Tunable laser and laser transmitter

A laser transmitter, comprising:

• a tunable laser and a signal modulation apparatus, wherein
• the tunable laser comprises a reflective semiconductor optical amplifier (SOA), a grating codirectional coupler, and a reflective microring resonator, wherein the grating codirectional coupler and the reflective microring resonator are both formed on a silicon base;
• an anti-reflection film is disposed on a first end surface of the reflective SOA, the first end surface is an end surface, coupled to a first waveguide of the grating codirectional coupler, of the reflective SOA, a highly reflective film is disposed on a second end surface of the reflective SOA, and the second end surface is an end surface opposite to the first end surface;
• a second waveguide of the grating codirectional coupler is coupled to the first waveguide, a first grating is disposed on the first waveguide, a second grating disposed opposite to the first grating is disposed on the second waveguide, the first grating and the second grating constitute a narrow-band pass filter, and the second waveguide is connected to the reflective microring resonator;
• and the reflective microring resonator comprises a first straight waveguide, a second straight waveguide, and an annular waveguide, the annular waveguide is located between the first straight waveguide and the second straight waveguide, and light field coupling exists between the first straight waveguide and the annular waveguide, and between the second straight waveguide and the annular waveguide;
• and
• the signal modulation apparatus is configured to modulate optical signals that are output from the first straight waveguide and the second straight waveguide into a polarization multiplexing high-order modulation signal.