Externally modulated lasers (EMLs) have proven to be key components for optical communication because of their compactness, low power consumption and speed. In this paper we present two different optical modulation schemes based on heterogeneously integrated InP-on-Si electro-absorption modulated DFB lasers. 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 and perform two roles: coupling the light to the underlying Si waveguide and simultaneously acting as modulators. These taper sections are electrically isolated from the DFB laser cavity. Each section can independently be driven with a 56 Gbps Non-Return-to-Zero On-Off-Keying (NRZ-OOK) signal resulting in 112 Gbps aggregate data transmission from the device over 2 km single mode fiber. The second scheme is an original method to generate an optical Pulse Amplitude Modulation (PAM) signal using the same device structure. By simultaneously directly modulating the DFB laser and one of the tapers as an EAM 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 of single mode fiber.
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