Efficient LiNbO3 balanced bridge modulator/switch with an ion-etched slot

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Abstract
A simple modified balanced bridge modulator or switch is reported. The modulator is comprised of only straight waveguides and an ion‐etched slot used for a conventional phase shifter. The slot excavated at the center of two coupled waveguides solves the coupling of them. 3‐dB coupler monitoring is performed here by a metal loading. The modulator is fabricated by diffusing Ti into z‐cut LiNbO3. Each patterned waveguide is fabricated by diffusing Ti into z‐cut LiNbO3. Each patterned waveguide is 7 μm wide and the spacing is 7 μm. The 3‐dB coupler is 2.9 mm long, and the excavated slot is 15 mm long, 4 μm wide, and 4.5 μm deep. The overall length is 20.8 mm. For the TM‐like fundamental mode, the half‐wave voltage was 2.8 V, the extinction ratio was −15 dB, and the optical insertion loss was as low as 2.6 dB at the 1.15‐μm wavelength.