  We report the first experimental observation of strong coupling effect in
one-dimensional moir\'e crystals. We study one-dimensional double-wall carbon
nanotubes (DWCNTs) in which van der Waals-coupled two single nanotubes form
one-dimensional moir\'e superlattice. We experimentally combine Rayleigh
scattering spectroscopy and electron beam diffraction on the same individual
DWCNTs to probe the optical transitions of structure-identified DWCNTs in the
visible spectral range. Among more than 30 structure-identified DWCNTs
examined, we experimentally observed and identified a drastic change of optical
transition spectrum in DWCNT with chirality (12,11)@(17,16). The origin of the
marked change is attributed to the strong intertube coupling effect in a
moir\'e superlattice formed by two nearly-armchair nanotubes. Our numerical
simulation is consistent to these experimental findings.
