A Silicon Photonic Integrated Packaged Coherent Receiver Front-End For Soft-Decision Decoding

In this paper, a packaged integrated coherent receiver and optical front-end for soft decision based on 25 Gbaud/s quadrature phase-shift keying (QPSK) is investigated for on-chip applications. The front-end consists of a 90° hybrid, balanced photodetectors, and unbalanced couplers monolithically integrated in a CMOS compatible silicon-on-insulator technology. The silicon photonic device is packaged onto a ceramic substrate with RF and dc connectors. The proposed front-end is an example of integration of system on chip. The integrated solution is able to provide 6.2 dB performance improvements over uncoded system without error correction. The front-end outperforms optical system with hard-decision forward error correction by 2.2 dB at the BER of 10^-7.