Optical amplifier device

1. An optical amplifier device comprising:

an input/output section that inputs incident light and outputs emission light;

a polarized light splitting section that causes a polarized light component of the incident light input from the input/output section to branch, and outputs first polarization mode light having a first polarization and second polarization mode light having a second polarization that is different from the first polarization;

a polarization converting section into which is input the first polarization mode light, the polarization section converting the first polarization to the second polarization and outputting first polarization converted light; and

an optical amplifying section that amplifies the first polarization converted light input to one end of a waveguide, outputs the resulting amplified first polarization converted light from another end of the waveguide, amplifies the second polarization mode light input to the other end of the waveguide, and outputs the resulting amplified second polarization mode light from the one end of the waveguide, wherein

an absolute value of a change in gain per unit intensity of the light input to the optical amplifying section is no greater than 0 . 16 dB/dBm,

the optical amplifying section includes:

an active layer that propagates the first polarization converted light and the second polarization mode light; and

an electrode that injects carriers into the active layer, and

with Γ representing a confinement coefficient that is a ratio between light confined in the active layer and light in the optical amplifying section and L representing length of the electrode in micrometers, the expression Γ×L<1500% μm is satisfied.

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

the optical amplifying section includes:

a first semiconductor optical amplifier;

a first waveguide that provides a connection between the one end of the optical amplifying section and the first semiconductor optical amplifier;

a second semiconductor optical amplifier connected in series with the first semiconductor optical amplifier; and

a second waveguide that provides a connection between the other end of the optical amplifying section and the second semiconductor optical amplifier, and

the first waveguide and the second waveguide have the same optical length.

3. The optical amplifier device according to claim 2 , wherein

the polarized light splitting section includes a Mach-Zehnder interferometer circuit that is formed by a quartz planar lightwave circuit and has a waveguide with an embedded mesa structure, and

a U-turn portion of an optical waveguide having a high mesa structure provides a connection between the first semiconductor optical amplifier and the second semiconductor optical amplifier.

4. The optical amplifier device according to claim 1 , wherein

the optical amplifying section includes a pair of light reflecting sections that reflect light, and

the light reflected by the pair of light reflecting sections is resonated by the active layer.

5. The optical amplifier device according to claim 4 , wherein

the pair of light reflecting sections are formed on both sides of the active layer to sandwich the active layer, and reflect light in a direction perpendicular to a direction of the propagation of the first polarization converted light and the second polarization mode light in the active layer.

6. The optical amplifier device according to claim 4 , wherein

the pair of light reflecting sections are formed in contact with the active layer, and reflect light in a direction parallel to a direction of the propagation of the first polarization converted light and the second polarization mode light in the active layer.

7. The optical amplifier device according to claim 1 , wherein

the first polarization is TM polarization, and

the second polarization is TE polarization.