Light In Waveguide Research Articles

Information processing at the speed of light.

In recent years, quantum computing has made significant strides, particularly in light-based technology. The introduction of quantum photonic chips has ushered in an era marked by scalability, stability, and cost-effectiveness, paving the way for innovative possibilities within compact footprints. This article provides a comprehensive exploration of photonic quantum computing, covering key aspects such as encoding information in photons, the merits of photonic qubits, and essential photonic device components including light squeezers, quantum light sources, interferometers, photodetectors, and waveguides. The article also examines photonic quantum communication and internet, and its implications for secure systems, detailing implementations such as quantum key distribution and long-distance communication. Emerging trends in quantum communication and essential reconfigurable elements for advancing photonic quantum internet are discussed. The review further navigates the path towards establishing scalable and fault-tolerant photonic quantum computers, highlighting quantum computational advantages achieved using photons. Additionally, the discussion extends to programmable photonic circuits, integrated photonics and transformative applications. Lastly, the review addresses prospects, implications, and challenges in photonic quantum computing, offering valuable insights into current advancements and promising future directions in this technology.

Cost-effective gaze tracking system based on polymer fiber specklegrams.

Gaze tracking technology has a wide range of applications in the fields of VR/AR glasses. In this paper, a plastic optical fiber (POF) is used as a light transmission waveguide to transmit the light reflected from the eye to the outside of the device for processing, thereby eliminating the need for in-device camera installations. By processing two fan-shaped surfaces on the POF at a 45° angle relative to the vertical direction, the POF gains the ability to couple light from the side. The reflected light of the eye can be transmitted to the outside of the device through the POF. The specklegram corresponding to 76 different gaze directions is classified by SE-Resnet18, and the accuracy reached 96.9%. The gaze tracking system is low cost and simple in structure and has potential application in fields such as AR glasses, human-computer interaction (HCI), and medical diagnosis.

AC‐Driven Plasmon Waveguide Integrated Electroluminescent Device

AbstractPhotonic elements have greater information‐carrying capabilities compared to electronic components, making the development of high‐speed, chip‐integrated optical communication devices crucial for addressing interconnect bottlenecks in high‐speed computing systems. Significant progress has been made in studying light sources and their transmission. Despite these advancements, achieving a satisfactory integration of photonic circuits with both light source and optical waveguide functions has remained a challenge. Here, a silver nanowire (AgNW) waveguide‐integrated light source is demonstrated driven by alternating current (AC) voltage. AgNW functions as both the electrode and waveguide to simplify the device structure, and the 2D transition metal dichalcogenides (TMDs) monolayer acts as the gain media in device. The electroluminescence (EL) can be tunably modulated via adjusting the frequency and voltage of the AC in this device, and it is also successfully coupled into the waveguide with its transmission distance up to 25 µm. The experiments of electroluminescence and waveguide transmission of different materials and their interlayer excitons have made a preliminary exploration of multiple wavelength transmission. It provides a new research platform forward in the development of chip‐integrated optical communication devices, thereby hopefully addressing the interconnect bottleneck and unlocking the potential for enhanced performance and efficiency in high‐speed computing systems.

Postmelting Encapsulation of Glass Microwires for Multipath Light Waveguiding within Phosphate Glasses.

Glass waveguides are the fundamental component of advanced photonic circuits and play a pivotal role in diverse applications, including quantum information processing, light generation, imaging, data storage, and sensing platforms. Up to date, the fabrication of glass waveguides relies mainly on demanding chemical processes or on the employment of expensive ultrafast laser equipment. In this work, we demonstrate an advanced, simple, low-temperature, postmelting encapsulation procedure for the development of glass waveguides. Specifically, silver iodide phosphate glass microwires (MWs) are drawn from splat-quenched glasses. These MWs are then incorporated in a controlled manner within transparent silver phosphate glass matrices. The judicious selection of glass compositions ensures that the refractive index of the host phosphate glass is lower than that of the embedded MWs. This facilitates the propagation of light inside the encapsulated higher refractive index MWs, leading to the facile development of waveguides. Importantly, we substantially enhance the light transmission within the MWs by leveraging the plasmon resonance effects due to the presence of silver nanoparticles spontaneously generated owing to the silver iodide phosphate glass composition. Employing this innovative approach, we have successfully engineered waveguide devices incorporating either one or two MWs. Remarkably, the dual MW devices are capable of transmitting light of different colors and in multipath direction, rendering the developed waveguides outstanding candidates for extending the functionalities of diverse photonic and optoelectronic circuits, as well as in intelligent signaling applications in smart glass technologies.

