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The enormous traffic growth sets a stringent requirement to upgrade short-reach optical links to 1.6 TbE capacity in an economically viable way. The power consumption and latency in these links should be as low as possible, especially for high-speed computing. This is possible to achieve using high baudrate on-off keying links thanks to a better noise tolerance and a relaxed requirement on linearity for electronics and photonics. In this regard, we demonstrate a 200 Gbaud on-off keying link without any optical amplification using an externally modulated laser with 3.3 dBm of modulated output power operating at 1541.25 nm wavelength. We achieve transmission over 200 meters of single-mode fiber with performance below 6.25% overhead hard-decision forward error correction threshold for each baudrate and all selection of modulation formats. We also show 108 Gbaud on-off keying link with superior performance without decision feedback equalizer up to 400 meters of single-mode fiber. In addition, we benchmark the short-reach optical link with 112 Gbaud four-level pulse amplitude modulation and 100 Gbaud six-level pulse amplitude modulation. For 108 Gbaud on-off keying and 112 Gbaud four-level pulse amplitude modulation, we can achieve an even lower bit error rate., QC 20230613

©2012 Optical Society of America., We experimentally demonstrate a new type of waveguide multiplexer device designed for silicon photonics, with a crosstalk level as low as -35 dB and an operational wavelength range of 300 nm. A compact device footprint of only 100 x 160 µm2 offers an excellent potential for integration with other silicon nanophotonic circuits., Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

Growing demands in high data capacity and low energy consumption have driven the development of high-performance optical interconnects for many commercial applications, such as links for long-haul, intra-/inter-datacenter, and 5G communication. Typically, the photonic devices used in these environments are optimized for operation at or above room temperature, however there is an existing and growing need for optimized photonic devices to operate in cryogenic and/or high-radiation environments. Applications of these optical interconnects range from control and readout from superconducting integrated circuits for quantum computing, to readout of tracking detectors in high-energy physics (HEP) particle accelerators, to readout of next-generation infrared (IR) focal plane array (FPA) detectors. Key to the success of these optical interconnects is the high-performance and ruggedization of the electro-optic modulator (EOM), typically implemented either as a remoted external device or as a directly modulated light source. This PhD dissertation addresses the challenges of optical interconnects for harsh environments in the following manner: (1) a novel and wavelength division multiplexed (WDM) scalable optical interconnect architecture has been developed—whereby the remoted EOM has been implemented as a microring resonator—and reduces both system complexity and energy consumption, (2) a high-speed optical link operating at cryogenic temperatures has been demonstrated—utilizing a silicon photonic based EOM—in addition to laser wavelength locking of the microring resonator, and (3) a semiconductor physics based model of the EOM has been developed to address the temperature dependent effects of the silicon p-n junction embedded in the microring resonator—based on the free-carrier plasma dispersion effect in doped silicon—to aid in the device design and optical interconnect link optimization for various harsh environment applications. Lastly, an outlook and suggested areas for

The explosive growth of data volume brought by the pervasiveness of artificial intelligence (AI) applications is calling for interconnect technologies that enable higher bandwidth capacity at a lower cost. In particular, optical interconnects based on silicon photonics are considered a promising substitute for electrical ones, given their cost-effectiveness and scalability enabled by a CMOS-compatible fabrication process. However, as the optical interconnects further penetrate the shorter-reach regime, several issues arise from the growing complexity of system integration and pose challenges to their design quality, including 1) inadequate support from design automation methodologies for the modeling and simulation of the optical interconnects, 2) oversimplified characterization of process variations, resulting in variation alleviation techniques with limited effectiveness, and 3) the lack of runtime reconfiguration strategies for the optical interconnects under traffic dynamics, leading to unoptimized energy efficiency. This dissertation is devoted to addressing the above issues by solutions proposed at the device, link, and system levels, paving the way to the quality design of variation-aware runtime-reconfigurable optical interconnects with optimized energy efficiency.The first part of this dissertation focuses on device-level methodologies for electronic-photonic design automation (EPDA), including compact models developed for lasers and modulators and a novel hierarchical spatial variation model characterized for silicon microring resonators. Extensively validated by measurement data, the library of device-level models enables accurate circuit-level simulation of optical links and variation-aware estimation of the link power budget, serving as the fundamentals of the optimization techniques proposed at the link and system levels.The second part of this dissertation proposes three link-level techniques to improve the energy efficiency of the optical interconnec

Optical interconnects enabled by silicon microring-based transceivers offer great potential for short-reach data communication in future high-performance computing systems. However, microring resonators are prone to process variations that harm both the energy efficiency and the yield of the fabricated transceivers. Especially in the application scenario where a batch of transceivers are fabricated for assembling multiple optical networks, how the transceivers are mixed and matched can directly impact the average energy efficiency and the yield of the networks assembled. In this study, we propose transceiver grouping for assembling communication networks from a pool of fabricated transceivers, aiming to optimize the network energy efficiency and the yield. We evaluated our grouping algorithms by wafer-scale measurement data of microring-based transceivers, as well as synthetic data generated based on an experimentally validated variation model. Our experimental results demonstrate that optimized grouping achieves significant improvement in the network energy efficiency and the yield across a wide range of network configurations, compared to a baseline strategy that randomly groups the transceivers. CCBY

[EN] We report recent advances in photonic-electronic integration developed in the European research project L3MATRIX. The aim of the project was to demonstrate the basic building blocks of a co-packaged optical system. Two-dimensional silicon photonics arrays with 64 modulators were fabricated. Novel modulation schemes based on slow light modulation were developed to assist in achieving an efficient performance of the module. Integration of DFB laser sources within each cell in the matrix was demonstrated as well using wafer bonding between the InP and SOI wafers. Improved semiconductor quantum dot MBE growth, characterization and gain stack designs were developed. Packaging of these 2D photonic arrays in a chiplet configuration was demonstrated using a vertical integration approach in which the optical interconnect matrix was flip-chip assembled on top of a CMOS mimic chip with 2D vertical fiber coupling. The optical chiplet was further assembled on a substrate to facilitate integration with the multi-chip module of the co-packaged system with a switch surrounded by several such optical chiplets. We summarize the features of the L3MATRIX co-package technology platform and its holistic toolbox of technologies to address the next generation of computing challenges.

