Arrayed Waveguide Grating Research Articles

Transmission Distance Extension of Directly Modulated Tunable V-cavity Laser Using AWG Wavelength Detuning

Directly modulated tunable lasers are highly desirable for constructing dense-wavelength division multiplexing (DWDM) access networks, owing to their advantages of low cost, compact size and low power consumption. However, the transmission distance for 10 Gbps is usually limited to about 10 km in the telecom C-band in standard single-mode fiber (SMF) due to wavelength chirp. Here we propose and demonstrate a simple technique for extending the transmission distance by detuning the wavelength of a tunable V-cavity laser with respect to DWDM multiplexers. Experiment results show that 10 Gbps signal can be transmitted error-free (BER<10−12) over 20 km SMF with a wavelength-detuning with respect to a Gaussian-type arrayed waveguide grating (AWG) without dispersion compensation. The power penalty is only 1 dB compared to the back-to-back transmission.

Si3N4 photonic integration platform at 1 µm for optical interconnects.

Vertical-cavity surface-emitting lasers (VCSELs) are the predominant technology for high-speed short-range interconnects in data centers. Most short-range interconnects rely on GaAs-based multi-mode VCSELs and multi-mode fiber links operating at 850 nm. Recently, GaAs-based high-speed single-mode VCSELs at wavelengths > 1 µm have been demonstrated, which increases the interconnect reach using a single-mode fiber while maintaining low energy dissipation. If a suitable platform for passive wavelength- and space-multiplexing were developed in this wavelength range, this single-mode technology could deliver the multi-Tb/s interconnect capacity that will be required in future data centers. In this work, we show the first passive Si3N4 platform in the 1-µm band (1030-1075 nm) with an equivalent loss < 0.3 dB/cm, which is compatible with the system requirements of high-capacity interconnects. The waveguide structure is optimized to achieve simultaneously single-mode operation and low bending radius, and we demonstrate a wide range of high-performance building blocks, including arrayed waveguide gratings, Mach-Zehnder interferometers, splitters and low-loss fiber interfaces. This technology could be instrumental in scaling up the capacity and reducing the footprint of VCSEL-based optical interconnects and, thanks to the broad transparency in the near-infrared and compatibility with the Yb fiber amplifier window, enabling new applications in other domains as optical microscopy and nonlinear optics.

5-Channel Polymer/Silica Hybrid Arrayed Waveguide Grating.

A 5-channel polymer/silica hybrid arrayed waveguide grating (AWG), fabricated through a simple and low-cost microfabrication process is proposed, which covers the entire O-band (1260–1360 nm) of the optical communication wavelength system. According to the simulation results, the insertion loss is lower than 4.7 dB and the crosstalk within 3-dB bandwidth is lower than ~−28 dB. The actual fiber–fiber insertion loss is lower than 14.0 dB, and the crosstalk of the 5 channels is less than −13.0 dB. The demonstrated AWG is ideally suitable for optical communications, but also has potential in the multi-channel sensors.

400 Gb/s Silicon Photonic Transmitter and Routing WDM Technologies for Glueless 8-Socket Chip-to-Chip Interconnects

Arrayed Waveguide Grating Router (AWGR)-based interconnections for Multi-Socket Server Boards (MSBs) have been identified as a promising solution to replace the electrical interconnects in glueless MSBs towards boosting processing performance. In this article, we present an 8-socket glueless optical flat-topology Wavelength Division Multiplexing (WDM)-based point-to-point (P2P) interconnect pursued within the H2020 ICT project ICT-STREAMS and we report on our latest achievements in the deployment of the constituent silicon (Si)-photonic transmitter and routing building blocks, exploiting experimentally obtained performance metrics for analyzing the 8-socket chip-to-chip (C2C) connectivity in terms of throughput and energy efficiency. We demonstrate an 8-channel WDM Si-photonic microring-based transmitter (Tx) capable of providing 400 (8 × 50) Gb/s non-return-to-zero (NRZ) Tx capacity and an 8 × 8 Coarse-WDM (CWDM) Si-AWGR with verified cyclic data routing capability in O-band. Following an overview of our recently demonstrated crosstalk (XT)-aware wavelength allocation scheme, that enables fully-loaded AWGR-based interconnects even for typical sub-optimal XT values of silicon integrated CWDM AWGRs, we validate the performance of a full-scale 8-socket interconnect architecture through physical layer simulations exploiting experimentally-verified simulation models for the underlying Si-photonic Tx and routing circuits. This analysis reveals a total aggregate capacity of 1.4 Tb/s for an 8-socket interconnect when operating with 25 Gb/s line-rates, which can scale to 2.8 Tb/s at an energy efficiency of just 5.02 pJ/bit by exploiting the experimentally verified building block performance at 50 Gb/s line. This highlights the perspectives for up to 69% energy savings compared to the standard QuickPath Interconnect (QPI) typically employed in electronic glueless MSB interconnects, while scaling the single-hop flat connectivity from 4- to 8-socket interconnection systems.