Visualization of Microcapillary Tips Using Waveguided Light.

The microcapillary, a glass tube with a nano/micrometer scale aperture, is used for manipulating small objects across diverse disciplines. A primary concern in using the microcapillary involves tip breakage upon contact. Here, we report a method for visualizing the microcapillary tip, enabling precise and instant determination of its contact with other objects. Illumination directed to the back aperture of the microcapillary induces waveguiding through the glass wall, enabling the visualization of the tip through scattering. We demonstrate that the tip scattering is sensitive to contact with an adjacent object owing to the near-field interaction of the waveguided light, providing a clear distinction between the contact and noncontact states. The key advantage of our method encompasses its minimal influence, irrespective of conductivity, and applicability to nanoscale systems. The versatility of our method is shown by the application to a wide range of tip diameters, various substrate and in-filling materials.

Exploring high-performance photonic crystal slow light waveguides through deep reinforcement learning

Supervised deep learning is not really suitable for automatic inverse design of photonic crystal waveguides. There are three reasons for this:(1) Pre-training of the network requires a large number of datasets, which leads to a lot of time spent in the physical simulation process. (2) The one-to-many mapping problem often arises during the reverse design process. (3) It is difficult to realize the inverse design of photonic structures beyond the performance of the dataset. These problems can be well addressed by deep reinforcement learning (DRL). Here, deep reinforcement learning is proposed for the first time for the design of complex slow-light photonic crystal waveguides. The design using DRL took less than 72 h to obtain a photonic crystal waveguide with a normalized delay bandwidth product of 0.449 and group index of 48.72. By increasing the scaling factor of bandwidth in the reward function to 0.25, the bandwidth value of the optimized slow-light waveguide increases to 50.01 nm with an NDBP value of 0.39. The slow-light performance of both structures is verified by FDTD. In addition, the NDBP value is further optimized to 0.46 if the size of the structural parameters is not constrained. Compared with deep learning, DRL can improve the sampling efficiency by more than an order of magnitude and is not plagued by the three problems mentioned above. This work confirms the effectiveness of DRL in the inverse design of energy band engineering. DRL can be widely used in the optimization of energy band related performance.

Violation of Bell inequality by photon scattering on a two-level emitter

Entanglement, the non-local correlations present in multipartite quantum systems, is a key resource for quantum technologies. It is therefore a major priority to develop simple and energy-efficient methods for generating high-fidelity entangled states. In the case of light, entanglement can be realized by interactions with matter but the required nonlinear interaction is often impractically weak. Here we show how a single two-level emitter deterministically coupled to light in a nanophotonic waveguide can be used to realize photonic quantum entanglement by excitation at the single-photon level. Efficient optical coupling enables mediation of two-photon interactions by the emitter, creating a strong nonlinearity that leads to entanglement. We experimentally verify energy–time entanglement by violating a Bell inequality in an interferometric measurement of the two-photon scattering response. The on-chip two-level emitter acts as a passive scatterer, so that no advanced spin control is required. As such, our method may provide a more efficient approach to synthesizing photonic entangled states for quantum simulators or metrology.

