Optical coupler and visible light source module

An optical coupler which couples a plurality of visible light beams having different wavelengths and has four side surfaces, the optical coupler comprising:

• a plurality of light input ports that are disposed on a first side surface of the optical coupler and are configured for each of the visible light beams output from a plurality of visible laser light sources to be input to each of the light input ports, respectively;
• a plurality of monitoring light output ports that are disposed on a second side surface of the optical coupler and are configured to output monitoring light beams to at least one photodetector monitoring outputs of the visible light beams from the laser light sources;
• one light output port that is disposed on a third side surface of the optical coupler and is configured for a coupled light beam, in which all visible light beams output from the visible laser light sources are coupled, to be output;
• and
• a plurality of multimode-interference-type optical coupling parts,
• wherein, among the multimode-interference-type optical coupling parts,
• a first multimode-interference-type optical coupling part is configured to be used with one input and two outputs, a light input side thereof being connected to a first light-input-side waveguide, which is connected to a first light input port among the light input ports, and a light output side thereof being connected to a first monitoring-light-output-side waveguide, which is connected to a first monitoring light output port among the monitoring light output ports, and a first connecting waveguide, which is connected to an light input side of a second multimode-interference-type optical coupling part,
• the second multimode-interference-type optical coupling part is configured to be used with two inputs and two outputs, a light input side thereof being connected to a second light-input-side waveguide, which is connected to a second light input port among the light input ports, and the first connecting waveguide, and a light output side thereof being connected to a second monitoring-light-output-side waveguide, which is connected to a second monitoring light output port among the monitoring light output ports, and a second connecting waveguide, which is connected to a light input side of a third multimode-interference-type optical coupling part, and
• the third multimode-interference-type optical coupling part is configured to be used with two inputs and two outputs, a light input side thereof being connected to a third light-input-side waveguide, which is connected to a third light input port among the light input ports, and the second connecting waveguide, and a light output side thereof being connected to a third monitoring-light-output-side waveguide, which is connected to a third monitoring light output port among the monitoring light output ports, and a light-output-port-connected waveguide connected to the light output port,
• the first monitoring-light-output-side waveguide, the second monitoring-light-output-output-side side waveguide, and the third monitoring-light-output-side waveguide are free of an intersection with any waveguides, and
• only light from the first light input port is received in the first monitoring-light-waveguide, only light from the second light input port is received in the second monitoring-light-output-side waveguide, and only light from the third light input port is received in the third monitoring-light-output-side waveguide.