Flexible broadband optical frequency comb generation assisted by injection locking of semiconductor laser

A broadband optical frequency comb (OFC) generator is proposed and experimentally demonstrated. Based on the injection locking process in a semiconductor laser diode, multiple coherent carriers with large intervals can be generated, which are further combined to give a much broader OFC through the electro-optical modulation (EOM) technique. The corresponding theoretical analysis and simulation have been given in detail. In the experimental demonstration, an OFC with 9 comb lines can be generated on a single carrier by the cascaded MZMs with a multi-harmonic RF drive signal. After tripling the number of carriers, the number of the comb lines becomes 27. By properly adjusting the carrier’s interval and drive signal frequency, the generated OFC shows great flexibility on spacing and the number of comb lines, where a 27-line OFC with FSR of 5 GHz and 6.5 GHz have been demonstrated respectively. In addition, by increasing the number of RF sources, the OFC with up to 43 comb lines can be generated in this system. Compared with the traditional OFC generation implemented by the EOM technique on a single optical carrier, three times optical spectrum extension or the number of comb lines increasing can be achieved. The Multi-carrier broaden spectrum method retains all the advantages of EOM-based OFC generation and overcomes its disadvantages, such as limited spectrum width and the number of comb lines. It provides a new idea for broadband OFC generation.