Optical Backplane Research Articles

See‐Through Flexible Photovoltaic Modules of Ultrathin Silicon Solar Microcells Enhanced by Synergistic Luminescent and Reflective Near‐Infrared Backplanes

AbstractUltrathin single‐crystalline silicon solar microcells assembled into see‐through and flexible modules have exhibited broadly applicable cost‐effective photovoltaics with reliable durability and efficiency. However, their module output power has suffered from inherent limitations caused by the inferior photon absorption property and the inactive see‐through windows. Herein a strategy is presented to enhance the performance of see‐through flexible ultrathin silicon microcell modules by employing visibly transparent but near‐infrared‐manipulatable optical backplanes, such as a luminescent waveguide gathering near‐infrared photons and a backside reflector mitigating near‐infrared photon escape. Simultaneous integration of these near‐infrared backplanes provides more photovoltaic gains to silicon solar modules than the sum of each backplane capability, and this synergy is due to the promoted properties of the photoluminescence process and waveguiding. The experimental module with ≈3‐µm thick silicon solar microcells can achieve up to ≈40%‐boosted output power generation when assisted by these backplanes. Detailed studies of optical and photovoltaic characterizations for near‐infrared backplanes and their integration modules elucidate the effectiveness of designed backplanes for see‐through flexible silicon photovoltaics.

Investigation on mode dispersion and lamination stability of multimode polymer waveguides for an optical backplane.

In this paper, two noteworthy issues of mode dispersion and lamination stability of multimode polymer waveguides for optical backplane are investigated. In the case of center launching by 50-µm graded-index (GI) multimode fiber (MMF), mode dispersion of polymer waveguides with different widths is analyzed theoretically and measured in the view of bit error rate (BER) curves. Compared with the waveguide with the width of 40 µm, 1-dB power penalty is observed by the 70-µm-width waveguide due to its larger mode dispersion. On the other hand, waveguide stability after laminating process with high temperature and pressure is measured experimentally. No significant changes in core shape and size are observed. The average insertion loss of 80 channels before and after lamination are 0.137 dB/cm and 0.192 dB/cm, respectively. Error-free transmission at 25 Gb/s is obtained by laminated waveguides. The results imply the feasibility and potential of multimode waveguides for optical backplane.

Flexibility and fragmentation aware routing, core and spectrum allocation for hybrid AoD nodes in SDM-EONs.

Space division multiplexing elastic optical network (SDM-EON) enables high-capacity transmission, in which the network nodes should provide high switching flexibility while limiting the complexity and costs of nodes. Architecture on demand (AoD) nodes can meet these requirements but the slow configuration time of optical backplane in AoD nodes makes it difficult to serve latency-sensitive requests. In this paper, we propose a hybrid optical backplane based on micro-electromechanical systems (MEMS) and semiconductor optical amplifier (SOA) switches to provide fast configuration time for AoD nodes. Moreover, we propose quantitative measures of node switching flexibility in SDM-EONs and of link configuration speed in AoD nodes. Based on the hybrid backplane architecture and the measurement approaches, we propose a flexibility and fragmentation aware routing, spectrum and core allocation algorithm and an AoD synthesis algorithm. Simulation results show that the hybrid AoD nodes with support of spatial lane change can reduce network blocking probability. The AoD based on this hybrid backplane structure can improve the network performance by 32.8% compared to the AoD based on the traditional MEMS. Compared with traditional reconfigurable optical add/drop multiplexers (ROADMs), the hybrid AoD nodes can control the number of wavelength selective switch (WSS) ports.

Research and implementation of communication system optical fiber interconnection of airborne IMA platform

On the IMA platform of airborne avionics system, optical fiber interconnection has become a trend. Aiming at the problems that must be solved in the realization of optical fiber interconnection of airborne IMA platform, such as optic-electric conversion, high-density and reliable connection and Anti-Harsh environment, this paper adopts optical modules, high-density optical backplane and other solutions, introduces high-density optical interfaces standard and ARINC series optical connectors standard, and realizes the optical fiber network interconnection of airborne IMA platform.

