency mixing provides distinct features in terms of wide frequency coverage, broad instantaneous bandwidth, small frequency‐dependent loss, and immunity to electromagnetic interference as compared with its electronic counterpart, which can be a key technical enabler for future broadband and multifunctional RF systems. Herein, all‐optical and optoelectronic microwave frequency mixing techniques are reviewed, with an emphasis on the latest advances in photonics‐based microwave frequency mixers with improved performance in terms of conversion efficiency, dynamic range, mixing‐spur suppression, mixing functionality, and polarization independence. Innovative applications enabled by photonics‐based microwave frequency mixers, such as radio‐over‐fiber communication systems, radar systems, satellite payloads and electronic warfare systems, are also reviewed. In addition, efforts in implementing integrated photonics‐based microwave mixers that lead to a dramatic reduction in size, weight, and power consumption are also reviewed.
A compact reconfigurable photonic microwave mixer is proposed and demonstrated based on a dual-polarization Mach-Zehnder modulator and an optical 90-deg hybrid. By simply changing the photodetection schemes, single-ended, double-balanced, I/Q, and image-reject mixing can be implemented. Thanks to the sidebands selection by an optical filter, unwanted mixing spurs are highly suppressed. In addition, the system is insensitive to environmental vibration because the optical path separation is minimized. An experiment is carried out. Reconfigurable mixing functionalities with very small phase dithering are verified. The mixing spurs are suppressed by more than 30 dB, and the image-reject ratio for image-reject mixing is about 40 dB.
A wideband-tunable optoelectronic oscillator (OEO) is proposed and experimentally demonstrated based on a tunable microwave photonic filter (MPF) consisting of a polarization modulator, a chirped fiber Bragg grating, and a polarization beam splitter (PBS). By simply adjusting the polarization state of the signal before the PBS, the center frequency of the MPF is tuned. The proposed OEO is experimentally demonstrated. A high-purity microwave signal with a tunable frequency within 5.8-11.8 GHz is generated. The single-sideband phase noise of the generated signal is −104.56 dBc/Hz at 10-kHz offset.
A compact scheme for photonic generation of a phase-coded microwave signal using a dual-drive Mach-Zehnder modulator (DMZM) is proposed and experimentally demonstrated. In the proposed scheme, the radio frequency (RF) carrier and the coding signal are sent to the two RF ports of the DMZM, respectively. By properly setting the amplitude of the coding signal and the bias voltage of the DMZM, an exact π-phase-shift phase-coded microwave signal is generated. The proposed scheme has a simple structure since only a single DMZM is required. In addition, good frequency tunability is achieved because no frequency-dependent electrical devices or wavelength-dependent optical devices are applied. The feasibility of the proposed scheme is verified by experiment. 2 or 2.5 Gb/s phase-coded 10 and 20 GHz microwave signals are successfully generated.
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