| 摘要 |
Disclosed is an optical waveguide element wherein a plurality of Mach-Zehnder waveguides to be used for DQPSK modulation and the like are integrated on a thin substrate and the on/off extinction ratio is improved. The optical waveguide element has the thin board, which is formed of a material having electrooptical effects and has a thickness of 20 μm or less, and an optical waveguide formed on the front surface or the rear surface of the thin board. The optical waveguide has the plurality of Mach-Zehnder waveguide sections, and multiplexes optical waves outputted from two or more Mach-Zehnder waveguide sections. In the multiplexing section in each Mach-Zehnder waveguide section (MZA), a triply branched waveguide, which is composed of a waveguide for output (c1) and two waveguides for radiation (b1, b2) disposed to sandwich the waveguide for output, is formed. High-order mode light absorption regions (d1, d2) are formed between the waveguide for output and the waveguides for radiation in the triply branched waveguide.
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