  We show that customized optical patterns can be generated by employing
feedback-based wavefront shaping without prior knowledge of the transmission
matrix of optical systems. To control the spatial distribution of intensity
within the target region, the overlap coefficient is employed as the key
feedback signal for wavefront shaping, and the optimal phase pattern for
generating the customized optical pattern is reached when the overlap
coefficient converges to unity. By using the overlap-coefficient optimized
wavefront shaping, we generate customized optical patterns such as multiple
focused spots of different intensity, cat image, and speckle patterns of
tailored intensity distribution. Besides, we also show that a sharp focusing
spot can be generated in highly scattering systems with the overlap-coefficient
optimized wavefront shaping, and the achieved signal-to-background ratio is
much higher than that achieved with the conventional wavefront shaping. Our
method provides new possibilities to control the interference of light for many
applications, such as optical imaging, quantum interference, and optical
trapping and manipulation.
