An optical multiplexer, configured to multiplex at least four optical signals into one optical signal, and comprising at least: a first polarization state adjusting component, a second polarization state adjusting component, a first optical path changing component, a second optical path changing component, a polarization beam combiner, and a beam combiner, wherein the first polarization state adjusting component is configured to adjust a polarization state of a first optical signal in the at least four optical signals before the first optical signal is input into the polarization beam combiner, so that the first optical signal and a third optical signal in the at least four optical signals are combined into one optical signal in the polarization beam combiner; the second polarization state adjusting component is configured to adjust a polarization state of a second optical signal in the at least four optical signals before the second optical signal is input into the polarization beam combiner, so that the second optical signal and a fourth optical signal in the at least four optical signals are combined into one optical signal in the polarization beam combiner; the first optical path changing component is configured to change a propagation direction of the third optical signal and a propagation direction of the fourth optical signal, so that the signals are input into the polarization beam combiner; the polarization beam combiner is configured to combine the first optical signal and the third optical signal that are received to obtain a fifth optical signal, and is further configured to combine the second optical signal and the fourth optical signal that are received to obtain a sixth optical signal; the second optical path changing component is configured to change a propagation direction of the fifth optical signal or a propagation direction of the sixth optical signal output by the polarization beam combiner, so that the fifth optical signal and the sixth optical signal are combined by the beam combiner into one optical signal after being input into the beam combiner; and the beam combiner is configured to combine the fifth optical signal and the sixth optical signal that are received into one optical signal; and wherein the optical multiplexer further comprises a third polarization state adjusting component and a fourth polarization state adjusting component, wherein the third polarization state adjusting component is configured to adjust a polarization state of the third optical signal before the third optical signal is input into the polarization beam combiner, so that the third optical signal in the adjusted polarization state and the first optical signal in the adjusted polarization state are combined into one optical signal in the polarization beam combiner; and the fourth polarization state adjusting component is configured to adjust a polarization state of the fourth optical signal before the fourth optical signal is input into the polarization beam combiner, so that the fourth optical signal in the adjusted polarization state and the second optical signal in the adjusted polarization state are combined into one optical signal in the polarization beam combiner; wherein the first optical path changing component and the second optical path changing component are reflectors or prisms; and characterized in that the first polarization state adjusting component and the second polarization state adjusting component are 1/4-wave plates, and the third polarization state adjusting component and the fourth polarization state adjusting component are 3/4-wave plates.