Battery-free optoelectronic patch for photodynamic and light therapies in treating bacteria-infected wounds

Light therapy is an effective approach for the treatment of a variety of challenging dermatological conditions. In contrast to existing methods involving high doses and large areas of illumination, alternative strategies based on wearable designs that utilize a low light dose over an extended period provide a precise and convenient treatment. In this study, we present a battery-free, skin-integrated optoelectronic patch that incorporates a coil-powered circuit, an array of microscale violet and red light emitting diodes (LEDs), and polymer microneedles (MNs) loaded with 5-aminolevulinic acid (5-ALA). These polymer MNs, based on the biodegradable composite materials of polyvinyl alcohol (PVA) and hyaluronic acid (HA), serve as light waveguides for optical access and a medium for drug release into deeper skin layers. Unlike conventional clinical photomedical appliances with a rigid and fixed light source, this flexible design allows for a conformable light source that can be applied directly to the skin. In animal models with bacterial-infected wounds, the experimental group with the combination treatment of metronomic photodynamic and light therapies reduced 2.48 log10 CFU mL−1 in bactericidal level compared to the control group, indicating an effective anti-infective response. Furthermore, post-treatment analysis revealed the activation of proregenerative genes in monocyte and macrophage cell populations, suggesting enhanced tissue regeneration, neovascularization, and dermal recovery. Overall, this optoelectronic patch design broadens the scope for targeting deep skin lesions, and provides an alternative with the functionality of standard clinical light therapy methods.

Molecular templating of layered halide perovskite nanowires.

Layered metal-halide perovskites, or two-dimensional perovskites, can be synthesized in solution, and their optical and electronic properties can be tuned by changing their composition. We report a molecular templating method that restricted crystal growth along all crystallographic directions except for [110] and promoted one-dimensional growth. Our approach is widely applicable to synthesize a range of high-quality layered perovskite nanowires with large aspect ratios and tunable organic-inorganic chemical compositions. These nanowires form exceptionally well-defined and flexible cavities that exhibited a wide range of unusual optical properties beyond those of conventional perovskite nanowires. We observed anisotropic emission polarization, low-loss waveguiding (below 3 decibels per millimeter), and efficient low-threshold light amplification (below 20 microjoules per square centimeter).

Broadband near-infrared emission in silicon waveguides

Silicon photonic integrated circuit foundries enable wafer-level fabrication of entire electro-optic systems-on-a-chip for applications ranging from datacommunication to lidar to chemical sensing. However, silicon’s indirect bandgap has so far prevented its use as an on-chip optical source for these systems. Here, we describe a fullyintegrated broadband silicon waveguide light source fabricated in a state-of-the-art 300-mm foundry. A reverse-biased p-i-n diode in a silicon waveguide emits broadband near-infrared optical radiation directly into the waveguide mode, resulting in nanowatts of guided optical power from a few milliamps of electrical current. We develop a one-dimensional Planck radiation model for intraband emission from hot carriers to theoretically describe the emission. The brightness of this radiation is demonstrated by using it for broadband characterization of photonic components including Mach-Zehnder interferometers and lattice filters, and for waveguide infrared absorption spectroscopy of liquid-phase analytes. This broadband silicon-based source can be directly integrated with waveguides and photodetectors with no change to existing foundry processes and is expected to find immediate application in optical systems-on-a-chip for metrology, spectroscopy, and sensing.

Non-resonant Bragg scattering four-wave mixing at near-visible wavelengths in low-confinement silicon nitride waveguides.

Quantum state coherent frequency conversion processes-such as Bragg-scattering four-wave mixing (BSFWM)-hold promise as a flexible technique for networking heterogeneous and distant quantum systems. In this Letter, we demonstrate BSFWM within an extended (1.2-m) low-confinement silicon nitride waveguide and show that this system has the potential for near-unity frequency conversion in visible and near-visible wavelength ranges. Using sensitive classical heterodyne laser spectroscopy at low optical powers, we characterize the Kerr coefficient (∼1.55 W-1m-1) and linear propagation loss (∼0.0175 dB/cm) of this non-resonant waveguide system, revealing a record-high nonlinear figure of merit (NFM = γ/α ≈ 3.85 W-1) for BSFWM of near-visible light in non-resonant silicon nitride waveguides. We predict how, at high yet achievable on-chip optical powers, this NFM would yield a comparatively large frequency conversion efficiency, opening the door to near-unity flexible frequency conversion without cavity enhancement and resulting bandwidth constraints.

