We report an electric field induced‐guide/antiguide optical intensity modulator which has a very wide optical bandwidth from 1 to 1.55 &mgr;m (ON/OFF ratio ≳ 13 dB from 1 to 1.55 &mgr;m for both TE and TM modes), which is the largest ever reported before for an intensity modulator. A TE mode ON/OFF ratio larger than 21 dB at 1.15 &mgr;m, and a propagation loss ∼1 dB at 1.3 &mgr;m has been measured. The electro‐optic effects, along with carrier effects have been exploited to increase the refractive index under the guide and adjacent antiguide electrodes by applying reverse biases to them.