Arrayed Waveguide Grating Research Articles

Mid-infrared arrayed waveguide gratings using a quantum cascade laser gain medium as core material

Mid-infrared photonics is a widely researched field with several applications, such as chemical sensing and spectroscopy. The development of photonic integrated circuits for the mid-infrared can enable the reduction in device size, weight, and power (SWaP) consumption. This paper demonstrates arrayed waveguide gratings working in the mid-infrared regime (5–5.4 µm). Our devices are fabricated on an InP-based quantum cascade laser platform with the gain medium as the waveguide core. To minimize the propagation losses caused by free carrier absorption and intersubband absorption in the unbiased QCL structure, we exposed the photonic chips to proton implantation. The performance of three sets of AWGs with different etch depths was characterized. The lowest waveguide losses were measured to be 2 dB/cm. The best performing 7×1 AWG and 13×1 AWG designs featured insertion losses of −2dB and −2.5dB, respectively. This study showcases the feasibility of applying such a platform for easy integration with active components like lasers and photodetectors, paving the path for on-chip mid-infrared applications.

Emitter design for efficient waveguide spectral lens

Abstract As an alternative to arrayed waveguide gratings (AWGs), the waveguide spectral lens (WSL) stands out with the ability to focus light in free space, thereby eliminating the need for relay optics between the chip and the camera. This becomes convenient in constructing a truly compact instrument for astronomical spectroscopic analysis. Besides dispersion and focusing, WSL offers another important function: the envelope of the diffraction orders can be manipulated via the output emitter, i.e., the waveguide array at the facet. Through careful emitter design, the diffraction efficiency can be largely improved because the side orders are well suppressed, and light is concentrated to the selected order. This feature, though particularly important for the photon-hungry astronomical application, has not been well explored in the previous works. Here, we come up with four emitter designs and evaluate their performance, including linear taper, parabolic taper, multimode interference (MMI), and slot MMI. A figure of merit (FoM) considering both diffraction efficiency and uniformity is introduced to identify the optimal structure. Experimental results agree well with the simulation and confirmed that the optimal parabolic taper can achieve a diffraction efficiency of 90.9%, making it the most attractive design. This work highlights the potential of WSLs for astronomical spectroscopy with an efficiency that rivals conventional blazed gratings. It may also inspire emitter designs for side-lobe suppression in optical phase array applications.

Federated learning-based wavelength demodulation system for multi-point distributed multi-peak FBG sensors

Machine learning-based demodulation of multi-peak fiber Bragg grating (FBG) sensors has been extensively studied, demonstrating superior performance compared to conventional algorithms because it can neglect potential physical constraints. As the number of real-world monitoring points increases, the volume of fiber-optic sensing data grows exponentially. This necessitates aggregating data from various regions (e.g., via Wi-Fi), unlike traditional single-point monitoring, which challenges server storage capacity and communication efficiency. To address these issues, this paper proposes a federated learning (FL)-based framework for efficient wavelength demodulation of multi-peak FBGs in multipoint monitoring. Specifically, an arrayed waveguide grating (AWG) with multiplexing capability is employed at different monitoring points to convert spectral features into multi-channel transmission intensities, serving as training data for local models. Subsequently, the local model parameters, trained independently at each point, are uploaded to a central server to derive the optimal global model for demodulation across different monitoring points. The proposed demodulation framework is validated through stress demodulation experiments on multi-peak FBG sensors. Experimental results indicate strong multi-peak extraction performance with a demodulation error of ±0.64 pm. Additionally, the method demonstrates excellent applicability for generating high-precision global demodulation models through multi-node cooperative work under various scenarios.

