Microcomb-driven silicon photonic systems.

Microcombs have sparked a surge of applications over the past decade, ranging from optical communications to metrology1-4. Despite their diverse deployment, most microcomb-based systems rely on a large amount of bulky elements and equipment to fulfil their desired functions, which is complicated, expensive and power consuming. By contrast, foundry-based silicon photonics (SiPh) has had remarkable success in providing versatile functionality in a scalable and low-cost manner5-7, but its available chip-based light sources lack the capacity for parallelization, which limits the scope of SiPh applications. Here we combine these two technologies by using a power-efficient and operationally simple aluminium-gallium-arsenide-on-insulator microcomb source to drive complementary metal-oxide-semiconductor SiPh engines. We present two important chip-scale photonic systems for optical data transmission and microwave photonics, respectively. A microcomb-based integrated photonic data link is demonstrated, based on a pulse-amplitude four-level modulation scheme with a two-terabit-per-second aggregate rate, and a highly reconfigurable microwave photonic filter with a high level of integration is constructed using a time-stretch approach. Such synergy of a microcomb and SiPh integrated components is an essential step towards the next generation of fully integrated photonic systems.

Integrated turnkey soliton microcombs.

Optical frequency combs have a wide range of applications in science and technology1. An important development for miniature and integrated comb systems is the formation of dissipative Kerr solitons in coherently pumped high-quality-factor optical microresonators2-9. Such soliton microcombs10 have been applied to spectroscopy11-13, the search for exoplanets14,15, optical frequency synthesis16, time keeping17 and other areas10. In addition, the recent integration of microresonators with lasers has revealed the viability of fully chip-based soliton microcombs18,19. However, the operation of microcombs requires complex startup and feedback protocols that necessitate difficult-to-integrate optical and electrical components, and microcombs operating at rates that are compatible with electronic circuits-as is required in nearly all comb systems-have not yet been integrated with pump lasers because of their high power requirements. Here we experimentally demonstrate and theoretically describe a turnkey operation regime for soliton microcombs co-integrated with a pump laser. We show the appearance of an operating point at which solitons are immediately generated by turning the pump laser on, thereby eliminating the need for photonic and electronic control circuitry. These features are combined with high-quality-factor Si3N4 resonators to provide microcombs with repetition frequencies as low as 15 gigahertz that are fully integrated into an industry standard (butterfly) package, thereby offering compelling advantages for high-volume production.

AlGaAs soliton microcombs at room temperature.

Soliton mode locking in high-Q microcavities provides a way to integrate frequency comb systems. Among material platforms, AlGaAs has one of the largest optical nonlinearity coefficients, and is advantageous for low-pump-threshold comb generation. However, AlGaAs also has a very large thermo-optic effect that destabilizes soliton formation, and femtosecond soliton pulse generation has only been possible at cryogenic temperatures. Here, soliton generation in AlGaAs microresonators at room temperature is reported for the first time, to the best of our knowledge. The destabilizing thermo-optic effect is shown to instead provide stability in the high-repetition-rate soliton regime (corresponding to a large, normalized second-order dispersion parameter D2/κ). Single soliton and soliton crystal generation with sub-milliwatt optical pump power are demonstrated. The generality of this approach is verified in a high-Q silica microtoroid where manual tuning into the soliton regime is demonstrated. Besides the advantages of large optical nonlinearity, these AlGaAs devices are natural candidates for integration with semiconductor pump lasers. Furthermore, the approach should generalize to any high-Q resonator material platform.

Strong hyperbolic-magnetic polaritons coupling in an hBN/Ag-grating heterostructure.

Strong coupling between hyperbolic phonon-polaritons (HP) and magnetic polaritons (MP) is theoretically studied in a hexagonal boron nitride (hBN) covered deep silver grating structure. It is found that MP in grating trenches strongly interacts with HP in an anisotropic hBN thin film, leading to a large Rabi splitting with near-perfect dual band light absorption. Numerical results indicate that MP-HP coupling can be tuned by geometric parameters of the structure. More intriguingly, the resonantly enhanced fields for two branches of the hybrid mode demonstrate unusually different field patterns. One exhibits a volume-confined Zigzag propagation pattern in the hBN film, while the other shows a field-localization near the grating corners. Furthermore, resonance frequencies of these strongly coupled modes are very robust over a wide-angle range. The angle-insensitive strong interaction of hyperbolic-magnetic polaritons with dual band intense light absorption in this hybrid system offers a new paradigm for the development of various optical detecting, sensing and thermal emitting devices.

Ultrahigh-Q AlGaAs-on-insulator microresonators for integrated nonlinear photonics.

