Fig. 4: The optical spectra of optical PAM4 (PAM4, four-level pulse amplitude modulation)/VSB (VSB, vestigial sideband)-PAM4 signals and the downstream y-polarised BERs (BERs, bit error rates) at different centre wavelengths of tunable optical VSB filter. | Communications Engineering

Fig. 4: The optical spectra of optical PAM4 (PAM4, four-level pulse amplitude modulation)/VSB (VSB, vestigial sideband)-PAM4 signals and the downstream y-polarised BERs (BERs, bit error rates) at different centre wavelengths of tunable optical VSB filter.

From: Bidirectional wavelength-division-multiplexing fibre-free-space optical communications using polarisation multiplexing technique and tunable optical vestigial sideband filter

Fig. 4

a The optical spectra of 30 Gb/s optical PAM4 and VSB-PAM4 signals. b The downstream y-polarised BERs as a function of the centre wavelength of the tunable optical VSB filter.

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