Error in Figure In the original article , there was a mistake in Figure 5c,d as published. The mistake was in the x-axis of the shown eye diagrams, and it was due to a coding error in the MATLAB plotting function that was used. The symbol rate in this work was 60 GBaud. This corresponds to a pulse duration of T = 1/60 GHz ≈ 16.67 ps. Since the x-axis in eye diagrams is commonly between 0 and 2T, the correct x-axis should have been 0~33.33 ps instead of 0~16.67 ps (previously). Another way to confirm the mistake is by noticing that, if 2T ≈ 16.67 ps was assumed, that should have corresponded to a symbol rate of 120 GBaud (instead of 60 GBaud). This is obviously not the case, and such high-speed modulation was never claimed in this work. The corrected Figure 5c,d appear below. The authors apologize for any inconvenience caused and state that the scientific conclusions are unaffected. The original article has been updated. Figure 5. 60 GBaud PAM-4 signal evaluation: (a) Experimental setup; (b) Bit-error rate (BER) versus received optical power at back-to-back (BTB) and after 2-kmSSMF transmissions, and (c,d) Eye diagrams after equalization. Measurements were performed at 25°C (I_b = 9.1 mA) and 50 °C (I_b = 15.1 mA).
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