Enhancement of the phase-modulation range by using cascaded injection-locked semiconductor lasers

The phase modulation of an injection-locked semiconductor laser can be controlled by tuning the injection-locking parameters. However, the phase-modulation range is limited to 180A degrees, which significantly hinders its widespread application. In this study, we investigated the phase-modulation characteristics of a single stage of an injection-locked laser configuration by considering a slave laser's bias control as a tuning parameter. Herein, we propose cascaded injection-locked laser configurations to enhance the phase-modulation range and theoretically demonstrate that the achievable phase-modulation range can be increased. The output of the slave laser is used as the input of the next slave laser to produce an accumulated phase modulation. The results show that a phase modulation of 360A degrees can be achieved using the cascaded configurations; moreover, the number of cascaded configurations required to achieve this range is determined for specific laser parameters.