M. Ashkan Seyedi

A 40 Gb/s PAM4 silicon microring resonator modulator transmitter in 65nm CMOS

A silicon photonic microring resonator modulator transmitter utilizes a segmented pulsed-cascode output stage for voltage level control to achieve PAM4 modulation on a single microring device. The 65nm CMOS transmitter achieves 40Gb/s operation at 3.04mW/Gb/s when driving depletion-mode microring modulators with 4.4Vppd swing.

Error-free DWDM transmission and crosstalk analysis for a silicon photonics transmitter.

Individual channels of a five-channel microring silicon photonics transmitter are used for bit error ratio analysis and demonstrate error-free transmission at 10Gb/s. Two channels of the same transmitter are concurrently modulated using an 80GHz channel spacing comb laser and demonstrate open eye diagrams at 10Gb/s and 12.5Gb/s. Finally, concurrent modulation with tunable lasers is done to quantify optical power penalty for link bit error ratio versus channel spacing from +100GHz to -100GHz. When using a comb laser for concurrent modulation, no direct power penalty is observed for an 80GHz channel separation.

Large-Signal Model for Small-Size High-Speed Carrier-Injection Silicon Microring Modulator

We develop a compact model for carrier-injection silicon microring modulators with diameters as small as 5 µm and data rates up to 25 Gb/s. This large-signal model can be co-simulated with CMOS driver circuits, and can accurately predict the optical eye diagrams.

PAM4 silicon photonic microring resonator-based transceiver circuits

Increased data rates have motivated the investigation of advanced modulation schemes, such as four-level pulseamplitude modulation (PAM4), in optical interconnect systems in order to enable longer transmission distances and operation with reduced circuit bandwidth relative to non-return-to-zero (NRZ) modulation. Employing this modulation scheme in interconnect architectures based on high-Q silicon photonic microring resonator devices, which occupy small area and allow for inherent wavelength-division multiplexing (WDM), offers a promising solution to address the dramatic increase in datacenter and high-performance computing system I/O bandwidth demands. Two ring modulator device structures are proposed for PAM4 modulation, including a single phase shifter segment device driven with a multi-level PAM4 transmitter and a two-segment device driven by two simple NRZ (MSB/LSB) transmitters. Transmitter circuits which utilize segmented pulsed-cascode high swing output stages are presented for both device structures. Output stage segmentation is utilized in the single-segment device design for PAM4 voltage level control, while in the two-segment design it is used for both independent MSB/LSB voltage levels and impedance control for output eye skew compensation. The 65nm CMOS transmitters supply a 4.4Vppd output swing for 40Gb/s operation when driving depletion-mode microring modulators implemented in a 130nm SOI process, with the single- and two-segment designs achieving 3.04 and 4.38mW/Gb/s, respectively. A PAM4 optical receiver front-end is also described which employs a large input-stage feedback resistor transimpedance amplifier (TIA) cascaded with an adaptively-tuned continuous-time linear equalizer (CTLE) for improved sensitivity. Receiver linearity, critical in PAM4 systems, is achieved with a peak-detector-based automatic gain control (AGC) loop.

Crosstalk analysis of ring resonator switches for all-optical routing.

Optical switches based on ring resonator cavities were fabricated by a silicon photonics foundry process and analyzed for optical crosstalk at various data rates and channel spacings. These devices were compared to commercial bandpass filters and at 20Gb/s, 0.5dB power penalty is observed due to spectral filtering for bit error ratio threshold of 1 × 10-9. Concurrent modulation at 20Gb/s with a channel spacing as narrow as 40GHz shows error-free transmission with 1dB power penalty as compared to wider channel spacing for the ring-based switch.

Data rate enhancement of dual silicon ring resonator carrier-injection modulators by PAM-4 encoding

Two rings are thermally tuned to near-resonance and individually modulated by two uncorrelated, NRZ encoded PRBS data sources at 1 GBd/s at different extinction ratios to achieve a 2 Gb/s. Experimental data is shown as a proof-of-concept for this approach.

Silicon Mach-Zehnder Interferometer modulator with PAM-4 data modulation at 64 Gb/s

This paper outlines the co-design and simulation of the photonics and electronics circuits for an optical modulator implementing a 4-level phase amplitude modulation scheme at 64 Gb/s. The photonics circuit is designed for an SOI process with a 300 nm top Si layer and is based on a Mach-Zehnder Interferometer architecture modulator using carrier depletion. The CMOS driver circuit employs two on-chip PRBS sources and tunable delay pre-driver segments. This driver is flip-chip bonded to the photonics die to complete the packaging. Details of the model are outlined below and a simulated optical eye diagram is presented.

Silicon photonic networks for exascale computers (Conference Presentation)

Recent trends show an explosion in the amount of data being created each year. In response to this trend new system architectures optimized for data-centric workloads are being developed. These architectures can only be brought to fruition by developing new technologies to transmit, compute, and store data. My talk will focus on the impact of photonics, and silicon photonics in particular, on these trends and discuss the work being done at HPE labs to advance these technologies

Silicon Photonics; Ring Modulator Transmitters

In this article silicon ring modulators transmitters are discussed. We introduce the various types of ring modulators and the modulation mechanisms currently used. A short survey of fabrication methods is followed by a review of the optical and electrical properties of ring modulators. Nonlinear effects and the applications of ring modulators are also discussed.

A 40Gb/s PAM4 optical DAC silicon microring resonator modulator transmitter

PAM4 modulation is currently being implemented in high-speed wireline communication standards in order to increase bandwidth density. This paper presents a transmitter which utilizes a low-area silicon microring resonator modulator with two separate phase shifter segments to realize high-speed PAM4 modulation with an optical DAC approach. The optical DAC is designed with an optimized MSB/LSB segment size ratio of 1.9:1 to generate a uniform four level output with independent MSB/LSB two-level NRZ drivers. Two differential high-swing segmented pulsed-cascode output stages drive the MSB/LSB segments with independent edge-rate and level controls that compensate for output level spacing and eye skew. The hybrid integrated prototype, with the optical DAC microring modulator fabricated in a 130nm silicon photonic process and the transmitter circuitry fabricated in a GP 65nm CMOS process, achieves 40Gb/s operation at 4.38mW/Gb/s when driving each differential terminal of the segmented depletion-mode microring modulator with 4.4Vppd swing.