Arrayed Waveguide Grating Router Research Articles

Integrated Wavelength-Tuned Optical mm-Wave Beamformer With Doubled Delay Resolution

Integrated optical true time delay lines attract lots of attention for optically controlled mm-wave beam steering due to its low-loss/broadband performance and stable/compact system architecture. However, for remotely-controlled networks, the techniques that require local-site actively-tuned elements would make the network control more complicated. A passive design using wavelength-tuning is regarded as a promising candidate. In this paper, an integrated wavelength-tuned optical mm-wave beamformer with doubled delay resolution is proposed and demonstrated in a generic InP platform. A bidirectional looped-back arrayed waveguide grating (AWG) module acts as the stepwise tunable delay unit. By introducing an extra AWG router for delay mode (positive/negative) selection and a bidirectional optical interface, a pure λ-tuned, resolution-doubled optical delay network is realized without using any active component (e.g. heaters, current injection) at the local site. This photonic passive design is more beneficial to the remotely-controlled mm-wave beam steering system. Furthermore, the AWG router potentially allows multi-port wavelength switching to support the scaling-up of the network. The fabrication-caused delay error of <; 1.1 ps is experimentally verified on-chip. A further proof-of-concept 38-GHz fiber-wireless beam steering system with a 186° angular steering is experimentally demonstrated using QAM-4 modulation. Accurate mm-wave phase shifts originated from the proposed optical beamformer are obtained, which proves the effectiveness of the tunable integrated beamformer.

A Multi-Floor Arrayed Waveguide Grating Based Architecture With Grid Topology for Datacenter Networks

This paper proposes a grid topology based passive optical interconnect (POI) architecture that is composed of multiple floors of arrayed waveguide grating routers (AWGRs) to offer high connectivity and scalability for datacenter networks. In the proposed POI signal only needs to pass one AWGR, and thus can avoid the crosstalk accumulation and cascaded filtering effects, which exist in many existing POI architectures based on cascaded AWGRs. Meanwhile, due to high connectivity, the proposed grid topology based POI also has the potential advantage of high reliability. Simulation results validate the network performance. With a proper node degree, the proposed grid topology can achieve acceptable blocking probability. Besides, steady performance is kept when the number of floors increases, indicating good scalability of the proposed POI.

Silicon Photonic Flex-LIONS for Bandwidth-Reconfigurable Optical Interconnects

This paper reports the first experimental demonstration of silicon photonic (SiPh) Flex-LIONS, a bandwidth-reconfigurable SiPh switching fabric based on wavelength routing in arrayed waveguide grating routers (AWGRs) and space switching. Compared with the state-of-the-art bandwidth-reconfigurable switching fabrics, Flex-LIONS architecture exhibits 21× less number of switching elements and 2.9× lower on-chip loss for 64 ports, which indicates significant improvements in scalability and energy efficiency. System experimental results carried out with an 8-port SiPh Flex-LIONS prototype demonstrate error-free one-to-eight multicast interconnection at 25 Gb/s and bandwidth reconfiguration from 25 Gb/s to 100 Gb/s between selected input and output ports. Besides, benchmarking simulation results show that Flex-LIONS can provide a 1.33× reduction in packet latency and >1.5× improvements in energy efficiency when replacing the core layer switches of Fat-Tree topologies with Flex-LIONS. Finally, we discuss the possibility of scaling Flex-LIONS up to N = 1024 ports (N = M × W) by arranging M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> W-port Flex-LIONS in a Thin-CLOS architecture using W wavelengths.

Crosstalk-Aware Wavelength-Switched All-to-All Optical Interconnect Using Sub-Optimal AWGRs

We propose a crosstalk (XT)-aware wavelength (λ)-detuning scheme to overcome the non-optimal in-band XT limiting all-to-all optical interconnects based on sub-optimal arrayed waveguide grating routers (AWGR). Experimental validation is demonstrated employing an 8 × 8 O-band cyclic Si-AWGR with 10 nm channel spacing and a 5.5 nm channel bandwidth, where the in-band XT limits the simultaneous use of the same λ in only 2 out of the 8 possible AWGR I/O routing scenarios, yielding a 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> error-floor when >3 channels at the same λ are launched. We present experimentally an 8 × 25 Gb/s λ-switched interconnect exploiting slightly detuned λ s around the central λ for realizing all 8 possible I/O routing scenarios, enabling an error-free all-to-all interconnect even for sub-optimal AWGRs. Error-free simultaneous transmission via the AWGR of all 8 channels using 4λs and a λ utilization factor 2 is shown, with a max. power penalty of 4.64 dB at 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> error-rate.

