Longer Wavelength GaAs-Based VCSELs for Extended-Reach Optical Interconnects

Data centers of today are increasing in size and are built to accommodate strong traffic demands while providing sustainably by having clients sharing resources under one roof. Their massive scale puts pressure on the server network topology and has incited a need for data transmission links that are energy efficient and capable of operation at high bit rates with reach up to a few kilometers. Optical interconnects (OIs) offer large bandwidth and low attenuation at long distances, and are therefore suitable for this task. The most commonly used OIs, with 850 nm GaAs-based vertical-cavity surface-emitting lasers (VCSELs) and multi-mode fiber (MMF), have a 25 Gb/s reach that is limited to a few hundred meters. However, the fiber chromatic dispersion and attenuation that limit the OI reach can be reduced significantly by increasing the wavelength of this very same technology. The upper limit of the GaAs-based VCSEL technology, with strained InGaAs quantum wells (QWs), is about 1100 nm.With further improved OI performance, new hyperscale data center topologies can be realized and explored. This will lead to a larger number of possible solutions in traffic engineering as well as for power management. 1060 nm VCSELs could soon open up for lane rates of 100+ Gb/s over distances up to 2 km and help reach the Tb/s link speed aim of data center OI standards, in which capacity is built up mainly by employing multiple parallel lanes, increasing symbol rate by going from binary to four-level pulse amplitude modulation (PAM-4), and optimizing with electrical mitigation techniques such as digital signal processing.In this work we show that 1060 nm GaAs VCSELs are suitable light sources for long-reach OIs by first demonstrating their overall stable performance and capability of error-free data transmission up to 50 Gb/s back-to-back and 25 Gb/s over 1 km of MMF. With PAM-4, we show 100 Gb/s error-free capability over 100 m of MMF, suitable for wavelength division multiplexed OIs that can transmit data at several wavelengths from 850 to 1060 nm over the same fiber channel. We also assemble single-mode 1060 nm VCSEL and single-mode fiber links and demonstrate 50 Gb/s error-free transmission over 1 km using pre-emphasis and 40 Gb/s over 2 km without the use of any electrical mitigation techniques. These results stem from careful VCSEL design, including strained InGaAs QWs with GaAsP barriers, doped AlGaAs distributed Bragg reflectors, a short optical cavity and multiple oxide layers. In addition, we show that the fabrication of such a device poses no increase in complexity and can be realized using standard processing techniques

Silicon optical modulators

Optical technology is poised to revolutionise short reach interconnects. The leading candidate technology is silicon photonics, and the workhorse of such interconnect is the optical modulator. Modulators have been improved dramatically in recent years. Most notably the bandwidth has increased from the MHz to the multi GHz regime in little more than half a decade. However, the demands of optical interconnect are significant, and many questions remain unanswered as to whether silicon can meet the required performance metrics. Minimising metrics such as the energy per bit, and device footprint, whilst maximising bandwidth and modulation depth are non trivial demands. All of this must be achieved with acceptable thermal tolerance and optical spectral width, using CMOS compatible fabrication processes. Here we discuss the techniques that have, and will, be used to implement silicon optical modulators, as well as the outlook for these devices, and the candidate solutions of the future

Data distribution satellite

A description is given of a data distribution satellite (DDS) system. The DDS would operate in conjunction with the tracking and data relay satellite system to give ground-based users real time, two-way access to instruments in space and space-gathered data. The scope of work includes the following: (1) user requirements are derived; (2) communication scenarios are synthesized; (3) system design constraints and projected technology availability are identified; (4) DDS communications payload configuration is derived, and the satellite is designed; (5) requirements for earth terminals and network control are given; (6) system costs are estimated, both life cycle costs and user fees; and (7) technology developments are recommended, and a technology development plan is given. The most important results obtained are as follows: (1) a satellite designed for launch in 2007 is feasible and has 10 Gb/s capacity, 5.5 kW power, and 2000 kg mass; (2) DDS features include on-board baseband switching, use of Ku- and Ka-bands, multiple optical intersatellite links; and (3) system user costs are competitive with projected terrestrial communication costs

