  We investigate the wave optics in spherically symmetric spacetimes:
Schwarzschild black hole, spherical star with a perfect absorbing surface, and
massless/massive Ellis wormholes. Assuming a point wave source, wave pattern
and power spectrums for scattering waves are obtained by solving the scalar
wave equation numerically. We found that the power spectrum at the observer in
the forward direction shows oscillations with two characteristic periods
determined by the interference effect associated with the photon sphere and the
diffraction effect due to the absorbing boundary condition inside of the photon
sphere.
