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We present a 70 Gb/s capable optical transmitter consisting of a 50 m long GeSi electro-absorption modulator (integrated in silicon photonics) and a fully differential driver designed in a 55 nm SiGe BiCMOS technology. By properly unbalancing the output stage, the driver can be dc-coupled to the modulator thus avoiding the use of on-chip or external bias-Ts. At a wavelength of 1560 nm, open eye diagrams for 70 Gb/s after transmission over 2 km standard single-mode fiber were demonstrated. The total power consumption is 61 mW, corresponding to 0.87 pJ/b at 70 Gb/s. Bit-error rate measurements at 50 Gb/s and 56 Gb/s (performed both back to back and with up to 2 km standard single-mode fiber) demonstrate large (0.4 UI at a BER of ) horizontal eye margins. This optical transmitter is ideally suited for datacenter applications that require densely integrated transceivers with a low power consumption.