Silicon Photonics for All-Optical Processing and High-Bandwidth-Density Interconnects

Silicon photonics has emerged in recent years as one of the leading technologies poised to enable penetration of optical communications deeper and more intimately into computing systems than ever before. The integration potential of power efficient WDM links at the first level package or even deeper has been a strong driver for the rapid development this field has seen in recent years. The integration of photonic communication modules with very high bandwidth densities and virtually no bandwidth-distance limitations at the short reach regime of high performance computers and data centers has the potential to alleviate many of the bandwidth bottlenecks currently faced by board, rack, and facility levels. While networks on chip for chip multiprocessors (CMP) were initially deemed the target application of silicon photonic components, it has become evident in recent years that the initial lower hanging fruit is the CMP's I/O links to memory as well as other CMPs. The first chapter of the thesis provides more detailed motivation for the integration of silicon photonic modules into compute systems and surveys some of the recent developments in the field. The second chapter then proceeds to detail a technical case study of silicon photonic microring-based WDM links' scalability and power efficiency for these chip I/O applications which could be developed in the intermediate future. The analysis, initiated originally for a workshop on optical and electrical board and rack level interconnects, looks into a detailed model of the optical power budget for such a link capturing both single-channel aspects as well as WDM-operation-related considerations which are unique for a microring physical characteristics. The holistic analysis for the full link captures the wavelength-channel-spacing dependent characteristics, provides some methodologies for device design in the WDM-operation context, and provides performance predictions based on current best-of-class silicon photonic devices. The key results of the analysis are the determination of upper bounds on the aggregate achievable communication bandwidth per link, identifying design trade-offs for bandwidth versus power efficiency, and highlighting the need for continued technological improvements in both laser as well as photodetector technologies to allow acceptable power efficiency operation of such systems.The third chapter, while continuing on the theme silicon photonic high bandwidth density links, proceeds to detail the first experimental demonstration and characterization of an on-chip spatial division multiplexing (SDM) scheme based on microrings for the multiplexing and demultiplexing functionalities. In the context of more forward looking optical network-on-chip environments, SDM-enabled WDM photonic interconnects can potentially achieve superior bandwidth densities per waveguide compared to WDM-only photonic interconnects. The microring-based implementation allows dynamic tuning of the multiplexing and demultiplexing characteristic of the system which allows operation on WDM grid as well device tuning to combat intra-channel crosstalk. The characterization focuses on the first reported power penalty measurements for on-chip silicon photonic SDM link showing minimal penalties achievable with 3 spatial modes concurrently operating on a single waveguide with 10-Gb/s data carried by each mode. The chapter also details the first demonstration of WDM combined with SDM operation with six separate wavelength-and-spatial 10-Gb/s channels with error free operation and low power penalties. The fourth, fifth, and sixth chapters shift in topic from the application of silicon photonics to communication links to the evolving use of silicon waveguides for nonlinear all-optical processing. The unique tight mode confinement in sub-micron cross-sections combined with the high response of silicon have motivated the development of four-wave mixing (FWM)-based processing silicon devices. The key feature of the silicon platform for these nonlinear processing platforms is the ability to finely and uniformly control the dispersive properties of the optical structures in a way that enables completely offsetting the material dispersion and achieve dispersion profiles required for effective parametric interaction of waves in the optical structures. Chapter four primarily introduces and motivates nonlinear processing in communication applications and focuses on recent achievements in non-silicon and silicon FWM platforms. Chapter five describes some of the author's contributions on parametric processing of high speed data in silicon nonlinear devices, with first of a kind demonstrations of wavelength conversion of 160-Gb/s optically time division multiplexed (OTDM) data as well as the wavelength-multicasting of a 320-Gb/s OTDM stream. The chapter then details a methodical characterization and demonstration of several record wavelength conversion experiments of data in silicon with 40-Gb/s data wavelength-converted across more than 100 nm with only 1.4-dB of power penalties as well as the wavelength and format conversion of 10-Gb/s data across up to 168 nm with sensitivity gains stemming from the format conversion of about 2 dB and a residual conversion penalty of only 0.1 dB, achieved by implementing an improved experimental setup. Both experiments highlight the performance uniformity of the conversion process for a wide range of probe-idler detuning settings, showcasing the silicon platform's unique broadband phase matching properties. The sixth chapter presents a slight shift in motivation for parametric processing from traditional telecom-wavelength applications to functionalities developed targeting mid-IR operation. Parametric-processing in the silicon platform at long wavelengths holds large potential for performance improvements due to the elimination of two-photon absorption in silicon at long wavelengths as well as silicon's dispersion engineering capabilities which uniquely position the silicon platform for effective phase matching of significantly wavelength detuned waves. Four-wave mixing signal generation and reception at mid-IR wavelengths are attractive candidates for tunable flexible operation with modulation and detection speeds which are currently only available at telecom wavelengths. With this vision in mind, several contributions detailing extension of FWM functionalities in silicon to operate at wavelengths close to 2 μm with performance equivalent to much smaller detuning setting measurements. The contributions detail the experimental demonstration of the first silicon optical processing functionalities achieved at such long wavelengths including the wavelength conversion and unicast of 10-Gb/s signals with up to 700 nm of probe-idler detuning, the combined two-stage 10-Gb/s FWM-link in which both data generation and detection at 1900 nm is facilitated by parametric processing in silicon with only 2.1-dB overall penalty, the first ever 40-Gb/s receiver at 1900 nm based on a FWM stage for simultaneous temporal demultiplexing and wavelength conversion, and lastly, the demonstration of a 40-Gb/s FWM-link operation with only 3.6 dB of penalty. The chapter concludes with a short discussion on possible extensions to enable silicon parametric processing at even longer wavelengths targeting the mid-IR spectral transmission window of 3-5 μm

