Methods and apparatuses for multiplexing and demultiplexing optical signals configured to suppress the four-wave mixing effect

An optical multiplexer, comprising:

• a first beam combiner comprising a first parallelepiped-shaped block having a first reflective surface, a first filter and a first antireflective sheet or plate on a same side of the first parallelepiped-shaped block as the first filter, the first beam combiner being configured to combine a first optical signal and a second optical signal into a first multi-channel polarized optical signal, wherein the first optical signal has a first polarization state and a first wavelength, the second optical signal has the first polarization state and a second wavelength, the first filter reflects the first optical signal and allows the second optical signal to pass through, and the first reflective surface and the first filter are on opposite sides of the first parallelepiped-shaped block;
• a second beam combiner comprising a second parallelepiped-shaped block having a second reflective surface, a second filter and a second antireflective sheet or plate on a same side of the second parallelepiped-shaped block as the second filter, the second beam combiner being configured to combine a third optical signal and a fourth optical signal into a second multi-channel polarized optical signal, wherein the third optical signal has a second polarization state and a third wavelength, the fourth optical signal has the second polarization state and a fourth wavelength, the second filter reflects the third optical signal and allows the fourth optical signal to pass through, and the second reflective surface and the second filter are on opposite sides of the second parallelepiped-shaped block;
• and
• a polarizing beam combiner comprising a third reflective surface and a polarization filter, the polarizing beam combiner being configured to combine the first and second multi-channel polarized optical signals into a multi-channel output signal.