Arrayed Waveguide Grating Research Articles

Wavelength-Division Multiplexing on an Etchless Lithium Niobate Integrated Platform

Arrayed waveguide gratings (AWGs) are widely used as (de)multiplexers in wavelength-division-multiplexed optical communication systems and as integrated spectrometers in optical sensing and imaging systems. Lithium niobate integrated photonics is a burgeoning field due to many excellent optical properties of lithium niobate and rapid development of wafer processing technologies. Here, we introduced a new strategy of low-loss waveguiding on an etchless lithium niobate integrated platform for realizing high-performance AWGs thereon. We experimentally demonstrated 4-, 8-, and 16-channel AWGs operating in both telecom and near-visible wavelength bands on the etchless lithium-niobate-on-insulator platform. All the channels have insertion losses below 9.1 dB and crosstalks less than −12.8 dB in the designed wavelength bands. With advantages of an ultrawide transparency window and strong electro-optic and nonlinear optical coefficients of lithium niobate, the demonstrated AWGs will find wide applications in on-chip high-capacity optical interconnects, ultrafast bioimaging, LiDAR, and astronomical spectrographs.

Precise path computation based on functional block-based disaggregation for future heterogeneous access-metro networks

Emerging 5G/6G mobile services are intended to cover a broad range of use cases, including applications requiring high bandwidth, low latency, and/or high reliability. To meet these diverse requirements, various optical network technologies and architectures, including optical node structures, transmission technologies, and virtualization technologies, have been extensively investigated. These novel technologies will be integrated to form a platform of future optical access-metro networks that support various mobile services. Such an optical access-metro platform will comprise heterogeneous node structures based on various optical functional blocks (e.g., wavelength selective switches, optical splitters, or arrayed waveguide gratings). To realize a versatile optical access-metro platform, a network resource management system that can universally handle heterogeneous node structures is indispensable. This study investigates the applicability of a functional block-based disaggregation (FBD) approach to such a resource-management system. Here, the previously proposed FBD model is extended to incorporate latency aware path computation. The results demonstrated that the FBD model could be successfully used with heterogeneous network structures, including both passive and switchable optical nodes. The precise path computation capability of the model was also demonstrated, and the scalability of the computation time was quantitatively evaluated in a parallel processing environment. Precise path computation can effectively consider both intra- and inter-node fiber connection lengths, which are useful for handling latency requirements based on an accurate representation of the propagation delay.

Demonstration of 2D beam steering using large-scale passive optical phased array enabled by multimode waveguides with reduced phase error

Optical phased arrays (OPAs) have received considerable attention as solid-state beam scanners. However, conventional OPAs that actively control the phase difference between arrays are characterized by excessive power consumption for high-precision beam emission. In this study, we fabricated an OPA comprising Bragg grating and arrayed waveguide grating (AWG). Multi-mode waveguide is used in AWG to reduce the effect of manufacturing error. This device realizes wide and high-resolution two-dimensional beam steering only by sweeping wavelength. FWHM of the emitted beam is 0.534° × 2.27°, and the steering range is 43.9° × 13.5° with 1/64 of the power consumption of conventional OPA.

Mode and orthogonal frequency division multiplexing using a single AWG-based MUX/DeMUX

An arrayed waveguide grating (AWG) configuration can simultaneously perform the optical discrete Fourier transform and multiplex and demultiplex (MUX/DeMUX) two optical modes, to optically generate/process orthogonal frequency division multiplexing (OFDM) signals in future scalable, converged two-mode optical communication systems. We use a single AWG-based MUX/DeMUX, inter-mode and intra-optical-subcarrier symbol interleaving to mitigate the mode/subcarrier crosstalk. We analyze the performance of a 2-mode × 8 optical-subcarrier × 10 Gbit/s, on-off keying (OOK), differential phase shift keying (DPSK), and differential quadrature phase shift keying (DQPSK) mode division multiplexing (MDM)-OFDM system, that can be used in high-speed, large-capacity short-range optical link, using only passive all-optical signal processing. We numerically demonstrate that it possible to achieve error-free transmission for an 8 subcarrier × 10 Gbit/s × 2 mode system, using OOK and DPSK modulation and for a 4 subcarrier × 10 Gbit/s × 2 mode system, using DQPSK modulation, using intra-optical-subcarrier symbol interleaving.

