High-performance Photonic Devices Research Articles

Slow Light Rainbow Trapping in a Uniformly Magnetized Gyromagnetic Photonic Crystal Waveguide

We present a hybrid gyromagnetic photonic crystal (GPC) waveguide composed of different GPC waveguide segments possessing various cylinder radii and waveguide widths but biased by a uniform external magnetic field. We demonstrate in frequency and time domains that based on the strong coupling of two counter-propagating topologically protected one-way edge states, the intriguing slow light rainbow trapping (SLRT) of electromagnetic (EM) waves can be achieved, that is, EM waves of different frequencies can be slowed down and trapped at different positions without cross talk and overlap. More importantly, due to the existence of one-way edge states, external EM waves can be non-reciprocally coupled to the SLRT waveguide channel, although the incident position of the EM wave is far away from the waveguide channel. Besides, the frequency range of the slow light states can also be easily regulated by tuning the intensity of an external magnetic field, which is very beneficial to solve the contradiction between slow light and broad bandwidth. Our results can be applied to the design of high-performance photonic devices, such as an optical buffer, optical switch, and optical filter.

Hybrids of perovskite nanocrystals and SiO2 microfiber for robust and long-haul transmittable fiber lasers

Fiber lasers have broad prospects for the development of tunable high-performance photonic equipment and active fiber devices. However, they are still facing challenges, such as the limited emission wavelength and relatively high pump energy. Perovskite nanocrystals possess a large absorption cross-section, high quantum efficiency, long Auger lifetime, and tunable emission wavelength, which have been recognized as the promising gain media. In this work, a unique method was developed to form a type of fiber laser device based on high-quality SiO2 microfibers integrated with solution-processed perovskite nanocrystals. By this way, the robust and efficient fiber laser with characteristics of long-haul transmission, tunable laser mode, and high polarization state was effectively obtained. Our results represent a significant advancement in fiber lasers based on favorable perovskite nanocrystals and high-quality SiO2 microfiber and provide new possibilities for active fiber devices.

Broadband Achromatic Metalens in Mid‐Wavelength Infrared

AbstractMetasurface provides a powerful platform to correct the chromatic aberration of conventional lenses in a flexible, integratable, and ultra‐compact manner. Mid‐wavelength infrared has promised many exciting applications ranged from molecular fingerprint detection to low‐light‐level night vision. Developing broadband achromatic metalens in mid‐wavelength infrared becomes necessary to meet the increasingly urgent demands on high performance photonic devices. Here, we demonstrate the broadband achromatic metalenses from 3.5 to 5 µm with all‐silicon metasurfaces. Large phase dispersion control range is achieved to realize metalenses with both large numerical apertures and sample sizes while maintaining high focusing efficiency. The experimental results verify the diffraction‐limited achromatic focusing and imaging of the metalenses in mid‐wavelength infrared. Additionally, we also demonstrate the versatility by successfully implementing the generation of the broadband achromatic focusing optical vortex (L = 2). This work represents a solid step toward practical implementation of metalens and may find applications in mid‐wavelength infrared imaging and detections.

Three-Dimensional Perovskite Nanopixels for Ultrahigh-Resolution Color Displays and Multilevel Anticounterfeiting.

Hybrid perovskites are emerging as a promising, high-performance luminescent material; however, the technological challenges associated with generating high-resolution, free-form perovskite structures remain unresolved, limiting innovation in optoelectronic devices. Here, we report nanoscale three-dimensional (3D) printing of colored perovskite pixels with programmed dimensions, placements, and emission characteristics. Notably, a meniscus comprising femtoliters of ink is used to guide a highly confined, out-of-plane crystallization process, which generates 3D red, green, and blue (RGB) perovskite nanopixels with ultrahigh integration density. We show that the 3D form of these nanopixels enhances their emission brightness without sacrificing their lateral resolution, thereby enabling the fabrication of high-resolution displays with improved brightness. Furthermore, 3D pixels can store and encode additional information into their vertical heights, providing multilevel security against counterfeiting. The proof-of-concept experiments demonstrate the potential of 3D printing to become a platform for the manufacture of smart, high-performance photonic devices without design restrictions.