Fabrication and transmission of optical polymer waveguide backplane for high - performance computers.

In this paper, a high-speed, large-capacity and compact optical backplane architecture for high-performance computers (HPC) is proposed and designed. The MT couplers is designed without additional mirror to divert the light from vertical cavity surface emitting laser (VCSEL) array by 90°. The light is then coupled into the optical waveguide through the MT. A bidirectional 8 channels polymer optical waveguide array with low insertion loss is designed and fabricated. The waveguides are embedded in the printed circuit board. We test the performance of 8 channels for the optical waveguide backplane. In the entire optical backplane, the averaged insertion loss of optical backplane with 50 μm input fiber is 1.62 dB with 850 nm VCSEL. The misalignment loss is 0.5 dB when the misalignment between waveguide and multi-mode fiber is 8.5 μm. Then, the transmission performances of 4 channels with different speed signals is demonstrated by off-line experiment. The optical backplane network can achieve 15 G data error-free transmission in the range of [-2 dBm, -10 dBm] received optical power (ROP). Based on VCSEL arrays, the optical interconnection network system can achieve 8 channels parallel signal transmission. In the optical backplane, the 10 Gbit / s data generated / processed by field programmable gate array (Xilinx Kintex-7) chips can realize error-free transmission. In large-capacity, high-speed parallel HPC, the designed optical backplane system can facilitate the establishment of a large number of parallel transmissions.

137 Gb/s PAM-4 Transmissions at 850 nm over 40 cm Optical Backplane with 25 G Devices with Improved Neural Network-Based Equalization

An improved neural network-based equalization method is proposed and experimentally demonstrated. The up-to-137 Gb/s transmission of four level pulse amplitude modulation (PAM-4) signals with 25 G class 850 nm optical devices is achieved over an in-house fabricated 40 cm optical backplane. An in-depth investigation is conducted regarding the impact of delayed taps and spans on equalization performance. A performance comparison of the proposed method with the traditional maximum likelihood sequence estimation (MLSE) and decision feedback equalization (DFE) is also undertaken. For the bit rate from 80 to 100 Gb/s, the proposed method achieves an adopted hard-decision forward error correction (HD-FEC) requirement at a received optical power (RoP) of −9 and −8 dBm, while DFE and MLSE cannot meet the HD-FEC requirement. When the bit rate increases from 120 to 137 Gb/s, the proposed equalization method still successfully maintains the acceptable system performance at an RoP of −4 and −2.5 dBm. Furthermore, the specific bit error rate (BER) performances for varied maximum achievable bit rate under different RoPs by applying MLSE and the proposed method are also analyzed. This provides an important potential solution to realize the future data centers.

Routing, modulation format, spectrum and core allocation in space-division-multiplexed programmable filterless networks

Abstract Elastic optical networks are considered as promising solutions to improve the spectral efficiency of optical networks and fulfill the diverse bandwidth requirements of heterogeneous network applications. Elastic filterless optical networks with passive broadcast-and-select architecture are introduced to offer network agility. However, the presence of unfiltered signals stems from the signal broadcast and the absence of filtering (so-called drop-and-waste transmission), can lead to an overhead in spectrum usage. This issue can be alleviated by combining the unprecedented flexibility of programmable architecture on demand (AoD) nodes with the extra diversity in spatial domain provided by space division multiplexing (SDM). In this paper, we propose a hardware-aware strategy based on the two-objective binary particle swarm optimization (BPSO) to solve the routing, modulation format, spectrum and core allocation (RMSCA) problem in programmable filterless SDM networks. The proposed BPSO-based hardware-aware RMSCA (BH-RMSCA) strategy aims at minimizing jointly the number of optical couplers and maximum backplane switch size inside the filterless AoD nodes. The physical layer impairment in terms of the inter-core crosstalk (XT) is taken into account in solving the resource allocation problem. Simulation results show that the proposed BH-RMSCA strategy successfully provides Pareto-optimal solutions with remarkable hardware savings compared to the benchmark methods. The cost-efficient network solutions are achieved at the expense of a favorable trade-off with the spectrum usage and the path length, especially for higher connected topology.

