Despite years of research and development, integrated laser sources remain a bottleneck for silicon photonics (SiPh). Integration of lasers into SiPh can be categorized as hybrid, heterogeneous, or monolithic. Hybrid approaches are the most mature. One example is the co-packaging of lasers with micro-optics and subsequent coupling of laser light to silicon waveguides. More scalable hybrid approaches include butt coupling of lasers and silicon waveguides without the use of micro-optics. This could be accomplished with two chips mounted side by side on a common carrier or by flip-chip bonding of laser chips into recesses adjacent to silicon waveguides. Heterogeneous approaches involve the intimate merging of traditionally incompatible materials and subsequent co-fabrication of these materials to form devices. This approach allows for best-in-class materials selection, however, co-fabrication requires complex fabrication processes. The term monolithic ordinarily refers to a single substrate and materials compatible with the substrate material. Germanium on silicon could be considered a monolithic approach, as could growth of III-V materials (such as indium phosphide (InP) and gallium arsenide) on silicon. This paper summarizes a novel 3D hybrid integration approach that is scalable, low cost, reliable, and that demonstrates superior thermal performance. The approach is based on flip-chip bonding and vertical coupling between InP and silicon waveguides. For the InP waveguide, vertical emission is achieved with a total internal reflection turning mirror. For the silicon waveguide, vertical coupling is achieved with a grating coupler. The InP chip is flip-chip bonded directly to the silicon substrate providing an effective heat sink.

Data centers collect and process information with a capacity that has been increasing from year to year at an almost exponential pace, while many datacenter applications are provided at no cost. This faces datacenter operators with the challenges of meeting exponentially increasing demands for network bandwidth without unreasonable increases in operation and infrastructure cost. In order to meet the requirements of moderate increase in operation and infrastructure cost new technologies are desired. Optical wireless technology could a) reduce the power consumption, b) increase the flexibility and scalability and c) reduce the network overload.. The OWC link could be deployed on top of the existing cable/fiber network layer, such that live migration could be done easily and dynamically and network topology is flexible and adapts quickly to changes in traffic, heat distribution, power consumption and characteristics of the applications. In addition, OWC could provide an easy way to maintains and scale up data centers which would reduce total cost of ownership and increase the return on investment. In this talk we will review the main OWC technologies, algorithms concepts and configurations which improve the performance of next generation data centers.

Datacenter networks are not only larger but with new applications increasing the east-west traffic and the introduction of the spine leaf architecture there is an urgent need for high bandwidth, low cost, energy efficient interconnects. This paper will discuss the role integrated photonics can have in achieving datacenter requirements. We will review the state of the art and then focus on advances in optical switch fabrics and systems. The optical switch is of particular interest from the integration point of view. Current MEMS and LCOS commercial solutions are relatively large with relatively slow reconfiguration times limiting their use in packet based datacenter networks. This has driven the research and development of more highly integrated silicon photonic switch fabrics, including micro ring, Mach-Zehnder and MEMS device designs each with its own energy, bandwidth and scalability, challenges and trade-offs. Micro rings show promise for their small footprint, however they require an energy efficient means to maintain wavelength and thermal control. Latency requirements have been traditionally less stringent in datacenter networks compared to high performance computing applications, however with the increasing numbers of servers communicating within applications and the growing size of the warehouse datacenter, latency is becoming more critical. Although the transparent optical switch fabric itself has a minimal additional latency, we must also take account of any additional latency of the optically switched architecture. Proposed optically switched architectures will be reviewed.

This paper discusses how to realize an optical circuit switching interconnect capable of more than 10 Tbps link bandwidth and more than 100,000 end points scalability. To keep continuous performance improvement of datacenters or high performance computers, high capacity and low latency interconnect network is essential. To handle such large bandwidth interconnect networks with low energy consumption, optical switch technologies will become inevitable. This paper firstly examines the scaling of the energy consumption of optical circuit switching networks based on the state of the art silicon photonics switch technology. Secondly to achieve Tbps-class link bandwidth, the WDM transmission technology and a shared WDM light source mechanism named “wavelength bank” are introduced. Due to the shared light source, each optical transceiver does not have to carry individual light sources, which enables simple WDM transceivers with cost-efficient silicon photonics technologies. Then a new optical switch control approach which reduces the control overhead time is discussed. In the proposed approach, the optical data plane itself represents the path destination, which enables a simple distributed-like control procedure. The proposed approach is expected to achieve the scalability and flexibility supporting more than 10 Tbps link bandwidth and more than 100,000 endpoints with 40 WDM channels. The proposed interconnect architecture offers direct end-to-end optical paths enabling low latencies with the “speed of light”. The paper also discusses some of the challenges which should be resolved to practically realize the future large bandwidth optical interconnect networks.

