Quantum-Dot Semiconductor Optical Amplifiers With Polarization-Independent Gains in 1.5-$\mu$ m Wavelength Bands

We have demonstrated a polarization-independent gain in semiconductor optical amplifiers that have columnar quantum dots surrounded by strained side barriers in 1.5-mum wavelength bands. We obtained a polarization-dependent gain of 0.5 dB with a gain of 10 dB and a saturation output power of 18 dBm at a wavelength of 1.55 mum.