Flexible Multimode Polymer Waveguide Arrays for Versatile High-Speed Short-Reach Communication Links

Optical interconnects play an important role in enabling high-speed short-reach communication links within next-generation high-performance electronic systems. Multimode polymer waveguides in particular allow the formation of high-capacity optical backplanes and cost-effective board-level optical interconnects. Their formation on flexible substrates offers significant practical advantages and enables their deployment in environments where shape and weight conformity become particularly important, such as in cars and aircraft. However, bending and twisting of flexible multimode waveguides can have a significant effect on their optical transmission performance due to mode loss and mode coupling. Moreover, the magnitude of the induced effects strongly depends on the launch conditions employed. In this paper, therefore, we present detailed loss, crosstalk, and bandwidth studies on flexible multimode waveguide arrays for different launch conditions regarding their use in real-world systems. The minimum radius to achieve a 1 dB excess bending loss is obtained for each launch condition as well as the crosstalk degradation due to bending. It is shown that for a 50 μm MMF input, a 6 mm bending radius is required for excess losses below 1 dB, while crosstalk below −35 dB is obtained in adjacent waveguides even under strong bending. Moreover, it is found that twisting has a small effect on the loss and crosstalk performance of the samples. Excess twisting loss less than 0.1 dB and crosstalk of −40 dB are obtained for three full 360° turns under a 50 μm MMF launch. Finally, the bandwidth studies carried out on the samples indicate than no significant bandwidth degradation is induced due to sample bending, with bandwidth-length product values larger than 150 GHz × m obtained for restricted launches. The set of results presented herein specify the deployment of this flexible polymer multimode waveguide technology in real-world systems and demonstrate its strong potential to implement low-loss high-bandwidth optical interconnects.

An optimized routing algorithm for the automated assembly of standard multimode ribbon fibers in a full-mesh optical backplane

Abstract In this paper a parametric, modular and scalable algorithm allowing a fully automated assembly of a backplane fiber-optic interconnection circuit is presented. This approach guarantees the optimization of the optical fiber routing inside the backplane with respect to specific criteria (i.e. bending power losses), addressing both transmission performance and overall costs issues. Graph theory has been exploited to simplify the complexity of the NxN full-mesh backplane interconnection topology, firstly, into N independent sub-circuits and then, recursively, into a limited number of loops easier to be generated. Afterwards, the proposed algorithm selects a set of geometrical and architectural parameters whose optimization allows to identify the optimal fiber optic routing for each sub-circuit of the backplane. The topological and numerical information provided by the algorithm are then exploited to control a robot which performs the automated assembly of the backplane sub-circuits. The proposed routing algorithm can be extended to any array architecture and number of connections thanks to its modularity and scalability. Finally, the algorithm has been exploited for the automated assembly of an 8x8 optical backplane realized with standard multimode (MM) 12-fiber ribbons.

Polymer selective laser curing for integrated optical switches

A simple in-layer electro optical switch has been prepared by selectively curing a photocurable optical polymer with a UV laser. The core of the device is a NOA-81 multimode waveguide grown by selective laser curing. The cladding is a positive calamitic liquid crystal, which allows tunability and switching of the waveguide by external driving electric signals. The effective refractive index in the guide changes upon switching the liquid crystal. Depending on the geometry, this setup leads to an electrooptical modulator or a switch between two levels of transmitted light. Full Text: PDF ReferencesT. Ako, A. Hope, T. Nguyen, A. Mitchell, W. Bogaerts, K. Neyts, and J. Beeckman, "Electrically tuneable lateral leakage loss in liquid crystal clad shallow-etched silicon waveguides", Opt. Express 23, 2846 (2015). CrossRef K. Kruse, C. Middlebrook, "Laser-direct writing of single mode and multi-mode polymer step index waveguide structures for optical backplanes and interconnection assemblies", Photon. Nanostruct. - Fundamentals and Appl. 13, 66 (2015). CrossRef A. Günther, A.B. Petermann, M. Rezem, M. Rahlves, M. Wollweber, and B. Roth, European Conf. Lasers and Electro-Optics - European Quantum Electronics Conference, Munich, Germany (2015).C. Florian, S. Piazza, A. Diaspro, P. Serra, M. Duocastella, "Direct Laser Printing of Tailored Polymeric Microlenses", ACS Appl. Mater. Interfaces, 8(27), 17028 (2016). CrossRef F. Costache, M. Blasl, "Optical switching with isotropic liquid crystals", Opt. Photonik 6, 29 (2011). CrossRef M. Cano-Garcia, R. Delgado, T. Zuo, M.A. Geday, X. Quintana, Jose M. Otón, 16th OLC Topical Meeting on the Optics of Liquid Crystals, Sopot, Poland (2015).S. Ishihara, H. Wakemoto, K. Nakazima, Y. Matsuo, "The effect of rubbed polymer films on the liquid crystal alignment", Liq. Cryst. 4(6), 669 (1989). DirectLink

