Novel Polarization-Dependence-Free Optical Injection-Locking Circuit Using $ lambda / 4$ Phase-Shift-Free HR DFB LD at $1.5 mu mathrm{m}$. - Keisuke Kasai; Shun Otsu; Masato Yoshida; Toshihiko Hirooka; Masataka Nakazawa (ECOC, 2025)