Multi-Point Cryogenic Temperature Sensor Based on Fresnel Reflection

A cost-effective and relatively simple-to-implement alternative to the well established multi-point fiber sensor platform has been demonstrated for the detection of cryogenic temperatures using the Fresnel-reflection and array waveguide gratings (AWGs). The cryogenic temperature detection has been carried out by monitoring the Fresnel reflected intensities from optical fiber facet coated with the epoxy resin and polymethyl metha acrylate (PMMA). Experimental results show that the temperature sensitivity of the epoxy coated sensor is 0.04 dB/K within 90∼298 K, while the sensitivity of PMMA is 0.03 dB/K. Furthermore, we demonstrated that the optical fiber sensors can be easily embedded in the host material and stable for repeated use, proving this platform as a versatile and robust sensing tool.

Performance Evaluation of a Hybrid Buffer-Based Optical Packet Switch Router

Abstract Recently, in the present day’s data center systems an explosive growth has been observed in data traffic, which restricts the speed of exiting data communication network. To solve such problem, fiber optical-based optical communication system is preferred choice. In this paper, an arrayed waveguide grating (AWG)-based optical packet switch is presented in which priority among packets is implemented effectively. This switch is a recirculating loop buffer-based switch in which a hybrid buffering (optical + electrical) technique is used for storing packets into the buffer. The power budget analysis of switch is presented in various conditions, when packet passes through the optical or electronic buffers. Comparison of optical and electronic buffering is done in terms of power required for the correct operation of the switch. In this paper, a comparison is performed between our proposed switch with recently published switch designs. The result presented in this paper clearly reveals that the performance of our proposed switch is far better than other previously published switch architecture. The major beauty of our proposed switch is that in this design priority among packets implemented effectively.

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.

Polarization Diversified 16λ Demultiplexer Based on Silicon Wire Delayed Interferometers and Arrayed Waveguide Gratings

We proposed novel 16λ demultiplexer based on cascaded connection of silicon-nanowire waveguide type delayed interferometric filters and arrayed waveguide gratings, and experimentally verified 100-GHz-spaced bandpass filtering operation with nearly identical insertion loss (<; 6 dB) and low crosstalk (<; -19.5 dB to <; -34.6 dB for a single channel, <; -12.7 dB for entire output channels). We also demonstrated polarization diversified operation with 32 Gbps non-return-to-zero (NRZ) signal transmissions in C-band range. We also verified the operation of 140-GHz-spaced bandpass filtering in O-band spectral range.

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.

Integration of Arrayed Waveguide Grating on Strip-Loaded Slot Waveguide for Sensing Applications

We demonstrate the integration of arrayed waveguide grating (AWG) de-multiplexer with a low loss and low index contrast platform, i.e., a striped-loaded slot waveguide (SLWG). The SLSW-AWG is designed to operate around the wavelength λ = 1550 nm with a four-output channel. The device experiences excellent output parameters: channel width δλ = 1.39 nm at -3dB, channel spacing Δλ = 2.43 nm and extinction ratio ER = 9.87 dB, useful for sensing applications.

Integrated tunable phase shifter based on energy-conserved phase amplification and its application for RF-OAM generation

Photonics-assisted microwave phase shifter is one of the essential components in communications. Phase amplification is a promising technology which efficiently enables compact photonics-assisted microwave phase shifter. Based on vector sum, the phase shift can be translated from amplitude attenuation to phase amplification. This issues an additional optical energy consumption and even more the highly dependent signal to noise ratio of phase-shifted microwave signal. In this paper, we propose an energy-conserved phase amplification concept to address this issue. Furthermore, based on this concept, we demonstrate a microwave photonic phase shift system with an integrated chip incorporating an arrayed waveguide gratings (AWG) structure. A multichannel continuous 360° phase shift over a frequency range of 12 GHz–20 GHz can be achieved by changing the optical carrier wavelength. Taking advantages of phase modulator and AWG structure, a reliable and efficient phase shifter for beam steering and orbital angular momentum (OAM) generation system can be realized without any other active device. The simulation results of OAM purity test show that better OAM beams can be obtained with the proposed phase shifter. This integration method has great potential in RF OAM generation and multiplexing system to improve the signal quality and reduce the system complexity.