Coherent time- and wavelength-division multiplexed point-to-multipoint optical access network using low-cost DFB lasers enabled by a frequency comb

Coherent reception, along with time- and wavelength-division multiplexing (TWDM), is a promising concept to simultaneously support multiple services in future high-speed point-to-multipoint passive optical networks (PONs). The next-generation PON 2 (NG-PON2) standard describes a TWDM-PON based on IM/DD intensity modulation and direct detection (IM/DD) which employs tunable-lasers and optical filters such as tunable optical filters or cyclic arrayed-waveguide gratings. Here, we investigate what we believe to be a novel coherent TWDM-PON architecture based on a frequency comb source in the optical line terminal (OLT), and thermally-tuned distributed-feedback (DFB) lasers in the optical network units (ONUs). For downstream operation, we broadcast multiple copies of two 25 GBd dual-polarization quadrature phase shift keying (DP-QPSK) signals, resulting in a total PON downstream capacity of 200 Gbit/s. The copies of the downstream signals are spanning ±2 nm (±250 GHz). In the ONUs, we align the wavelengths of the DFB lasers, which act as local oscillators (LOs), to one of the downstream signals by a thermal heater or by changing the direct current. In upstream, the already aligned DFB lasers act as transmit lasers and the frequency comb as LO. We demonstrate TWDM upstream by emulating two ONUs with 25 GBd DP-QPSK, resulting in a total PON upstream capacity of 200 Gbit/s.

Monolithic integration of waveguide amplifiers and passive polymer photonic devices using photolithography

The monolithic integration of rare-earth-doped waveguide amplifiers with passive photonic devices has long been a subject of extensive research. Herein, we propose a method for active-passive monolithic integration based on polymer photonic integrated devices. The monolithic integration of passive devices with active waveguide amplifiers is achieved by spin-coating an active layer atop a passive polymer waveguide and subjecting specific regions of the active layer to selective photolithography. To validate the proposed monolithic integration scheme's impact on the performance of passive devices, performance tests were conducted on both passive and active-passive integrated 8-channel arrayed waveguide grating (AWG) devices. The crosstalk (CT) of the AWG devices before and after adding the active layer ranged from −12.04 dB to −14.72 dB and from −10.02 dB to −14.88 dB, respectively, with channel spacings of 9.29 nm and 8.80 nm, indicating consistent performance of the passive devices with the addition of the active layer. In a 0.5 cm-long active waveguide, internal net gain was achieved across all eight channels of the AWG, with a gain bandwidth ranging from 1518 nm to 1580 nm. Notably, an internal net gain of 9.5 dB was attained at 1527 nm. The successful integration of rare-earth-doped waveguide amplifiers with passive components on a monolithic chip has been achieved for the first time, requiring only two straightforward photolithography steps. This milestone not only preserves the inherent functionality of passive components but also enables effective signal amplification. This technological innovation holds the promise of fully harnessing the potential of rare-earth-doped waveguide amplifiers in the realm of photonic integrated circuits, thereby catalyzing significant breakthroughs and advancements in the field of optoelectronics.

Large bandwidth array waveguide grating design for FBG interrogation system

The array waveguide grating (AWG) demodulation method has been widely used in recent years. However, the resolution and total measurement range of AWG-based Fiber Bragg Grating (FBG) interrogation systems are limited by the output characteristics of AWGs. We designed and fabricated a multi-channel SiO2-based AWG as a key component of FBG Interrogation. To increase the dynamic range of demodulation, a multimode interference coupler (MMI) structure is introduced in the middle of the input waveguide and the input slab waveguide. From the simulation results, the 3-dB bandwidth of the AWG is increased from 1.04 nm to 1.86 nm. We test the performance of the interrogation system based on this AWG. The results demonstrate that the system can achieve continuous demodulation in the C-band, with an interrogation accuracy better than 20.22 pm and a wavelength resolution of 1 pm.