The rapid increasing traffic in data centers (DCs) puts tremendous pressure to the present multi-tier network architectures and electrical switching techniques. Switching traffic in the optical domain featuring ultra-high bandwidth, therefore, has been intensively investigated to build the high capacity data center networks (DCNs). To handle the variable traffic pattern in DCs, the network reconfigurability with adaptable optical bandwidth allocation is of key importance to flexibly assign the optical bandwidth. To this end, we propose and experimentally evaluate a software-defined networking enabled reconfigurable optical DCN with dynamic bandwidth allocation in this work, based on novel optical top of racks exploiting a wavelength selective switch. Experimental assessments show that the proposed solution can automatically reallocate the optical bandwidth in real-time to adapt the dynamic traffic pattern. Compared with the conventional optical DCN with static bandwidth provision, the end-to-end latency performance of the reconfigurable scheme with adaptable bandwidth allocation improves of 58.3% and the average packet loss decreases one order of magnitude. Moreover, the reconfigurable optical DCN features deterministic latency performance, with much lower time variations of packets delivery completion. Based on the experimental parameters, the simulation platform is also built to validate the good scalability of the proposed reconfigurable DCN. Numerical results illustrate the negligible performance degradation (11%) as the network scales from 2560 to 40 960 servers.

We experimentally evaluate the high-speed on-off keying (OOK) and four-level pulse amplitude modulation (PAM4) transmitter's performance in C-band for short-reach optical interconnects. We demonstrate up to 100 Gbaud OOK and PAM4 transmission over a 400 m standard single-mode fiber with a monolithically integrated externally modulated laser (EML) having 100 GHz 3 dB bandwidth with 2 dB ripple. We evaluate its capabilities to enable 800 GbE client-side links based on eight, and even four, optical lanes for optical interconnect applications. We study the equalizer's complexity when increasing the baud rate of PAM4 signals. Furthermore, we extend our work with numerical simulations showing the required received optical power (ROP) for a certain bit error rate (BER) for the different combinations of the effective number of bits (ENOB) and extinction ratio (ER) at the transmitter. We also show a possibility to achieve around 1 km dispersion uncompensated transmission with a simple decision feedback equalizer (DFE) for a 100 Gbaud OOK, PAM4, and eight-level PAM (PAM8) link having the received power penalty of around 1 dB., QC 20210611

In this work, we investigated the optical response of a self-written waveguide (SWW) in detail by heating the structure from room temperature up to 60 °C. Previous results indicated a decrease in the optical transmission with increasing temperature for certain waveguide parameters. Based on new experimental measurements, we have identified material parameters resulting in opposite behaviour. An experimental setup was conceived to verify these results. Hereby, we were able to show that we can adjust material parameters such as refractive index and the corresponding density of the material by adapting the curing time applied during the fabrication of the waveguides. This, in turn, affects the material’s response during the heating process. We showed that a limitation of the external curing time changes the internal conditions of the SWW and the cladding in a manner that the numerical aperture increases with the temperature, which subsequently also results in an increase in the optical transmission. In this study, we explain this unexpected behavior of the SWW and point towards possible future applications. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

In the last decades, the optical adhesives have become highly promising due to their widespread applications in the numerous optical fields. There are outnumbered research studies about them and their numerous fields of application. One of these promising applications is the usage of self-written waveguides (SWW) which enable a rigid and low loss connection between two optical components. Nevertheless, there are not enough research studies about the temperature dependency of the optical transmission through the SWW that is inspected in this study. This master’s project is devoted to study the transmission of a laser beam by temperature through SWW created in the NOA 68 photopolymer medium. To verify the data from the experiment, a model is designed, simulated using the Multiphysics optical simulation software (COMSOL), and then, the simulation results are compared with the experimental data. Furthermore, the research studies do not propose anything for the durations of the internal- and external curing where the waveguide is attenuated highest that makes it very vital for the waveguide formation. This study removed the blurriness in the curing times and guide the scientists in establishing an efficient waveguide made out of NOAs. To achieve this goal, a thermal simulation of the waveguide is made, an SWW is formed, and the experimental results of the power output, and the refractive-index profile of the waveguide are analyzed. Then, the RIs of the SWW and its cladding are measured in the refractive-index profilometer and the results are used to make the simulation in the software.

In this paper, for the first time, we propose a photonic-aided digital-to-analog converter (PADAC) to break through transmitter-side bandwidth limitation in intensity modulation and direct detection (IM-DD) systems. By this method, bandwidth of receiver-side devices can be fully utilized, and nonlinear distortions in high-data-rate electrical signals are avoided. Experimental results indicate that, with only linear equalization, 120 GBaud PAM-4 and PAM-6 signals have been successfully generated and detected below 6.25%-OH HD-FEC and 20%-OH SD-FEC limits, respectively.