Foundry-Enabled Scalable All-to-All Optical Interconnects Using Silicon Nitride Arrayed Waveguide Router Interposers and Silicon Photonic Transceivers

This paper summarizes our latest results of integrated all-to-all optical interconnect systems using compact, low-loss silicon nitride (SiN) arrayed waveguide grating router (AWGR) through AIM photonics’ multiple-project-wafer services. In particular, we have designed, taped out, and initially characterized a chip-scale silicon photonic low-latency interconnect optical network switch (Si-LIONS) system with an 8 × 8 200 GHz spacing cyclic SiN AWGR, 64 microdisk modulators, and 64 on -chip germanium photodector (PD). The 8 × 8 SiN AWGR in design has a measured insertion loss of 1.8 dB and a crosstalk of –13 dB, with a footprint of 1.3 mm × 0.9 mm. We measured an error-free performance of the microdisk modulator at 10 Gb/s upon 1Vpp voltage swing. We demonstrated wavelength routing with error-free data transmission using the on -chip modulator, SiN AWGR, and an external PD. We have designed and taped out the optical interposer version of the all-to-all system using SiN waveguides and low-loss chip-to-interposer couplers. Finally, we illustrate our preliminary designs and results of 16 × 16 and 32 × 32 SiN AWGRs, and discuss the possibility of scaling beyond 1024 × 1024 all-to-all interconnections with reduced number of wavelengths (e.g., 64) using the Thin-CLOS architecture.

Crosstalk-Mitigated AWGR-Based Two-Dimensional IR Beam-Steered Indoor Optical Wireless Communication System With a High Spatial Resolution

In this paper, a crosstalk-mitigated transmission scheme in arrayed waveguide grating router (AWGR) based two dimensional infrared beam-steered optical wireless communication (OWC) system is proposed for indoor applications. By creating polarization orthogonality between the odd and even AWGR channels, high crosstalk tolerance between spectrally overlapping AWGR channels is realized experimentally. Because two signals with orthogonal polarization states will not beat with each other in a photodiode. The optical crosstalk on the orthogonal polarization state will not generate a beat note upon detection and thus crosstalk in the electrical domain can be largely reduced. Reduced crosstalk leads to a reduction in the required spectral guard band and/or an improved tolerance to spectral overlap, which allows higher spectral efficiency. Moreover, the port number of an AWGR can be increased by simply shortening the spatial gap between adjacent output waveguides on a chip. The higher port number can support the high spatial resolution of the steered OWC system. This technique can also tolerate the wavelength misalignment between AWGRs and lasers, which relaxes the design of low crosstalk AWGRs and high wavelength stable lasers. A 20 Gbit/s data rate, four-level pulse amplitude modulation OWC transmission has been experimentally demonstrated over 1.2-m free-space link. The experimental results show that the proposed scheme can maintain stable, low crosstalk impact with an apparent improvement of the responsivity.

O-Band Silicon Photonic Transmitters for Datacom and Computercom Interconnects

Today, the datacenter ecosystems are fueling the demand for novel transmitter (ΤΧ) technologies complying with the off-board, on-board, and chip-to-chip computing needs. This has set a new class of requirements for the TX infrastructure that should now offer multiple credentials, namely: high-speed, O-band operation for avoiding dispersion compensation in long distances, wavelength-division multiplexing (WDM) capabilities for higher throughput and multicasting/broadcasting support, and tight co-packaging with low-power electronics. Silicon (Si) photonic TXs have been extensively studied toward high-speed and WDM TX engines targeting mainly C-band. Only a limited number of Si-Pho O-band TXs have been reported, however with ≤32 Gb/s/channel line-rate capabilities and with a WDM portfolio that has not been fully explored yet. In this paper, we introduce a novel silicon photonic high-speed O-band TX hardware platform that can meet the current datacom and computercom interconnect requirements. We demonstrate a ring modulator (RM) based four-channel WDM TX at 4 × 40 Gb/s non-return-to-zero (NRZ) operation that supports wavelength parallelism in unicast operation but can also pave the way toward WDM TX engines for the post-100 GbE TX era. Moreover, we present a broadband Si Mach–Zehnder modulator employed in a WDM modulation scheme of 2 × 25 Gb/s NRZ signals and demonstrate multicasting when combined with a 8 × 8 passive arrayed waveguide grating router (AWGR) wavelength router, addressing the broadcasting needs of traffic usually encountered in cache-coherent multisocket settings. Finally, we further demonstrate the tight synergy of O-band Si-RM modulators with high-speed CMOS electronics, presenting an RM-based TX assembly prototype employing a fully depleted silicon-on-insulator CMOS driver, delivering 50-Gb/s NRZ operation.