From Chip to Cloud: Optical Interconnects in Engineered Systems

The high-performance server compute landscape is changing. The traditional model of building general-purpose enterprise compute boxes that end-users can configure with storage and networking to assemble their desired compute environments, has evolved to purpose-built systems optimized for specific applications. This tight integration of hardware and software components together with high-density midboard optical modules and an optical backplane allows for unprecedented levels of switching and compute efficiencies and has fueled the penetration of optical interconnects deep “inside the box,” particularly for switch scale-up. We briefly review earlier 40 G/port switching systems based on active optical cables, and present our newest system: An all-optically-interconnected 100 G/port 8.2 Tb/s InfiniBand packet switch ASIC with 41 ports running 100 Gb/s per port interconnected by 12-channel midboard optical transceivers with 25 Gb/s per channel per direction of optical I/O. Using a blind-mate optical backplane, these components enable systems with up to 50 Tb/s bandwidth in a 2U standard rack mount configuration with industry-leading density, efficiency, and latency. For even tighter co-integration of optical interconnects with switch and processor ASICs, we discuss photonic multichip module and interposer packaging technologies that will further improve system energy efficiencies and overcome impending system I/O bottlenecks.

Experimental Demonstration of Multivendor and Multidomain EON With Data and Control Interoperability Over a Pan-European Test Bed

The operation of multidomain and multivendor EONs can be achieved by interoperable sliceable bandwidth variable transponders (S-BVTs), a GMPLS/BGP-LS-based control plane, and a planning tool. The control plane is extended to include the control of S-BVTs and elastic cross connects, which combine a large port-count fiber-switch (optical backplane) and bandwidth-variable wavelength-selective switches, enabling the end-to-end provisioning and recovery of network services. A multipartner testbed is built to demonstrate and validate the proposed end-to-end architecture. Interoperability among S-BVTs is experimentally tested between different implementations. In this case, transponders are configured using the proposed control plane. The achieved performance with hard-decision and soft-decision FECs using only the information distributed by the control plane is measured against the performance of the single-vendor implementation, where proprietary information is used, demonstrating error-free transmission up to 300 km.

All-Optical Programmable Disaggregated Data Centre Network Realized by FPGA-Based Switch and Interface Card

This paper reports an FPGA-based switch and interface card (SIC) and its application scenario in an all-optical, programmable disaggregated data center network (DCN). Our novel SIC is designed and implemented to replace traditional optical network interface cards, plugged into the server directly, supporting optical packet switching (OPS)/optical circuit switching (OCS) or time division multiplexing (TDM)/wavelength division multiplexing (WDM) traffic on demand. Placing the SIC in each server/blade, we eliminate electronics from the top of rack (ToR) switch by pushing all the functionality on each blade while enabling direct intrarack blade-to-blade communication to deliver ultralow chip-to-chip latency. We demonstrate the disaggregated DCN architecture scenarios along with all-optical dimension-programmable N × M spectrum selective Switches (SSS) and an architecture-on-demand (AoD) optical backplane. OPS and OCS complement each other as do TDM and WDM, which can support variable traffic flows. A flat disaggregated DCN architecture is realized by connecting the optical ToR switches directly to either an optical top of cluster switch or the intracluster AoD optical backplane, while clusters are further interconnected to an intercluster AoD for scaling out.