阵列波导光栅解复用器的偏振相关损耗的优化

阵列波导光栅解复用器的偏振相关损耗的优化

SDN-Enabled Sliceable Transceivers in Disaggregated Optical Networks

We design and implement programmable (SDN-enabled) sliceable bandwidth/bitrate variable transceivers (S-BVTs) based on multicarrier modulation (MCM) with direct detection (DD), tailored for disaggregated metro networks. A first level of disaggregation is assessed by considering an S-BVT architecture composed of a set of white box bandwidth/bit rate variable transceivers (BVTs) from multiple manufaturers/providers. An OpenConfig vendor-neutral model is adopted for the implementation of the SDN agents that configure the S-BVTs according to the network requirements/targets. Additionally, a fully disaggregated metro network is envisioned by considering a fixed/flexi-grid dense wavelength division multiplexing (DWDM) network with white box ROADM/OXC nodes. The impact of the filter narrowing effect is assessed considering different network node architectures based on either flexible wavelength selective switches (WSSes) or arrayed waveguide gratings (AWGs). Thanks to the transceiver inherent modularity, flexibility and bit rate variability, up to 8 network nodes can be traversed ensuring a target capacity of 50 Gb/s per slice at a 4.62 · 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> BER.

Silicon Nitride (Si3N4) (De-)Multiplexers for 1-μm CWDM Optical Interconnects

We discuss the design and demonstration of 4-channel coarse wavelength-division (de-)multiplexers based on cascaded Mach-Zehnder interferometer (MZI) lattice filters and arrayed waveguide gratings (AWG) on a 150 nm silicon nitride (Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) platform. The 1 × 4 (de-)multiplexers are designed for a channel separation of 25 nm and operate within 990-1065 nm for bottom emitting vertical cavity surface emitting lasers (VCSEL)-based optical links. For Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> Gaussian AWGs, we demonstrate crosstalk <; -35 dB at the peak transmission band with insertion loss <; 0.5 dB. Measurements were performed over many dies, and pass-band standard deviations for channel 1-4 are 0.49, 0.66, 0.42, and 0.37 nm, respectively. Results for flat-top AWGs indicate crosstalk <; -20 dB, with insertion loss <; 3 dB for the best devices. Flat-top cascaded 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> order and 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> order MZI lattice filters show a minimum of crosstalk <; -15 dB and <; -20 dB, respectively. The pass-band temperature shift was determined to be 14.5 pm/°C, which is lower than reported values for silicon. The device footprint of the Gaussian and flat-top AWGs are both ~670 × 200 μm. The device footprint of the flat-top cascaded 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> order and 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> order lattice filters are 1160 × 470 μm and 1570 × 470 μm, respectively. We believe the Si3N4 platform has potential for its use in CWDM and possibly DWDM transceiver/optical-modules for data/computer communication in high temperature environments up to 80 °C.

Ultracompact 40-Channel Arrayed Waveguide Grating on Silicon Nitride Platform at 860 nm

Arrayed waveguide gratings (AWG) have been widely used as wavelength multiplexers and demultiplexers in dense wavelength division multiplexing communications. In this letter, we describe a highly compact 40-channel AWG fabricated on the silicon nitride platform for operation with a center wavelength near 860 nm for use in spectral domain optical coherence tomography. The total footprint of the AWG is 910μm × 680μm. The transmission spectrum of the fabricated device was measured. The AWG had a channel spacing of 1.5 nm and optical spectral range of 60 nm, in accord with the design. The measured insertion loss was 1.3 dB for the central channels and 1.8 dB for the outmost channels. The inter-channel crosstalk varied from 17.2 dB to 19.7 dB for the central 20 channels.

Three-dimensional grid architecture supporting discretionary direct communication among optical network units in metro-access networks

In this paper, a three-dimensional grid architecture supporting discretionary direct communication among optical network units (ONUs) is proposed. By setting up one $N \times N\hspace{3pt}$N×N arrayed waveguide grating (AWG) and two coarse wavelength division multiplexers in the remote node (RN), the optimal path selection of discretionary direct communication among ONUs can be carried out. At the same time, the construction of the RN is simple. By combining with a three-band wavelength allocation, downstream and upstream signals as well as direct-communication signals can be simultaneously transmitted. By utilizing a four-level protection mechanism, three kinds of optical fiber fault protection (i.e., feeder fiber fault protection, distribution fiber fault protection, and interconnecting fiber fault protection) can be achieved. Besides, both the scalability and the reliability of the network can be greatly improved. Finally, the feasibility of the proposed architecture is demonstrated by the simulation experiment.

