Optical device and optical communication apparatus

An optical communication apparatus comprising:

• a processor that performs signal processing on an electric signal;
• a light source that generates light;
• a modulator that includes
• an optical waveguide that is formed of a thin-film lithium niobate (LN) substrate and through which light passes;
• and
• an electrode that applies voltage to the optical waveguide, and
• modulates a phase of the light that passes through the optical waveguide in accordance with an electric field in the optical waveguide, the electric field corresponding to the voltage;
• a tap coupler that includes at least a part formed of the thin-film LN substrate, and splits a part of the light that passes through an inside of the optical waveguide;
• and
• a monitor that is coupled to the tap coupler and monitors the part of the light split by the tap coupler;
• wherein
• the tap coupler includes a delayed interferometer that splits a part of the light that passes through the optical waveguide, at a split ratio corresponding to a phase difference of light that passes through an inside of the tap coupler from the optical waveguide;
• and
• wherein the delayed interferometer includes
• a first coupler that receives the light input from the optical waveguide and splits the input light;
• a first waveguide that is formed of the thin-film LN substrate and through which one part of light split from the first coupler passes;
• a second waveguide that is formed of the thin-film LN substrate, through which other part of light split from the first coupler passes, and that delays optical output as compared to the first waveguide;
• and
• a second coupler that multiplexes the one part of light from the first waveguide and the other part of light from the second waveguide, and splits the multiplexed light with a phase difference at a split ratio corresponding to the phase difference.