Indoor Smoking Detection Based on YOLO Framework with Infrared Image

This study recommends combining the efficacy of YOLO with the greater visibility provided by infrared imaging to create a better indoor smoking detection system. The YOLO system divides photos into a grid and anticipates bounding boxes and class probabilities at the same time, making it an obvious choice for its real-time item detection capabilities. The approach improves its robustness by identifying heat signals associated with smoking sessions and overcoming limitations posed by low-light or blocked circumstances. The addition of infrared images significantly improved the system's performance in low-light conditions. A dual spectrum thermal camera is used in the entire indoor smoking detection system to obtain a large collection of infrared images representing various interior locations with documented smoking episodes. During the training phase, data augmentation processes such as random rotations, flips, and brightness and contrast fluctuations were used to improve the system's performance. The CIoU loss function improved the system's localization accuracy significantly, reducing false positives and improving overall detection performance. The combination of YOLO and infrared photography, in conjunction with data augmentation and the CIoU loss function, not only improves indoor smoking detection but also demonstrates the benefits of merging several technologies in the development of more effective and adaptive systems

Roadmap of optical communications

© 2016 IOP Publishing Ltd. Lightwave communications is a necessity for the information age. Optical links provide enormous bandwidth, and the optical fiber is the only medium that can meet the modern society's needs for transporting massive amounts of data over long distances. Applications range from global high-capacity networks, which constitute the backbone of the internet, to the massively parallel interconnects that provide data connectivity inside datacenters and supercomputers. Optical communications is a diverse and rapidly changing field, where experts in photonics, communications, electronics, and signal processing work side by side to meet the ever-increasing demands for higher capacity, lower cost, and lower energy consumption, while adapting the system design to novel services and technologies. Due to the interdisciplinary nature of this rich research field, Journal of Optics has invited 16 researchers, each a world-leading expert in their respective subfields, to contribute a section to this invited review article, summarizing their views on state-of-the-art and future developments in optical communications

Further infrared systems studies for the earth resources program Final report

Design of multispectral scanner for orbital earth resources detectio