In the field of optical networks, a laser, a laser modulation method and a laser combination system are disclosed. The laser includes a gain medium, a resonant cavity, and a second microring resonator. The resonant cavity includes a first cavity mirror and a second cavity mirror. The first cavity mirror is located at one port of the gain medium, the second cavity mirror is located at another port of the gain medium, and the second cavity mirror includes a splitter, a first microring resonator, and a reflecting grating.