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Progress on femtosecond laser machined monolithic micro-devices: three dimensional dielectrophoretic actuator for switching optics Tao Yang, Yves Bellouard Eindhoven University of Technology Introduction Figure 3: experimental and simulation values of cantilever deflection under increasing direct voltage; dielectrophoretic force calculated on a volume of 20×100×100 μm3 in cantilever. To explore the capability of femtosecond laser for fabricating monolithic three dimensional devices, a dielectrophoretic actuator is demonstrated. Dielectrophoresis is derived from electrostatic action on dielectrics, due to an induced dipole moment under a non-uniform electric field [1]. This actuator makes up of a high aspect ratio cantilever located in a V shape groove out of a single piece of fused silica. It is simple monolithic and potentially all transparent and can be used for actuating dielectrics. Figure 1: diagram of dielectrophoretic actuation of fibre. The force is independent on voltage bias. Arrow indicates the dielectrophoretic force on fibre. Curved lines denote electric field. Euler-Bernoulli beam theory is adopted to analyse dynamic response of the actuator [2]. Alternating voltage is superimposed onto direct voltage and it leads to the vibration of cantilever between equilibrium axis position and maximum amplitude position near bottom of V groove. Primary resonance and superharmonic resonance are found by experiment. Primary resonance along field gradient direction is 223 Hz and its corresponding superharmonic is 111 Hz, whereas the primary resonance orthogonal to field gradient is 640 Hz. Frequency doubling is also caught in low frequency domain. Experiment Both sides of the V groove are coated with gold to serve as electrodes. The cantilever is insulated from either side of the groove. A calibrated camera system is adopted for imaging and measuring deflection of cantilever. Both direct and alternating voltage can be applied to the actuator. Frequency sweeping is conducted to study resonance. 50 µm Figure 4: intensity profile of transmitted HeNe laser beam through cantilever waveguide. The high aspect ratio cantilever can act as a waveguide, thus the entire actuator works as an optical switch when driven at DC mode. It can also serve as a butt coupler. Outlook Figure 2: (left) camera image of cantilever tip and V shape groove. (right) scanning electron microscope top view of surface quality. Modelling and results Analytical expression is used to predict dielectrophoretic force on cantilever and its deflection [1]. When applying direct voltage, the cantilever shows stable deflection independent on voltage bias. The deflection also exhibits nonlinear change with linearly increasing applied voltage. / Department of Mechanical Engineering / Microsystems Dielectrophoretic actuation distinguishes itself from traditional electrostatic actuation by getting rid of electrode on movable non-conductive component. It is also capable of more degree-of-freedom motion and easily coupled to other functionalities within a monolithic transparent MEMS system thanks to the three dimensional fabrication capability of femtosecond laser machining. Further applications of femtosecond laser processing and dielectrophoretic actuation could be found in adaptive and integrated optics. References [1] H.A. Pohl, “The motion and precipitation of suspensoids in divergent electric fields”, J. Appl. Phys., 22-869 (1951). [2] S.M. Han, H. Benaroya and T. Wei, “Dynamics of transversely vibrating beams using four engineering theories”, J. Sound and Vibration 225, 935 (1999).