Novel Bloch wave excitation platform based on few-layer photonic crystal deposited on D-shaped optical fiber

With the goal of ultimate control over the light propagation, photonic crystals currently represent the primary building blocks for novel nanophotonic devices. Bloch surface waves (BSWs) in periodic dielectric multilayer structures with a surface defect is a well-known phenomenon, which implies new opportunities for controlling the light propagation and has many applications in the physical and biological science. However, most of the reported structures based on BSWs require depositing a large number of alternating layers or exploiting a large refractive index (RI) contrast between the materials constituting the multilayer structure, thereby increasing the complexity and costs of manufacturing. The combination of fiber–optic-based platforms with nanotechnology is opening the opportunity for the development of high-performance photonic devices that enhance the light-matter interaction in a strong way compared to other optical platforms. Here, we report a BSW-supporting platform that uses geometrically modified commercial optical fibers such as D-shaped optical fibers, where a few-layer structure is deposited on its flat surface using metal oxides with a moderate difference in RI. In this novel fiber optic platform, BSWs are excited through the evanescent field of the core-guided fundamental mode, which indicates that the structure proposed here can be used as a sensing probe, along with other intrinsic properties of fiber optic sensors, as lightness, multiplexing capacity and easiness of integration in an optical network. As a demonstration, fiber optic BSW excitation is shown to be suitable for measuring RI variations. The designed structure is easy to manufacture and could be adapted to a wide range of applications in the fields of telecommunications, environment, health, and material characterization.

Ultrafast mode-locking in highly stacked Ti3C2Tx MXenes for 1.9-μm infrared femtosecond pulsed lasers

Abstract Metallic 2D materials can be promising saturable absorbers for ultrashort pulsed laser production in the long wavelength regime. However, preparing and manipulating their 2D structures without layer stacking have been nontrivial. Using a combined experimental and theoretical approach, we demonstrate here that a metallic titanium carbide (Ti3C2Tx), the most popular MXene 2D material, can have excellent nonlinear saturable absorption properties even in a highly stacked state due to its intrinsically existing surface termination, and thus can produce mode-locked femtosecond pulsed lasers in the 1.9-μm infrared range. Density functional theory calculations reveal that the electronic and optical properties of Ti3C2Tx MXene can be well preserved against significant layer stacking. Indeed, it is experimentally shown that 1.914-μm femtosecond pulsed lasers with a duration of 897 fs are readily generated within a fiber cavity using hundreds-of-layer stacked Ti3C2Tx MXene saturable absorbers, not only being much easier to manufacture than mono- or few-layered ones, but also offering character-conserved tightly-assembled 2D materials for advanced performance. This work strongly suggests that as-obtained highly stacked Ti3C2Tx MXenes can serve as superb material platforms for versatile nanophotonic applications, paving the way toward cost-effective, high-performance photonic devices based on MXenes.

Numerical Analysis of Reconfigurable and Multifunctional Barium Titanate Platform Based on Photonic Crystal Ring Resonator

A novel reconfigurable, reversible and multifunctional nanostructure platform is designed with ultracompact size, high extinction ratio, large bandwidth and low optical loss. The proposed structure consists of a ring resonator and photonic crystal waveguides. The single nanoscale structure is used to realize the five different high-performance photonic devices such as, electro-optic tunable filter, reconfigurable switch, 1 × 5 power splitter, 4 × 2 reversible encoder and SR flip-flop. These miniature optical device performance parameters are numerically analyzed and optimized by finite-difference-time-domain (FDTD) method. A multifunctional ring resonator coupled waveguide structure is designed with a very small footprint of 179 μm2, large bandwidth of 45.2 nm, the fast response time of 215 fs and high data rate of 4.651 Tbps. Hence, the proposed nanostructure can be highly suitable for photonic interconnects, lightwave communication networks and quantum computing.

Waveguide-integrated high-performance magneto-optical isolators and circulators on silicon nitride platforms

Optical isolators and circulators are important components for photonic integrated circuits. Despite significant progress on silicon-on-insulator (SOI) platforms, integrated optical isolators and circulators have rarely been reported on silicon nitride (SiN) platforms. In this paper, we report monolithic integration of magneto-optical (MO) isolators on SiN platforms with record-high performances based on standard silicon photonics foundry process and MO thin film deposition. We successfully grow high-quality MO garnet thin films on SiN with large Faraday rotation up to - − 5900 d e g / c m . We show superior MO figure of merit (FoM) of MO/SiN waveguides compared to that of MO/SOI in an optimized device design. We demonstrate transverse magnetic (TM)/transverse electric (TE) mode broadband and narrowband optical isolators and circulators on SiN with high isolation ratio, low cross talk, and low insertion loss. In particular, we observe 1 dB insertion loss and 28 dB isolation ratio in a SiN racetrack resonator-based isolator at 1570.3 nm wavelength. The low thermo-optic coefficient of SiN also ensures excellent temperature stability of the device. Our work paves the way for integration of high-performance nonreciprocal photonic devices on SiN platforms.

