The present disclosure discloses a photonic chip. The photonic chip receives a first optical signal and a second optical signal with different wavelengths from two optical sources, respectively. The photonic chip includes a polarization multiplexing element (PME). The PME receives the first and the second optical signals from the first and the second optical sources respectively and combines the first and the second optical signals into a single optical path. The PME polarizes the first optical signal to have a different polarization than the second optical signal and transmits the combined first and the second optical signals in a common waveguide.