Backdrop: IMDD and Digital Coherent

We demonstrate an O-band silicon photonics 2x2x2λ wavelength selective switch (WSS) based on Coupled Ring Resonators (CRR). The optical switch achieves a record-low average polarization dependent loss (PDL) of 0.41dB.

We present a Silicon PIC with 8λ highly doped micro-ring modulators for extreme environment optical readout. Junctions were validated at 4K and 20 MRad TID. Room temperature eye diagrams are open at 53.125 Gbps.

Presented is an O-band silicon photonics dual-polarization coherent/IMDD modulator integrated with semiconductor optical amplifiers and tunable laser to enhance the short-reach link budget. The laser demonstrated output power >6 dBm and a <250 kHz linewidth over a 14 nm tuning range. Modulators paired with custom 64 Gbaud QPSK drivers exhibited improved analog link sensitivity compared to similar devices without integrated gain sections. They also demonstrated 53 Gbaud dual-polarization PAM4 operation when characterized with a linear driver and MaxLinear 100G/lane DSP board. Both optical links achieved BERs at the KP4-FEC threshold and overall transmitter assembly energy consumption <6.9 pJ/bit without any thermal control when at steady room temperatures.

A fully packaged O-band coherent transmitter, comprising a fiber-attached MRM -based silicon photonic transmitter and a co-designed electronic integrated circuit on a custom PCB, achieved 100 Gbps QPSK modulation below the HD-FEC bit error rate threshold. © 2024 The Author(s)

We report a 0.91 pJ/bit, differential dual-channel TIA with variable gain reaching 64 dBΩ in 90-nm SiGe measured in a reconfigurable PAM4/QPSK O-band receiver at 53.125 Gbaud with BERs below the KP4-FEC threshold of 2.2e-4.

We report the first net 400 Gbps/λ O-band coherent, dual-polarization, 60 Gbaud 16QAM link using SiP TX/RX PICs with heterogeneously integrated lasers, operating below the 15% overhead SD-FEC limit over 2 km without external amplifiers.

We demonstrate the first 200-G O-band coherent PON using a heterogeneously-integrated SiP PIC transmitter as an OLT and PIC/EIC receivers as ONUs. A joint DSCM and NOMA scheme is presented for flexibly dense access scenarios.

We report a net 400 Gbps/ $\lambda$ O-band, dual-polarization, intradyne coherent link using silicon photonic (SiP) transmitter and receiver photonic integrated circuits (PIC) with heterogeneously integrated lasers and semiconductor optical amplifiers (SOA). Operation below the 15.3% overhead 2×10 -2 open forward error correction (O-FEC) threshold was achieved for 60 Gbaud 16QAM over 2 km and 100 Gbaud QPSK over 10 km without external optical amplification. These results demonstrate the potential for implementing SiP PICs with integrated lasers and SOAs in future short-reach coherent links.

We report the first O-band link with electrically reconfigurable intensity-modulation direct-detection (IMDD) and coherent operation using custom silicon photonic chips packaged with commercial electronic chips. Transmission below the KP4-FEC threshold is shown using commercial 53 Gbaud PAM4 digital signal processing (DSP) for 16QAM (200 Gbps/λ) and PAM4 (100 Gbps/λ). Efficient operation of the packaged full link at 12 and 11.2 pJ/bit is achieved for the PAM4 and 16QAM modes, respectively.

A 1310-nm (O-band) coherent optical Link is demonstrated for short-range optical interconnects that operate to 56-GBd symbol rate (SR) (112 Gbps) with FEC-acceptable BER. The coherent optical receiver (CORX) leverages a monolithic 45-nm CMOS SOI photonic-enabled process to realize an energy-efficient quadrature phase shift keying (QPSK) demodulation. Co-design of the optical and electronic circuit elements supports high-speed operation and low-power consumption. The coherent link is demonstrated with an optical transmitter photonic IC (PIC) fabricated in silicon photonic (SiPh) process with laser diodes wirebonded to a 90-nm SiGe driver electronic RFIC. The transmitter operates at 5.9-pJ/bit energy efficiency (EE) while the receiver achieves 0.73 pJ/bit and, to our knowledge, is the best EE reported for a coherent optical receiver.