Electrically Tunable Four-Wave-Mixing in Graphene Heterogeneous Fiber for Individual Gas Molecule Detection.

Detection of individual molecules is the ultimate goal of any chemical sensor. In the case of gas detection, such resolution has been achieved in advanced nanoscale electronic solid-state sensors, but it has not been possible so far in integrated photonic devices, where the weak light-molecule interaction is typically hidden by noise. Here, we demonstrate a scheme to generate ultrasensitive down-conversion four-wave-mixing (FWM) in a graphene bipolar-junction-transistor heterogeneous D-shaped fiber. In the communication band, the FWM conversion efficiency can change steeply when the graphene Fermi level approaches 0.4 eV. In this condition, we exploit our unique two-step optoelectronic heterodyne detection scheme, and we achieve real-time individual gas molecule detection in vacuum. Such combination of graphene strong nonlinearities, electrical tunability, and all-fiber integration paves the way toward the design of versatile high-performance graphene photonic devices.

Bound states in the continuum and exceptional points in dielectric waveguide equipped with a metal grating

Bound states in the continuum (BICs) and exceptional points (EPs) have been the subjects of recent intensive research as they exhibit exotic phenomena that are significant for both fundamental physics and practical applications. We investigated the emergence of the Friedrich–Wintgen (FW) type BIC and the EP in a dielectric waveguide comprising a metal grating, focusing on their dependence on the grating thickness. The BIC emerges at a branch near the anti-crossing formed of the two waveguide modes, for a grating of any thickness. With the grating-thickness change, the anti-crossing gap varies and the branch at which the BIC appears flips. We show that, when the slit is single mode, the BIC appears in the vicinity of the crossing between the two waveguide modes in the empty-lattice (zero slit-width) limit, while the results satisfy the criteria for the branch at which the BIC appears in the previous reports. In addition, we find that the EP appears near the BIC in the same device only on selecting the grating thickness. The BIC and EP in the dielectric waveguide comprising a metal grating, particularly with such tunability, are expected to result in the development of functional and high-performance photonic devices in addition to being a platform for the fundamental research of non-Hermitian systems.

Integrated coherent optical receiver with feed-forward carrier recovery.

Coherent optical communication provides optical links with a high spectral efficiency and sensitivity. An essential feature of a coherent optical receiver is to phase lock the optical local oscillator to the carrier of the incoming signal. In this work, we propose and demonstrate, for the first time, a novel coherent optical receiver, where the relative instantaneous phase between the incoming optical carrier and a semiconductor laser (SCL), serving as the optical local oscillator, is first detected using a balanced photodiode, filtered, and used in a feed-forward scheme to modify the phase of the optical local oscillator, effectively recovering the input carrier, which is then used for data recovery. The proposed architecture leverages high-performance on-chip photonic devices to realize a low-power coherent optical receiver without utilizing a phase-locked loop and eliminates the required high data-rate ADC, lowering the complexity of the backend DSP. The photonic part of the implemented prototype was integrated on a 180 nm silicon-on-insulator photonic process within a footprint of 1.0 mm × 0.8 mm. Clock and data recovery at 10 GBaud/s with bit-error-rates better than 10-6 and 10-3 for optical BPSK and QPSK have been demonstrated, respectively.

Subwavelength structured silicon waveguides and photonic devices

Abstract Subwavelength structures such as subwavelength gratings (SWGs) and subwavelength metamaterials are capable of tailoring the optical properties of materials and controlling the flow of light at the nanoscale. The effective indices of the subwavelength structured strip and slab waveguides can be changed in a wide range by choosing an appropriate duty cycle or a filling factor of silicon, which provides an effective method to manipulate the optical field and achieve effective index matching for functional devices. Recent advances in nanofabrication techniques have made it possible to implement subwavelength structures in silicon strip and slab waveguides. Here we review various approaches used to design subwavelength structures and achieve exotic optical responses and discuss how these structures can be used to realize high-performance silicon photonic devices. Both one-dimensional SWG devices and two-dimensional subwavelength metamaterial devices are covered in this review, including subwavelength structure–based polarization handling devices, mode manipulation devices, and building blocks for integrated optical interconnects. Perspectives on subwavelength structured silicon photonic devices are also discussed.

