O-Band Subwavelength Grating Filters in a Monolithic Photonics Technology

The data communications industry has begun transitioning from electrical to optical interconnects in datacenters in order to overcome performance bottlenecks and meet consumer needs. To mitigate the costs associated with this change and achieve performance for 5G and beyond, it is crucial to explore advanced photonic devices that can enable high-bandwidth interconnects via wavelength-division multiplexing (WDM) in photonic integrated circuits. Subwavelength grating (SWG) filters have shown great promise for WDM applications. However, the small feature sizes necessary to implement these structures have prohibited them from penetrating into industrial applications. To explore the manufacturability and performance of SWG filters in an industrial setting, we fabricate and characterize O-band subwavelength grating filters using the monolithic photonics technology at GLOBALFOUNDRIES (GF). We demonstrate a low drop channel loss of -1.2 dB with a flat-top response, a high extinction ratio of -30 dB, a 3 dB channel width of 5 nm and single-source thermal tunability without shape distortion. This filter structure was designed using elements from the product design kit provided by GF and functions in a compact footprint of 0.002 mm2 with a minimum feature size of 150 nm.Comment: 4 pages, 3 figure

Photonic integration enabling new multiplexing concepts in optical board-to-board and rack-to-rack interconnects

New broadband applications are causing the datacenters to proliferate, raising the bar for higher interconnection speeds. So far, optical board-to-board and rack-to-rack interconnects relied primarily on low-cost commodity optical components assembled in a single package. Although this concept proved successful in the first generations of optical-interconnect modules, scalability is a daunting issue as signaling rates extend beyond 25 Gb/s. In this paper we present our work towards the development of two technology platforms for migration beyond Infiniband enhanced data rate (EDR), introducing new concepts in board-to-board and rack-to-rack interconnects. The first platform is developed in the framework of MIRAGE European project and relies on proven VCSEL technology, exploiting the inherent cost, yield, reliability and power consumption advantages of VCSELs. Wavelength multiplexing, PAM-4 modulation and multi-core fiber (MCF) multiplexing are introduced by combining VCSELs with integrated Si and glass photonics as well as BiCMOS electronics. An in-plane MCF-to-SOI interface is demonstrated, allowing coupling from the MCF cores to 340x400 nm Si waveguides. Development of a low-power VCSEL driver with integrated feed-forward equalizer is reported, allowing PAM-4 modulation of a bandwidth-limited VCSEL beyond 25 Gbaud. The second platform, developed within the frames of the European project PHOXTROT, considers the use of modulation formats of increased complexity in the context of optical interconnects. Powered by the evolution of DSP technology and towards an integration path between inter and intra datacenter traffic, this platform investigates optical interconnection system concepts capable to support 16QAM 40GBd data traffic, exploiting the advancements of silicon and polymer technologies

Design Of An All-Optical WDM Lightpath Concentrator

A design of a nonblocking, all-optical lightpath concentrator using wavelength exchanging optical crossbars and WDM crossbar switches is presented. The proposed concentrator is highly scalable, cost-efficient, and can switch signals in both space and wavelength domains without requiring a separate wavelength conversion stage

VCSEL and Integration Techniques for Wavelength-Multiplexed Optical Interconnects

GaAs-based vertical-cavity surface-emitting lasers (VCSELs) are dominating short-reach optical interconnects (OIs) due to their high modulation speed, low power consumption, circular output beam and low fabrication cost. Such OIs provide the high bandwidth connectivity needed for interconnecting servers and switches in data centers. With the rapidly increasing use of Internet-based applications and services, higher bandwidth connectivity and higher aggregate capacity VCSEL-based OIs are needed. Until now, this has been achieved mostly through an increase of the lane rate by higher speed VCSELs and higher order modulation formats. Furthermore, spatial-division-multiplexing has proven effective for increasing the aggregate capacity. Much higher capacity can be achieved by multiple wavelengths per fiber, known as wavelength-divisionmultiplexing (WDM). Moreover, smaller footprint and higher bandwidth density WDM transceivers can be built using monolithic multi-wavelength VCSEL arrays with densely spaced VCSELs. This requires a VCSEL technology where the wavelength of individual VCSELs can be precisely set in a post-epitaxial growth fabrication process and a photonic integrated circuit (PIC) for multiplexing and fiber coupling. Flip-chip integration over grating couplers (GCs) is considered for interfacing VCSELs with waveguides on the PIC. In this thesis, an intra-cavity phase tuning technique is demonstrated for setting the resonance wavelength of VCSELs in a monolithic array with an accuracy in spacing of <1 nm. Uniform performance over the array is achieved by spectral matching and balancing of mirror reflectances, optical confinement factor and optical gain. Single transverse and polarization mode VCSELs, as required for flip-chip integration over GCs, with a record output power of 6 mW are also demonstrated.Finally, an investigation of angled flip-chip integration of a VCSEL over a GC on a silicon photonic integrated circuit (Si-PIC) is presented. Dependencies of coupling efficiency and optical feedback on flip-chip angle and size of the VCSEL die are studied using numerical FDTD simulations. Moreover, flip-chip integration of a VCSEL over a GC on a Si-PIC is experimentally demonstrated. The insertion loss from the VCSEL at the input GC to a singlemode fiber, multimode fiber or flip-chip integrated photodetector over the output GC was measured and quantified. The latter forms an on-PIC optical link

High Efficiency Silicon Photonic Interconnects

Silicon photonic has provided an opportunity to enhance future processor speed by replacing copper interconnects with an on chip optical network. Although photonics are supposed to be efficient in terms of power consumption, speed, and bandwidth, the existing silicon photonic technologies involve problems limiting their efficiency. Examples of limitations to efficiency are transmission loss, coupling loss, modulation speed limited by electro-optical effect, large amount of energy required for thermal control of devices, and the bandwidth limit of existing optical routers. The objective of this dissertation is to investigate novel materials and methods to enhance the efficiency of silicon photonic devices. The first part of this dissertation covers the background, theory and design of on chip optical interconnects, specifically silicon photonic interconnects. The second part describes the work done to build a 300mm silicon photonic library, including its process flow, comprised of basic elements like electro-optical modulators, germanium detectors, Wavelength Division Multiplexing (WDM) interconnects, and a high efficiency grating coupler. The third part shows the works done to increase the efficiency of silicon photonic modulators, unitizing the χ(3) nonlinear effect of silicon nanocrystals to make DC Kerr effect electro-optical modulator, combining silicon with lithium niobate to make χ(2) electro-optical modulators on silicon, and increasing the efficiency of thermal control by incorporating micro-oven structures in electro-optical modulators. The fourth part introduces work done on dynamic optical interconnects including a broadband optical router, single photon level adiabatic wavelength conversion, and optical signal delay. The final part summarizes the work and talks about future development

Merging Plasmonics and Silicon Photonics Towards Greener and Faster “Network-on-Chip” Solutions for Data Centers and High-Performance Computing Systems

Endocrinolog

Chapter Merging Plasmonics and Silicon Photonics Towards Greener and Faster “Network-on-Chip” Solutions for Data Centers and High-Performance Computing Systems

Endocrinolog