PLC-Based Arrayed Waveguide Grating Design for Fiber Bragg Grating Interrogation System.

A fiber Bragg grating (FBG) interrogator is a scientific instrument that converts the wavelength change of FBG sensors into readable electrical signals. To achieve miniaturization and integration of FBG interrogator, we designed and fabricated a 36-channel array waveguide grating (AWG) on silica-based planar lightwave circuits (PLC) as a key device in a built FBG interrogation system. It is used to achieve continuous demodulation in C-band, while maintaining high resolution. This AWG has a 1.6 nm channel spacing, 3-dB bandwidth of 1.76 nm, non-adjacent channel crosstalk of −29.76 dB, and insertion loss of 3.46 dB. The dynamic range of the FBG interrogation system we built was tested to be 1522.4–1578.4 nm, with an interrogation resolution of 1 pm and accuracy of less than 1 pm in the dynamic range of 1523.16–1523.2 nm. The test results show that the FBG interrogation technology, based on AWG, can realize FBG wavelengths accurately demodulated, which has high application value in aerospace, deep sea exploration, and environmental monitoring, as well as other fields.

Parallel arrayed waveguide grating for wavelength-mode hybrid multiplexing.

The combination of wavelength division multiplexing (WDM) and mode division multiplexing (MDM) will increase the optical communication capacity significantly. In this configuration, we need multiple WDM devices serving as the inputs of the MDM device to excite modes at all the wavelengths. However, there is still no demonstration of integrated parallel WDM devices specifically designed for wavelength-mode hybrid multiplexing. Here, we propose and demonstrate a single 2 × 8 arrayed waveguide grating (AWG) for the multiplexing of 2 linearly polarized (LP) modes at 4 wavelengths with an MDM device. This parallel AWG concept can be further extended to support more wavelengths and introduce more spatial modes for high-capacity data transmission.

Monolithically Integrated 8 × 8 Transmitter-Router Based on Tunable V-Cavity Laser Array and Cyclic Arrayed Waveguide Grating Router

A monolithic 8 × 8 transmitter-router chip fabricated on InGaAlAs-InP multi-quantum well wafer for distributed wavelength routing network in the O-band with a channel spacing of 400 GHz is experimentally demonstrated. A tunable V-cavity laser (VCL) array, a cyclic-arrayed waveguide grating router (AWGR) and a semiconductor amplifier (SOA) array are integrated using the quantum-well intermixing (QWI) technique for its fabrication simplicity and cost effectiveness. A 200 GHz-spaced compact-size VCL is demonstrated with a 27 nm tuning range and a side-mode suppression ratio (SMSR) around 40 dB using a single-electrode controlled tuning. The chip output power is 24.6 mW. Measurement results of the transmitter-router chip show that all 64 input-output combinations have cyclic response spectra. After passing through the SOA with 80 mA bias current, an output power of about 9.6 mW and optical signal-to-noise ratio (OSNR) up to 39 dB have been measured. The demonstrated transmitter-router chip is fabricated on the same quantum well structure without requiring multiple epitaxial growth and complex grating fabrication. The characteristics of multi-wavelength and multi-port transmissions enable the distributed optical routing networks with flexible bandwidth allocation, which can find wide application in datacenters and high-performance computers.

The O-band 20-channel 800 GHz Arrayed Waveguide Grating based on silica platform for 1 Tb/s or higher-speed communication system

A 20-channel 800 GHz spacing silica based arrayed waveguide grating (AWG) is designed and fabricated. We extend the wavelength allocation in IEEE 802.3bs from 8 channels to 20 channels in the O-band, which improves the transmission capacity of the chip to meet the increasing demand of network traffic. The insertion loss is less than 1.59 dB by adopting a spot-size converter (SSC). The polarization-dependent loss (PDL) is less than 0.3 dB at the center wavelength of each channel. With a flat-top of spectrum, 1 dB bandwidth is more than 2.8 nm, and the adjacent crosstalk is less than −20 dB. The transmission of 28.9 Gb/s NRZ and 57.8 Gb/s PAM4 signals in a single channel are successfully realized.

