Negative Frequency-Chirped 112-Gb/s PAM-4 Using an Integrated Germanium Franz-Keldysh Modulator

• Published in: IEEE photonics technology letters Vol. 30; no. 16; pp. 1443 - 1446
• Main Authors: Tong, Yeyu, Hu, Zhouyi, Wu, Xinru, Liu, Jie, Chan, Chun-Kit, Shu, Chester, Tsang, Hon Ki
• Format: Journal Article
• Language: English
• Published: New York IEEE 15.08.2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Bandwidth; Chirp; Electro-absorption modulators; Equalization; Error correction; Germanium; Linearity; Modulators; Optical attenuators; optical interconnects; Optical modulation; PAM-4; Pulse amplitude modulation; Semiconductor optical amplifiers; Silicon; silicon photonics; Waveform generators
• ISSN: 1041-1135; 1941-0174
• DOI: 10.1109/LPT.2018.2852331

Integrated germanium-on-silicon Franz-Keldysh modulators (Ge-EAMs) offer a small footprint and low-energy-per-bit performance for high-speed data communications. In this letter, we study the use of Ge-EAMs for four-level pulse amplitude modulation (PAM-4), and report on the linearity of the modulator in terms of its spurious-free dynamic range. The experimental results show that the negative frequency chirp from the modulator can improve the transmission distance of the PAM-4 signal. Using pre-equalization with a 25-GHz bandwidth-limited arbitrary waveform generator, we obtained a data rate of 112 Gb/s with a bit-error-rate of <inline-formula> <tex-math notation="LaTeX">2.5\times 10^{-3} </tex-math></inline-formula> under the 7% overhead hard-decision forward error correction threshold. We observed an extended transmission distance in our 112-Gb/s PAM-4 experiment on a standard single-mode fiber thanks to the negative frequency chirp of the modulator.