Frequency-Domain-Interleaved Optical Transceivers Enabled by Ultra-Wideband InP-HBT Analog ICs for Beyond-400-Gb/s/lane IMDD Systems

Abstract

This paper presents frequency-domain-interleaved optical transceivers enabled by ultra-wideband analog integrated circuits (ICs) based on InP heterojunction bipolar transistor (HBT) technology. The rapid growth of artificial intelligence (AI) data centers is driving demand for future Ethernet systems operating beyond 400 Gb/s/lane, where symbol rates exceeding 200 GBaud are required. However, the limited bandwidth of digital-to-analog and analog-to-digital converters (DACs and ADCs) integrated into digital signal processors (DSPs) remains a major bottleneck. To address this issue, we present and validate a frequency-domain-interleaved transceiver architecture that extends the effective signal bandwidth using ultra-wideband up-conversion and down-conversion circuits. The architecture relaxes the bandwidth requirements of baseband electrical interfaces by allocating the signal spectrum across multiple frequency bands. For validation, we developed mixer ICs and active combiner ICs with 200-GHz-class bandwidths using 250-nm InP-HBT technology with fT/fmax of 460/480 GHz. Ultra-broadband test modules equipped with 0.8-mm coaxial connectors were also developed to support operation up to 150 GHz. Using these ICs and modules, we experimentally demonstrate intensity-modulation and direct-detection (IMDD) optical transmission over 11 km at a net bit rate of 651 Gb/s/lane using 248-GBaud probabilistically shaped (PS) twelve-level pulse-amplitude modulation (PAM-12) signals. These results highlight the effectiveness of frequency-domain interleaving in extending the signal bandwidth of future IMDD optical transceivers operating beyond 400 Gb/s/lane.