Toolkit for Photonic Integrated Circuits Based on Inverted Rib Waveguides

We have performed an exploration of inverted rib waveguide platform for use in optical backplanes. This entailed the design, optimization, and characterization of a variety of passive optical components that may serve as a basis for the functions required of an on-chip optical networks. The presented design introduces an inverted-rib template, which consists of a polymer waveguide layer. We have successfully fabricated and demonstrated low-loss waveguides, and also functional passive devices such as directional couplers, multimode interferometers, waveguide bends and crossings, and distributed Bragg reflectors. We also demonstrate a way of coupling active components (e.g., in silicon) to such a photonic integrated circuit.

Glass‐based Manufacturing and Prototyping Platform PhotPack

AbstractThere has been considerable progress in utilizing fully automated machines for the assembly of micro‐optical systems in recent years. Such systems integrate laser sources, passive optical elements, electro‐optical components and detectors into tight packages, and efficiently couple light to waveguides in photonic integrated circuits (PIC), optical backplanes, free space or optical fibers. The required electro‐optical and optical components are placed and aligned passively and actively, depending on optical and mechanical component tolerances. For one, the relative placing of all components is controlled actively by camera systems, and, more importantly, some or all active components are actually operated, and actively aligned with live feedback from internal and external power and beam image detectors. High precision (and also fast) active optical alignment machines nowadays exist, with more than adequate degrees of freedom and accuracies, so that best optical beam qualities and coupling efficiencies can be achieved.

Performance analysis of communication links based on VCSEL and silicon photonics technology for high-capacity data-intensive scenario.

To face the increased demand for bandwidth, cost-effectiveness and simplicity of future Ethernet data communications, a comparison between two different solutions based on directly-modulated VCSEL sources and Silicon Photonics technologies is carried out. Also by exploiting 4-PAM modulation, the transmission of 50-Gb/s and beyond capacity per channel is analyzed by means of BER performance. Applications for optical backplane, very short reach and in case of client-optics networks and intra and inter massive data centers communications (up to 10 km) are taken into account. A comparative analysis based on the power consumption is also proposed.

Laser-direct writing of single mode and multi-mode polymer step index waveguide structures for optical backplanes and interconnection assemblies

A laser direct writing (LDW) method is implemented as a cost efficient polymer waveguide (WG) fabrication method for prototyping large substrates for optical backplanes and optical interconnection assemblies. The LDW setup utilizes a 3-axis air-bearing motion platform to reduce WG fabrication error to within ±0.15μm. A UV laser diode coupled single mode fiber with a focusing lens module is capable of LDW WGs at both multimode (50μm) and single mode (6μm) dimensions. Correlation between LDW parameters and fabricated WG dimensions using Dow Corning® OE-4140 UV-Cured Optical Elastomer (ncore=1.5142, nclad=1.5064) is discussed theoretically and confirmed experimentally for both applications. A theoretical model is developed and utilized for producing LDW multi-mode (0.04dB/cm, λ=850nm) and single mode (0.55dB/cm, λ=1310nm) WGs. Measured propagation losses of LDW WGs are comparable to losses of photolithographic multi-mode (0.04dB/cm @ 850nm) and single mode (0.59dB/cm @ 1310nm) WG builds. LDW multi-mode and single mode WG radial bend and crossing losses are evaluated for advanced optical communication channel routing capabilities and do not exhibit significant deviations from photolithographic-manufactured WG device loss.

Evaluating Availability of Optical Networks Based on Self-Healing Network Function Programmable ROADMs

