Wavelength Multiplexing Research Articles

Metasurface Enabled Multi‐Target and Multi‐Wavelength Diffraction Neural Networks

AbstractBenefiting from low power consumption and high processing speed, there is a growing interest in diffraction neural networks (DNNs), which are typically showcased with 3D printing devices, leading to large volumes, high costs, and low levels of integration. Metasurfaces can desirably manipulate wavefronts of electromagnetic waves, providing a compact platform for mimicking DNNs with novel functions. Although multi‐wavelength and multi‐target recognition provides a richer and more detailed understanding of complex environments, existing architectures are primarily trained to classify a single target at a specific wavelength. A metasurface approach is proposed to design multiplexed DNNs that can classify multiple targets and spatial sequences across various wavelengths in multiple channels. To realize multi‐task processing, the dielectric metasurface is designed based on phase and wavelength multiplexing, which can integrate multi‐target DNNs with different tasks such as operating at distinct wavelengths and classifying diverse targets. The efficacy of this method is exemplified through the numerical simulation and experimental demonstration of recognizing a single target with two wavelengths, two targets at a single wavelength, and two targets at dual wavelengths. This compact metasurface approach enables the design of multi‐target and multi‐wavelength DNNs, opening a new window to develop massively parallel processing and versatile artificial intelligence systems.

Mid‐Infrared Single‐Photon Compressive Spectroscopy

AbstractSensitive mid‐infrared (MIR) spectroscopy plays an indispensable role in various photon‐starved conditions. However, the detection sensitivity of conventional MIR spectrometers is severely limited by excessive noises of the involved infrared sensors, especially for multi‐pixel arrays in parallel spectral acquisition. Here, an ultra‐sensitive MIR single‐pixel spectrometer is devised and implemented, which relies on high‐fidelity spectral upconversion and wavelength‐encoding compressive measurement. Specifically, a MIR nanophotonic supercontinuum from 3.1 to 3.9 µm is nonlinearly converted to the NIR band via synchronous chirped‐pulse pumping, which facilitates both the precise spectral mapping and sensitive upconversion detection. The upconverted signal is then spatially dispersed onto a programmable digital micromirror device, before being registered by a single‐element silicon detector. Consequently, the spectral information can be deciphered from the correlation between encoded patterns and recorded measurements, which results in a spectral resolution of 0.5 under an illumination flux down to 0.01 photons nm–1 pulse–1. Moreover, faithful reconstructions at sub‐Nyquist sampling rates are demonstrated using the compressive sensing algorithm, which leads to a 95% reduction in data acquisition time. The presented single‐pixel computational spectrometer features wavelength multiplexing, high throughput, and efficient sampling, which thus paves a new way for sensitive and fast spectroscopic analysis at the single‐photon level.

All-optical generation of full-range symmetry-tunable triangular-shaped pulses via wavelength multiplexing

A novel, to the best of our knowledge, all-optical approach for generating full-range symmetry-tunable triangular-shaped pulses through wavelength multiplexing is proposed and experimentally demonstrated. Two light-waves with a specified wavelength interval are injected in parallel into two commercial push–pull Mach–Zehnder modulators (MZMs) to carry the baseband radio frequency input. A tunable optical delay line (ODL) followed by one MZM is utilized to introduce the desired phase shift. By multiplexing the modulated signals carried on two wavelengths, triangular-shaped pulses can be achieved by the opto-electronic conversion. In this approach, by simply adjusting the DC bias voltages and the delay time offered by ODL, the triangular-shaped pulse with any self-defined symmetrical coefficient can be obtained. A complete theoretical analysis on the operation principle is presented and verified. The triangular-shaped pulses with full-range tunable symmetrical coefficients at the repetition rate of 5 GHz are successfully generated. This approach features all-optical architecture, ultra-wide system bandwidth, full-range tunable symmetry (0%–100%) and excellent reconfigurability, which are highly desired for the high-performance triangular-shaped pulse generator.

