Efficient Mid-Infrared Electro-Optical Waveguide Modulators Using Ferroelectric Barium Titanate

Mid-Infrared (mid-IR) electro-optical (E-O) modulators are critical components in developing broadband optical communication since present E-O modulators were mainly operated in the near Infrared (NIR) range. Meanwhile, the conventional ferroelectric E-O material - lithium niobate (LiNbO
₃
or LN) has lower Pockels effect comparing to barium titanate (BaTiO
₃
or BTO). This work demonstrated an E-O modulator in the mid-IR region applying a BTO substrate with low-loss titanium dioxide (TiO
₂
) waveguides. The TiO
₂
waveguide device was first fabricated on a Si wafer by the complementary metal-oxide-semiconductor (CMOS) fabrication process. A fundamental waveguide mode was observed at λ = 2.5-02.7 μm, and an optical loss of 2.33 dB/cm was obtained. To achieve an efficient E-O modulation, the TiO
₂
waveguide was bonded with a <;001> BaTiO
₃
single crystalline wafer that has a strong Pockels effect. The measured E-O coefficient γ
_eff
at λ = 2.6 μm was 119.7 pm/V, which is five times higher than the conventional LiNbO
₃
modulators, and a large modulation depth of 8.45 dB was accomplished.