Aluminum gallium arsenide (AlGaAs) and related III-V semiconductors have excellent optoelectronic properties. They also possess strong material nonlinearity as well as high refractive indices. In view of these properties, AlGaAs is a promising candidate for integrated photonics, including both linear and nonlinear devices, passive and active devices, and associated applications. Low propagation loss is essential for integrated photonics, particularly in nonlinear applications. However, achieving low-loss and high-confinement AlGaAs photonic integrated circuits poses a challenge. Here we show an effective reduction of surface-roughness-induced scattering loss in fully etched high-confinement AlGaAs-on-insulator nanowaveguides by using a heterogeneous wafer-bonding approach and optimizing fabrication techniques. We demonstrate ultrahigh-quality AlGaAs microring resonators and realize quality factors up to 3.52 × 106 and finesses as high as 1.4 × 104. We also show ultra-efficient frequency comb generations in those resonators and achieve record-low threshold powers on the order of ∼20 µW and ∼120 µW for the resonators with 1 THz and 90 GHz free-spectral ranges, respectively. Our result paves the way for the implementation of AlGaAs as a novel integrated material platform specifically for nonlinear photonics and opens a new window for chip-based efficiency-demanding practical applications.

On-chip high-efficiency wavelength multicasting of PAM3/PAM4 signals using low-loss AlGaAs-on-insulator nanowaveguides.

Nonlinear optics-based optical signal processing (OSP) could potentially increase network flexibility because of its transparency, tunability, and large bandwidth. A low-loss, high nonlinearity, and compact integrated material platform is always the pursuit of OSP. In this Letter, a high-efficiency, one-to-six wavelength multicasting of 10 Gbaud pulse-amplitude modulation (PAM3/PAM4) signals using a 6 cm long Al0.2Ga0.8As-on-insulator nanowaveguide is experimentally demonstrated for the first time, to the best of our knowledge. The low-loss, combined with the high nonlinear coefficient of the AlGaAsOI platform, enables us to achieve -11.2dB average conversion efficiency clear eye diagrams and <2.1dB power penalty at KP4-forward error correction threshold (2.4×10-4) for all the output PAM3/PAM4 multicasting channels. This result points to a new generation of nonlinear OSP photonic integrated circuits.

Light Confinement Effect Induced Highly Sensitive, Self-Driven Near-Infrared Photodetector and Image Sensor Based on Multilayer PdSe2 /Pyramid Si Heterojunction.

In this study, a highly sensitive and self-driven near-infrared (NIR) light photodetector based on PdSe2 /pyramid Si heterojunction arrays, which are fabricated through simple selenization of predeposited Pd nanofilm on black Si, is demonstrated. The as-fabricated hybrid device exhibits excellent photoresponse performance in terms of a large on/off ratio of 1.6 × 105 , a responsivity of 456 mA W-1 , and a high specific detectivity of up to 9.97 × 1013 Jones under 980 nm illumination at zero bias. Such a relatively high sensitivity can be ascribed to the light trapping effect of the pyramid microstructure, which is confirmed by numerical modeling based on finite-difference time domain. On the other hand, thanks to the broad optical absorption properties of PdSe2 , the as-fabricated device also exhibits obvious sensitivity to other NIR illuminations with wavelengths of 1300, 1550, and 1650 nm, which is beyond the photoresponse range of Si-based devices. It is also found that the PdSe2 /pyramid Si heterojunction device can also function as an NIR light sensor, which can readily record both "tree" and "house" images produced by 980 and 1300 nm illumination, respectively.

Strong longitudinal coupling of Tamm plasmon polaritons in graphene/DBR/Ag hybrid structure.

In this paper, strong longitudinal coupling of the Tamm plasmon polaritons (TPPs) is investigated in a graphene/DBR/Ag slab hybrid system. It is found that TPPs can be excited at both the top graphene and the bottom silver slab interface, which can strongly interact with each other in this coupled structure. Numerical simulation results demonstrate that the vertical Tamm plasmon coupling can be either tuned by adjusting the geometric parameters or actively controlled by the Fermi energy in graphene sheet as well as the incident angle of light, allowing for strong light-matter interaction with a tunable dual-band perfect absorption. Moreover, the coupling strength of the hybrid modes exhibits a large tuning range, from a large Rabi splitting to an extremely narrow induced transparency in this coupled regime. Coupled mode theory has been employed to explain the strong coupling phenomenon. The controllable TPP coupling with an ultrahigh dual-band absorption capability offered by this simple layered structure opens new avenues for developing a broad range of graphene-based active optoelectronic and polaritonic devices.

Heterogeneous silicon photonics sensing for autonomous cars.

