  Potentially habitable planets around nearby stars less massive than
solar-type stars could join targets of the spectroscopy of the planetary
reflected light with future space telescopes. However, the orbits of most of
these planets occur near the diffraction limit for 6-m-diameter telescopes.
Thus, while securing contrast-mitigation ability under a broad spectral
bandwidth and a finite stellar angular diameter, we must maintain planetary
throughput even at the diffraction-limited angles to be able to reduce the
effect of the photon noise within a reasonable observation time. A
one-dimensional diffraction-limited coronagraph (1DDLC) observes planets near
the diffraction limit with undistorted point spread functions but has a
finite-stellar diameter problem in wideband use. This study presents a method
for wide-spectral-band nulling insensitive to stellar-angular-diameter by
adding a fiber nulling with a Lyot-plane phase mask to the 1DDLC. Designing the
pattern of the Lyot-plane mask function focuses on the parity of the amplitude
spread function of light. Our numerical simulation shows that the planetary
throughput (including the fiber-coupling efficiency) can reach about 11% for
about 1.35-$\lambda/D$ planetary separation almost independently of the
spectral bandwidth. The simulation also shows the raw contrast of about
$4\times10^{-8}$ (the spectral bandwidth of 25%) and $5\times10^{-10}$ (the
spectral bandwidth of 10%) for $3\times 10^{-2}$ $\lambda/D$ stellar angular
diameter. The planetary throughput depends on the planetary azimuthal angle,
which may degrade the exploration efficiency compared to an isotropic
throughput but is partially offset by the wide spectral band.
