Radar has been widely used for military, security, and rescue purposes, and modern radar should be reconfigurable at multi-bands and have programmable central frequencies and considerable bandwidth agility. Microwave photonics or photonics-assisted radio-frequency technology is a unique solution to providing such capabilities. Here, we demonstrate an all-optical central-frequency-programmable and bandwidth-tailorable radar architecture that provides a coherent system and utilizes one mode-locked laser for both signal generation and reception. Heterodyning of two individually filtered optical pulses that are pre-chirped via wavelength-to-time mapping generates a wideband linearly chirped radar signal. The working bands can be flexibly tailored with the desired bandwidth at a user-preferred carrier frequency. Radar echoes are first modulated onto the pre-chirped optical pulse, which is also used for signal generation, and then stretched in time or compressed in frequency several fold based on the time-stretch principle. Thus, digitization is facilitated without loss of detection ability. We believe that our results demonstrate an innovative radar architecture with an ultra-high-range resolution.
Herein, two different monomers,
pyrrole (Py) and ethylenedioxythiophene (EDOT), are loaded into a
self-assembled bis-urea host 1 and oxidatively
polymerized within its nanochannels, dramatically changing the properties
of the crystalline complexes. Molecular dynamics (MD) simulation of
both monomers within the channel demonstrates that they diffuse through
the confinement upon applying thermal energy, which may facilitate
the polymerization reaction. The structures of these host–guest
complexes are characterized before and after polymerization using
solid-state and photophysical measurements. The host maintains its
columnar morphology during polymerization at 90 °C using iodine
as an oxidizing agent. Intriguingly, upon dissolution of the host
and recovery by filtration, the polymers exhibit memory of their nanoreactor
environment, displaying unusual order by scanning electron microscopy,
powder X-ray diffraction, and small- and wide-angle X-ray analysis.
Solid-state 13C cross-polarized magic angle spinning NMR
suggests that polypyrrole (PPy) exhibits primarily α,α′
linkages with some contributions from the quinoid form. Similarly,
poly(ethylenedioxythiophene) (PEDOT) also exhibits formation of primarily
α,α′ linkages with minor quinoid contributions.
Both the 1·PPy and 1·PEDOT crystals
show a 103-fold increase in conductivity to ∼10–6 S/cm versus host 1 crystals, which are
nonconductive ∼10–9 S/cm. Overall, supramolecular
polymerization strategies have the potential to readily modulate the
properties of nanostructured materials.
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