Optical device, optical hybrid circuit, and optical receiver

An optical device, comprising:

• a first coupler configured to split an optical signal;
• a second coupler configured to cause optical signals to interfere with each other;
• a first waveguide configured to couple the first coupler to the second coupler, the first waveguide includes a first phase shifter region having a section narrower in width than an end of the first phase shifter region;
• and
• a second waveguide configured to couple the first coupler to the second coupler, the second waveguide includes a second phase shifter region having a section wider in width than an end of the second phase shifter region, wherein the first phase shifter region and the second phase shifter region are aligned at substantially the same length-wise position and have substantially the same length;
• wherein each of the first phase shifter region and the second phase shifter region has a longitudinal length of 50 μm or less;
• and
• wherein the first phase shifter region includes a tapered section extending from an input end of the first phase shifter region and then linearly tapering in a longitudinal direction to an end of the tapered section, where a reverse-tapered section begins linearly-reverse tapering and then extending to an output end of the first phase shifter region in the longitudinal direction.