III–V-on-Silicon C-Band High-Speed Electro-Absorption-Modulated DFB Laser

Externally modulated lasers have proven to be key components for optical communication because of their compactness, low-power consumption, and speed. In this paper, we present unique heterogeneously integrated InP-on-Si electro-absorption-modulated DFB lasers, which were used to implement two optical modulation schemes. The first scheme uses a double-sided externally modulated DFB laser. Two taper sections on each side of the single DFB laser are fabricated with an identical epitaxial structure as the laser and perform two roles: coupling the light to the underlying Si waveguide and acting as modulators. These taper sections are electrically isolated from the DFB laser cavity. Each section can independently be driven with a 56-Gb/s non-return-to-zero (NRZ) on-off-keying signal resulting in 112-Gb/s aggregate data transmission from the device over 2-km non-zero dispersion-shifted single-mode fiber. The second scheme is an original method to generate an optical pulse amplitude modulation (PAM) signal using a similar device structure. By simultaneously directly modulating the DFB laser and one of the tapers (operating as an electro-absorption modulator) with two independent NRZ signals, we demonstrate the generation of a PAM-4 signal. In this way, the PAM-4 signal generation can be shifted from the electrical to the optical domain in a rather simple and power efficient way. We demonstrate the transmission of 25-Gbaud PAM-4 over 2-km non-zero dispersion-shifted single-mode fiber.