Auger-type process in ultrathin ReS2

The dramatic enhancement of charge carrier interaction makes many-body effects of great prominence in two-dimensional materials. Here we report the defect-assisted Auger scattering combined with band-to-band Auger recombination as playing the dominant recovery mechanism in the charge carriers of atomically thin-layered ReS2. Time resolved transient absorption spectra investigation reveals two different decay processes over the visible and near- infrared range, which is attributed to the shallow and deep defects introduced by the existence of sulfur (S) vacancy. A rate equation system is invoked to rationalize our peculiar pump and temperature dependence of carrier dynamics quantitatively. These findings provide theoretical insights into the significant role played by nonradiative Auger processes and may pave the way for the development of diverse ReS2-based high performance photonic and optoelectronic devices.

Wavelength-Tunable Mid-Infrared Lasing from Black Phosphorus Nanosheets.

Van der Waals layered semiconductor materials own unique physical properties and have attracted intense interest in developing high-performance electronic and photonic devices. Among them, black phosphorus (BP) is distinct for its layer number-tuned direct band gap which spans from near- to mid-infrared (MIR) waveband. In addition, the puckered honey comb crystal lattice endows the material with highly linear-polarized emission and marked anisotropy in carrier transportation. These unique material properties render BP as an intriguing and promising building block for constructing mid-infrared-ranged coherent light sources. Here, a room temperature surface-emitting MIR laser based on single crystalline BP nanosheets coupled with a distributed Bragg reflector cavity is reported. MIR stimulated emission at 3611 nm is achieved with a near-unity linear polarization, which exhibits robust thermal stability up to 360 K. Most importantly, the lasing wavelength can be tuned from 3425 to 4068 nm by varying the cavity length via thickness control of BP layer. The demonstrated highly polarized lasing output and wavelength-tunable capacity of the proposed device scheme in MIR spectral range opens up promising opportunities for a broad array of applications in polarization-resolved IR imaging, range-finding, and free space quantum communications.

Enhanced Photocurrent Owing to Shuttling of Charge Carriers across 4-Aminothiophenol-Functionalized MoSe2-CsPbBr3 Nanohybrids.

Mixed-dimensional van der Waals nanohybrids (MvNHs) of two-dimensional transition-metal dichalcogenides (TMDs) and zero-dimensional perovskites are highly promising candidates for high-performance photonic device applications. However, the growth of perovskites over the surface of TMDs has been a challenging task due to the distinguishable surface chemistry of these two different classes of materials. Here, we demonstrate a synthetic route for the design of MoSe2-CsPbBr3 MvNHs using a bifunctional ligand, i.e., 4-aminothiophenol. Close contact between these two materials is established via a bridge that leads to the formation of a donor-bridge-acceptor system. The presence of the small conjugated ligand facilitates faster charge diffusion across MoSe2-CsPbBr3 interfaces. Density functional theory calculations confirm the type-II band alignment of the constituents within the MvNHs. The MoSe2-CsPbBr3 nanohybrids show much higher photocurrent (∼2 × 104-fold photo-to-dark current ratio) as compared to both pure CsPbBr3 nanocrystals and pristine MoSe2 nanosheets owing to the synergistic effect of pronounced light-matter interactions followed by efficient charge separation and transportation. This study suggests the use of a bifunctional ligand to construct a nanohybrid system to tune the optoelectronic properties for potential applications in photovoltaic devices.

Controlling the alignment of 1D nanochannel arrays in oriented metal-organic framework films for host-guest materials design.

Controlling the direction of molecular-scale pores enables the accommodation of guest molecular-scale species with alignment in the desired direction, allowing for the development of high-performance mechanical, thermal, electronic, photonic and biomedical organic devices (host–guest approach). Regularly ordered 1D nanochannels of metal–organic frameworks (MOFs) have been demonstrated as superior hosts for aligning functional molecules and polymers. However, controlling the orientation of MOF films with 1D nanochannels at commercially relevant scales remains a significant challenge. Here, we report the fabrication of macroscopically oriented films of Cu-based pillar-layered MOFs having regularly ordered 1D nanochannels. The direction of 1D nanochannels is controllable by optimizing the crystal growth process; 1D nanochannels align either perpendicular or parallel to substrates, offering molecular-scale pore arrays for a macroscopic alignment of functional guest molecules in the desired direction. Due to the fundamental interest and widespread technological importance of controlling the alignment of functional molecules and polymers in a particular direction, orientation-controllable MOF films will open up the possibility of realising the potential of MOFs in advanced technologies.