Significant advances in silicon photonics over the last two decades have led to a wide array of robust photonic devices that have found many applications including in telecommunications. Despite these advances, the cost of optical interfacing (packaging) of photonic integrated circuits (ICs) makes up the bulk of the manufacturing cost of these chips. In this dissertation, I will present my research in developing compact, efficient and low-cost adiabatic couplers that can enable lower-cost and higher-throughput manufacturing of photonic ICs. I will also present a novel method for designing compact, highly efficient and high misalignment tolerance multi-segment couplers for chip-to-chip connectivity. This technology was also extended to ion-exchange glass waveguides which can provide a platform for more efficient chip-to-chip communication and more economical integration of photonic and electronic components. I will further demonstrate electro-optic modulation using silicon micro-disk modulators and wavelength division multiplexing at cryogenic temperatures which is pivotal to the advancement of cryogenic computing systems including cryogenic supercomputers of the future.

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works, Optical switching techniques have the potential to enable the optical data center network (DCN) interconnections providing high capacity and fast switching capabilities, overcoming thus the bandwidth and latency bottleneck of present electrical switch-based multi-tiered DCNs. The rapid growth of multi-tenant applications with heterogeneous traffic require specialized quality of service (QoS) in terms of packet loss and latency to the DCN infrastructure. Slicing the DCNs into dedicated pieces according to the deployed applications, differentiated QoS, and high resource utilization can be provided. However, slicing the optical DCNs still needs to be investigated because the Software-defined Networking (SDN) technique is developed for the electrical networks, not fully supporting the properties of the optical network. Additionally, Network Slices (NS) need to be automatically provisioned and reconfigured, to provide flexible slice interconnections in support of the multi-tenant applications to be deployed. In this article, we propose and experimentally assess the automatic and flexible NSs configurations of optical OPSquare DCN controlled and orchestrated by an extended SDN control plane for multi-tenant applications with differentiated QoS provisioning. Optical Flow Control (OFC) protocol has been developed to prevent packet losses at switch sides caused by packet contentions. The extended OpenFlow (OF) protocol of SDN is deployed as well in support of the optical switching characteristics. Based on the collected resource topology of data plane, the optical network slices can be dynamically provisioned and automatically reconfigured by the SDN control plane. Meanwhile, experimental results validate that the priority assignment of application flows supplies dynamic QoS performance to various slices running applications with specific requirements in terms of packet loss and transmission latency. In addition, the capability of exposing traffic statistics information of d, This work is supported by Olympics project (ESTAR17207) and Metro-Haul project (G.A. 761727)., Peer Reviewed, Postprint (author's final draft)

We show 100 Gbaud PAM4 400 meters link with performance below the 7% HD-FEC limit of 5x10-3 without optical amplification and post-equalization. We also show 300 Gbps PAM8 line rate transmission over 400 meters of SSMF in C-band., QC 20201210

We demonstrate bidirectional >1.3Tb/s transmission on a 125 µm cladding 8-core MCF using 32GBaud 8-PAM signals on 4 cores/direction and evaluate the average and dynamic crosstalk and skew. These are shown to be well under the system requirements, despite the MCF's high spatial density., QC 20201126

Datacenters experience an enormous traffic growth due to the vast amount of data to be stored, transmitted and processed [1]-[4]. Technical and economic challenges arise to keep up the bandwidth scalability. Therefore, cost-efficient short reach optical interconnects for 400 GbE intra-datacenter links are critical. Attractive solutions are proposed based on eight optical lanes thanks to compatibility with 100 GbE building blocks, where two optical lanes based 100 GbE solution is already being deployed [4]. Solutions for 400 GbE based on four optical lanes or even two optical lanes using high bandwidth components may be more attractive to reduce cost, power consumption and complexity of parallelism [5], [6]. In this talk, we report on several experimental demonstrations for short reach optical interconnects in C-band. We experimentally evaluate high-speed on-off keying (OOK) and 4-level pulse amplitude modulation (PAM4) and 8-level PAM8 transmitter performance in C-band for short reach optical interconnects. We demonstrate 100 Gbaud PAM4 transmission over 400 meters long standard single mode fiber without optical amplification. We also show results of numerical simulations showing achievable transmission reach in C-band for multilevel modulation at 100 Gbaud over standard single mode fiber with simple decision feedback equalizer. This paves the way for cost-effective short reach optical interconnects with multilevel modulation at 100 Gbaud and higher., QC 20200427

Microring-based silicon photonic transceivers are promising to resolve the communication bottleneck of future high-performance computing systems. To rectify process variations in microring resonance wavelengths, thermal tuning is usually preferred over electrical tuning due to its preservation of extinction ratios and quality factors. However, the low energy efficiency of resistive thermal tuners results in nontrivial tuning cost and overall energy consumption of the transceiver. In this study, we propose a hybrid tuning strategy which involves both thermal and electrical tuning. Our strategy determines the tuning direction of each resonance wavelength with the goal of optimizing the transceiver energy efficiency without compromising signal integrity. Formulated as an integer programming problem and solved by a genetic algorithm, our tuning strategy yields 32%∼53% savings of overall energy per bit for measured data of 5-channel transceivers at 5∼10 Gb/s per channel, and up to 24% saving for synthetic data of 30-channel transceivers, generated based on the process variation models built upon measured data. We further investigated a polynomial-time approximation method which achieves over 100x speedup in tuning scheme computation, while still maintaining considerable energy-per-bit savings. © 2019 Association for Computing Machinery.

