Optical semiconductor device and reception apparatus

1. An optical semiconductor device comprising:

a first optical coupler including a first input port, a second input port, a first output port, and a second output port;

a first optical branching device including a third input port, a fourth input port, a third output port, and a fourth output port;

a second optical coupler including a fifth input port, a sixth input port, a fifth output port, and a sixth output port;

a second optical branching device including a seventh input port, a seventh output port, and an eighth output port;

a first single mode waveguide configured to connect the second input port and the third output port;

a second single mode waveguide configured to connect the fourth output port and the fifth input port;

a third single mode waveguide configured to connect the sixth input port and the seventh output port; and

a fourth single mode waveguide configured to connect the eighth output port and the first input port,

the first single mode waveguide includes a first core,

the second single mode waveguide includes a second core

the third single mode waveguide includes a third core,

the fourth single mode waveguide includes a fourth core, and

the first core includes:

a first core taper configured to be directly connected to the second input port and becomes narrower in width as a distance from the second input port increases, and

a second core taper configured to be directly connected to the third output port and becomes narrower in width as a distance from the third output port increases.

2. The optical semiconductor device according to claim 1 , wherein

the first optical coupler includes a channel-type first multimode waveguide,

the first optical branching device includes a channel-type second multimode waveguide,

the second optical coupler includes a channel-type third multimode waveguide, and

the second optical branching device includes a channel-type fourth multimode waveguide.

3. The optical semiconductor device according to claim 1 , wherein the first single mode waveguide, the second single mode waveguide, the third single mode waveguide, and the fourth single mode waveguide are provided over a common plane.

4. The optical semiconductor device according to claim 3 , wherein

the first single mode waveguide includes:

a first slab configured to extend from the first core in a direction parallel to the plane,

the second single mode waveguide includes:

a second slab configured to extend from the second core in a direction parallel to the plane,

the third single mode waveguide includes:

a third slab configured to extend from the third core portion in a direction parallel to the plane,

the fourth single mode waveguide includes:

a fourth slab configured to extend from the fourth core in a direction parallel to the plane,

the second core includes:

a third core taper configured to be directly connected to the fourth output port and becomes narrower in width as a distance from the fourth output port increases, and

a fourth core taper configured to be directly connected to the fifth input port and becomes narrower in width as a distance from the fifth input port increases,

the third core includes:

a fifth core taper configured to be directly connected to the sixth input port and becomes narrower in width as a distance from the sixth input port increases, and

a sixth core taper configured to be directly connected to the seventh output port and becomes narrower in width as a distance from the seventh output port increases, and

the fourth core includes:

a seventh core taper configured to be directly connected to the eighth output port and becomes narrower in width as a distance from the eighth output port increases, and

an eighth core taper configured to be directly connected to the first input port and becomes narrower in width as a distance from the first input port increases.

5. The optical semiconductor device according to claim 4 , wherein, in the directions parallel to the plane, the first slab, the second slab, the third slab, and the fourth slab are separated from each other.

6. The optical semiconductor device according to claim 5 , wherein

the first slab includes:

a first slab taper configured to be located at a side of the first core taper and becomes wider in width as a distance from the second input port increases, and

a second slab taper configured to be located at a side of the second core taper and becomes wider in width as a distance from the third output port increases,

the second slab includes:

a third slab taper configured to be located at a side of the third core taper and becomes wider in width as a distance from the fourth output port increases, and

a fourth slab taper configured to be located at a side of the fourth core taper and becomes wider in width as a distance from the fifth input port increases,

the third slab portion includes:

a fifth slab taper configured to be located at a side of the fifth core taper and becomes wider in width as a distance from the sixth input port increases, and

a sixth slab taper configured to be located at a side of the sixth core taper and becomes wider in width as a distance from the seventh output port increases, and

the fourth slab portion includes:

a seventh slab taper configured to be located at a side of the seventh core taper and becomes wider in width as a distance from the eighth output port increases, and

an eighth slab taper configured to be located at a side of the eighth core taper and becomes wider in width as a distance from the first input port increases.

7. The optical semiconductor device according to claim 1 , further comprising:

a fifth single mode waveguide configured to connect to the first output port;

a sixth single mode waveguide configured to connect to the second output port;

a seventh single mode waveguide configured to connect to the third input port;

an eighth single mode waveguide configured to connect to the fourth input port;

a ninth single mode waveguide configured to connect to the fifth output port;

a tenth single mode waveguide configured to connect to the sixth output port; and

an eleventh single mode waveguide configured to connect to the seventh input port.

8. The optical semiconductor device according to claim 1 , wherein the first single mode waveguide, the second single mode waveguide, the third single mode waveguide, and the fourth single mode waveguide are rib-type waveguide.

9. A reception apparatus comprising:

a first optical coupler including a first input port, a second input port, a first output port, and a second output port;

a first optical branching device including a third input port, a fourth input port, a third output port, and a fourth output port;

a second optical coupler including a fifth input port, a sixth input port, a fifth output port, and a sixth output port;

a second optical branching device including a seventh input port, a seventh output port, and an eighth output port;

a first single mode waveguide configured to connect the second input port and the third output port;

a second single mode waveguide configured to connect the fourth output port and the fifth input port;

a third single mode waveguide configured to connect the sixth input port and the seventh output port; and

a fourth single mode waveguide configured to connect the eighth output port and the first input port,

the first single mode waveguide includes a first core,

the second single mode waveguide includes a second core

the third single mode waveguide includes a third core,

the fourth single mode waveguide includes a fourth core, and

the first core includes:

a first core taper configured to be directly connected to the second input port and becomes narrower in width as a distance from the second input port increases, and

a second core taper configured to be directly connected to the third output port and becomes narrower in width as a distance from the third output port increases.