PON transceiver technologies for ≥50 Gbits/s per λ: Alamouti coding and heterodyne detection [Invited]

There has been an ongoing quest for transceiver technologies to be employed in next-generation passive optical networks (PONs) beyond 25G due to the growing number of subscribers and connected devices per subscriber and the ever-increasing bandwidth demand per device/application. Given the cost and loss/power budget requirements, the candidates seem to be digital signal processing (DSP)-aided intensity-modulation/direct detection (IM-DD) and low-complexity coherent transceivers. Here, we experimentally demonstrate a 100G coherent-lite PON using a novel transceiver DSP chain that utilizes a frequency-diverse dual-polarization RF pilot tone pair. The proposed scheme enables the implementation of Alamouti coding for single-carrier signaling, which is used in conjunction with heterodyne detection, achieving a significant complexity reduction in a coherent optical network unit (ONU) receiver. It consists of a single balanced photodiode followed by an analog-to-digital converter, offering comparable optical complexity to its DD counterpart, at the expense of DSP complexity in the ONU. The performance of a transceiver architecture facilitated by the proposed DSP was assessed in both back-to-back operation and up to 80 km standard single-mode fiber transmission using an $ \sim 1\,\,\text{MHz} $∼1MHz linewidth distributed feedback laser as an ONU laser. At the hard-decision forward error correction (7% overhead) threshold, assumed to be $ 4 \times {10^{ - 3}} $4×10
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, a receiver sensitivity of $ - {29.6}\,\,\text{dBm}$−29.6dBm and a loss budget of 36.6 dB at a launch power of 7 dBm are achieved.