Design of Novel Fiber Optical Flexible Routing System

In this paper, we propose a new versatile routing device that utilizes arrayed waveguide gratings (AWGs), optical switches, and optical circulators to implement reconfigurable optical add/drop multiplexers (ROADMs), optical interleavers, and optical cross-connect (OXC). With the development of dense wavelength division multiplexing (DWDM) technology, ROADM and OXC technologies have also been put into practical use. Thus, the optical signal can be routed directly in the optical network according to its wavelength without the need for optical-electrical-optical (OEO) conversion. Although different optical network units (ONUs) have different bandwidth requirements, the use of optical interleavers has successfully solved the connection problem between old and new systems. According to the numerical experiments of static characteristics, the proposed routing device can effectively implement three different functionalities, thereby providing greater flexibility for fiber optic network applications.

107 Gb/s Ultra-High Speed, Surface-Normal Electroabsorption Modulator Devices

Short reach communication systems, such as datacenters and access networks, exhibit steep capacity growth and require opto-electronic technologies with small size, low complexity, and low power consumption. Here, we demonstrate large-scale arrays of reflective surface normal electroabsorption modulators (SNEAMs). With very small active volumes, SNEAMs enable ultra-wide electro-optic bandwidth (>>65 GHz). We show modulation at 25 Gbit/s with 1 Vpp drive voltage on packaged SNEAMs and ultra-high bit-rate modulation at 107 Gbit/s with bare chips. These modulators are polarization-independent and have very low total input/output coupling loss of 0.7 dB to single-mode-fibers. We package SNEAM arrays with arrayed waveguide gratings into wavelength division multiplexing transmitters. Due to their broad wavelength range of modulation, SNEAMs do not need power hungry wavelength tuning or locking systems. Future co-integration of SNEAM arrays with low-power electronic driver arrays will enable high-capacity, low-power electro-optic engines.

Integration of Mid-Infrared Light Sources on Silicon-Based Waveguide Platforms in 3.5–4.7 μm Wavelength Range

Mid-infrared light sources are attracting attention for use in spectroscopic sensing, thermal imaging, and infrared countermeasures. Integration of these sources on Si-based waveguides allows for more functional and complex photonic circuits to be integrated on a single chip. This paper focuses on the key aspects of this integrated platform. The operation of silicon-on-insulator waveguides beyond 4.0 μm wavelength with increasing waveguide core thickness is discussed, and the effects of various cladding materials on waveguide propagation loss is demonstrated. Low loss waveguides and Mach-Zehnder interferometers in Ge-on-Si waveguide platform are discussed and beam combiners in the form of arrayed waveguide gratings are demonstrated in both the platforms. Interband cascade lasers are integrated on silicon-on-insulator waveguides with direct bonding to realize Fabry-Perot lasers. Power scaling of integrated lasers is validated by integrating quantum cascade lasers with silicon-on-insulator beam combiners. Results for the first integrated Fabry-Perot quantum cascade lasers on Ge-on-Si waveguides are discussed, together with the potential use of these waveguides to provide a better heat sink for integrated mid-infrared light sources.

Analysis of AWG-Based Optical Data Center Switches

Abstract Optical packet switching (OPS) is an emerging area of research in next-generation datacenter applications. There is an exponential growth in the internet traffic due to applications such as social networking, cloud computing, video streaming, etc. Fiber optical network plays a critical role in various data center (DC) operations. Large bandwidth of the optical fiber made OPS, a promising technology for DCs. Arrayed waveguide gratings (AWGs) are used more frequently in the core of optical packet switches due to its low insertion loss and wavelength dependent routing pattern. Optical switching function can be performed by AWG if each input port is properly equipped with Tunable wavelength converters (TWCs). This paper presents analysis of four optical packet switches namely AWG and Feedback Loop Buffer based switch, AWG and Electronic Memory based switch, Petabit Optical Switch, AWG and Feedback Loop Buffer Loss Compensated based Switch. Switches are analyzed for Bit Error Rate (BER) and energy consumption. The power and noise analysis is performed for calculating the total power required for correct operation of switch and to determine the BER using physical layer analysis. Minimum power level is determined so that received bits are decoded correctly. Energy consumption per bit is also evaluated to identify architecture consuming less energy in the considered architectures.