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We study analytically and experimentally the performance limits of a Si-photonic (SiP) balanced coherent receiver (CRx) co-packaged with transimpedance amplifiers (TIAs) in a colorless WDM scheme. Firstly, the CRx architecture is depicted and characterization results are presented. Secondly, an analytical expression for the signal-to-noise ratio (SNR) at the CRx output is rigorously developed and various noise sources in the context of colorless reception are outlined. Thirdly, we study experimentally the system-level CRx performance in colorless reception of 16 × 112 Gbps PDM-QPSK WDM channels. Using a 15.5 dBm local oscillator (LO) power, error free transmissions over 4800 and 4160 km at received powers of -3 and -21 dBm per channel, respectively, were achieved in a fully colorless and preamplifierless reception. Next, a set of measurements on one of the center WDM channels is performed where the LO power, received signal power, distance, and number of channels presented to the CRx are swept to evaluate the performance limits of colorless reception. Results reveal that the LO beating with optical noise incoming with the signal is a dominant noise source regardless of received signal power. In the high received signal power regime (~0 dBm/channel), the self-beat noise from out-of-band (OOB) channels is an additional major noise source especially for small LO-to-signal power ratio, short reach and large number of OOB channels. For example, at a received signal power of 0 dBm/channel after 1600 km transmission, the SNR difference between the fully filtered and colorless scenarios, where 1 and 16 channels are passed to the CRx respectively, grows from 0.5 to 3.3 dB as the LO power changes from 12 to 0 dBm. For low received power (~-12 dBm/channel), the effect of OOB channels becomes minor while the receiver shot and thermal noises become more significant. We identify the common mode rejection ratio (CMRR) and sensitivity as the two important CRx specifications that impact the performance at high and low received signal power regimes, respectively. Finally, an excellent match between experimental and analytical SNRs is proven after the derived SNR model is fitted to the experimental data in a least-squares sense. The model is then used to predict that the CRx can operate colorlessly for a fully populated WDM spectrum with 80 channels provided that the LO-to-signal power ratio is properly set.

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We experimentally study the sensitivity limits of an integrated Si-photonic dual-polarization balanced coherent receiver co-packaged with transimpedance amplifiers. For 28 Gbaud PDM-QPSK and PDM-16QAM signals, we compare colorless and optical preamplifierless reception to the case where an optical preamplifier and optical filters are used before the receiver. Back-to-back receiver sensitivities are evaluated. After propagation over an SMF-28e + EDFA amplified link and assuming a 3.8 × 10 −3 FEC threshold, colorless/preamplifierless reception using the Si-photonic receiver allows for error-free transmission of 112 Gbps PDM-QPSK over 4800 km at a received power of −23 dBm and of 224 Gbps PDM-16QAM over 640 km at a received power of −17 dBm. Finally, a 16 × 112 Gbps PDM-QPSK WDM experiment is carried out. Using the Si-photonic receiver for colorless/preamplifierless reception of all channels, we achieve error-free transmission for all channels over 4160 km at a received power of −21 dBm per channel. Results reveal that the receiver provides excellent sensitivity while allowing us to save cost, footprint, and power if used in a colorless/preamplifierless scheme.Index Terms-Integrated Si-photonic receiver, polarization division multiplexing (PDM), wavelength division multiplexing (WDM), forward error correction (FEC)

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