Dynamic capacity sharing with multi-wavelength integrated transmitters in hybrid datacenter networks

In datacenters, bursty and unevenly distributed traffic may lead to serious network performance degradation. Various methods, including reconfigurable optical circuit switching (OCS), traffic control techniques, valiant load balancing (VLB), and so on, have been proposed to solve this problem. Based on these solutions, our method makes a trade-off between cost and performance. In this paper, we propose to use multi-wavelength tunable transmitters in our previously proposed modular arrayed waveguide grating (AWG)-based interconnection network. We discuss how the multiple wavelengths can be shared in the network and then propose a computational model to study its blocking probability. Closed-form equations for low network load cases are also derived to provide the analytical expression for the blocking probability. We verify the accuracy of our computational model through simulations. Comparing the blocking probability of networks with and without multi-wavelength integrated transmitters, we show that network performance can be considerably improved after replacement. When traffic burstiness is 1.25 and traffic skewness is 0.08, the blocking probability is reduced from 0.14 to 3.60×10−3 after replacing in each sending module one fixed laser with multi-wavelength tunable transmitters with four wavelengths. Furthermore, we also discuss how different factors influence the blocking probability and the maximum load with the given network performance requirement.

Arrayed waveguide gratings (AWGs) in ZBLAN fibers for switchable dual-wavelength fiber lasers in the O- and S-band regions

Arrayed waveguide gratings (AWGs) in ZBLAN fibers for switchable dual-wavelength fiber lasers in the O- and S-band regions

Matrix analysis of high-density arrayed waveguides: Crosstalk suppression by bending

For many photonic devices, crosstalk between densely packed waveguides poses a major problem leading to unreliable or inefficient operation of the device. In this work, a general method for modeling the crosstalk, not only in straight waveguide arrays but also in curved ones, is introduced. The method is based on a matrix analysis of electromagnetic field coupling between closely spaced waveguides. As an example, we show how bending of waveguides in an array reduces the crosstalk. The approach can help overcome the crosstalk problem in a variety of photonic integrated devices, including phased waveguide arrays, arrayed waveguide gratings, optical multiplexers, and high-density interconnects between optical and electronic components. Published by the American Physical Society 2024

Research on flexible and fast tunable laser in coherent optical communications

A flexible and fast tunable laser based on hybrid integration is proposed, which can realize single and multi-wavelength reconfigurable output by controlling the on or off of semiconductor optical amplifiers (SOAs) array in combination with a tunable arrayed waveguide grating (AWG). The wavelength switching time achieves <0.8 ns. The stable output power of the tunable laser is >16 dBm with >70 dB side mode suppression ratio (SMSR) and 6.4 nm tunability. The designed laser exhibits narrow linewidths down to 1 kHz and longitudinal mode spacing of 0.8 nm, which is suitable for ITU-T standards and the output power meets the requirements of coherent optical communications. A broadened spot-size converter (SSC) for bi-directional transmission is designed and implemented with a power coupling efficiency about 0.93 and an optical bandwidth of more than 200 nm. Demonstration of the 100 Gb/s quadrature phase shift keying (QPSK) self-homodyne coherent optical transmission based on designed laser is achieved.

Accelerating Convolutional Processing by Harnessing Channel Shifts in Arrayed Waveguide Gratings

AbstractConvolutional neural networks are a powerful category of artificial neural networks that can extract features from raw data to provide greatly reduced parametric complexity and enhance pattern recognition and the accuracy of prediction. Optical neural networks offer the promise of dramatically accelerating computing speed while maintaining low power consumption even when using high‐speed data streams running at hundreds of gigabit/s. Here, we propose an optical convolutional processor (CP) that leverages the spectral response of an arrayed waveguide grating (AWG) to enhance convolution speed by eliminating the need for repetitive element‐wise multiplication. Our design features a balanced AWG configuration, enabling both positive and negative weightings essential for convolutional kernels. A proof‐of‐concept demonstration of an 8‐bit resolution processor is experimentally implemented using a pair of AWGs with a broadband Mach–Zehnder interferometer (MZI) designed to achieve uniform weighting across the whole spectrum. Experimental results demonstrate the CP's effectiveness in edge detection and achieved 96% accuracy in a convolutional neural network for MNIST recognition. This approach can be extended to other common operations, such as pooling and deconvolution in Generative Adversarial Networks. It is also scalable to more complex networks, making it suitable for applications like autonomous vehicles and real‐time video recognition.

Compact Silicon-Arrayed Waveguide Gratings with Low Nonuniformity.