Nonvolatile multilevel adjustable optical switch based on plasmonic slot waveguide and GST segmented structure

Optical computing has gradually demonstrated its efficiency in handling increasingly complex computational demands, attracting widespread attention. Optical switches can effectively control and modulate optical signals, providing flexibility and efficiency for optical computing systems. However, traditional optical switches face performance issues such as power consumption, switching speed, and compactness, severely limiting the implementation of large-scale photonic integrated circuits and optical neural networks. This paper proposes an innovative design structure for a non-volatile multi-level adjustable optical switch by combining a plasmonic slot waveguide with segmented phase-change materials. Modulation of waveguide light transmission is achieved by adjusting the phase state of Ge2Sb2Te5(GST). At a wavelength of 1550 nm, a low insertion loss of 0.5dB has been achieved, with approximately an 85% difference in optical transmittance between amorphous state (aGST) and crystalline state (cGST). The high transmittance difference contributes to achieving a wide range of weight variations and supports precise weight updates. Based on this design, we successfully implemented a handwritten digit recognition task with an accuracy of 95%, laying the foundation for future more efficient memory computing neural morphic networks.

A CsPbBr3/CdS-based hybrid bidirectional optoelectronic device with light-emitting, modulation, and detection functions

Optoelectronic integrated circuits, with a broad photonic transportation bandwidth, have emerged as a promising solution to fulfill the escalating demands for high-volume information transportation and processing. However, challenges persist in developing optoelectronic integrated circuits based on low-dimensional nanostructures, including limited integration density and high energy consumption. Here, we demonstrate a bidirectional optoelectronic device by integrating a light-emitting/harvesting CsPbBr3 nanoplate with a waveguiding/modulating/detecting CdS nanobelt. By configuring the CsPbBr3 nanoplate in a Schottky-type device structure with a metal electrode, bright electroluminescence was attained at a bias voltage of 18 V. Thanks to the electric field-tuned phonon-coupling effect, the waveguided light in the CdS nanobelt exhibited a high modulation depth of up to 94%, rendering it an excellent building block as optical modulators and optical switches. Moreover, the integrated nanostructure device showcased functionality in the photodetection mode. The proposed device architecture holds promise for broader applications, potentially extending to other perovskite-coupled II–VI semiconductor optoelectronic integrated circuits for expanding integration capacity and enhancing optoelectronic performance.

Continuous-wave second-harmonic generation in the far-UVC pumped by a blue laser diode

Far-UVC light in the wavelength range of 200–230 nm has attracted renewed interest because of its safety for human exposure and effectiveness in inactivating pathogens. Here we present a compact solid-state far-UVC laser source based on second-harmonic generation (SHG) using a low-cost commercially-available blue laser diode pump. Leveraging the high intensity of light in a nanophotonic waveguide and heterogeneous integration, our approach achieves Cherenkov phase-matching across a bonded interface consisting of a silicon nitride (SiN) waveguide and a beta barium borate (BBO) nonlinear crystal. Through systematic investigations of waveguide dimensions and pump power, we analyze the dependencies of Cherenkov emission angle, conversion efficiency, and output power. Experimental results confirm the feasibility of generating far-UVC, paving the way for mass production in a compact form factor. This solid-state far-UVC laser source shows significant potential for applications in human-safe disinfection, non-line-of-sight free-space communication, and deep-UV Raman spectroscopy.

Efficient light couplers to topological slow light waveguides in valley photonic crystals.

We numerically and experimentally demonstrate efficient light couplers between topological slow light waveguides in valley photonic crystals (VPhCs) and wire waveguides. By numerical simulations, we obtained a high coupling efficiency of -0.84 dB/coupler on average in the slow light regime of a group index ng = 10 - 30. Experimentally, we fabricated the couplers in a Si slab and measured the transmitted power of the devices. We realized a high coupling efficiency of approximately -1.2 dB/coupler in the slow light region of ng = 10 - 30, which is close to the result from the numerical simulations. These demonstrations will lay the groundwork for low-loss photonic integrated circuits using topological slow light waveguides.