Silicon traveling-wave Mach-Zehnder modulators are monolithically integrated with tunable inductive terminations for low-power, variable equalization circuits. Equalizing subthreshold forward-biased modulators doubled EO bandwidth for 56 Gbit/s transmission below KP4-FEC thresholds while consuming 360 fJ/bit.

We present the first >200 Gbps/lambda, 0 -band optical link with integrated transmitter and receiver photonic and electronic ICs. 224 Gbps/lambda, DP-QPSK transmission is demonstrated below the 3.8.10(-3) HD-FEC threshold with 6.8 pJ/bit power consumption. (c) 2022 The Author(s)

Scaling data centers to 200 Gbps/lane with direct detection may not provide sufficient link budget for optical switches. Analog coherent detection leverages phase and polarization of optical signals to scale efficiently without requiring digital signal processing and employs integrated lasers to maximize link budgets for optical switches. We report the first O-band silicon photonics coherent transmitter integrated with hybrid semiconductor optical amplifiers and tunable lasers. The laser demonstrated <6 dBm output power with ∼700 kHz linewidths across its 14 nm tuning spectrum. 64 Gbaud QPSK transmission was demonstrated with BER ∼4e-4 and ∼6.6 pJ/bit energy-efficiency when utilizing SiGe BiCMOS drivers.

Coherent optical links are becoming increasingly attractive for intra-data center applications as data rates scale. Realizing the era of high-volume short-reach coherent links will require substantial improvements in transceiver cost and power efficiency, necessitating a reassessment of conventional architectures best-suited for longer-reach links and a review of assumptions for shorter-reach implementations. In this work, we analyze the impact of integrated semiconductor optical amplifiers (SOAs) on link performance and power consumption, and describe the optimal design spaces for low-cost and energy-efficient coherent links. Placing SOAs after the modulator provide the most energy-efficient link budget improvement, up to 6 pJ/bit for large link budgets, despite any penalties from nonlinear impairments. Increased robustness to SOA nonlinearities makes QPSK-based coherent links especially attractive, and larger supported link budgets enable the inclusion of optical switches, which could revolutionize data center networks and improve overall energy efficiency.

Upgraded particle colliders will require high bandwidth readout capable of withstanding extremely high levels of radiation. Optical links Silicon photonics is a promising solution, but conventional high-speed modulators cannot survive radiation damage. Preliminary results show hardening techniques capable of enduring 1 Grad of total ionizing dose, but without yet demonstrating high speed modulation. Ring resonator modulators were designed with various radiation hardness by design techniques and irradiated. Most promising is a highly doped ring resonator modulator with an 18 GHz bandwidth that survived 300 MRad of total ionizing dose.

We report the first demonstration of a full O-band coherent link for intra-data center applications, including custom photonic and electronic integrated circuits for the transmitter and receiver. Full-link 112 Gbps (56 Gbaud QPSK) transmission is shown with $2.1\cdot 10^{-4}$ measured BER, and record baud rate 128 Gbps (64 Gbaud QPSK) transmission is shown for the stand-alone coherent transmitter. The link architecture is based on analog coherent detection (ACD), which improves power consumption substantially by performing functions in the analog domain that are normally implemented with power-hungry digital signal processing (DSP). Energy efficiency of 9.5 pJ/bit is demonstrated for the O-band coherent link, with 12.5 pJ/bit expected with next-generation circuits that include integrated optical gain. These results show the potential for next-generation data center networks based on low-power O-band coherent links.

An O-band coherent optical receiver (CORX) is integrated in a 45-nm monolithic CMOS SOI process. The CORX operates to 80 Gbps with FEC-acceptable BER at 1.2 pJ/bit energy efficiency. To our knowledge, this is the first monolithically-integrated Silicon CMOS CORX.