Array waveguide gratings (AWGs) have been widely used in multi-purpose and multi-functional integrated photonic devices for Microwave photonics (MWP) systems. In this paper, we compare the effect of output waveguide configurations on the performance of AWGs. The AWG with an output waveguide converging on the grating circle had larger crosstalk and lower nonuniformity. We also fabricated a 1 × 8 AWG with an output waveguide converging onto the SOI's grating circle, whose central operation wavelength was around 1550 nm. The fabricated AWG has a chip size of 500 μm × 450 μm. Experimental results show that the adjacent channel crosstalk is -12.68 dB. The center channel insertion loss, as well as 3 dB bandwidth, are 4.18 dB and 1.22 nm at 1550 nm, respectively. The nonuniformity is about 0.494 dB, and the free spectral range is 19.4 nm. The proposed AWG is expected to play an important role in future MWP systems given its good nonuniformity and insertion loss level.

Astrophotonics-current capabilities and the road ahead [Invited

Astrophotonics represents a cutting-edge approach in observational astronomy. This paper explores the significant advancements and potential applications of astrophotonics, highlighting how photonic technologies stand to revolutionize astronomical instrumentation. Key areas of focus include photonic wavefront sensing and imaging, photonic interferometry and nulling, advanced chip fabrication methods, and the integration of spectroscopy and sensing onto photonic chips. The role of single-mode fibers in reducing modal noise, and the development of photonic integral field units (IFUs) and arrayed waveguide gratings (AWGs) for high resolution, spatially resolved spectroscopy will be examined. As part of the Sydney regional-focus issue, this review aims to detail some of the current technological achievements in this field as well as to discuss the future trajectory of astrophotonics, underscoring its potential to unlock important new astronomical discoveries.

Frequency Octupling Radio over Fiber System with Multiple Remote Antenna Units

Bidirectional radio over fiber (RoF) transmission to multiple remote antenna units (RAUs) with frequency octupling is proposed in this paper. The proposed RoF system uses a dual-port Mach-Zehnder modulator (DP-MZM) and an arrayed waveguide grating (AWG) to generate millimeter-wave (mm-wave) to four different RAUs. Bit Error Rate (BER) and received optical power are key parameters used to measure the performance of the system. From the simulation results, it is shown that the proposed system achieves an acceptable performance a fiber distance of 50 km with a BER of 10-12. Furthermore, the results indicate that the dispersion-induced power penalties for both uplink and downlink transmission of all RAUs are less than 1 dB. In summary, the proposed system simplifies the RoF system by reusing wavelengths and utilizing low RoF frequency through the frequency-octupling technique.

Anisotropy-free arrayed waveguide gratings on X-cut thin film lithium niobate platform of in-plane anisotropy

Arrayed waveguide grating is a versatile and scalable integrated light dispersion device, which has been widely adopted in various applications, including, optical communications and optical sensing. Recently, thin-film lithium niobate emerges as a promising photonic integration platform, due to its ability of shrinking largely the size of typical lithium niobate based optical devices. This would also enable multifunctional photonic integrated chips on a single lithium niobate substrate. However, due to the intrinsic anisotropy of the material, to build an arrayed waveguide grating on X-cut thin-film lithium niobate has never been successful. Here, a universal strategy to design anisotropy-free dispersive components on a uniaxial in-plane anisotropic photonic integration platform is introduced for the first time. This leads to the first implementation of arrayed waveguide gratings on X-cut thin-film lithium niobate with various configurations and high-performances. The best insertion loss of 2.4 dB and crosstalk of −24.1 dB is obtained for the fabricated arrayed waveguide grating devices. Applications of such arrayed waveguide gratings as a wavelength router and in a wavelength-division multiplexed optical transmission system are also demonstrated.

