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ispartof: JOURNAL OF LIGHTWAVE TECHNOLOGY vol:40 issue:13 pages:4357-4363 status: published

We demonstrate a temperature and wavelength shift resilient silicon transmission and routing interconnect system suitable for multi-socket interconnects, utilizing a dual-strategy CLIPP feedback circuitry that safeguards the operating point of the constituent photonic building blocks along the entire on-chip transmission-multiplexing-routing chain. The control circuit leverages a novel control power-independent and calibration-free locking strategy that exploits the 2nd derivative of ring resonator modulators (RMs) transfer function to lock them close to the point of minimum transmission penalty. The system performance was evaluated on an integrated Silicon Photonics 2-socket demonstrator, enforcing control over a chain of RM-MUX-AWGR resonant structures and stressed against thermal and wavelength shift perturbations. The thermal and wavelength stress tests ranged from 27°C to 36°C and 1309.90 nm to 1310.85 nm and revealed average eye diagrams Q-factor values of 5.8 and 5.9 respectively, validating the system robustness to unstable environments and fabrication variations.

We present carrier-injection-based photonic switches, engineered for optical pulse distribution with maximum energy efficiency. We apply small-signal analysis and for the first time large-signal modelling to methodically optimize the switches for minimum energy consumption and to classify the electronic contributions from resistance, capacitance, and diode. We present optimized electronic switch activation, which yields a sixfold reduction in energy consumption and we show how static power consumption becomes a negligible factor for optical pulse switching. We demonstrate that with adjusted phase shifter dimensions, MZI-based switches can operate with additional 50% enhanced energy efficiency with down to 4 pJ per switching operation. We show even further efficiency improvement using ring-based designs, allowing an additional improvement of 50% in energy efficiency and we discuss the trade-off between efficiency and optical bandwidth associated to the Q-factor. We benchmark carrier-injection-based switches together with comparable technologies of the silicon photonics platform and identify carrier-injection to be the most suitable technology for pulse switching applications.

A silicon photonic circuit comprising all the building blocks necessary to demonstrate optical communication between two sockets interconnected through an Arrayed Waveguide Grating Router (AWGR) is reported. The article focuses on the robustness of the interconnection scheme to the unavoidable wavelength and thermal fluctuations observed in real datacenter environments. To improve the reliability of the system, a feedback control mechanism, based on contactless integrated photonic probes (CLIPP) and heater actuators, is added to the interconnection to monitor in parallel the working point of each sensitive device and keep it locked in real-time. Experimental results demonstrate successful operations in a 30 Gbit/s data routing scenario at $\text{5}\cdot \text{10}^{-11}$ bit error rate, irrespective of sudden wavelength shifts of up to 200 pm or of iterated thermal variations in a 10 $^\circ$ C temperature range, with a recovery time of around 30 ms. These results prove that AWGR-based interconnections equipped with real-time drift compensation systems can be a viable option in multi-socket layouts even in highly demanding environments.

Arrayed Waveguide Grating Router (AWGR)-based interconnections for Multi-Socket Server Boards (MSBs) have been identified as a promising solution to replace the electrical interconnects in glueless MSBs towards boosting processing performance. In this article, we present an 8-socket glueless optical flat-topology Wavelength Division Multiplexing (WDM)-based point-to-point (P2P) interconnect pursued within the H2020 ICT project ICT-STREAMS and we report on our latest achievements in the deployment of the constituent silicon (Si)-photonic transmitter and routing building blocks, exploiting experimentally obtained performance metrics for analyzing the 8-socket chip-to-chip (C2C) connectivity in terms of throughput and energy efficiency. We demonstrate an 8-channel WDM Si-photonic microring-based transmitter (Tx) capable of providing 400 (8 x 50) Gb/s non-return-to-zero (NRZ) Tx capacity and an 8 x 8 Coarse-WDM (CWDM) Si-AWGR with verified cyclic data routing capability in O-band. Following an overview of our recently demonstrated crosstalk (XT)-aware wavelength allocation scheme, that enables fully-loaded AWGR-based interconnects even for typical sub-optimal XT values of silicon integrated CWDM AWGRs, we validate the performance of a full-scale 8-socket interconnect architecture through physical layer simulations exploiting experimentally-verified simulation models for the underlying Si-photonic Tx and routing circuits. This analysis reveals a total aggregate capacity of 1.4 Tb/s for an 8-socket interconnect when operating with 25 Gb/s line-rates, which can scale to 2.8 Tb/s at an energy efficiency of just 5.02 pJ/bit by exploiting the experimentally verified building block performance at 50 Gb/s line. This highlights the perspectives for up to 69% energy savings compared to the standard QuickPath Interconnect (QPI) typically employed in electronic glueless MSB interconnects, while scaling the single-hop flat connectivity from 4- to 8-socket interconnection systems.

