1. Technical Field
The present invention relates to an optical amplifier device.
2. Related Art
An optical amplifier device is known that uses a polarization diversity circuit to split input light into TE polarized light and TM polarized light, keep the TE polarized light as-is, convert the TM polarized light into TE polarized light, and input the TE polarized light resulting from the conversion into an SOA (Semiconductor Optical Amplifier), such as shown in Non-Patent Document 1.
Non-Patent Document 1: K. Morito and S. Tanaka, “Record High Saturation Power (+22 dBm) and Low Noise FIG. 5.7dB) Polarization-Insensitive SOA Module”, IEEE PHOTONICS TECHNOLOGY LETTERS, 17, 6, 1298-1300, (2005)
The gain of the light in the SOA differs for the TE polarized light and the TM polarized light. With an optical amplifier device that uses a polarity diversity circuit, the TM polarized light is converted into TE polarized light and then input to the SOA. As a result, the difference in optical gain caused by the polarization direction can be decreased. However, the gain of the SOA also depends on the intensity of the light input to the SOA. Therefore, in the polarity diversity circuit, if there is a difference between the intensity of the light that is input to the SOA after being converted from TM polarized light to TE polarized light and the intensity of the light input to the SOA as the split TE polarized light, there is also a difference in gain between these two lights.
The difference in gain caused by the polarization direction is referred to as PDG (Polarized Dependent Gain). When the polarization direction of signal light input to an optical amplifier device changes randomly, PDG occurs and there is fluctuation in the intensity of the light output from the optical amplifier device, which causes signal error. Accordingly, in order to reduce the signal error, it is necessary to decrease the PDG.