Abstract

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-κ 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.

400-Gb/s direct modulation using a DFB+R laser

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Digital quadrature amplitude modulation with optimized non-rectangular constellations for 100 Gb/s transmission by a directly-modulated laser

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112 Gb/s transmission with a directly-modulated laser using FFT-based synthesis of orthogonal PAM and DMT signals

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Opt. Express 23(15) 19202-19212 (2015)

Squeezing out the last few bits from band-limited channels with entropy loading

Di Che and William Shieh
Opt. Express 27(7) 9321-9329 (2019)