  We demonstrate polarization multiplexed dissipative Kerr solitons in an
on-chip silicon nitride micro-resonator. In our experiment, TE- and
TM-polarized soliton can be individually generated and controlled, thanks to
their weak mutual interaction as the result of sufficiently different
repetition rates and orthogonal polarization states. Furthermore, we find that
TE- and TM-polarized solitons usually exhibit uncorrelated time jitters,
therefore the frequency and phase coherence between the polarization
multiplexed soliton microcombs change dramatically as a function of pump laser
parameters, by optimizing which we achieve narrow dual-microcomb beat note
linewidth as small as 4.4 kHz. Potential applications of on-chip polarization
multiplexed soliton microcombs include Kerr comb spectral expansion, dual-comb
metrology, and measurement of quantum entanglements.
