Speckle reduction technique using the self-coherent camera for the common-path visible nulling coronagraph

Direct detection of faint exoplanets is challenging due to a high-contrast ratio between a primary star and a planet. A high-contrast imaging system has an important role in directly detecting exoplanets. The system consists of coronagraph and speckle reduction technique. A common-path visible nulling coronagraph (VNC) is one of the attracting methods for high-contrast observation because of a simple optical configuration and achromatic stellar elimination. We introduced a spatial light modulator (SLM) into the common-path VNC to suppress residual speckles caused by wavefront aberrations. The SLM can potentially generate a huge dark hole thanks to its large pixel format. As a focal plane wavefront sensor, we utilized the self-coherent camera (SCC) method for the common-path VNC. We carried out the laboratory demonstration of the speckle reduction technique for the common-path VNC combined with the SCC methods. The experimental results show an initial contrast of 2.2 × 10-5 and a final contrast of 1.3 × 10-6 in monochromatic light at a wavelength of 633 nm. We discuss the limiting factors of the contrast for improvement of our demonstration to achieve the higher contrast.