Peter De Heyn

Silicon photonics integrated circuits: a manufacturing platform for high density, low power optical I/O’s

Silicon photonics integrated circuits are considered to enable future computing systems with optical input-outputs co-packaged with CMOS chips to circumvent the limitations of electrical interfaces. In this paper we present the recent progress made to enable dense multiplexing by exploiting the integration advantage of silicon photonics integrated circuits. We also discuss the manufacturability of such circuits, a key factor for a wide adoption of this technology.

Fabrication-Tolerant Four-Channel Wavelength-Division-Multiplexing Filter Based on Collectively Tuned Si Microrings

We demonstrate a robust, compact and low-loss four-channel wavelength-division multiplexing (WDM) filter based on cascaded double-ring resonators (2RR) in silicon. The flat-top channel response obtained by the second-order filter design is exploited to compensate for the detrimental effects of local fabrication variations and their associated phase errors on the ring-based filter response. Full wafer-scale characterization of a cascaded, four-channel 2RR filter with channel spacing of 300 GHz shows an average worst-case insertion loss below 1.5 dB and an average worst-case crosstalk below -18 dB across the wafer, representing a substantial improvement over a first-order based ring (1RR) design. The robust 2RR filter design enables the use of a simple collective thermal tuning mechanism to compensate for global fabrication variations as well as for global temperature fluctuations of the WDM filter, the WDM laser source, or both. Highly uniform collective heating is demonstrated using integrated doped silicon heaters. The compact filter footprint of less than 50×50 μm2 per channel enables straightforward scaling of the WDM channel count to 8 channels and beyond. Such low-loss collectively tuned ring-based WDM filters can prove beneficial in scaling the bandwidth density of chip-level silicon optical interconnects.

High-Responsivity Low-Voltage 28-Gb/s Ge p-i-n Photodetector With Silicon Contacts

We report a high-performance germanium waveguide photodetectors (WPDs) without doping in germanium or direct metal contacts on germanium, grown on and contacted through a silicon p-i-n diode structure. Wafer-scale measurements demonstrate high responsivities larger than 1.0 A/W across the C-band and low dark current of ~3 nA at -1 V and ~8 nA at -2 V. Owing to its small dimensions, the Ge WPD exhibits a high optoelectrical 3-dB bandwidth of 20 and 27 GHz at low-bias voltages of -1 and -2 V, respectively, which are sufficient for operation at 28 Gb/s. The reduced processing complexity at the tungsten contact plug module combined with the high responsivity makes these Ge WPD devices particularly attractive for emerging low-cost CMOS-Si photonics transceivers.

Highly Uniform 25 Gb/s Si Photonics Platform for High-Density, Low-Power WDM Optical Interconnects

We report on electro-optical device performance in a fully integrated 25Gb/s Si photonics platform running on a 130-nm CMOS toolset. Extensive uniformity data is presented for ring modulators, Ge photodetectors and compact ring-based WDM filters.

Imec iSiPP25G silicon photonics: a robust CMOS-based photonics technology platform

Silicon photonics has become in the past years an important technology adopted by a growing number of industrial players to develop their next generation optical transceivers. However most of the technology platforms established in CMOS fabrication lines are kept captive or open to only a restricted number of customers. In order to make silicon photonics accessible to a large number of players several initiatives exist around the world to develop open platforms. In this paper we will present imec’s silicon photonics active platform accessible through multi-project wafer runs.

22.5 A 4×20Gb/s WDM ring-based hybrid CMOS silicon photonics transceiver

Silicon photonics (SiPh) has been identified as a prime technology targeting cost-effective short-range optical links [1]. Wavelength-division multiplexing (WDM) is an attractive approach for enabling high aggregate transceiver bandwidth without increasing the number of optical fibers used in the link. Ring-based optical modulators and wavelength-selective filters are attractive devices for scalable WDM SiPh transceivers owing to their compact footprint and moderate power required for thermal tuning. In this paper, we report on a thermally controlled ring-based flip-chip integrated CMOS-SiPh transceiver with 4 channels operating at 20Gb/s.

Co-integration of Ge detectors and Si modulators in an advanced Si photonics platform

A Si photonics platform is described, co-integrating advanced passive components with Si modulators and Ge detectors. This platform is developed on a 200mm CMOS toolset, compatible with a 130nm CMOS baseline. The paper describes the process flow, and describes the performance of selected electro-optical devices to demonstrate the viability of the flow.

In-Band Label Extractor Based on Cascaded Si Ring Resonators Enabling 160 Gb/s Optical Packet Switching Modules

Photonic integration of optical packet switching modules is crucial to compete with existing electronic switching fabrics in large data center networks. The approach of coding the forwarding packet information in an in-band label enables a spectral-efficient and scalable way of building low-latency large port count modular optical packet switching architecture. We demonstrate the error-free operation of the four in-band label extraction from 160 Gb/s optical data packets based on photonic integrated silicon-on-insulator ring resonators. Four low-loss cascaded ring resonators using the quasi-TM mode are used as narrowband filters to ensure the detection of four optical labels as well as the error-free forwarding of the payload at limited power penalty. Due to the low-loss and less-confined optical quasi-TM mode the resonators can be very narrowband and have low insertion loss. The effect of the bandwidth of the four ring resonators on the quality of the payload is investigated. We show that using four rings with 3dB bandwidth of 21 pm and only an insertion loss of 3 dB, the distortion on the payload is limited (<;1.5 dB power penalty), even when the resonances are placed very close to the packets central wavelength. We also investigate the optical power requirements for error-free detection of the label as function of their spectral position relative to the center of the payload. The successful in-band positioning of the labels makes this component very scalable in amount of labels.

Advances in silicon photonics WDM devices

System performance scaling imposes an increase of package-to-package aggregate bandwidths to interface chips in high performance computing. This scaling is expected to encounter several I/O bottlenecks (pin count, speed, power consumption) when implemented in the electrical domain. Several optical interface technologies are being proposed among which silicon photonics, considered as a promising candidate. In this paper we will review the recent progress made in this technology that may enable multi-channel WDM links for package-to-package interconnects: 1.0V drivers with microring modulators and compact manufacturable microring filters with efficient thermal tuning.

Electrically tunable absorption in graphene-integrated silicon photonic crystal cavity

We demonstrate 17 dB extinction ratio in an electrically gated graphene-integrated silicon photonic crystal cavity by applying −1.2 V gate voltage. The shift of resonance wavelength for the same voltage range is 0.75 nm. The size of the graphene layer is only 5 μm2.