Inverse Design of a Wavelength (De)Multiplexer for 1.55- and 2-μm Wavebands by Using a Hybrid Analog-Digital Method

Inverse Design of a Wavelength (De)Multiplexer for 1.55- and 2-μm Wavebands by Using a Hybrid Analog-Digital Method

Multimode interference coupler based on general interference for integrated optical and quantum optic devices: a review

Integrated optics play important role in the development for optical network devices, optical processing, instrumentation and quantum information device. Here, multimode interference (MMI) coupler is one of basic component preferred for these integrated optic devices in which MMI coupler based on general interference (GIMMI) has been focused for large scale integrated optic devices because of compact size in comparison to MMI coupler based restricted interference (RIMMI). In this paper, we have reviewed different GIMMI structures reported previously. Different waveguide materials are mentioned and compared for fabrication of GIMMI device. The coupling behaviors and modal analysis of GIMMI couplers and their different tapered structures are estimated by using simple model based on sinusoidal modes showing reduced coupling lengths in down tapered structures in comparison to other structures. The excess loss, polarization dependence loss and crosstalk versus fabrication tolerances are obtained to compare their performances revealing almost same losses and fabrication tolerance. The paper reports the use of the GIMMI coupler in wavelength multiplexing, power splitting, switching, optical processing. Finally, Quantum optic application of GIMMI coupler is shown indicating high quantum fidelity of 50:50 coupling ratio.

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 >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.

Benefits of flexibility in current and future IM-DD based TDM-PON [Invited

Due to continuously emerging high bandwidth applications, research and standardization of time division multiplexed passive optical networks (TDM-PONs) have focused on increasing the peak bitrate. However, increasing the bitrate while supporting the stringent optical power budget of a PON becomes increasingly challenging because of the larger chromatic dispersion penalties as well as reduced receiver sensitivity when the bitrate of the intensity modulation with direct-detection (IM-DD) based PON is increased. Also, increasing bitrate generally causes higher power consumption, which leads to more challenging thermal designs and misalignment with environmental targets. In this paper we give an overview of flexible concepts that can help achieve the required optical power budget and support reduced power consumption of a future IM-DD based TDM-PON. We demonstrate that a flexible PON can provide an increased overall throughput or an extended reach and power budget with the use of flexible modulation formats, probabilistic and geometric shaping, and flexible rate forward error correction (FEC). Another dimension of flexibility in the form of a configurable optical distribution network (ODN) is described and its merits and challenges are discussed. Flexible concepts based on interleaving of FEC codewords can align signal processing like FEC decoding and the protocol processing closer to the user-rate of an optical network unit (ONU), which leads to reduced power consumption. Flexibility based on multiple channels based on wavelength multiplexing or spatial multiplexing enables optimization of the power consumption to the amount of traffic on the PON. Several flexible concepts have already been adopted in the PON standards. We highlight flexible gain FEC for upstream 50G PON, the transmitter dispersion eye closure (TDEC) metric, and the flexible split-ratio ODN for power saving. Flexible modulation has not been adopted yet in PON standards, but it is expected that flexibility is more and more needed to support the performance, cost effectiveness, and power conservation of future optical access systems.

Ultraviolet-visible spectroscopy with all-dielectric multi-foci dispersive metalens

Metasurfaces are a cutting-edge development in optical technology miniaturization, enabling the manipulation of light at a microscopic scale while providing unprecedented control over its intrinsic characteristics, such as amplitude, polarization, and phase. Researchers have been making significant progress in advancing and developing high-efficiency and functionally versatile metasurfaces, aiming to achieve miniaturization and overcoming the technological limitations of conventional components. This article is intended to develop a single-layered, highly transmissive all-dielectric multi-foci metalens that serves as a compact spectrometer for portable investigative measurements within the ultraviolet to the visible spectrum, especially for 290–460nm band. The proposed metalens can achieve top-notch performance by precisely mapping the wavelength information into subwavelength diffraction-limited focusing spots. This approach helps in accomplishing simultaneous spectral splitting and focusing on the same plane. The proposed metalens consists of an array of intelligently optimized nanoantennas made of a CMOS-compatible silicon nitride material. It exploits a unique phase and wavelength multiplexing strategy to create highly dispersive multi-foci metalens, making it an ideal choice for an ultra-compact, high-resolution, and dual-band meta-spectrometer. We expect our proposed framework to have numerous applications in the industrial and medical fields, enabling diagnosis, detection, and assessment within a compact platform.