In this paper, we present a new type of optical fiber, called universal fiber, which can be used for both multimode and single mode transmissions. The fiber is a multimode fiber that has an LP01 mode field diameter approximately matched to that of standard single mode fiber. First, we will present the universal fiber design concept and discuss design tradeoffs for both single mode and multimode operations. Then we will show characterizations of a preliminary experimental fiber and present system testing results with 110 m, 150 m and 2700 m system reach using 100G SR4, 40G sWDM multimode and 100G CWDM4 single mode transceivers, respectively, which demonstrate both multimode and single mode transmission capabilities of universal fiber.

We propose a chip-scale silicon photonics transceiver using multimode optical wiring to realize low-cost and high-productivity optical interconnection usable for several short-reach applications. We also present hybrid-integrated low-power- consumption chip-scale optical transmitters/receivers called “optical I/O cores.” The optical I/O cores provide clear eye opening in a wide range of temperature operation without clock data recovery. We show the design of one such optical I/O core and evaluate its performance for a wide range of temperatures. Finally, we introduce an example of LSI system based on the optical I/O approach.

As a promising platform technology for optical switches, silicon photonics is recently attracting much attention. In this paper, we demonstrate compact 8 × 8 silicon photonic switch modules with low loss, low polarization sensitivity, and low cross-talk properties. An optical circuit including 152 thermo-optical switch elements and spot size converters were formed within a silicon chip size of 12 mm × 14 mm. The developed module where a silicon photonic chip was assembled with a fiber array showed about 6-dB average excess optical loss, including optical coupling loss, on all 64 paths of the 8 × 8 optical switch. Measured polarization dependent loss was about 0.6 dB on average over 64 paths and cross-talk was less than -35 dB. These optical switch modules are intended for applying to ROADMs in telecom optical networks, but, the port count extensibility using multiple compact modules and the faster switching capability of the optical switch are also useful for datacenter applications where hybrid network scheme with electronic packet switches and optical circuit switches is intensively investigated.

Emerging short-reach data center interconnect (typically in the range of tens of km) is a scenario wherein the capacity has to be maximized over point-to-point optical links without intermediate optical amplification, i.e. unrepeated links. For this application, cost and compactness of the optical transceiver form factor to fit the faceplate density requirement are essential to keep up with the bandwidth demand inside hyper-scale data centers. For the optical module to fit in the current dimensions of client routers without compromising the performance, both the electronics and the optics have to be efficiently designed. As far as the opto-electronic is concerned, photonic integrated circuits (PIC) have been discussed in the community so that all the photonic functionalities are performed accordingly with the physical dimensions, power budget and performance specifications. This paper addresses the basic building blocks of silicon photonics coherent optical transceivers, from the design to experimental validation. In addition to the silicon optical modulator, basic components such as polarization splitter-rotators (PSRs) and optical filters will be addressed.

Ever-increasing intra-datacenter traffic will spur the introduction of high-baud rates and high-order modulation formats. Increasing symbol rates and modulation levels decreases tolerance against transmission impairment that includes chromatic dispersion. Transmission distance in warehouse-scale datacenters can be several kilometers, and then management of chromatic dispersion is necessary. Dispersion-compensating fibers are widely deployed in backbone networks, however, applying them in datacenters is not cost-effective since wavelength channels are coarsely multiplexed. In digital coherent systems, signal distortion due to chromatic dispersion can be resolved in digital domain; however, it will take long time before coherent systems can be introduced in datacenter networks because of their high cost. In this paper, we propose a novel impairment mitigation method employing machine learning. The proposed method is effective even after non-coherent detection and hence it can be applied to cost-sensitive intra-datacenter networks. The machine learns optimum symbol-decision criteria from a sequence of dispersed training signals, and it discriminates payload signals in accordance with the established decision criteria. With the scheme, the received signals can be demodulated in the presence of large chromatic dispersion. The transmission distance thus can be extended without relying on costly optical dispersion compensation. Since information of transmission links is not a priori required, the proposed scheme can easily be applied to any datacenter network. We conduct transmission experiments using 400-Gbps channels each of which comprises 8-subcarrier 28-Gbaud 4-ary pulse-amplitude-modulation (PAM-4) signals, and confirm the effectiveness of the proposed scheme.