Systematic design of a robust half-W1 photonic crystal waveguide for interfacing slow light and trapped cold atoms

Novel platforms interfacing trapped cold atoms and guided light in nanoscale waveguides are a promising route to achieve a regime of strong coupling between light and atoms in single pass, with applications to quantum non-linear optics and quantum simulation. A strong challenge for the experimental development of this emerging waveguide-QED field of research is to combine facilitated optical access for atom transport, atom trapping via guided modes and robustness to inherent nanofabrication imperfections. In this endeavor, here we propose to interface Rubidium atoms with a photonic-crystal waveguide based on a large-index GaInP slab. With a specifically tailored half-W1 design, we show that a large chiral coupling to the waveguide can be obtained and guided modes can be used to form two-color dipole traps for atoms down to 115 nm from the edge of the structure. This optimized device should greatly improve the level of experimental control and facilitate the atom integration.

Enabling Waveguide Optics in Rhombohedral-Stacked Transition Metal Dichalcogenides with Laser-Patterned Grating Couplers.

Waveguides play a key role in the implementation of on-chip optical elements and, therefore, lie at the heart of integrated photonics. To add the functionalities of layered materials to existing technologies, dedicated fabrication protocols are required. Here, we build on laser writing to pattern grating structures into bulk noncentrosymmetric transition metal dichalcogenides with grooves as sharp as 250 nm. Using thin flakes of 3R-MoS2 that act as waveguides for near-infrared light, we demonstrate the functionality of the grating couplers with two complementary experiments: first, nano-optical imaging is used to visualize transverse electric and magnetic modes, whose directional outcoupling is captured by finite element simulations. Second, waveguide second-harmonic generation is demonstrated by grating-coupling femtosecond pulses into the slabs in which the radiation partially undergoes frequency doubling throughout the propagation. Our work provides a straightforward strategy for laser patterning of van der Waals crystals, demonstrates the feasibility of compact frequency converters, and examines the tuning knobs that enable optimized coupling into layered waveguides.

Ultra-compact electro-optic phase modulator based on a lithium niobate topological slow light waveguide.

Electro-optic modulators (EOMs) are essential devices of optical communications and quantum computing systems. In particular, ultra-compact EOMs are necessary for highly integrated photonic chips. Thin film lithium niobate materials are a promising platform for designing highly efficient EOMs. However, EOMs based on conventional waveguide structures are at a millimeter scale and challenging to scale down further, greatly hindering the capability of on-chip integration. Here, we design an EOM based on lithium niobate valley photonic crystal (VPC) structures for the first time. Due to the high effective refractive index introduced by the strong slow light effect, the EOM can achieve an ultra-compact size of 4 μm×14 μm with a half-wave voltage of 1.4 V. The EOM has a high transmittance of 0.87 in the 1068 nm because of the unique spin-valley locking effect in VPC structures. The design is fully compatible with current nanofabrication technology and immune to fabrication defects. Therefore, it opens a new possibility in designing lithium niobate electro-optic modulators and will find broad applications in optical communication and quantum photonic devices.

