O-Band Silicon Photonic Transmitters for Datacom and Computercom Interconnects

Abstract

Today, the datacenter ecosystems are fueling the demand for novel transmitter (TX) technologies complying with the off-board, on-board, and chip-to-chip computing needs. This has set a new class of requirements for the TX infrastructure that should now offer multiple credentials, namely: high-speed, O-band operation for avoiding dispersion compensation in long distances, wavelength-division multiplexing (WDM) capabilities for higher throughput and multicasting/broadcasting support, and tight copackaging with low-power electronics. Silicon (Si) photonic TXs have been extensively studied toward high-speed and WDM TX engines targeting mainly C-band. Only a limited number of Si-Pho O-band TXs have been reported, however with ≤32 Gb/s/channel line-rate capabilities and with a WDM portfolio that has not been fully explored yet. In this paper, we introduce a novel silicon photonic high-speed O-band TX hardware platform that can meet the current datacom and computercom interconnect requirements. We demonstrate a ring modulator (RM) based four-channel WDM TX at 4 × 40 Gb/s non-return-to-zero (NRZ) operation that supports wavelength parallelism in unicast operation but can also pave the way toward WDM TX engines for the post-100 GbE TX era. Moreover, we present a broadband Si Mach-Zehnder modulator employed in a WDM modulation scheme of 2 × 25 Gb/s NRZ signals and demonstrate multicasting when combined with a 8 × 8 passive arrayed waveguide grating router (AWGR) wavelength router, addressing the broadcasting needs of traffic usually encountered in cache-coherent multisocket settings. Finally, we further demonstrate the tight synergy of O-band Si-RM modulators with high-speed CMOS electronics, presenting an RM-based TX assembly prototype employing a fully depleted silicon-on-insulator CMOS driver, delivering 50-Gb/s NRZ operation.

Silicon circuits for chip‐to‐chip communications in multi‐socket server board interconnects

“…Figure 4c illustrates a four‐channel SiPho Tx [12] that comprises a four‐channel RM modulator array interconnected by a cascaded double‐ring resonator‐based multiplexer (MUX), with a channel spacing of 2.25 nm. An aggregate Tx bandwidth of 160 Gb/s was achieved with each RM operating at 40 Gb/s, with the demonstrator featuring a high power efficiency of ∼1 pJ/bit, excluding the laser.…”

“…Each socket is equipped with a SiPho WDM TxRx, responsible for optically interfacing the CPU with the server board, by employing multiple RM modulators resonating at different wavelengths while powered from WMD continuous wave (CW) lasers. Figures 4 and 5 depict a time and performance evolution of SiPho Tx and TxRx demonstrations for MSBs, which were developed within the European research project H2020-ICT-STREAMS, progressing from single-lane 50 Gb/s towards WDM layouts that can reach an aggregate bandwidth of 400 Gb/s [11][12][13][14]. More specifically,…”

“…This first demonstration validated the low‐power and high‐speed credentials of RM‐based Tx, achieving 50 Gb/s line rates and a low PC of 0.8 pJ/bit, excluding the heater and laser power requirements, as this first prototype lacked an integrated thermal heater. Indicative results of the performance of the O‐band Tx are depicted in Figure 4b, including an optical eye diagram at the Tx egress at 50 Gb/s, along with bit error rate (BER) measurements performed after 52 km of SSMF fibre, validating the capabilities of the Tx even for inter‐DC interconnections. Figure 4c illustrates a four‐channel SiPho Tx [12] that comprises a four‐channel RM modulator array interconnected by a cascaded double‐ring resonator‐based multiplexer (MUX), with a channel spacing of 2.25 nm. An aggregate Tx bandwidth of 160 Gb/s was achieved with each RM operating at 40 Gb/s, with the demonstrator featuring a high power efficiency of ∼1 pJ/bit, excluding the laser.…”

“…With EOPCBs typically offering a low waveguide loss figure at the O-band [10] and rather high propagation losses at the C-band, the experimental AWGR-based demonstrations reported so far, almost exclusively in the Cband regime, are not compatible with MSB topologies with >4 sockets. Under these circumstances, we have recently demonstrated the main subsystems that allow for the realization of an O-band MSB optical interconnect [11][12][13][14][15][16][17], including an 8�50 Gb/s O-band silicon photonics (SiPho) TxRx [14], a 16�16 O-band SiPho AWGR [16] and an automated thermal drift compensation system [17].…”

Low-Cost 400 Gbps DR4 Silicon Photonics Transmitter for Short-Reach Datacenter Application

“…Due to its compatibility with mature CMOS manufacturing techniques, compact size and cost effectiveness, integrated silicon photonics have been well developed as an engine for optical transceivers [ 1 , 2 , 3 , 4 ] and widely deployed in datacenters for high-speed, short-reach connections. Transceiver engines combine many elemental silicon photonics components, such as waveguides, splitters, I/O couplers, phase shifters and multiplexers (MUXs) and are able to process 100 Gb/s or 400 Gb/s signals, which currently dominate 500 m to 2 km intra-datacenter communications.…”