Optical Modulator
Provided is an optical modulator that can be adjusted to an optimum bias condition even in a dual-electrode type structure. An optical modulator including a semiconductor layer with a pn junction in an optical waveguide core, and an RF electrode and a ground electrode for applying a radio frequency (RF) signal to the semiconductor layer, the optical modulator modulating an optical signal by applying a bias voltage to the semiconductor layer together with the RF signal, the optical modulator including: a bias electrode disposed to face the ground electrode inside a substrate, in which the RF electrode and the bias electrode are connected to the semiconductor layer.
1 . An optical modulator comprising:
a semiconductor layer with a pn junction in an optical waveguide core;
an RF electrode and a ground electrode configured to apply a radio frequency (RF) signal to the semiconductor layer, an optical signal being modulated by applying a bias voltage to the semiconductor layer together with the RF signal; and
a bias electrode disposed to face the ground electrode inside a substrate, wherein
the RF electrode and the bias electrode are connected to the semiconductor layer.
2 . The optical modulator according to claim 1 , wherein
a capacitor is formed by the ground electrode and the bias electrode, and
the semiconductor layer is connected to the ground electrode in terms of alternating current for the RF signal, and is connected to the bias electrode in terms of direct current for the bias voltage.
3 . The optical modulator according to claim 1 , wherein the ground electrode includes a first ground electrode and a second ground electrode sandwiching the RF electrode, and constitutes a coplanar waveguide (CPW) together with the RF electrode, the bias electrode includes a first bias electrode facing the first ground electrode and a second bias electrode facing the second ground electrode, and the first bias electrode is connected to the semiconductor layer.
4 . The optical modulator according to claim 1 , wherein the ground electrode and the bias electrode overlap and face each other over a plurality of layers in a direction perpendicular to a surface of the substrate.