We experimentally demonstrate 276-Gbps net rate 128QAM-DMT transmission at soft-FEC limit in an IM/DD system with a single C-band packaged EML, a DAC and a photo-detector, proposing a lattice pilot algorithm for channel equalization with only 1% overhead reaching spectral efficiency of 5.82-bits/Hz per lane., QC 20210914

With next-generation optical interconnects for data centers aiming for 0.8 Tb/s or 1.6 Tb/s, 100 Gbaud capable transmitters from a single-laser source will become indispensable. However, these lane rates would require bandwidths of 70 GHz or more, doubling the bandwidth requirements of the electrical and optical components with respect to the fastest current generation of optical interconnects running at 53 Gbaud PAM-4. In this paper, we propose an integrated 4:1 optical serializer topology to achieve 104 Gbaud NRZ and PAM-4 transmission using only quarter rate components at the transmitter. We show 104 (208) Gbit/s OOK (PAM4) transmission using four GeSi EAMs over 1 km of SMF. For 104 Gbaud OOK, clearly open eyes are obtained, while for PAM-4 the performance is limited by the non-linear E/O-transfer function of the EAM. However, adding pre-emphasis in the electrical driver or replacing the single EAM with our previously demonstrated optical DAC topology -consisting of two EAMs in parallel with a 90° phase difference between each- could substantially improve these results. Additionally, we discuss the possibility of a four channel transmitter (4 x 208 Gb/s) from a single mode locked laser, amounting to a 832 Gb/s rate based on the current demonstrator.

In this paper, based on a wet etched silicon interposer, we propose a 2.5D assembly of two dimensional optical transceivers for 400 Gbps parallel optical interconnections. In this opto-electronic packaging, two dimensional optical matrix is formed as 250 μm in both the x -and y-directions by exploiting commercial opto-electronic arrays, and a compact optical interface is used to couple the light channels with fiber ribbons. Each quadrant of the optical matrix is connected with its CMOS IC part via impedance matched co-planner wave guides. The shortest traces between optics and CMOS ICs can be 300 μm, benefiting from flip-chip technology. The process flow of silicon interposer fabrication is illustrated. With flip-chip bonding, 25 Gbps 2D 16-channel receiver is assembled on the silicon interposer, and the sub-module, including the optical interface, is scaled down to 4 mm by 6 mm. In addition, the performance of this assembled module is fully characterized. Uniform and clear eye patterns are captured for all of the channels. Receiver sensitivities are also tested for all channels at 25.78 Gbps, 2 31-1 PRBS, with the variation less than 1.5 dB at error free operation.

Ultracompact optical submodules for parallel optical interconnects are demonstrated based on a three-level silicon interposer, which is fabricated through a low-cost wet etching process. Using three steps of wet etching of silicon, a multilevel cavity is formed for embedding and flip-chipping optical and electrical dies, and opening optical through-silicon vias. In order to reduce thermal coupling between CMOS and GaAs dies, a 50- μ m thermal isolation air gap is formed between dies as a part of the assembly concept, and thermal simulations and experiments are carried to validate its effectiveness. Based on this 3-D packaging concept, compact 4 mm ×6 mm, 10-Gb/s 12-channel transmitter and receiver submodules are fully assembled and tested. Clear and uniform eye patterns for both modules are captured at 10 and 15 Gb/s for every channel. Bit error rate (BER) testing is also performed. Both transmitter and receiver submodules show uniform BER curves, with receiver sensitivity spreading less than 1 dB at a BER lower than 10 -12. Also, crosstalk for both modules is tested, yielding only a 0.1- and 0.8-dB additional penalty for transmitter and receiver, respectively.

This paper highlights the challenges faced by the current datacenter networks, where using photonic technology offers a numbers of obvious advantages. Some existing optical intra-datacenter network architectures will be presented along with new ideas allowing for reduction of energy consumption and required spectrum resources.

We transmit 80 Gbaud/λ/core PAM4 signal enabled by 1.55 μm EML over 1 km 7-core fiber. The solution achieves single-wavelength and single-fiber 1.04 Tbit/s post-FEC transmission enhancing bandwidth-density for short-reach optical interconnects., QC 20181031

Integrated polymer photonics brings low cost and high fabrication flexibility to optoelectronic industry. However, this platform needs to overcome several issues to be effective enough for practical applications. In this letter, we experimentally demonstrate a decrease of propagation losses and polarization sensitivity of polymer waveguide-based devices as a result of thermal treatment. Heating of poly(methyl methacrylate) strip optical waveguides above the glass transition temperature initiates a waveguide surface reflow due to a decrease of the polymer viscosity and surface tension energy. This results in a decrease of surface roughness and shape change from rectangular to cylindrical. Thus, scattering losses and polarization sensitivity are minimized., Export Date: 9 May 2018; Article; CODEN: IPTLE; Correspondence Address: Marinins, A.; School of Engineering Sciences, KTH Royal Institute of TechnologySweden; email: marinin@kth.se; Funding details: 608099; Funding details: SEAS, Harvard School of Engineering and Applied Sciences; Funding details: 324391; Funding details: 2016-04510; Funding details: Knut och Alice Wallenbergs Stiftelse; Funding details: KTH, Kungliga Tekniska Högskolan; Funding text: Manuscript received March 14, 2017; revised January 21, 2018; accepted January 22, 2018. Date of publication January 24, 2018; date of current version February 12, 2018. This work was supported in part by EU Project ICONE under Grant 608099, in part by the EU Project GRIFFON under Grant 324391, in part by the Swedish ICT-TNG Program, in part by the Vetenskapsrädet Project PHASE under Grant 2016-04510, and in part by the Knut and Alice Wallenberg Foundation. (Corresponding author: Aleksandrs Marinins.) A. Marinins, A. Kakkar, R. Schatz, and S. Popov are with the School of Engineering Sciences, KTH Royal Institute of Technology, 10044 Stockholm, Sweden (e-mail: marinin@kth.se; adityak@kth.se; rschatz@kth.se; sergeip@kth.se). QC 20180529