Integrated 800 Gb/s O-band WDM optical transceiver enabled by hybrid InP-polymer photonic integration

We propose and demonstrate a novel O-band wavelength division multiplexing (WDM) optical transceiver enabled by the hybrid photonic integration of indium phosphide (InP) components into a polymer-based photonic motherboard called PolyBoard. The optical engine hosts an eight-fold InP electro-absorption modulated laser (EML) array at the transmitter part exhibiting &gt;35GHz electro-optical bandwidth and an eight-fold InP photodiode (PD) array at the receiver part with 50 GHz bandwidth, butt-end coupled to the PolyBoard motherboard, which accommodates passive arrayed waveguide gratings (AWGs) at the transmitter and receiver sides, responsible for performing the wavelength multiplexing and demultiplexing functionalities, respectively. What we believe to be a novel thin-film-based O-band half-wave plate is placed at the receiver side AWG, ensuring the polarization insensitivity of the prototype. The optical engine’s design is discussed in the manuscript, demonstrating experimental results from its static and dynamic evaluation. Individual characterization of the transmitter and receiver sides of the optical engine is presented before evaluating the optical engine as a whole in a loopback configuration. The obtained results underscore the potential of the proposed hybrid photonic integrated transceiver for supporting 800 Gb/s capacity in intra-datacenter optical interconnects for transmission distances up to 2 km.

Bidirectional passive optical interconnected data center

AbstractA novel bidirectional passive optical interconnection is proposed for data centers (DCs). The interconnection is based on a coupler of arrayed waveguide grating. The nodes distribute on both sides and simultaneously, bidirectional transmission is allowed. Compared with the traditional passive optical interconnected DCs, the scale is doubled, and the throughput is increased. The crosstalk in simultaneously bidirectional transmission is tested and the results show it is very little. The transmission between the nodes on the same side is relayed by one node on the other side. Some relay methods are proposed, and the relay efficiency is evaluated.

Silicon monolithic wavelength selective switch utilizing arrayed waveguide gratings and Bragg grating filters

Silicon monolithic wavelength selective switch utilizing arrayed waveguide gratings and Bragg grating filters

A flat-top arrayed waveguide grating base on cascading ‘A’ shape multimode interference

Today, large bandwidth is required to increase data transmission speeds, this requires an optimized design of the photonic devices. To achieve increasing bandwidth in the wavelength division multiplexing device’s arrayed waveguide grating (AWG). We have cascaded a special ‘A’ shape multimode interference (MMI) structure at the end of the input waveguide. ‘A’ shape structure is better able to get the ideal light field distribution, making the flattening effect more perfect. The ‘A’ shape MMI is designed by the linear spreading equation, the structure of the MMI can be easily and conveniently manufactured in a practical application. Simulation results show that increasing the 1 dB bandwidth to 0.7 nm and the 3 dB bandwidth to 1.6 ± 0.2 nm, the insertion loss is measured at 3.5 ± 0.3 dB, and the channel crosstalk is below −30 dB. It paves the path to achieve increasing bandwidth of AWG.

Efficient ultra-broadband low-resolution astrophotonic spectrographs

Broadband low-resolution near-infrared spectrographs in a compact form are crucial for ground- and space-based astronomy and other fields of sensing. Astronomical spectroscopy poses stringent requirements including high efficiency, broad band operation (&gt; 300 nm), and in some cases, polarization insensitivity. We present and compare experimental results from the design, fabrication, and characterization of broadband (1200 - 1650 nm) arrayed waveguide grating (AWG) spectrographs built using the two most promising low-loss platforms - Si3N4 (rectangular waveguides) and doped-SiO2 (square waveguides). These AWGs have a resolving power (λ/Δλ) of ∼200, free spectral range of ∼ 200-350 nm, and a small footprint of ∼ 50-100 mm2. The peak overall (fiber-chip-fiber) efficiency of the doped-SiO2 AWG was ∼ 79% (1 dB), and it exhibited a negligible polarization-dependent shift compared to the channel spacing. For Si3N4 AWGs, the peak overall efficiency in TE mode was ∼ 50% (3 dB), and the main loss component was found to be fiber-to-chip coupling losses. These broadband AWGs are key to enabling compact integrations such as multi-object spectrographs or dispersion back-ends for other astrophotonic devices such as photonic lanterns or nulling interferometers.