Enabling Scalable Disintegrated Computing Systems With AWGR-Based 25D Interconnection Networks

2.5D integrated systems exploiting electronic interposers to tightly integrate multiple processor dies into the same package suffer from significant performance degradation caused by the large latency overheads of their die-to-die multihop electrical interconnection networks. Silicon-photonic interposers with wavelength-routed interconnects can overcome this issue by enabling directly connected, scalable topologies while exhibiting low-energy optical communication even at large distances. This paper studies the use of an arrayed waveguide grating router (AWGR) as a scalable, low-latency silicon-photonic interconnection fabric for computing systems with up to 256 cores. Our results indicate that AWGRs could be a key enabler for large-scale interposer systems, offering an average performance speed-up of at least 1.25&#x00D7; with 1.32&#x00D7; lower power for 256 cores compared to state-of-the-art electrical networks, while offering a more compact solution compared to alternative photonic interconnects.

Uniform-loss cyclic arrayed waveguide grating router using a mode-field converter based on a slab coupler and auxiliary waveguides.

We designed and fabricated a silica-based 16×16 cyclic arrayed waveguide grating router (AWGR) with improved channel loss uniformity using a simple mode-field converter composed of a slab coupling region and auxiliary waveguides placed at the interface between the arrayed waveguides and the output star coupler of the AWGR. The mode-field converter transforms the fundamental Gaussian-shaped mode in the arrayed waveguides to a complex mode field which produces a flat-top far field at the image plane of the output star coupler. It does not change the overall construction of the AWGR and does not increase the device size. The experimental results show that loss non-uniformity for a 16×16 AWGR with 1.6nm wavelength channel spacing is reduced from 3 to 0.5dB after adapting the mode-field converter, and the crosstalk is improved by about 2dB.

提高损耗均匀性的氮氧化硅阵列波导光栅路由器

提高损耗均匀性的氮氧化硅阵列波导光栅路由器

H OEIN: A Hierarchical Hybrid Optical/Electrical Interconnection Network for Exascale Computing Systems

The performance of high-performance computing (HPC) systems is largely determined by the interconnection network. The rising demand for computing capability leads to an expansion of the interconnection network and a corresponding increase in system cost and power consumption. The growing use of optical interconnects not only reduces the network cost and power consumption, but also meets the system-scaling bandwidth demands. However, unlike in an electrical switch, the lack of a buffer in the optical switch makes it hard to operate an all-optical network at packet-level granularity. In this paper, we propose a hierarchical hybrid optical/electrical interconnection network (H $^2$ OEIN) based on low-radix switches and arrayed waveguide grating routers (AWGRs). In the lower layers, the use of low-radix switches results in lower cost and power consumption. The modular structure composed of low-radix switches facilitates the expansion of the network. At higher layers, high bandwidth and fast switching can be achieved using AWGR based optical interconnects. Because the higher layers of the network are passive, the power consumption can be reduced to a large extent. Network simulation results show that H $^2$ OEIN reduces the cost by 25 percent and the power consumption by 45 percent compared to a dragonfly network in configurations with over 300,000 nodes.