In this paper, we propose a new carrier depletion-type hybrid III-V/Si optical phase shifter using a n-III-V/p-Si hetero-junction, which can be fabricated with direct epitaxial growth of III-V semiconductors on Si. We numerically analyzed the performance of the III-V/Si hybrid optical phase shifter by comparing the performance in reverse bias operation with that of pure Si or III-V p-n optical phase shifters. The hybrid III-V/Si optical phase shifter showed improved modulation efficiency and lower optical loss compared to pure Si and III-V p-n optical phase shifters, owing to the large electron-induced refractive index change of III-V compound semiconductors, while avoiding the large hole-induced optical loss of III-V compound semiconductor. The simulation study suggests the feasibility of a very low voltage-length product $(V_{ {\pi }} L)$ of $0.07~\text {V}\cdot \text {cm}$ , a low insertion loss ( $\alpha $ ) of 16 dB/cm, and a very low $\alpha ~V_{ {\pi }}L$ product close to 1 $\text {V}\cdot \text {dB}$ at $1.31~\mu $ m, which is 10 $\times$ lower than for Si p-n optical phase shifters.

ESD robustness for self-protected advanced Silicon photonic components integrated into optical interposers is reported, including industry-first CDM data. HBM performance in reverse bias polarity is shown to be the limiting factor and is correlated to the optical component width. The Ge-EAM modulator with heater is found to be the weakest element CDM-wise.

Today, the datacenter ecosystems are fueling the demand for novel transmitter (ΤΧ) 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 co-packaging 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.

We present an O-band silicon microring modulator with up to 50 Gb/s modulation rates, co-packaged with a 1V-CMOS driver in a dispersion un-compensated, transmission experiment through 52 km of standard single-mode fiber. The experimental results show 10(-9) error-rate operation with a negligible power penalty of 0.2 dB for 40 Gb/s and wide-open eye diagrams for 50 Gb/s data, corresponding to a record high bandwidth-distance product of 2600 Gb.km/s. A comparative analysis between the proposed transmitter assembly and a commercial LiNbO3 modulator revealed a moderate increase of 3.8 dB in power penalty, requiring only 20% of the driving voltage level used by the commercial modulator.

We report O-band GeSi quantum-confined Stark effect waveguide-coupled electro- absorption modulator with 50GHz bandwidth. Static extinction ratio of 5.2dB, insertion loss of 7.6dB and 60Gb/s NRZ-OOK operation are shown for a 2V swing.

Future high-performance applications require in-package optical modules to enable the high bandwidth requirements. This is enabled by the co-integration of a silicon photonics module with a host IC in a single package. Since the silicon photonic elements are very sensitive to temperature changes, the optical performance can be affected by the thermal coupling effects in these co-integrated packages.In this paper, a thermal modeling study is presented for the test case of a BGA package that contains a 300W host IC and an Si photonics optical I/O module with 32 channels. The thermal model, calibrated with global package level measurements, are well as with local device measurements, shows a large level of thermal coupling from the host IC to the optical module. Although the thermal coupling between individual photonic elements is shown to be in the order of 1%, the combined thermal coupling for the 32 channels reaches 28%, indicating the clear need for a detailed thermal analysis.

We present an O-band any-to-any chip-to-chip (C2C) interconnection at 40 Gb/s suitable for up to 8-socket direct connectivity in multi-socket server boards, utilizing integrated low-energy photonics for the transceiver and routing functions. The C2C interconnect exploits an Si-based ring modulator as its transmitter and a co-packaged photodiode/transimpedance amplifier enabled receiver interconnected over an 8 x 8 Si-based arrayed waveguide grating router, allowing for a single-hop flat-topology interconnection between eight nodes. A proof-of-concept demonstration of the C2C interconnect is presented at 25 and 40 Gb/s for eight possible routing scenarios, revealing clear eye diagrams at both data rates with extinction ratios of 4.8 +/- 0.3 and 4.38 +/- 0.31 dB, respectively, among the eight routed signals.

We present a linear equivalent circuit model for the depletion-type Si microring modulator (MRM). Our model consists of three blocks: one for parasitic components due to interconnects and pads, one for the electrical elements of the core p-n junction, and the third for a lossy LC tank representing Si MRM optical modulation characteristics. Model parameter values are extracted from measurement of a fabricated Si MRM device. Simulated modulation characteristics with our equivalent circuit show very good agreement with measured results. Using our model, we can analyze Si MRM modulation frequency response characteristics and perform gain-bandwidth product optimization of the entire Si photonic transmitter composed of a Si MRM and electrical driver circuits.

