Light combining/dividing element and light modulator

A light combining/dividing element, comprising:

• a core made of a semiconductor,
• the core including:
• a first core;
• second through N-th cores each having a thickness equal to that of the first core, the second through N-th cores being arranged in parallel to each other;
• and
• an multi-mode interference (MMI) part having a first end surface and a second end surface, the first end surface being connected to the first core, the second end surface facing the first end surface and being connected to each of the second through N-th cores,
• the MMI part including:
• a channel waveguide including the second end surface, the channel waveguide having a width greater than a sum of respective widths of the second through N-th cores;
• and
• a rib waveguide including the first end surface, the rib waveguide including (i) a rib having a thickness equal to that of each of the first through N-th cores and (ii) slabs each having a thickness thinner than that of the rib,
• the rib having a width which becomes narrower from a width equal to that of the channel waveguide to a width equal to that of part of the first core which part is located at a boundary between the first core and the rib,
• wherein a width of each of the slabs has a value of 0 (zero) at a boundary between the channel waveguide and the rib waveguide and at a boundary between the first core and the rib waveguide.