Energy-Efficient Dynamic Lightpath Adjustment in a Decomposed AWGR-Based Passive WDM Fronthaul

To cope with the explosion of mobile traffic demand, cloud radio access networks (C-RAN) have been recently proposed. In C-RANs, the two main elements of traditional base stations (BSs), i.e., the baseband unit (BBU) and the remote radio head (RRH), are separated, and the BBU can be virtualized and located in a remote location together with BBUs of other BSs. High-bandwidth digitized baseband signals must be exchanged between BBUs and RRHs through a large-capacity fronthaul network. Wavelength division multiplexing (WDM) technology is an efficient solution to provide sufficient fronthaul bandwidth with a large number of optical transceivers. With the fixed connections between BBUs and RRHs in the traditional C-RAN, the utilization of optical transceivers as well as BBUs is inefficient. In this paper, we propose a decomposed arrayed waveguide grating router (AWGR)-enabled passive WDM fronthaul, and we formulate the minimal energy consumption problem as integer linear programming, with the objective of minimizing the energy consumption caused by optical transceivers and BBUs, etc. We also design two dynamic lightpath adjustment heuristics by light-path reconfiguration to improve energy efficiency. In addition, we take AWGR decomposition into consideration to reduce the tuning range of tunable transceivers and free spectrum range of AWGR, hence lowering the deployment cost of transport network components. Numerical evaluation shows that our proposed schemes achieve significant energy savings compared to fixed lightpath allocation.

Silicon-based cyclic arrayed waveguide grating routers with improved loss uniformity

We present silicon-on-insulator (SOI)-based cyclic arrayed waveguide grating routers (AWGRs) with improved channel loss uniformity in the full free spectral range (FSR) by using dual-tapered auxiliary waveguides between the ends of arrayed waveguides. The field distribution at the image plane of the output free propagation region (FPR) is adjusted by the auxiliary waveguides and a flat-top shape can be obtained by appropriate optimization. 8×8 and 15×15 AWGRs with optimized auxiliary waveguides, having a channel spacing of 3.2 nm and 1.6 nm, respectively, are fabricated and the measured loss non-uniformity is less than 0.5 dB, significantly improved by at least 1.5 dB compared with conventional AWGRs.

Experimental Demonstration of a 64-Port Wavelength Routing Thin-CLOS System for Data Center Switching Architectures

This paper reports on the results of the design, fabrication, and experimental demonstration of a wavelength routing Thin-CLOS system based on arrayed waveguide grating routers (AWGRs) for intra-data-center applications. By using M2 W-port AWGRs, this architecture allows increasing by a factor of M the scalability provided by a wavelength router using a single W-port AWGR. The fabricated Thin-CLOS system has 64 ports and makes use of M2 = 4 AWGRs with W = 32 ports and 100 GHz channel spacing. The system fits in a 1U rack enclosure and consumes less than 10 W. We demonstrated error-free performance at 10 Gb∕s per wavelength with a power penalty of <3 dB under a worst-case crosstalk scenario. The adopted 64-port Thin-CLOS architecture makes use of four 32-port silica AWGRs to reduce the impact of in-band crosstalk while guaranteeing nonblocking connectivity among the 64 ports and using only W = 32 distinct wavelengths.

High-Capacity Optical Wireless Communication Using Two-Dimensional IR Beam Steering

The free-space narrow infrared beams can offer unprecedented data capacity to devices individually, as they can provide non-shared connections that have a large link power budget. By means of a fully passive module based on a high port count arrayed waveguide grating router (AWGR), many infrared beams can be 2D steered individually using wavelength tuning. By applying the defocusing techniques, a compact beam steering module has been realized. A simultaneous communication at up to 112 Gbit/s PAM-4 per beam has been shown with an 80-ports AWGR, thus offering a total wireless throughput beyond 8.9 Tbit/s. The wireless provisioning of multiple ultrahigh-definition video streams has been demonstrated in a proof-of-concept laboratory setup.

PODCA: A Passive Optical Data Center Network Architecture

Optical interconnects have gained great attention recently as a promising solution offering high throughput, low latency, scalability, and reduced energy consumption compared to electrical interconnects. However, some active optical components, such as tunable wavelength converters and micro-electro-mechanical systems (MEMS) switches, suffer from high cost or slow reconfiguration times, and have been roadblocks to the realization of all-optical interconnects. In this paper, we propose three versions of a passive optical data center network architecture (PODCA), depending on the size of the network. Our key device is the arrayed waveguide grating router (AWGR), a passive device that can achieve contention resolution in the wavelength domain. In our architectures, optical signals are transmitted from fast tunable transmitters; pass through couplers, AWGRs, and demultiplexers; and are received by wide-band receivers. Our architecture can scale to over 2 million servers. Simulation results indicate that PODCA exhibits lower latency and higher throughput even at high-input loads compared with electrical data center networks such as Fat-Tree and Flattened Butterfly, and comparable performance with other optical interconnects such as DOS and Petabit, but at much lower cost and power consumption. The packet latency of PODCA in our simulation experiments is below 19 μs, and the throughput is 100%. Furthermore, we compare the power consumption and capital expenditure (CapEx) cost of PODCA with the other four architectures. Results show that PODCA can save at least 75% on power consumption and 50% on CapEx.