A temperature independent hybrid AWG device based on silica/pentafluorostyrene‐glycidylmethacrylate‐fluoroethylmethacrylate terpolymer overclad

The terpolymer (PFS–GMA–TFEMA) was prepared and coated on silica waveguide for polymeric optical overclad. In our study, athermal characteristics were realised by adjusting the coefficient of negative thermal expansion of the synthesised terpolymer overclad, and the positive thermo-optic coefficient of the silica thin film. The measured values were −1.11 × 10–4 /K and 0.79 × 10–5 /K (dn/dT). The thermal properties according to the temperature change indicated that the wavelength had shifted by about 0.15 nm from 20 to 90°C, with little change over 50°C. When the temperature increased, the wavelength shift of the silica/terpolymer hybrid arrayed waveguide grating was −0.002 nm/°C, compared to the 0.01 nm/°C of silica arrayed waveguide grating. Terpolymer overclad arrayed waveguide grating showed a centre wavelength loss of 5.334 dB, loss uniformity of 0.864 dB, a polarisation dependent loss of 0.162 dB, and a non-adjacent crosstalk of −31.67 dB.

Demonstration of a bi-directionally tunable arrayed waveguide grating with ultra-low thermal power using S-shaped architecture and parallel-circuit configuration.

A thermally bi-directionally tunable arrayed waveguide grating (TBDTAWG) is proposed and demonstrated on a silicon-on-insulator (SOI) platform. The device is composed of passive and active designs for realizations of an AWG and fine tuning of its filtering responses. Given that the required length difference between adjacent arrayed waveguides for the SOI platform is considerably short (∼3-5 µm) due to a high index contrast, an S-shaped architecture with a larger footprint instead of a rectangular one is employed in the AWG. Bi-directionally tunable functions, i.e., both red- and blue-shift tunable functions, can be achieved by using two triangular thermal-tuning regions with complementary phase distributions in the S-shaped architecture despite using only materials with positive thermo-optic coefficients, i.e., Si and SiO2. Measurement results illustrate that both red- or blue-shifted spectra can be achieved and a linear bi-directional shift-to-power ratio of ±30.5 nm/W as well as a wide tuning range of 8 nm can be obtained under an electrical voltage range of 0-2.5 V, showing an agreement between the measurement results and two-dimensional simulation results. This also shows the potential of the proposed TBDTAWG for automatically stabilizing the spectral responses of AWG-based (de)multiplexers for coarse or dense wavelength division multiplexing communication systems by using a feedback control circuit.

Fabry-Perot interferometric sensor demodulation system utilizing multi-peak wavelength tracking and neural network algorithm.

For FPI sensor demodulation systems to be used in actual engineering measurement, they must have high performance, low cost, stability, and scalability. Excellent performance, however, necessitates expensive equipment and advanced algorithms. This research provides a new absolute demodulation system for FPI sensors that is high-performance and cost-effective. The reflected light from the sensor was demultiplexed into distinct channels using an array waveguide grating (AWG), with the interference spectrum features change translated as the variation of the transmitted intensity in each AWG channel. This data was fed into an end-to-end neural network model, which was utilized to interrogate multiple interference peaks' absolute peak wavelengths simultaneously. This architecturally simple network model can achieve remarkable generalization capabilities without training large-scale datasets using an appropriate data augmentation strategy. Experiments show that in simultaneous multi-wavelength and cavity length interrogations, the proposed system has the precision of up to ± 14 pm and ± 0.07 µm, respectively. The interrogation resolution can theoretically reach the pm level benefit from the neural network method. Furthermore, the system's outstanding demodulation repeatability and suitability were demonstrated. The system is expected to provide a high-performance and cost-effective, reliable solution for practical engineering applications.

Ultrawide-band Low Polarization Sensitivity 3-µm SOI Arrayed Waveguide Gratings

An ultrawide-band (UWB), O- to L- band, polarization insensitive (PI) 1 × 12 100 GHz channel spacing arrayed waveguide grating (AWG) is designed and realized in 3-μm Silicon-on-Insulator (SOI) platform. PI and UWB operations are achieved by directly exploiting the UWB 3-μm PI silicon waveguide as the arrayed waveguide. The PI AWG can be employed as demultiplexer and multiplexer in photonic integrated circuits (PIC)s, such as UWB wavelength selective switches (WSS)s. Experimental results demonstrate UWB (O- to L- band) and PI 1 × 12 AWG operation with −0.82 dB to −1.52 dB insertion losses, <−35 dB average cross-talk, 0.18 dB to 1.27 dB polarization dependent loss (PDL), and 0.006 nm to 0.041 nm polarization dependent wavelength shift (PDWS). Error-free operation at 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−9</sup> BER were measured with power penalties <0.1 dB, <0.2 dB, and <0.8 dB for 10 Gb/s, 20 Gb/s and 35 Gb/s NRZ-OOK PRBS 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sup> -1 multi-band data, respectively.

