No abstract

Photonic-integrated circuits (PICs) using ferroelectric materials are expected to be used in many applications because of its unique optical properties such as large electro-optic coefficients. In this study, a novel PIC based on a ferroelectric thin-film platform was designed and fabricated, where high-speed optical modulator, spot-size converters (SSCs), and a variable optical attenuator (VOA) were successfully integrated. A ferroelectric lanthanum-modified lead zirconate titanate (PLZT) thin film was epitaxially-grown by using a modified sol-gel method, and it exhibits large electro-optic coefficients (>120 pm/V) and low propagation loss (1.1 dB/cm). The optical modulator, a Mach-Zehnder type, exhibited a half-wave voltage (Vπ) of 6.0 V (VπL = 4.5 Vcm) and optical modulation up to 56 Gb/s. Also, the VOA (with attenuation range of more than 26 dB) was successfully integrated with the modulator. As a result, it is concluded that the developed ferroelectric platform can pave the way for photonic integration.

We experimentally investigated the photo-induced direct current (DC) drift of a lead lanthanum zirconate titanate (PLZT) Mach-Zehnder modulator with large optical input power. We clarify the mechanism by which short-term and long-term DC drifts arise and discuss each case of DC drift. We reveal that short-term DC drift can be reduced by adjusting the buffer-layer resistivity of the PLZT modulator. We also found that the impurity level of the buffer layer affects long-term DC drift.