Heterogeneous silicon photonics is uniquely positioned to address the photonic sensing needs of upcoming autonomous cars and provide the necessary cost reduction for widespread deployment. This is because it allows for wafer-scale active/passive integration, including optical sources. We present our recent research and the development of interferometric optical gyroscopes and LiDAR sensors. More specifically, we show a fully integrated gyroscope front-end occupying an area of only 4.5 mm2. We also show the first dense pitch optical phased array using heterogeneous phase shifters. The 4 µm pitch heterogeneous phase shifters provide very low V2π of only 0.35-1.4 V across 200 nm, low residual amplitude modulation of only 0.1-0.15 dB for 2π phase shift, extremely low static power consumption (<3 nW), and high speed (> 1 GHz). All of these factors make them ideal for next-generation LiDAR systems that employ optical phased arrays.

Strong coupling of optical interface modes in a 1D topological photonic crystal heterostructure/Ag hybrid system.

We theoretically investigate the strong coupling of a topological photonic state (TPS) and Tamm plasmon polaritons (TPPs) in a graphene embedded one-dimensional topological photonic crystal (TPC)/Ag structure in visible range. It is shown that the strong interaction of a TPS at the TPC heterointerface and TPP at the Ag surface enables a large Rabi splitting up to 96.8 meV with a dual-narrow-band perfect absorption. A spectral linewidth of the hybrid mode can be 0.3 nm with a Q factor of 1078. The numerical results also reveal that mode coupling can be either tuned by adjusting the geometric parameters or actively controlled by the incident angle, offering a remarkable polarization-independent strong light-matter interaction. The coupled mode theory is employed to explain the strong TPS-TPP coupling. The polarization-independent and controllable strong mode coupling with a dual-narrow-band perfect absorption in this simple lamellar geometry offers new possibilities for developing various on-chip optical detection, sensing, filtering, and light-emitting devices.

Low loss (Al)GaAs on an insulator waveguide platform.

In this Letter, we demonstrate a low loss gallium arsenide and aluminum gallium arsenide on an insulator platform by heterogenous integration. The resonators on this platform exhibit record high quality factors up to 1.5×106, corresponding to a propagation loss ∼0.4 dB/cm. For the first time, to the best of our knowledge, the loss of integrated III-V semiconductor on insulator waveguides becomes comparable with that of the silicon-on-insulator waveguides. This Letter should have a significant impact on photonic integrated circuits (PICs) and become an essential building block for the evolving nonlinear PICs and integrated quantum photonic systems in the future.

[Internal fixation of lateral and medial borders for displaced scapular body fractures via minimally invasive approach:results of 23 cases].

OBJECTIVE: To evaluate the efficacy of internal fixation of lateral and medial borders for displaced scapular body fractures via the minimally invasive approach. METHODS: The internal fixation of lateral and medial borders via minimally invasive approach was applied in surgical treatment of 23 patients with scapular body comminuted fractures from January 2014 to June 2018. The lateral approach was made straightly orienting over the lateral border of scapula. The dissection was taken down to the deltoid fascia. The deltoid was retracted cephalically, revealing the external rotators. Blunt dissection was used down to the lateral border between infraspinatus and teres minor, exposing the fracture site. The medial incision was done along the medial border of the scapula over site of the fracture. Dissections were taken down to the fascia and the periosteum. A subperiosteal dissection was then performed to elevate the infraspinatus to the degree necessary to visualize the fracture. The medial and lateral borders of scapula body were fixed with plates and screws in a frame-like way. RESULTS: One patient developed the delayed healing of the incisions due to liquefactive fat necrosis. The other 22 patients showed no complications of the incisions. The glenopolar angle (GPA) of fractured scapula was increased from preoperative (25±12) degrees to postoperative (41±5) degrees (P<0.01). The healing time of fractures healed was 3-8 months, with an average time of (4.4±1.3) months. CONCLUSIONS: The lateral-medial combined fixation through minimally invasive surgical approach for the scapula body fractures allows visualization of fracture reduction without extensive muscular or subcutaneous flaps, and is associated with successful fracture healing and high functional scores of the shoulder.

Vertical liquid controlled adiabatic waveguide coupler.

A broadband vertical liquid controlled optical waveguide coupler (LCC) is demonstrated. The fabricated vertical LCC with silicon nitride (SiN) waveguides can switch light between 2 stacked photonic circuit layers with zero energy consumption in a steady switch state. In combination with low-loss interlayer waveguide crossovers they enable large scale non-volatile switch circuits with low loss. The fabricated vertical LCC has a loss less than 2.0 dB in bar state and less than 2.6 dB in cross state over the telecommunication wavelength range 1260 nm to 1630 nm. Interlayer waveguide crossovers with the same interlayer oxide thickness as the LCC have a loss less than 0.06 dB over the same wavelength range. The crosstalk of the LCC is less than -21 dB over the wavelength range 1500 nm to 1630 nm for both bar and cross state.