Chip-scale integrated light sources are a crucial component in a broad range of photonics applications. III-V semiconductor nanowire emitters have gained attention as a fascinating approach due to their superior material properties, extremely compact size, and capability to grow directly on lattice-mismatched substrates including silicon. However, their practical applications are still in the early stages due to the difficulties in achieving high-performance nanowire emitters and integrating nanowire emitters with photonic platforms. In this dissertation, we demonstrate III-V nanowire-based lasers monolithically integrated on silicon-on-insulator (SOI) platforms, which can be potentially employed for chip-scale optical communications and photonic integrated circuits. For this, selective-area epitaxy of InGaAs nanowires on 3D structured SOI platforms is developed by catalyst-free metal-organic chemical vapor deposition. Nanowires are precisely positioned on 3D structures, including waveguides and gratings, with nearly 100 % nanowire growth yield and wide bandgap tuning ranges. Next, nanowire array-based bottom-up photonic crystal cavities are demonstrated on SOI substrates. InGaAs/InGaP core/shell nanowire arrays form 1D and 2D photonic crystal cavities on SOI layers, and single-mode room-temperature lasing from these bottom-up cavities is achieved by optically pumping the nanowire arrays. We also show that the nanowire array lasers are effectively coupled with SOI waveguides, which is achieved by integrating bottom-up nanowires on pre-patterned SOI platforms. The lasing wavelengths of nanowire array lasers are in the ranges of 1,100–1,440 nm, which covers telecommunication wavelengths, all operating at room temperature. It is also shown that arrays of proposed lasers with individually tunable wavelengths can be integrated on a single chip by lithographically tuning the cavity geometries. In summary, the III-V nanowire lasers on silicon demonstrated in this dissertat

With the increasing number of processing cores on a single die, the traditional Networks-on-Chip (NoCs) interconnects hardly keep up with the demands of high-bandwidth and low-latency communication. Various optical interconnection networks [1–3] with the optical on-chip optical crossbars have been proposed to meet the ultra-high on-chip bandwidth requirements. More recently, optical interconnection networks have been further developed, where they have not only covered the intra-chip but also inter-chip communication. These networks consist of two different interconnection parts: the optical intra-chip and inter-chip for on-chip and among-the-chips communication, respectively. An inter/intra-chip optical interconnection network, I2CON, was proposed in [4]. It consisted of two different interconnection parts: the optical inter-chip network and the optical intra-chip network. One key issue for these WDM inter/intra-chip optical interconnection network is the crosstalk noise. Crosstalk noise is an intrinsic characteristic of the optical components. Depending on the architecture of the network, the crosstalk noise can be intensified among numerous optical components in various combinations. Moreover, with the presence of a large number of wavelengths in one single waveguide (i.e. WDM-based), crosstalk noise from different wavelengths may affect the detected signal on a wavelength. Hence, in this thesis, we analyze the crosstalk noise and its impact on the SNR of the inter/intra-chip optical interconnection network. We also investigate a method, called Adaptive Power Control (APC) in order to reduce the crosstalk noise. We demonstrate the effect of this method in a candidate of the inter/intra-chip optical interconnection network, called I2CON.

Nanoscale semiconductor lasers have been developed recently using either metal, metallo-dielectric, or photonic crystal nanocavities. While the technology of nanolasers is steadily being deployed, their expected performance for on-chip optical interconnects is still largely unknown due to a limited understanding of some of their key features. Specifically, as the cavity size is reduced with respect to the emission wavelength, the stimulated and the spontaneous emission rates are modified, which is known as the Purcell effect in the context of cavity quantum electrodynamics. This effect is expected to have a major impact in the 'threshold-less' behavior of nanolasers and in their modulation speed; but its role is poorly understood in practical laser structures, characterized by significant homogeneous and inhomogeneous broadening and by a complex spatial distribution of the active material and cavity field. In this paper, we investigate the role of the Purcell effect in the stimulated and spontaneous emission rates of semiconductor lasers taking into account the carriers' spatial distribution in the volume of the active region over a wide range of cavity dimensions and emitter/cavity linewidths, enabling the detailed modeling of the static and dynamic characteristics of either micro-or nano-scale lasers using single-mode rate-equations analysis. The ultimate limits of scaling down these nanoscale light sources in terms of Purcell enhancement and modulation speed are also discussed showing that the ultrafast modulation properties predicted in nanolasers are a direct consequence of the enhancement of the stimulated emission rate via reduction of the mode volume.

