SWDM PAM4 Transmission Over Next Generation Wide-Band Multimode Optical Fiber

Two system transmission experiments are reported which indicate the feasibility of transmitting an aggregated speed of >200 Gb/s over a single next-generation wide-band multimode optical fiber (NG-WBMMF) using a shortwave wavelength division multiplexing (SWDM) and a four-level pulse amplitude modulation (PAM4), using optics rated for <inline-formula><tex-math notation="LaTeX">${\text{25 Gb/s}}$</tex-math></inline-formula> NRZ operation. The first experiment leverages predistorted KR4 <inline-formula><tex-math notation="LaTeX">${\text{51.5625 Gb/s}}$</tex-math> </inline-formula> electrical PAM4 signaling generated by an arbitrary waveform generator to drive SWDM TOSAs at 850, 880, 910, and 940 nm. The received optical PAM4 signals are then post processed offline with linear equalizers to improve the eye quality. Detailed analysis of the height and width of the received optical eyes indicates an aggregated <inline-formula><tex-math notation="LaTeX">${\text{206.25 Gb/s}}$</tex-math></inline-formula> speed is achievable on a single NG-WBMMF beyond 150 m. In the second experiment, a commercial PAM4 IC evaluation kit with real-time digital signal processing is adopted to generate and detect PAM4 signals at KP4 FEC rate of <inline-formula> <tex-math notation="LaTeX">${\text{53.125 Gb/s}}$</tex-math></inline-formula> per wavelength. The SWDM wavelength range is extended with additional tests at 980 nm. Pre-FEC BER below threshold of <inline-formula> <tex-math notation="LaTeX">${\text{2.4}}\times {\text{10}}^{-4}$</tex-math></inline-formula> is achieved up to 300 m across all five wavelengths demonstrating an aggregated speed of <inline-formula><tex-math notation="LaTeX"> ${\text{265.625 Gb/s}}$</tex-math></inline-formula> over a single MMF.