We demonstrate a 200G capable WDM O-band optical transceiver comprising a 4-element array of Silicon Photonics ring modulators (RM) and Ge photodiodes (PD) co-packaged with a SiGe BiCMOS integrated driver and a SiGe transimpedance amplifier (TIA) chip. A 4 x 50 Gb/s data modulation experiment revealed an average extinction ratio (ER) of 3.17 dB, with the transmitter exhibiting a total energy efficiency of 2 pJ/bit. Data reception has been experimentally validated at 50 Gb/s per lane, achieving an interpolated 10E-12 bit error rate (BER) for an input optical modulation amplitude (OMA) of -9.5 dBm and a power efficiency of 2.2 pJ/bit, yielding a total power efficiency of 4.2 pJ/bit for the transceiver, including heater tuning requirements. This electro-optic subassembly provides the highest aggregate data-rate among O-band RM-based silicon photonic transceiver implementations, highlighting its potential for next generation WDM Ethernet transceivers. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.

Carrier-depletion monolithic III-V/Si optical phase modulators are proposed and numerically investigated. Thanks to the larger carrier-induced refractive index change of the III-Vs compared to Si, the III-V/Si phase modulator is predicted to achieve 0.07-Vcm modulation efficiency at 16-dB/cm optical loss at 1310-nm wavelengths.

We demonstrate an O band 40Gb/s silicon microring modulator assembled with a 1V driver in a 52km metro transmission experiment without dispersion compensation, achieving a record high bandwidth distance product of 2080 Gbkm/s.

We demonstrate a microbump flip-chip integrated 14nm-FinFET CMOS-Silicon Photonics (SiPh) technology platform enabling ultra-low power Optical I/O transceivers with 1.6Tb/s/mm2 bandwidth density. The transmitter combines a differential FinFET driver with a Si ring modulator, enabling 40Gb/s NRZ optical modulation at 154fJ/bit dynamic power consumption in a 0.015mm2 footprint. The receiver combines a FinFET trans-impedance amplifier (TIA) with a Ge photodiode, enabling 40Gb/s NRZ photodetection with −10.3dBm sensitivity at 75fJ/bit power consumption, in a 0.01mm2 footprint. High-quality data transmission and reception is demonstrated in a loop-back experiment at 1330nm wavelength over standard single mode fiber (SMF) with 2dB link margin. Finally, a 4×40Gb/s, 0.1mm2 wavelength-division multiplexing (WDM) transmitter with integrated thermal control is demonstrated, enabling Optical I/O scaling substantially beyond 100Gb/s per fiber.

We discuss recent progress in the performance of modulators and photodetectors co-integrated in a silicon photonics platform, and capable of operation in the O-band or C-band at 56Gb/s single-lane NRZ data rates and beyond.

High speed optical interconnects require low-power compact electro-optical transmit modules comprising driver circuits and optical modulators. This letter presents a low power 56 Gb/s non-return-to-zero CMOS inverter-based driver in 28 nm fully depleted silicon-on-insulator CMOS driving a 46 GHz silicon photonic microring modulator. The driver delivers 1 Vpp to the microring modulator from a 75 mVpp input while only consuming 40 mW (710 fJ/bit at 56 Gb/s). The realized transmitter shows 4 dB extinction ratio when running of a 1 V supply voltage. Transmission experiments up to 2 km of single mode fiber show a bit-error-ratio less than $1\cdot 10^{-9}$ at 56 Gb/s.

We present an accurate, easy-to-use large-signal SPICE circuit model for depletion-type silicon ring modulators (Si RMs). Our model includes both the electrical and optical characteristics of the Si RM and consists of circuit elements whose values change depending on modulation voltages. The accuracy of our model is confirmed by comparing the SPICE simulation results of 25 Gb/s non-return-to-zero (NRZ) modulation with the measurement. The model is used for performance optimization of monolithically integrated Si photonic NRZ and pulse-amplitude-modulation 4 transmitters in the standard SPICE circuit design environment.

The next generations of data centers require a scalable optical transceiver technology. In this paper we present a silicon photonics platform supporting single-channel data rates of 50Gb/s and above. Advanced process options include 50GHz GeSi electro-absorption modulators, high efficiency thermo-optic phase shifters with P-pi

The influence of self-heating on the static transmission characteristics of depletion-type Si micro-ring modulators (MRMs) is investigated. Self-heating, caused by free-carrier absorption of the input light inside the doped ring waveguide, increases the effective refractive index of the ring waveguide and results in the red-shifted resonance wavelength. This phenomenon is modeled based on the coupled-mode equation with a newly-introduced self-heating coefficient R . The accuracy of our model is confirmed by measurement. In addition, dependence of R on device size and doping concentration is experimentally investigated and the resulting dependence is explained.

We present an accurate model for self-heating effect in depletion-type Si micro-ring modulator which describes incident-power dependent transmission and dynamics. Its accuracy is confirmed with measurement. It can be useful for determining optimal modulation conditions.