Highly-functional photonic sensor networks integrated in thin polymer foils offer great potential for versatile applications in the life sciences, medicine, environmental analytics or production technology. For their realization, suitable low-cost and high-throughput production techniques need to be developed. Here, we describe work towards this goal, i.e. the fabrication of multimode polymer waveguides through a combination of thermal imprint and doctor blading. For imprint master stamp fabrication, a combined Bosch and O2 plasma etching process in silicon is utilized. We also demonstrate stamp fabrication by an additive manufacturing method, i.e. by employing maskless UV lithography, to enhance the flexibility and cost-effectiveness of our approach. We, thus, realize various all-polymer waveguide arrays, beam splitters, and grating couplers which serve as basic elements to create more complex photonic circuits. We also demonstrate polymer based transmission lines comprising semiconductor as well as organic light sources and detectors. We discuss both the integration of semiconductor light sources and detectors such as verticalcavity surface-emitting lasers (VCSEL) and photo detectors as well as organic light emitting diodes (OLEDs) and organic photo detectors. In first applications, we combine these elements to create sensor arrays for measuring temperature, strain or refractive index. We show results of various sensor types utilizing different measurement principles implemented in laboratory environments so far. For example, a waveguide array containing a linear discontinuity which serves as elongation zone for displacement, strain or tilt measurement by detecting the intensity variation of the transmitted light propagating inside the structure is presented. In future, we plan to create more powerful sensor photonics networks for reliable and robust applications in real life, e.g. for point-of-care testing or production monitoring.

We experimentally evaluate high-speed intensity modulation/direct detection (IM/DD) transmissions with a 1.55-μm broadband electro-absorption modulated laser and pulse amplitude modulations (PAM). We demonstrate 80 Gb/s/λ PAM-4 and 96 Gb/s/λ PAM-8 transmissions with low-complexity digital equalizers at the receiver. Performance comparison with different types of equalizers are performed, including linear symbol-spaced feed-forward equalizer (FFE), fractional (half-symbol) spaced FFE and decision feedback equalizer (DFE), with different tap number. It is found that for both cases, a 6-tap symbol-spaced FFE is sufficient to achieve a stable performance with bit-error-rate below the 7% overhead hard decision forward error correction (7%-OH HD-FEC) threshold over a 4 km standard single mode fiber link. Practical considerations including comparison between adaptive and static equalizer implementation and tolerable fiber chromatic dispersion are discussed.

We propose an optical interconnect architecture based on heatsink topology to enhance reliability for large-scale datacenters. The experimental demonstration has been carried out to verify the transmission performance of the proposed architecture., QC 20180514

Modular design has recently emerged as an efficient solution to build large data center (DC) facilities. Modular DCs are based on stand-Alone prefabricated modules (i.e., PODs) that can be easily installed and interconnected. PODs can generate a large amount of traffic and thus require an ultra-high-capacity interconnection network. However, current electronic and optical interconnect architectures applied to modular DCs may experience major scalability problems in terms of high energy consumption and cabling complexity. To address these problems, we investigate five optical interconnect architectures based on spatial division multiplexing (SDM), and for each architecture, we propose a resource allocation strategy. We also present an extensive comparison among the SDM architectures in terms of cost and performance (i.e., blocking probability and throughput), with the objective to find the architecture offering the best trade-off between cost and performance for given DC sizes and traffic load values. Our results demonstrate that, in small modular DCs with low traffic load, an architecture based only on SDM is the best option, while in medium DCs with medium traffic load, an architecture based on coupled SDM and flexgrid wavelength division multiplexing (WDM) with spectral flexibility is the best solution. Finally, for large DCs with high traffic load values, the best trade-off between cost and performance is achieved by an SDM architecture that is based on uncoupled SDM and flexgrid WDM., QC 20170601

We report on a 116 Gb/s on-off keying (OOK), four pulse amplitude modulation (PAM) and 105-Gb/s 8-PAM optical transmitter using an InP-based integrated and packaged externally modulated laser for high-speed optical interconnects with up to 30 dB static extinction ratio and over 100-GHz 3-dB bandwidth with 2 dB ripple. In addition, we study the tradeoff between power penalty and equalizer length to foresee transmission distances with standard single mode fiber., QC 20211102

This paper deals with resource management in optical interconnection networks. It first proposes an optical resource management framework as a platform to develop and evaluate efficient solutions for multipoint-to-multipoint optical communication systems with a centralized controller. The paper then focuses on studying the optical resource scheduling (ORS) problem as a core element in the framework by applying the classical open-shop scheduling theory. The ORS problem can therefore be solved by adopting the existing preemptive and nonpreemptive open-shop scheduling algorithms. In an optical network with nonnegligible reconfiguration delay, a preemptive algorithm may incur high reconfiguration overhead resulting in worse performance compared to the nonpreemptive strategy. Motivated by this fact, this paper proposes an adaptive open-shop scheduling (AOS) algorithm that dynamically decides the optimal scheduling strategy according to traffic condition and system parameters, such as reconfiguration delay, nonpreemptive approximation ratio, and number of involved optical interfaces. The solution is assessed by means of an analytical model that allows to quantify the network performance in terms of packet delay and potential energy savings obtained by the sleep mode operation. As a possible application scenario, the inter- and intrarack optical interconnection networks in data centres are considered. Analytical results demonstrate how the proposed AOS outperforms the nonpreemptive and preemptive scheduling strategies for typical configurations used in data center networks. In addition, the reconfiguration delay and wake-up time of optical devices are identified as performance-determining factors., QC 20170620

We introduce physical-layer network coding for a passive optical interconnect architecture in datacenter networks. Results reveal that half of the wavelengths can be saved to obtain latency in the magnitude of microseconds., QC 20171130

