56-Gb/s PAM4 × 8-Channel VCSEL-Based Optical Transceiver for Co-Packaged Optics

We report the design and transmission characteristics of 56-Gb/s PAM4 × 8-channel VCSEL-based optical transceiver for Co-Packaged Optics and 400-Gb/s QSFP-DD AOCs. This optical transceiver employs the world smallest 0.3-mm pitch LGA for the electrical interface. When operating the module by a bit stream of 56-Gb/s PAM4 PRBS-13Q in a loopback link system, we observed that the BER is less than the KP4 FEC threshold and the power budget meets the specification of Open Eye MSA.