Bio-inspired and bio-integrated photonic materials and devices: feature issue introduction

Recent progresses in materials design, synthesis and characterization, together with emerging methods for device fabrication and system assembly, have lead to high performance photonic materials, devices, and systems in bio-adaptable and/or bio-compatible formats, thereby enabling advanced bio-related photonic platforms. In this feature issue, 10 papers represent the most recent progress in various aspects of bio-inspired and bio-integrated materials from silicon, perovskites and organics, devices like photodetectors, plasmonic sensors and light emitters, and their diverse applications in areas including sensing, prosthesis and therapy. Although this feature issue only provides a glimpse of the vast field of bio-related photonics, we hope that it can offer a guideline for researchers involved in this emerging area.

High-Q Si3N4 microresonators based on a subtractive processing for Kerr nonlinear optics.

Microresonator frequency combs (microcombs) are enabling new applications in frequency synthesis and metrology - from high-speed laser ranging to coherent optical communications. One critical parameter that dictates the performance of the microcomb is the optical quality factor (Q) of the microresonator. Microresonators fabricated in planar structures such as silicon nitride (Si3N4) allow for dispersion engineering and the possibility to monolithically integrate the microcomb with other photonic devices. However, the relatively large refractive index contrast and the tight optical confinement required for dispersion engineering make it challenging to attain Si3N4 microresonators with Qs > 107 using standard subtractive processing methods - i.e. photonic devices are patterned directly on the as-deposited Si3N4 film. In this work, we achieve ultra-smooth Si3N4 microresonators featuring mean intrinsic Qs around 11 million. The cross-section geometry can be precisely engineered in the telecommunications band to achieve either normal or anomalous dispersion, and we demonstrate the generation of mode-locked dark-pulse Kerr combs as well as soliton microcombs. Such high-Qs allow us to generate 100 GHz soliton microcombs, demonstrated here for the first time in Si3N4 microresonators fabricated using a subtractive processing method. These results enhance the possibilities for co-integration of microcombs with high-performance photonic devices, such as narrow-linewidth external-cavity diode lasers, ultra-narrow filters and demultiplexers.

Generation of cesium lead halide perovskite nanocrystals via a serially-integrated microreactor system: Sequential anion exchange reaction

Inorganic perovskite nanocrystals (NCs) of cesium lead mixed halides (CsPb(X/Y)3, X = Br, Y = Cl and I) are promising optical materials for developing the high-performance photonic devices. Traditionally, anion-exchange reaction in perovskite halide NCs provides a simple substitutional way to tune the composition and emitting color with good luminescence properties in the human eye detectable visible spectral regions. However, prior synthetic procedures of perovskite NCs have employed conventional flask-based reactions which limit the fine control of perovskite NCs because of extremely fast anion-exchange kinetics. To overcome such problems, we demonstrate a droplet-based microfluidic system with simple, fast, and high-throughput parametric screening for the synthesis of perovskite NCs. By using the customized microfluidic operational system consisting of serially integrated two microfluidic reactors and heating block, we have successfully synthesized CsPbX3 perovskite NCs. In addition, we can finely control the anion-exchange reaction which can generate the formation of CsPb(X/Y)3 perovskite NCs with a wide range of visible spectrum (410–630 nm). Ultimately, we have established their potential applications in the development of solid-state lighting-based flexible display systems.

On‐Demand Nanoscale Manipulations of Correlated Oxide Phases

AbstractControlling material properties at the nanoscale is a critical enabler of high performance electronic and photonic devices. A prototypical material example is VO2, where a structural phase transition in correlation with dramatic changes in resistivity, optical response, and thermal properties demonstrates particular technological importance. While the phase transition in VO2 can be controlled at macroscopic scales, reliable and reversible nanoscale control of the material phases has remained elusive. Here, reconfigurable nanoscale manipulations of VO2 from the pristine monoclinic semiconducting phase to either a stable monoclinic metallic phase, a metastable rutile metallic phase, or a layered insulating phase using an atomic force microscope is demonstrated at room temperature. The capability to directly write and erase arbitrary 2D patterns of different material phases with distinct optical and electrical properties builds a solid foundation for future reprogrammable multifunctional device engineering.