Y-cut LiNbO/sub 3/ directional coupler with a self-aligned electrode

A 2/spl times/2 Y-cut LiNbO/sub 3/ directional coupler switch using a self-aligned uniform /spl Delta//spl beta/ electrode is fabricated by the proton diffusion method. Our design method makes it possible to form the electrode without the delicate alignment of the electrode pattern mask and optical waveguide. The switching voltage is also reduced due to the enhanced electro-optic efficiency by using the self-aligned electrode. To achieve the initial cross state of the uniform /spl Delta//spl beta/ switch that is essential for low crosstalk, we control the proton diffusion time successively after the proton exchange. The measured crosstalk level of the directional coupler switch is -23 dB/spl sim/-29 dB and its voltage-length product is as small as 9.6 Vmm.<
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