We demonstrate a compact thermo-optic variable optical attenuator (VOA) based on the cutoff effect of W1 photonic crystal waveguide (PCW). In experiment, a variable attenuation range of 29 dB is achieved with a device length of only 16.8 μm. The coupling loss is also reduced by 7.5± 2.5 dB through introducing low-group-index tapers between the W1 PCW and strip waveguide. This VOA provides the largest variable attenuation range in the reported tunable PCW device to our knowledge.
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