Highly integrated optical components are strongly demanded because they enable wavelength-division multiplexing optical communication systems to achieve smaller footprints, lower power consumption, and enhanced reliability. Variable optical attenuator (VOA) arrays are often used with optical switches in cascaded form for reconfigurable optical add-drop multiplexer systems. Although VOAs and optical switches based on polymer waveguide technology are commercially available, it is still not viable to integrate these two array devices on a single chip because of significant interchannel crosstalk. In this work, we resolved the issue of crosstalk and integrated the arrays of optical switch and VOA on a single chip by incorporating a self-assembled scattering monolayer (SASM). The SASM was effective for scattering the planar guided mode; consequently, the crosstalk into an adjacent channel was significantly reduced, to less than -35 dB.