Multispectral Polarization States Generation with a Single Metasurface

AbstractPolarization state generation plays an important role in optics and are applied in many fields. Multispectral polarization manipulation can increase information capacity. To meet the requirement of miniaturization and integration, it is desirable to generate multispectral polarization states with a compact optical device. a metasurface device is proposed and experimentally demonstrated, which can simultaneously realize wavelength separation and polarization generation. A geometric metasurface is used to realize the phase and wavelength multiplexing. Six polarization states with different wavelengths are generated. Customized polarization states with predesigned wavelength information can add extra degrees of freedom for carrying information, opening a new window for portable polarization optics where low‐cost and miniaturized systems are in high demand.

Dual-optical-multiplexing-based multi-image invisible visual cryptography

In earlier research, the concept of using diffractive optics to indirectly achieve invisible visual cryptography (VC) was proposed. In this approach, the extraction process does not require complex optical implementations or additional computations. However, the system’s security and the capacity still need to be improved. Correspondingly, this paper introduces a multi-image invisible VC system based on dual optical multiplexing. Under the conditions of diffraction distance multiplexing and wavelength multiplexing, the visual keys of secret images are concealed within a phase key in the Fresnel domain. This method enhances the system’s security through dual optical multiplexing and ensures a certain capacity for information concealment. Optical experiments verify that the easy extraction and the high repeatability are all obtainable in the method.

Effect of non-uniform carrier injection on two-state lasing in quantum dot microdisks with split electrical contact

In this papaer, the emission characteristics of InAs/InGaAs quantum dot (QD) microdisk lasers, of different cavity diameters, with a top split electrical contact formed using the focused ion beam technique are investigated. The dependences of the threshold currents of two-state lasing (i.e. currents corresponding to the start of the ground- and excited-state lasing) for microdisks of 24 and 28 μm diameters on the electrical contact area are presented. The contact area was found to influence the threshold currents of two-state lasing in microdisks. It is shown that a decrease in the area of the injected electrical contact leads to a decrease in the current corresponding to the start of the excited-state lasing, while the ground-state (GS) lasing threshold remains virtually unchanged. The temperature evolution of the threshold currents for two-state lasing was also studied in microdisks with different electrical contact areas. We demonstrate that the use of contacts of different areas is a method of controlling the threshold currents of two-state lasing and can be used in engineering of QD lasers intended, for example, for multi-level signal transmission with wavelength multiplexing by switching from the GS to excited-state lasing.

On-chip wavelength division multiplexing by angled multimode interferometer fabricated on erbium-doped thin film lithium niobate on insulator

Abstract Photonic-integrated circuits based on erbium-doped thin film lithium niobate on insulator has attracted broad interests with insofar various waveguide amplifiers and microlasers demonstrated. Wideband operation facilitated by the broadband absorption and emission of erbium ions necessitates the functional integration of wavelength filter and multiplexer on the same chip. Here, a low-loss wavelength division multiplexer at the resonant pumping and emission wavelengths (∼1480 nm and 1530–1560 nm) of erbium ions based on angled multimode interferometer is realized in the erbium-doped thin film lithium niobate on insulator fabricated by the photolithography assisted chemomechanical etching technique. The minimum on-chip insertion losses of the fabricated device are <0.7 dB for both wavelength ranges, and a 3-dB bandwidth of >20 nm is measured at the telecom C-band. Besides, direct visualization of the multimode interference pattern by the visible upconversion fluorescence of erbium ions compares well with the simulated light propagation in the multimode interferometer. Spectral tuning of the wavelength division multiplexer by structural design is also demonstrated and discussed.