CMOS compatible athermal silicon photonic filters based on hydrogenated amorphous silicon.

We report for the first time, wavelength filters with reduced thermal sensitivity, based on a combination of crystalline silicon and hydrogenated amorphous silicon (a-Si:H) waveguides, integrated on the same silicon on an insulator wafer through a Complementary Metal Oxide Semiconductor (CMOS) compatible process flow. To demonstrate the concept, we design and fabricate Mach Zehnder Interferometers (MZIs) and Arrayed Waveguide Gratings (AWGs) based on this approach, and we measure thermal drift <1[pm/°K] in MZIs and <10 [pm/°K] in AWGs at C band.

Radiation-hardened silicon photonic passive devices on a 3 µm waveguide platform under gamma and proton irradiation.

Silicon photonics is considered to be an ideal solution as optical interconnect in radiation environments. Our previous study has demonstrated experimentally that radiation responses of device are related to waveguide size, and devices with thick top silicon waveguide layers are expected to be less sensitive to irradiation. Here, we design radiation-resistant arrayed waveguide gratings and Mach-Zehnder interferometers based on silicon-on-insulator with 3 µm-thick silicon optical waveguide platform. The devices are exposed to 60Co γ-ray irradiation up to 41 Mrad(Si) and 170-keV proton irradiation with total fluences from 1×1013 to 1×1016 p/cm2 to evaluate performance after irradiation. The results show that these devices can function well and have potential application in harsh radiation environments.

Integrated scanning spectrometer with a tunable micro-ring resonator and an arrayed waveguide grating

Integrated spectrometers with both wide optical bandwidths and high spectral resolutions are required in applications such as spectral domain optical coherence tomography (SD-OCT). Here we propose a compact integrated scanning spectrometer by using a tunable micro-ring resonator (MRR) integrated with a single arrayed waveguide grating for operation in the 1265–1335-nm range. The spectral resolution of the spectrometer is determined by the quality factor of the MRR, and the optical bandwidth is defined by the free spectral range of the arrayed waveguide grating. The spectrometer is integrated with on-chip germanium photodetectors, which enable direct electrical readout. A 70-nm optical bandwidth and a 0.2-nm channel spacing enabled by scanning the MRR across one free spectral range are demonstrated, which offer a total of 350 wavelength channels with 31-kHz wavelength scanning speed. The integrated spectrometer is applied to measure different spectra and the interference signals from an SD-OCT system, which shows its great potential for future applications in sensing and imaging systems.

12 Gbit/s indoor optical wireless communication system with ultrafast beam-steering using tunable VCSEL.

Optical wireless communication (OWC) using line-of-sight connections has great application potential for indoor scenes due to its advantages of high data transmission speed and privacy. In our proposed system, we use infrared tunable vertical-cavity surface-emitting laser (VCSEL) as light source, array waveguide gratings (AWG) combined with 6 × 6 integrated optical fiber arrays as a router to realize ultrafast beam-steering and high capacity point-to-point data transmission, which makes the indoor OWC system compact, low-cost, and easy to install. The high tuning rate of VCSEL enables the channel switching to be completed within 1.7 µs. Based on the modulation format of non-return-to-zero on-off keying (NRZ-OOK), a data rate of 12 Gbit/s per channel can be realized with high sensitivity through 3.1 m free space when the detected optical power is low. The system is proved to be a flexible link with high-speed communication for mobile terminals in a limited space.