Passive optical interconnects (POIs) have recently been considered as a promising solution to offer high bandwidth and low power consumption for data center networks. This paper proposes a medium access control protocol for a POI based on arrayed waveguide gratings (AWGs) to facilitate efficient collision-free communications. In order to efficiently accommodate bursty traffic generated by the servers in the data center, we develop a tailored dynamic bandwidth allocation (DBA) algorithm, which is able to schedule resources in both time and spectrum. In the simulation, not only the impact of DBA algorithm parameters but also the system configurations, such as wavelength tuning time, line rate, and the size of the interconnect, have been investigated. For a typical link utilization on an optical interconnect at the top of the rack, the proposed resource allocation scheme ensures both low latency (<0.1 ms) and a low frame drop ratio (almost zero)., QC 20171204

In this paper, a novel flex-grid all-optical interconnect scheme that supports transparent multi-hop connections in data centers is proposed. An inter-rack all-optical multi-hop connection is realized with an optical loop employed at flex-grid wavelength selective switches (WSSs) in an intermediate rack rather than by relaying through optical-electric-optical (O-E-O) conversions. Compared with the conventional O-E-O based approach, the proposed all-optical scheme is able to off-load the traffic at intermediate racks, leading to a reduction of the power consumption and cost. The transmission performance of the proposed flex-grid multi-hop all-optical interconnect scheme with various modulation formats, including both coherently detected and directly detected approaches, are investigated by Monte-Carlo simulations. To enhance the spectrum efficiency (SE), number-of-hop adaptive bandwidth allocation is introduced. Numerical results show that the SE can be improved by up to 33.3% at 40 Gbps, and by up to 25% at 100 Gbps. The impact of parameters, such as targeted bit error rate (BER) level and insertion loss of components, on the transmission performance of the proposed approach are also explored. The results show that the maximum SE improvement of the adaptive approach over the non-adaptive one is enhanced with the decrease of the targeted BER levels and the component insertion loss., Funding Details: VR, Swedish Research Council. QC 20161121

Traditional semiconductor light emitting diodes (LEDs) have low modulation speed because of long spontaneous emission lifetime. Spontaneous emission in semiconductors (and indeed most light emitters) is an inherently slow process owing to the size mismatch between the dipole length of the optical dipole oscillators responsible for light emission and the wavelength of the emitted light. More simply stated: semiconductors behave as a poor antenna for its own light emission. By coupling a semiconductor at the nanoscale to an external antenna, the spontaneous emission rate can be dramatically increased alluding to the exciting possibility of an antenna-LED that can be directly modulated faster than the laser. Such an antenna-LED is well-suited as a light source for on-chip optical communication where small size, fast speed, and high efficiency are needed to achieve the promised benefit of reduced power consumption of on-chip optical interconnect links compared with less efficient electrical interconnect links. Despite the promise of the antenna-LED, significant challenges remain to implement an antenna-coupled device in a monolithically integrated manner. Notably, most demonstrations of antenna-enhanced spontaneous emission have relied upon optical pumping of the light emitting material which is useful for fundamental studies; however, an electrical injection scheme is required for practical implementation of an antenna-LED.In this dissertation, demonstration of an electrically-injected III--V antenna-LED is reported: an important milestone toward on-chip optical interconnects. In the first part of this dissertation, the general design principles of enhancing the spontaneous emission rate of a semiconductor with an optical antenna is discussed. The cavity-backed slot antenna is shown to be uniquely suited for an electrically-injected antenna-LED because of large spontaneous emission enhancement, simple fabrication, and directional emission of light. The design, fabricat

Optical interconnects have started to replace electrical interconnects in the communications between racks and circuit boards with potential benefits in bandwidth, delay, power efficiency, and crosstalk. Silicon photonics has emerged to be a highly promising enabling technology for the short-reach nanophotonic interconnects because it offers favorable CMOS compatibility and high integration level. The fast-growing complexity of photonic integrated circuit (PIC) and close electro-optical integration call for computer-aided design (CAD) for integrated photonics, and electronic-photonic design automation (EPDA) including accurate behavior models and efficient simulation methodologies for integrated electro-optical systems. Also, the nanophotonic devices are highly sensitive to fabrication process variation and thermal variation effects, which requires proper modeling, optimization, and management schemes. To address these problems, this thesis is dedicated to the following two tasks: (1) compact modeling and circuit-level simulation of nanophotonic interconnects, and (2) power-efficient management of the variation effects in nanophotonic interconnects.The first part of the thesis develops compact models for key components in nanophotonic interconnects including silicon microring modulators, diode lasers, electro-absorption modulators (EAM), photodetectors, etc. These compact models are developed based on their electrical and optical properties, and are then extensively validated by measurement data. The model parameters are extracted from common electrical and optical tests. Implemented in Verilog-A, the models are used in SPICE simulations of optical links, whose results again agree well with measurement data. The compact model library and the simulation methodology enable electro-optical co-simulations and optical device design explorations in the circuit-level.In the second part of the thesis, we propose modeling methods and power-efficient management schemes for th

With the fast development of processor chips, power-efficient, high-bandwidth, and low-latency inter-chip interconnects become more and more important. Studies show that the bandwidth of traditional electrical interconnects will become bottlenecks in the near future. Optical interconnects promise high bandwidth, low latency, and could improve the chip pin performance for manycore processors. They are becoming potential alternatives for electrical interconnects. On the other hand, gaps between data rates of electrical interconnects and optical interconnects are continuously increasing. Electrical-optical (E-O) interface and optical-electrical (O-E) interface, which convert data between parallel electrical interconnects and serial optical interconnects, become more and more important. We systematically modelled optical and electrical interconnects in terms of crosstalk noises, attenuation, and receiver sensitivities. We modelled E-O and O-E interfaces in terms of energy efficiencies, areas and latencies. A new type of interfaces, which serialize and deserialize data by optical weaving technologies, are proposed alongside. We developed a tool called optical and electrical interfaces and links (OEIL). It can be used to analyze energy consumption, bandwidth density, area, and latency of electrical and optical interconnects, as well as the E-O and O-E interfaces. We propose an optical inter/intra-chip processor-memory communication network, called MOCA, which can significantly improve system performance and energy efficiency. We propose a method to optimize the floorplan of optical fat tree based network-on-chip, which can effectively reduce the number of crossings and minimize the interconnect length.