Wavelength multiplexing system based on ring resonators

Wavelength Division Multiplexing, WDM, is a technology developed for applications in telecommunications with the purpose of combining numerous wavelength signals into one single fibre. The aim of this research is the characterization of WDM systems of ring resonators with planar optical waveguides. The optical responses for different configurations, dimensions, and materials are analysed by doing a parametric study both considering analytical expressions and a Finite Element Tool. The results are from add-drop topologies with one, two and three rings. The main difference between topologies with the same parameters is the number of resonance wavelengths, which is higher due to the increase in the number of ring-shaped waveguides. It is concluded that adjusting the rings’ dimensions, the resonant wavelengths are tuned. Furthermore, the higher the rings’ radius the lower is the free spectral range, that can take values from 40 nm to 90 nm. Then, the number of resonant peaks in a wavelength range may change. Also, 1500–5000 describes the values computed for the quality factor, whereas the full width at half maximum varies within some units of nanometres. For models with different core materials, the higher transmittances decrease with lower core refractive indexes and the resonance width increases. These are new degrees of freedom to tune the response of the device that can definitely work as optical wavelength multiplexer, having losses from 20% to 40% considering the transmitted optical power.

Simultaneous generation of wavelength multiplexing and polarization multiplexing from a wavelength-tunable ultrafast fiber laser

A wavelength-tunable mode-locked erbium-doped all-fiber laser delivering both wavelength multiplexing and polarization multiplexing asynchronous pulses is experimentally demonstrated, which is challenging in previous studies. The numerical simulations validate the experimental observations and reveal that the cavity birefringence and polarization dependent loss (PDL) induced by the wavelength division multiplexer play a significant role in the formation of different types of asynchronous pulses. Our results not only provide insights into the physical mechanism of the asynchronous pulses generation, but also offer a potential low-complexity light source for dual-comb applications.

An Analysis of Various Design Pathways Towards Multi-Terabit Photonic On-Interposer Interconnects

In the wake of dwindling Moore’s Law, to address the rapidly increasing complexity and cost of fabricating large-scale, monolithic systems-on-chip (SoCs), the industry has adopted dis-aggregation as a solution, wherein a large monolithic SoC is partitioned into multiple smaller chiplets that are then assembled into a large system-in-package (SiP) using advanced packaging substrates such as silicon interposer. For such interposer-based SiPs, there is a push to realize on-interposer inter-chiplet communication bandwidth of multi-Tb/s and end-to-end communication latency of no more than 10 ns. This push comes as the natural progression from some recent prior works on SiP design, and is driven by the proliferating bandwidth demand of modern data-intensive workloads. To meet this bandwidth and latency goal, prior works have focused on a potential solution of using the silicon photonic interposer (SiPhI) for integrating and interconnecting a large number of chiplets into an SiP. Despite the early promise, the existing designs of on-SiPhI interconnects still have to evolve by leaps and bounds to meet the goal of multi-Tb/s bandwidth. However, the possible design pathways, upon which such an evolution can be achieved, have not been explored in any prior works yet. In this paper, we have identified several design pathways that can help evolve on-SiPhI interconnects to achieve multi-Tb/s aggregate bandwidth. We perform an extensive link-level and system-level analysis in which we explore these design pathways in isolation and in different combinations of each other. From our link-level analysis, we have observed that the design pathways that simultaneously enhance the spectral range and optical power budget available for wavelength multiplexing can render aggregate bandwidth of up to 4 Tb/s per on-SiPhI link. We also show that such high-bandwidth on-SiPhI links can substantially improve the performance and energy-efficiency of the state-of-the-art CPU and GPU chiplets based SiPs.

Photothermal metasurface with polarization and wavelength multiplexing.

