A novel variable optical attenuator (VOA) based on the photonic crystal (PC) cavity with liquid crystals is demonstrated. Two photonic crystal waveguides are connected by photonic crystal cavity. The point defect of photonic crystal cavity is filled with phenylacetylene liquid cyrstals. The output of optical attenuator is controlled by adjusting rotation angle of the liquid cyrstals orientation vector. The VOA properties are numerically investigated by using the finite difference time domain (FDTD) method and plane wave expansion method. Numerical simulation shows that the attenuator based the PC cavity can be changed by adjusting the applied field. Furthermore
the attenuator performs output of 3.40%~99.58% at the wavelength of 1.55 m.
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