Liquid-crystal on Silicon (LCoS) microdisplays are one of the competing technologies to implement wavelength selective switches (WSS) for optical telecommunications. Last generation LCoS, with more than 4 megapixels, have decreased pixel size to values smaller than 4 microns, what increases interpixel cross-talk effects such as fringing-field. We proceed with an experimental evaluation of a 3.74 micron pixel size parallel-aligned LCoS (PA-LCoS) device. At 1550 nm, for the first time we use time-average Stokes polarimetry to measure the retardance and its flicker magnitude as a function of voltage. We also verify the effect of the antireflection coating when we try to characterize the PA-LCoS out of the designed interval for the AR coating. Some preliminary results for the performance for binary gratings are also given, where the decrease of modulation range with the increase in spatial frequency is shown, together with some residual polarization effects.

The use of optical interconnects is a promising solution to the increasing demand for high speed mass data transmission used in integrated circuits as well as device to device data transfer applications. For the purpose, low cost polymer waveguides are a popular choice for routing signal between devices due to their compatibility with printed circuit boards. In optical interconnect, coupling from an external light source to such waveguides is a critical step, thus a variety of couplers have been investigated such as grating based couplers [1,2], evanescent couplers [3], and embedded mirrors [4–6]. These couplers are inherently micro-optical components which require fast and scalable fabrication for mass production with optical quality surfaces/structures. Low NA laser direct writing has been used for fast fabrication of structures such as gratings and Fresnel lenses using a linear laser direct writing scheme, though the length scale of such structures are an order of magnitude larger than the spot size of the focused laser of the tool. Nonlinear writing techniques such as with 2-photon absorption offer increased write resolution which makes it possible to fabricate sub-wavelength structures as well as having a flexibility in feature shape. However it does not allow a high speed fabrication and in general are not scalable due to limitations of speed and area induced by the tool’s high NA optics. To overcome such limitations primarily imposed by NA, we propose a new micro-optic fabrication process which extends the capabilities of 1D, low NA, and thus fast and scalable, laser direct writing to fabricate a structure having a length scale close to the tool's spot size, for example, a mirror based and 45 degree optical coupler with optical surface quality. The newly developed process allows a high speed fabrication with a write speed of 2600 mm²/min by incorporating a mask based lithography method providing a blank structure which is critical to creating a 45 degree slop

We report on a 116 Gb/s on-off keying (OOK), four pulse amplitude modulation (PAM) and 105-Gb/s 8-PAM optical transmitter using an InP-based integrated and packaged externally modulated laser for high-speed optical interconnects with up to 30 dB static extinction ratio and over 100-GHz 3-dB bandwidth with 2 dB ripple. In addition, we study the tradeoff between power penalty and equalizer length to foresee transmission distances with standard single mode fiber.

Optical interconnects have recently emerged as a promising solution to address the bandwidth and power-consumption requirements in next-generation high-performance computing and intra-datacenter applications as they offer a high data throughput with potentially low power consumption. Leveraging the mature silicon complementary metal-oxide-semiconductor (CMOS) fabrication technology, silicon photonics offers a unique potential platform to build low-cost, high-speed, energy-efficient, compact devices and modules for intra-datacenter optical interconnects which require a link distance up to ~10 km. One of the key building blocks for such a photonics link is the on-chip light source emitting at Telecom/Datacom wavelengths. As silicon is transparent in these wavelengths, other direct bandgap materials, like III-V compound, need to be integrated in this platform for the light emission. In this thesis, we demonstrate and propose a number of on-chip light sources on III-V and III-V-on-silicon substrate including (i) direct-modulated waveguide-integrated microspiral disk lasers, (ii) hybrid silicon waveguide-integrated microspiral disk lasers and (iii) a 2-channel hybrid silicon transmitter using a microspiral disk laser as a single element. We investigate direct-modulated waveguide-coupled microspiral disk lasers on InP substrate. We employ spatially selective injection by means of a ring-shaped p-contact on top of the microdisk rim region to selectively inject current to the whispering-gallery-like modes and thus enhance the laser performance. We report room-temperature continuous-wave electrically injected AlGaInAs/InP waveguide-coupled microspiral disk lasers with a disk radius of 30 and 40 μm. For a 30 μm microspiral disk laser gaplessly coupled with a 100 μm-long passive waveguide that is directly connected to an on-chip AlGaInAs/InP photodiode, we estimate a laser output power of at least 200 μW upon a 70 mA injection. We realize small-signal modulation with a 3 dB ba

AWG-based passive optical interconnects (POIs) are considered a high-capacity and energy-efficient solution for datacenter networks. We concentrate on a cascaded AWG-based POI and analyze network performance to gain insights on efficiency of such an architecture. Asia Communications and Photonics Conferene (ACP)., QC 20201207

We propose to add optical amplifier(s) to passive optical interconnect (POI) at top-of-rack in datacentres and validate this approach by introducing impairment constraints into POIs design. It is shown that one amplifier can improve scalability by a factor of 16., QC 20170628