Extremely low noise characteristics of DFB laser module with doubled optical isolator scheme

The authors have theoretically clarified that the optical feedback ratio should be suppressed to less than -70dB, then they have developed a DFB laser module with 'doubled' optical isolator scheme for the first time. An extremely low RIN value below -150dB/Hz has been achieved for the case with fiber far-end reflection. Temperature independent RIN characteristics have been also demonstrated.