  Context. In the context of direct imaging of exoplanets, coronagraphs are
commonly proposed to reach the required very high contrast levels. However,
wavefront aberrations induce speckles in their focal plane and limit their
performance. Aims. An active correction of these wavefront aberrations using a
deformable mirror upstream of the coronagraph is mandatory. These aberrations
need to be calibrated and focal-plane wavefront-sensing techniques in the
science channel are being developed. One of these, the self-coherent camera, of
which we present the latest laboratory results. Methods. We present here an
enhancement of the method: we directly minimized the complex amplitude of the
speckle field in the focal plane. Laboratory tests using a four-quadrant
phase-mask coronagraph and a 32x32 actuator deformable mirror were conducted in
monochromatic light and in polychromatic light for different bandwidths.
Results. We obtain contrast levels in the focal plane in monochromatic light
better than 3.10^-8 (RMS) in the 5 - 12 {\lambda}/D region for a correction of
both phase and amplitude aberrations. In narrow bands (10 nm) the contrast
level is 4.10^-8 (RMS) in the same region. Conclusions. The contrast level is
currently limited by the amplitude aberrations on the bench. We identified
several improvements that can be implemented to enhance the performance of our
optical bench in monochromatic as well as in polychromatic light.