Technologies for creating cost-effective light-emission optical sub-assemblies (OSAs) are discussed from the point of view of laser diodes. A lens-integrated surface-emitting laser (LISEL), consisting of a DFB laser, integrated mirror, and integrated convex lens, has the potential to achieve light-emission OSAs. An OSA based on the LISEL is proposed, and the capabilities of direct and passively aligned optical coupling, isolator-free operation, non-hermetic packaging, and on-wafer testing are introduced.

Near-infrared Ge photonic devices on a Si platform are presented toward low-cost, low-energy and high-capacity optical communications. Using Ge epitaxial layers selectively grown by chemical vapor deposition on Si-on-insulator layers, Ge photodiodes (PDs) of vertical pin structures are integrated with Si optical waveguides. The integrated Ge PDs show high responsivities as large as 0.8 A/W at 1.55 μm with the 3-dB cutoff frequency more than 10 GHz. SiGe/Ge heterostructures have potential applications to higher-performance devices. One application is to low-noise and low-voltage avalanche photodiodes (APDs), where a SiGe layer is inserted at the interface between the optical absorption layer of Ge and the carrier-multiplication layer of Si or Ge. The band discontinuity at the interface enhances the impact ionization for photo-generated carriers injected via SiGe. Fabricated APDs show an enhanced multiplication gain. The other application of SiGe is to a stressor to control the direct bandgap of Ge. As a proof of concept, a tensile-strained Si0.2Ge0.8 overlayer is shown to induce a compressive stress in the underlying Ge mesa stripe, leading to a blue shift in the absorption edge of Ge.

Emerging requirements for inter-office/inter-datacenter short reach links for data center interconnects (DCI) and metro transport networks have led to various inter-office and inter-datacenter optical interface technologies. These technologies are bringing significant changes to systems and network architectures. In this paper, we present a system and ZR optical interface technologies for DCI and metro transport networks, then introduce the latest challenges facing the system framework. There are two trends in reach extension; one is to use Ethernet and the other is to use digital coherent technologies. The first approach achieves reach extension while using as many existing Ethernet components as possible. It offers low costs as reuses the cost-effective components created for the large Ethernet market. The second approach adopts low-cost and low power coherent DSPs that implement the minimal set long haul transmission functions. This paper introduces an architecture that integrates both trends. The architecture satisfies both datacom and telecom needs with a common control and management interface and automated configuration.

100GBASE-LR4 is an unamplified standard for Ethernet at 100 Gb/s data rate, allowing for connection distances up to 10km, while 100GBASE-ER4 calls for larger optical budget in order to reach at least 40km. We discuss these for high-speed communication between data centers, with particular emphasis on the optical amplification (SOAs) included in the transceiver modules in order to enable long-distance links.

Bit Error Ratio (BER) dependence on received power was studied for 40Gb/s NRZ short optical fiber transmission, including a series of four low return loss (RL~21dB) and low insertion loss (IL~0.1dB) connections. The calculated power penalty (PP) was 0.15dB for BER~10^-11. Although the fiber length was within DFB laser’s coherent length of ~100m and the multi path interference (MPI) value was 34.3dB, no PP of BER was observed. There was no PP due to low MPI probably because the polarization of the signal pulses were not aligned for optical interference, indicating that NRZ systems have a high resistance to MPI.

In order to meet the recent vast demands of ICT bandwidth, high speed transmission systems, such as 100G, 200G and 400G, have been developed and installed with extremely high pace. De-fact standardization bodies such as IEEE802.3/OIF have played important roles in the industry for leading the proper concepts/designs of the leading edge high speed transceivers. Reviewing the recent activities of these standardization bodies, the future migration towards 800G and 1.6T with small form factor transceivers are examined. The high bandwidth per channel technology, such as 100GHz and beyond, is a key factor to realize the next generation transceivers such as 800G and 1.6T.

We propose a time-division hybrid-user data flow model scheme based on semi-Markov state-transition algorithm for multiclass business and service in Integrated Sensing Network (ISN). Two typical flow models, visual sense and auditory sense service models, are set up due to the real situation of service stratum traffic, respectively. The experimental system based on the Asynchronous Optical Packet Switching (AOPS) network simulation platform is established for the feasibility of the proposed data flow model. The results show that the proposed models achieve reasonable packet loss rate and delay time in the case of different business and service levels.