200-Gb/s Direct Modulation of a 50-GHz Class Laser With Advanced Digital Modulations

Directly modulated lasers (DML) dominate the short reach optical interconnect market. For years, the bandwidth of commercial DMLs has been limited to a level of 25 GHz, which can support a speed up to around 100 Gb/s via advanced modulations like Nyquist-shaped 4-ary pulse amplitude modulation (PAM-4), carrier-less amplitude phase (CAP) modulation, subcarrier multiplexing, and discrete multitone (DMT). To scale with the capacity evolution of interconnect applications, it is in urgent demand to develop DMLs operated at 50G class and even beyond. In this article, we exploit a newly designed 50G-class short-cavity distributed Bragg reflector (DBR) laser, called the two-
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DBR laser, and demonstrate its capability of supporting 200 Gb/s per wavelength direct modulation and direct detection transmissions. Combining high-speed electronics with the 50G-class DML, we demonstrate a variety of advanced digital modulations including Nyquist-shaped 100-GBaud PAM-4, 80-GBaud PAM-8, and 50-GHz DMT signals, with the maximum net bit rate of 236 Gb/s. The DML exhibits an ultra-low chirp parameter of 1.0, which enables isolator-free operation and dispersion-tolerant transmission over tens of kilometers at O-band.