Silicon photonic 8 × 8 cyclic Arrayed Waveguide Grating Router for O-band on-chip communication.

We report an 8 × 8 silicon photonic integrated Arrayed Waveguide Grating Router (AWGR) targeted for WDM routing applications in O-band. The AWGR was designed for cyclic-frequency operation with a channel spacing of 10 nm. The fabricated AWGR exhibits a compact footprint of 700 × 270 μm2. Static device characterization revealed 3.545 dB maximum channel loss non-uniformity with 2.5 dB best-case channel insertion losses and 11 dB channel crosstalk, in good agreement with the simulated results. Successful data routing operation is demonstrated with 25 Gb/s signals for all 8 × 8 AWGR port combinations with a maximum power penalty of 2.45 dB.

Suppression of thermal wavelength drift in widely tunable DS-DBR laser for fast channel-to-channel switching.

We present a simple and effective method for suppressing thermally induced wavelength drift in a widely tunable digital supermode distributed Bragg reflector (DS-DBR) laser monolithically integrated with a semiconductor optical amplifier (SOA). For fast thermal compensation, pre-compensatory currents are injected into the gain medium section of the DS-DBR laser and the SOA. This method can be easily applied to existing commercial tunable lasers, since it is implemented without any modification to manufacturing process. Experimental results exhibit that wavelength stability is noticeably improved to ± 0.01 nm. We also experimentally demonstrate a fast channel-to-channel switching in a wavelength-routed optical switching system employing a 90 × 90 arrayed waveguide grating router (AWGR). The measured switching time is less than 0.81 µs.

Performance improvement for silicon-based arrayed waveguide grating router

We analyze the impact of aberration on spectral performance of silicon-based arrayed waveguide grating (AWG) router with the conventional design using a constant pitch along the grating circle for the array waveguides near the free propagation region (FPR), and simulation results show that due to existence of large aberration, side lobes occur in spectral responses of peripheral output channels for the center input light while more serious side lobes appear in most output channels within a free spectral range (FSR) for the edge channel input. Therefore, there is a high crosstalk in conventional N × N silicon AWG, which is very detrimental for router applications. In order to address it, a simple design with a constant projected period on a line tangent to the grating at its pole for the array waveguides near the FPR is proposed, and aberrations of all output wavelengths within a FSR are kept at a rather low level both for the center and edge input. Then we fabricate two kinds of AWG routers with the conventional and proposed design respectively on a SOI wafer, and experimental results show that spectral responses of the AWG router with the proposed design are significantly improved compared to those obtained in the conventional design, especially for the edge channel input.

OPSquare: A Flat DCN Architecture Based on Flow-Controlled Optical Packet Switches

Aiming at solving the scaling issues of bandwidth and latency in current hierarchical data center network (DCN) architectures, we propose and investigate a novel optical flat DCN architecture in which the number of interconnected ToRs scales as the square of the optical packet switches&#x2019; (OPS) port count (OPSquare). The proposed flat DCN architecture consists of two parallel inter- and intra-cluster networks that are built on a single-hop OPS with nanosecond time and wavelength switching for efficient statistical multiplexing operations. Fast optical flow control is implemented for solving packet contentions that may occur at the buffer-less optical switches. The performance of OPSquare DCN in terms of scalability, packet loss, latency, and throughput is assessed by a numerical simulation employing OMNeT++ under realistic data center (DC) traffic. The results report a server-to-server latency of less than 2 &#x03BC;s (including packet retransmission), a packet loss &lt;10&#x2212;5 at a load of 0.4, and a DC size of 10,240 servers with a ToR buffer size equal to 50 KB for all traffic patterns. Moreover, the cost and power consumption of the OPSquare DCN have been studied and compared with fat-tree DCN based on electrical switches and H-LION connected by an arrayed wave guide grating router (AWGR). The results indicate 23.8% and 39% cost and power savings, respectively, for the OPSquare DCN supporting 160,000 servers with respect to the fat-tree DCN. The OPSquare has a cost saving of 56% compared with H-LION for a 160,000-server DCN.