Nonlinear silicon nitride waveguides based on a PECVD deposition platform.

In this work, we present a nonlinear silicon nitride waveguide. These waveguide are fabricated by readily available PECVD, conventional contact UV-lithography and high-temperature annealing techniques, thus dramatically reducing the processing complexity and cost. By patterning the waveguide structures firstly and then carrying out a high-temperature annealing process, not only sufficient waveguide thickness can be achieved, which gives more freedom to waveguide dispersion control, but also the material absorption loss in the waveguides be greatly reduced. The linear optical loss of the fabricated waveguide with a cross-section of 2.0 × 0.58 µm2 was measured to be as low as 0.58 dB/cm. The same loss level is demonstrated over a broad wavelength range from 1500 nm to 1630 nm. Moreover, the nonlinear refractive index of the waveguide was determined to be ~6.94 × 10-19 m2/W, indicating that comparable nonlinear performance with their LPCVD counterparts is expected. These silicon nitride waveguides based on a PECVD deposition platform can be useful for the development of more complicated on-chip nonlinear optical devices or circuits.

Fabrication and characterization of on-chip silicon nitride microdisk integrated with colloidal quantum dots.

We designed and fabricated free-standing, waveguide-coupled silicon nitride microdisks hybridly integrated with embedded colloidal quantum dots. An efficient coupling of quantum dot emission to resonant disk modes and eventually to the access waveguides is demonstrated. The amount of light coupled out to the access waveguide can be tuned by controlling its dimensions and offset with the disk edge. These devices open up new opportunities for both on-chip silicon nitride integrated photonics and novel optoelectronic devices with quantum dots.

All-optical NRZ wavelength conversion based on a single hybrid III-V/Si SOA and optical filtering.

We demonstrate all-optical wavelength conversion (AOWC) of non-return-to-zero (NRZ) signal based on cross-gain modulation in a single heterogeneously integrated III-V-on-silicon semiconductor optical amplifier (SOA) with an optical bandpass filter. The SOA is 500 µm long and consumes less than 250 mW electrical power. We experimentally demonstrate 12.5 Gb/s and 40 Gb/s AOWC for both wavelength up and down conversion.

Nanoscale and Single-Dot Patterning of Colloidal Quantum Dots.

Using an optimized lift-off process we develop a technique for both nanoscale and single-dot patterning of colloidal quantum dot films, demonstrating feature sizes down to ~30 nm for uniform films and a yield of 40% for single-dot positioning, which is in good agreement with a newly developed theoretical model. While first of all presenting a unique tool for studying physics of single quantum dots, the process also provides a pathway toward practical quantum dot-based optoelectronic devices.

Low-loss silicon nitride waveguide hybridly integrated with colloidal quantum dots.

Silicon nitride waveguides with a monolayer of colloidal quantum dots embedded inside were fabricated using a low-temperature deposition process and an optimized dry etching step for the composite layers. We experimentally demonstrated the luminescence of the embedded quantum dots is preserved and the loss of these hybrid waveguide wires is as low as 2.69dB/cm at 900nm wavelength. This hybrid integration of low loss silicon nitride photonics with active emitters offers opportunities for optical sources operating over a very broad wavelength range.

5 x 20 Gb/s heterogeneously integrated III-V on silicon electro-absorption modulator array with arrayed waveguide grating multiplexer.

We present a five-channel wavelength division multiplexed modulator module that heterogeneously integrates a 200 GHz channel-spacing silicon arrayed-waveguide grating multiplexer and a 20 Gbps electro-absorption modulator array, showing the potential for 100 Gbps transmission capacity on a 1.5x0.5 mm² footprint.

Mesenchymal Stem Cell-derived Exosomes Affect Macrophage Phenotype: A Cell-free Strategy for the Treatment of Skeletal Muscle Disorders.

The process of tissue damage, repair, and regeneration in the skeletal muscle system involves complex inflammatory processes. Factors released in the inflammatory microenvironment can affect the phenotypic changes of macrophages, thereby changing the inflammatory process, making macrophages an important target for tissue repair treatment. Mesenchymal stem cells exert anti-inflammatory effects by regulating immune cells. In particular, exosomes secreted by mesenchymal stem cells have become a new cell-free treatment strategy due to their low tumorigenicity and immunogenicity. This article focuses on the mechanism of the effect of exosomes derived from mesenchymal stem cells on the phenotype of macrophages after skeletal muscle system injury and explores the possible mechanism of macrophages as potential therapeutic targets after tissue injury.