Low-loss integrated dynamic polarization controller based on silicon photonics

<sec>A dynamic polarization controller (DPC) is an important component in fiber optic communication, optical imaging, and quantum technologies. The DPC can transform any input state of polarization (SOP) into any desired SOP to overcome polarization-related impairments resulting from high internally and externally induced birefringence. In this work, a low-loss silicon photonics-integrated DPC is designed and demonstrated experimentally. The whole chip is fabricated by using industry-standard silicon-on-insulator technology. Using the edge-coupling method, the coupler loss is reduced to less than 2 dB, and the total loss of DPC is reduced to 5.7 dB. Using a variable-step simulated annealing method, for a low-noise photodetector and high-static-extinction-ratio device, a dynamic polarization extinction ratio can reach more than 30 dB. The size of the DPC on the chip is 5.20 mm × 0.12 mm × 0.80 mm.</sec><sec>The DPC utilizes a 0°/45°/0°/45° structure, which can realize arbitrary polarization-based coordinate conversion with endless polarization control. The 0° and 45° transform structures and matrices are presented, and the principle of the 0° and 45° structures is explained in detail by using the Poincaré sphere.</sec><sec>A simulation using Lumerical is conducted to optimize the polarization rotator-splitter, which can transform the TM<sub>0</sub> mode light in one waveguide into the TE<sub>0</sub> mode light in the other waveguide while the TE<sub>0</sub> mode light in one waveguide remains unchanged. Based on the optimized structure, the static polarization extinction ratio of DPC can be measured to be a value greater than 40 dB.</sec><sec>The thermal phase shift (TPS) is characterized by using a Mach–Zehnder modulator. The length of the TPS is 400 μm, and the resistance of the metal heater is 2.00 kΩ. The maximum power consumed by the four TPSs is a total of 0.2 W. The modulation bandwidth of the DPC designed by our group is approximately 30 kHz. By considering an applied voltage of 5.6 V in the case of the TPS, the bandwidth–voltage product is 5.6 × 30 = 168 kHz·V.</sec><sec>To optimize the DPC parameters, such as the step length, electronic noise, and static polarization extinction ratio, numerical simulation results of the simulated annealing approach are analyzed in detail.</sec><sec>In conclusion, a low-loss silicon photonics-integrated DPC is designed and demonstrated experimentally. A dynamic polarization extinction ratio is obtained to be greater than 30 dB by using the variable-step simulated annealing method. The DPC is expected to be utilized in fiber or quantum communication systems to minimize size and further decrease costs.</sec>

Parity-time symmetry characterization and dynamics of periodically modulated four-channel optical waveguides

The control of parity-time (PT) symmetry in cosmic-time PT symmetry system is of great significance, but the experimental realization of such an optical configuration using current technology faces enormous challenges. On the contrary, the periodic modulation method is a more feasible alternative. It is worth noting that periodic modulation in optical system is mainly performed through the cyclic change of complex refractive index materials. Unlike the traditional method of aligning periodically modulated waveguides in parallel to gain-dissipative waveguides to satisfy PT symmetry, an innovative physical model introduced in this work, features the cross-placement of these waveguides, marking it the first instance to use this configuration to manipulate PT symmetry. In this work, the influence of periodic modulation on the energy spectrum of the system in the high-frequency approximation is studied, and the dynamical evolution of light in a non-Hermitian four-channel optical waveguide is elucidated through a synergistic method of combining analytical method and numerical method. Adjusting the modulation parameter <i>A/ω</i> reveals a dual capability: it modulates the range of the real energy spectrum and precisely controls the PT symmetry of the system. Notably, at <i>A/ω</i>=0, this structure exhibits a completely real energy spectrum, which is different from the traditional parallel four-channel waveguide configuration. Furthermore, as <i>A/ω</i> varies from 0 to 2.4, the relative intensity and optical periodicity in each waveguide exhibit enhanced stability compared with their traditionally arranged counterparts. Furthermore, our examination of PT symmetry’s effect on light tunneling dynamics in individual waveguide reveals that in the unbroken PT symmetry phase, light oscillates periodically between waveguides, whereas in the broken PT symmetry phase, light propagation in each waveguide becomes stable. In the presence of waveguide coupling, it is observed that each waveguide in the system can obtain steady-state light regardless of the initial light injection point. Furthermore, under weak coupling between the gain-dissipative two-channel waveguide and the neutral waveguide, light, regardless of its entry point, will localize in the gain waveguide with propagation distance, disappear from other waveguides, and ultimately reach a steady-state configuration. The findings reveal that unlike the scenario of traditional four-channel optical waveguide system, the periodic modulation not only narrows the range of existence for the fully real energy spectrum but also enables its earlier observation. Furthermore, the relative light intensity and optical periodicity in the four-channel waveguide exhibit greater stability against variations of modulation parameters. Hence, this theoretical exploration not only profoundly summarizes the universal principle of PT-symmetric tetramers, but also elucidates that spontaneous PT symmetry breaking greatly changes the optical transmission characteristics, transforming periodic light propagation into steady-state illumination, and providing an enhanced and more robust configuration for the manipulation of PT symmetry.