We present the concept and design, and we report on the experimental performance of a broadband Variable Optical Attenuator (VOA) for integration with large-core rectangular multimode waveguides. Operation of an individual 221 mu m x 111 mu m optical waveguide channel employing a MEMS actuated dual-shutter to continuously modulate the intensity of the optical input signal is demonstrated experimentally. The MEMS actuated dualshutter is fabricated in a 211 mu m thick device layer of a Silicon-On-Insulator wafer by Deep Reactive Ion Etching. Electrostatic comb drive actuators allow a displacement of more than 63 mu m at 86 V, resulting in a continuously tunable attenuator efficiency of up to 99.97% at an operating wavelength of 532 nm with a reconfiguration time < 0.5 ms.