Low-Latency Optical Wireless Data-Center Networks Using Nanoseconds Semiconductor-Based Wavelength Selectors and Arrayed Waveguide Grating Router

In order to meet the massively increasing requirements of big-data applications, data centers (DCs) are key infrastructures to cope with the associated demands, such as high performance, easy scalability, low cabling complexity and low power consumption. Many research efforts have been dedicated to traditional wired data center networks (DCNs). However, DCNs’ static and rigid topology based on optical cables significantly limits their flexibility, scalability, and even reconfigurability. The limitations of this wired connection can be addressed with optical wireless technology, which avoids cable complexity problems while allowing dynamic adaption and fast reconfiguration. Here, we propose and investigate a novel optical wireless data-center network (OW-DCN) architecture based on nanoseconds semiconductor optical amplifier (SOA)-based wavelength selectors and arrayed waveguide grating router (AWGR) controlled by fast field-programmable gate array (FPGA)-based switch schedulers. The full architecture, including the design, packet-switching strategy, contention solving methodology, and reconfiguration capability, is presented and demonstrated. Dynamic switch scheduling with a FPGA-based switch scheduler processing optical label and software-defined network (SDN)-based reconfiguration were experimentally confirmed. The proposed OW-DCN was also achieved with a power penalty of less than 2 dB power penalty at BER &lt; 1 × 10−9 for a 50 Gb/s OOK transmission and packet-switching transmission.

Wavelength (DE)MUX-and-Switch Based on 5.5%-Δ-Silica PLC/Silicon Photonics Hybrid Platform

Silicon-based optical media present several desirable properties for a wide range of applications. Herein, we propose a novel hybrid integration scheme that combines a silicon photonics platform and a 5.5%--silica planar-lightwave circuit (PLC) platform. By exploiting the performance advantages of each platform, we fabricated a polarization-insensitive low-crosstalk 8 8 silicon photonics switch butt-jointed with a compact 5.5%--silica PLC-based 100-GHz 8-channel arrayed waveguide grating (AWG). The device was driven by a smartphone-sized (9 cm 13.5 cm) control board. The fabricated device exhibits a fiber-to-fiber insertion loss of 12.6 dB, an average polarization-dependent loss of less than 0.57 dB, and less than -40 dB leakage to non-target output ports. We also demonstrate two uses of the proposed device. The first is the DEMUX and Switch operation, in which the spectrally divided light by the AWG is routed to an arbitrary output port by a subsequent switch. The second is the Switch and MUX operation, in which arbitrary wavelengths from arbitrary input ports are merged by the AWG. No spectral degradation was observed in either operation. These results demonstrate the potential of the 5.5%--PLC/silicon photonics hybrid platform for compact, low-power, and fast-switching applications.

Design and fabrication of SU-8 polymer arrayed waveguide gratings based on flexible PDMS substrates.

We investigated and fabricated 1×8 and 1×16 traditional/saddle arrayed waveguide grating (AWG) wavelength division multiplexing devices on flexible substrates. The core layer was made of the negative epoxy photoresist SU-8, and polydimethylsiloxane (PDMS) material was selected for the cladding based on the high refractive index difference. A chemical modification method of PDMS was proposed to enhance the film-forming characteristics of the SU-8 core layer on PDMS substrates. After fabricating and characterizing the optical properties of the AWGs, the dimensions of the proposed 1×8 and 1×16 AWGs were 0.9×0.8cm2 and 1.1×0.9cm2, respectively. Experimental results showed that the saddle-type 1×8 and 1×16 AWGs had good signal transmission characteristics, and the insertion losses were only 5.1 dB and 6.8 dB, respectively, which were lower than those of traditional-type AWGs with the same dimensions and number of waveguides.

Analysis of the performance of an All-optical Network using Arrayed Waveguide and Fiber Bragg Grating Demultiplexers

This work aims to discuss a study of numerical simulations of the performance of arrayed waveguide grating (AWG) and fiber Bragg grating (FBG) demultiplexers in a fiber optical network in a special class of fiber denominated fiber of photonic crystal (PCF) considering the dispersive and non-linear effects. The proposed method is based on numerical simulations in a wavelength division multiplexing (WDM) network configuration in PCF. For the simulation and analysis, the commercial OptiGrating software was used, a versatile numerical tool used to model integrated devices that incorporate FBG and OptiSystem software to simulate fiber propagation with non-linear and dispersive characteristics. The analysis of the performance of the systems was done through a comparison between the values obtained in terms of Bit Error Rate (BER) and Quality Factor (Q Factor) in a dense WDM system with spacing between 50 GHz channels, and 12 Gbit/s transmission rate. The results show that the FBG demultiplexer in terms of the BER and the Q factor for the PCF was the one that obtained the best performance, when compared the FBG demultiplexer with SMF and the AWG demultiplexer obtained excellent results for both fibers.