Optical coherence tomograph

An optical coherence tomograph comprising:

• a light source configured to output light, the light source being configured to vary a wavelength of the light to be output;
• a branching portion configured to separate the light from the light source into irradiation light and reference light;
• a reference optical system configured to transmit the reference light from the branching portion;
• an irradiation optical system configured to
• transmit the irradiation light from the branching portion so that an object is irradiated therewith, and
• transmit reflection light of the irradiation light reflected by the object;
• a coherence portion configured to generate coherent light by causing the reflection light from the irradiation optical system and the reference light from the reference optical system to be coherent;
• a coherent light output portion configured to output the coherent light;
• and
• a coupling element configured to function as the branching portion and the coherence portion, wherein
• the reference optical system, the coupling element, and the coherent light output portion are structured with a waveguide formed over a substrate and are integrated over the substrate;
• wherein the reference optical system includes a variable optical attenuator structured with a waveguide, and an arrayed waveguide grating is positioned apart from the variable optical attenuator in a direction intersecting a direction in which unnecessary light is output from the variable optical attenuator.