This application discloses a polarization processing optical device, method, and system. In specific implementation, the polarization processing optical device includes a polarization beam splitter (PBS), a polarization rotator (PR), a coupler, and a phase tuner (PT), where one port of the PBS is configured to input a continuous light source, and the other two ports of the PBS are respectively connected to the PR and one port of the coupler; and the PR is connected to another port of the coupler; the PT is disposed on a connection between the PBS and the coupler or a connection between the PR and the coupler; and at least one port of the coupler is configured to output single-polarization light, and the PT is configured to control output optical power of the first coupler. The polarization processing optical device may convert an optical energy in a random polarization state into an optical energy in a single polarization state, and realize optical splitting with a specific proportion. According to the apparatus, an optical transmitter and/or receiver may use a conventional optical fiber to connect a light source and an optical modulator, so that costs are reduced.