Controlling temperature distribution at the micro/nano-scale brings new applications in many fields such as physics, chemistry and biology. This paper proposes a photothermal metasurface that employs polarization and wavelength multiplexing to regulate various temperature distributions at the micro/nano-scale. Such a photothermal metasurface is numerically validated by the finite element method. Firstly, the inversion algorithm is used to calculate the thermal power density distribution, which is decided by a given temperature distribution. Then, based on the bottom-up design method, (a) the library of absorption cross sections of gold nanoparticles is established by resizing nanoparticles; (b) the single pixel is constructed for wavelength and polarization multiplexing; (c) the overall structure of a photothermal metasurface is optimized and established. Finally, four given temperature distributions, combining the multiplexing of two orthogonal polarizations and two wavelengths, are achieved in the same area. The simulation results well confirm the feasibility of photothermal multiplexing. Such photothermal metasurface provides solutions for flexible control of temperature distribution at the micro/nano-scale.

Multiple single-channel cryptosystem based on QZ decomposition, CMYK color space fusion and wavelength multiplexing

Multiple single-channel cryptosystem based on QZ decomposition, CMYK color space fusion and wavelength multiplexing

Asymmetric multi-image wavelength multiplexing cryptosystem using QZ algorithm and unequal modulus decomposition

An asymmetric multi-image cryptosystem based on wavelength multiplexing is proposed in this paper. Multi-image characteristic of the encryption process has been realized by the QZ synthesis process. Unequal modulus decomposition is used to make the scheme robust to any basic cryptographic attacks. The encryption process has a complex setup that involves phase retrieval algorithms but the decryption is quite simple and fast and can be realized on the hybrid system. Although the scheme is validated on grayscale multi-images, it can also process color images. Cryptosystem is exposed to statistical attacks, noise attacks, and data loss attacks, apart from basic cryptographic attacks. Simulation established the fortitude of the cryptosystem to these attacks. We also analyzed the key space and key sensitivity, and the results show that the cryptosystem has a large key space to resist any brute-force attack. Comparative analysis with similar schemes on multi-image reveals that the cryptosystem has several merits and it is secure against basic and special attacks.

Recent advances in metamaterial integrated photonics

Since the invention of the silicon subwavelength grating waveguide in 2006, subwavelength metamaterial engineering has become an essential design tool in silicon photonics. Employing well-established nanometer-scale semiconductor manufacturing techniques to create metamaterials in optical waveguides has allowed unprecedented control of the flow of light in photonic chips. This is achieved through fine-tuning of fundamental optical properties such as modal confinement, effective index, dispersion, and anisotropy, directly by lithographic imprinting of a specific subwavelength grating structure onto a nanophotonic waveguide. In parallel, low-loss mode propagation is readily obtained over a broad spectral range since the subwavelength periodicity effectively avoids losses due to spurious resonances and bandgap effects. In this review we present recent advances achieved in the surging field of metamaterial integrated photonics. After briefly introducing the fundamental concepts governing the propagation of light in periodic waveguides via Floquet–Bloch modes, we review progress in the main application areas of subwavelength nanostructures in silicon photonics, presenting the most representative devices. We specifically focus on off-chip coupling interfaces, polarization management and anisotropy engineering, spectral filtering and wavelength multiplexing, evanescent field biochemical sensing, mid-infrared photonics, and nonlinear waveguide optics and optomechanics. We also introduce a nascent research area of resonant integrated photonics leveraging Mie resonances in dielectrics for on-chip guiding of optical waves, with the first Huygens’ metawaveguide recently demonstrated. Finally, we provide a brief overview of inverse design approaches and machine-learning algorithms for on-chip optical metamaterials. In our conclusions, we summarize the key developments while highlighting the challenges and future prospects.

Entangled-Based Quantum Wavelength-Division-Multiplexing and Multiple-Access Networks.

This paper investigates the mathematical model of the quantum wavelength-division-multiplexing (WDM) network based on the entanglement distribution with the least required wavelengths and passive devices. By adequately utilizing wavelength multiplexers, demultiplexers, and star couplers, N wavelengths are enough to distribute the entanglement among each pair of N users. Moreover, the number of devices employed is reduced by substituting a waveguide grating router for multiplexers and demultiplexers. Furthermore, this study examines implementing the BBM92 quantum key distribution in an entangled-based quantum WDM network. The proposed scheme in this paper may be applied to potential applications such as teleportation in entangled-based quantum WDM networks.