Figure | Ultrahigh isolation via optical circular-polarization purification. (IMAGE)
Caption
a, schematic of the improved experimental apparatus with an extra Rb vapor cell. The backward probe purified through Cell2 was used to characterize the isolation ratio in Cell1. b, transmittance of the backward probe against its polarization, which is controlled by the angle of the QWP (near port 2) with a forward signal power of 150 mW and a backward probe power of 1 mW. The zero angle corresponds to a linear polarization. The four lines show the corresponding theoretical predictions under different conditions, while the dots are the experimental results. Shaded areas denote noise floors from different causes. c, the improved measurement of the isolation ratio (red circles) by using the NLNR effect for circular-polarization purification and an etalon to eliminate laser background noise, compared to the results without purification (blue diamonds). These two results correspond to 45° in b . The highest isolation ratio reaches 63.4 dB with a 2.1 GHz bandwidth for 60 dB isolation. The black line is the theoretical prediction of the ideal isolation ratio, while the red and blue lines are the results considering two different noise floors to fit the experimental data.
Credit
Zhu-Bo Wang et al.
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CC BY