Due to the large transmission speeds and enormous volume of transferred data, network reliability performance and cost-efficiency are among the key concerns in optical network design. Reducing the number of used optical components with higher failure probability within nodes represents a promising approach for achieving reliable and cost-effective optical network operation as it reduces the correlated risk of connection failures and enables reusing idle components as redundancy for failure recovery. This can result in greater overall network availability and lower loss of data and related revenue. Recently introduced synthetic network function programmable optical nodes implemented by architecture on demand (AoD) support the aforementioned approach by offering high levels of flexibility, modularity, and scalability. In AoD nodes, an optical backplane (i.e., optical switch) hosts optical components and enables arbitrary node configurations by cross-connecting attached modules. As a result, each lightpath passing through the node uses only the components necessary for fulfilling the switching and processing requirements. AoD nodes can perform switching at the wavelength and waveband granularity and also support switching of lightpaths at the fiber level by connecting an input fiber directly to the targeted output, referred to as fiber switching (FS). The latter functionality is particularly beneficial for the availability aspect, as it helps decrease the number of failure-prone components traversed by each lightpath, allowing them to be reused as redundancy. In this paper we demonstrate and evaluate self-healing capabilities of AoD nodes arising from their flexibility and ability to employ idle components for failure recovery. To improve efficiency of self-healing by increasing the number of idle components within nodes, we propose a routing algorithm which obtains a targeted portion of lightpaths switched at the fiber level, called the enforced FS (EFS) algorithm. We study the impact of AoD on network availability at different traffic switching granularities and compare it to traditional hard-wired node architecture via simulation. The results show significant improvements of availability and recovery time due to node-level restoration, with reduced network outage time and operator revenue losses. Finally, to the best of our knowledge, for the first time we experimentally demonstrate two novel hard-wired and synthetic reconfigurable optical add–drop multiplexer architectures with redundancy and all-optical self-healing capabilities.

Optical Backplane Based on Ring-Resonators: Scalability and Performance Analysis for 10 Gb/s OOK-NRZ

The use of architectures that implement optical switching without any need of optoelectronic conversion allows us to overcome the limits imposed by today’s electronic backplane, such as power consumption and dissipation, as well as power supply and footprint requirements. We propose a ring-resonator based optical backplane for router line-card interconnection. In particular we investigate how the scalability of the architecture is affected by the following parameters: number of line cards, switching-element round-trip losses, frequency drifting due to thermal variations, and waveguide-crossing effects. Moreover, to quantify the signal distortions introduced by filtering operations, the bit error rate for the different parameter conditions are shown in case of an on-off keying non-return-to-zero (OOK-NRZ) input signal at 10 Gb/s.

A 40 Gb/s Optical Bus for Optical Backplane Interconnections

Optical technologies have received large interest in recent years for use in board-level interconnects. Polymer multimode waveguides in particular, constitute a promising technology for high-capacity optical backplanes as they can be cost-effectively integrated onto conventional printed circuit boards (PCBs). This paper presents the first optical backplane demonstrator based on the use of PCB-integrated polymer multimode waveguides and a regenerative shared bus architecture. The backplane demonstrator is formed with commercially-available low-cost electronic and photonic components onto conventional FR4 substrates and comprises two opto-electronic (OE) bus modules interconnected via a prototype regenerator unit. The system enables interconnection between the connected cards over four optical channels, each operating at 10 Gb/s. Bus extension is achieved by cascading OE bus modules via 3R regenerator units, overcoming therefore the inherent limitation of optical bus topologies in the maximum number of cards that can be connected to the bus. Details of the design, fabrication, and assembly of the different parts of this optical bus backplane are presented and related optical and data transmission characterisation studies are reported. The optical layer of the OE bus modules comprises a four-channel three-card waveguide layout that is compatible with VCSEL/PD arrays and ribbon fibres. All on-board optical paths exhibit insertion losses below 13 dB and intra-channel crosstalk lower than -29 dB. The robustness of the signal distribution from the bus inputs to all respective bus output ports in the presence of input misalignment is demonstrated, while 1 dB input alignment tolerances of approximately ±10 μm are obtained. The electrical layer of the OE bus modules comprises the essential driving circuitry for 1×4 VCSEL and PD arrays and the corresponding control and power regulation circuits. The interface between the optical and electrical layers of the bus modules is achieved with simple OE connectors that enable end-fired optical coupling into and out of the on-board polymer waveguides. The backplane demonstrator achieves error-free (BER <; 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> ) 10 Gb/s data transmission over each optical channel, enabling therefore, an aggregate interconnection capacity of 40 Gb/s between any connected cards.