Multimode and single-mode fiber compatible graded-index multicore fiber for high density optical interconnect application

We designed and fabricated a graded-index (GI) multicore fiber (MCF) compatible with both standard multimode and single-mode fiber for high density optical interconnect application in large-scale data centers. The proposed fiber supports long-distance multimode transmission at 850 nm as well as quasi-single mode transmission at 1310 nm and 1550 nm. The parameters of the GI-MCF have been optimized to obtain both a small differential mode delay at 850 nm and a small mode field diameter mismatch of less than 0.5 μm with single-mode fiber at 1310 nm and 1550 nm with a negligible inter-core crosstalk. In experiment, we successfully realized the multimode operation over 1 km-long GI-MCF at 850 nm and the quasi-single mode operation over 12.4 km-long GI-MCF at 1310 nm and 1550 nm at a data rate of 7×10-Gb/s. The multi-wavelengths multicore transmission was demonstrated for the first time. The experiment results imply that the proposed GI-MCF satisfies various requirements in such as operating wavelength, accessible distance and interconnect density of large-scale data center, and can effectively reduce the fiber numbers and system complexity.

Real-time 100 Gbps/λ/core NRZ and EDB IM/DD transmission over multicore fiber for intra-datacenter communication networks

A BiCMOS chip-based real-time intensity modulation/direct detection spatial division multiplexing system is experimentally demonstrated for both optical interconnects. 100 Gbps/λ/core electrical duobinary (EDB) transmission over 1 km 7-core multicore fiber (MCF) is carried out, achieving KP4 forward error correction (FEC) limit (BER < 2E-4). Using optical dispersion compensation, 7 × 100 Gbps/λ/core transmission of both non-return-to-zero (NRZ) and EDB signals over 10 km MCF transmission is achieved with BER lower than 7% overhead hard-decision FEC limit (BER < 3.8E-3). The integrated low complexity transceiver IC and analog signal processing approach make such a system highly attractive for the high-speed intra-datacenter interconnects.

Quantification of N2O and NO emissions from a small-scale pond-ditch circulation system for rural polluted water treatment

The pond-ditch circulation system (PDCS) is an efficient and economical solution for the restoration of degraded rural water environments. However, little is known about nitrous oxide (N₂O) and nitric oxide (NO) emissions in the microbial removal process of nitrogen in PDCSs, and their contribution to nitrogen removal. The aim of this study was to quantify N₂O and NO emissions from the PDCS, evaluate their capacities, and elucidate the key environmental factors controlling them. The results showed that N₂O and NO fluxes were in the ranges 1.1-2055.1μgNm^-2h^-1 and 0.1-6.8μgNm^-2h^-1 for the PDCS, respectively. Meanwhile, the N₂O and NO fluxes from the two ponds in the PDCS were significantly higher than those in the static system. Moreover, the amount of N₂O and NO emissions in the PDCS accounted for 0.17-4.32% of the total nitrogen (TN) removal. According to the partial least squares (PLS) approach and Pearson's correlation coefficients, nitrate nitrogen in water (W-NO₃^--N), dissolved oxygen in water (W-DO), dissolved oxygen in sediment (DO), pH in water (W-pH), pH in sediment (pH), total kjeldahl nitrogen (TKN), and soil organic carbon (SOC) significantly affected the N₂O flux (p<0.05), whereas W-NO₃^--N, DO, and nitrite nitrogen in sediment (NO₂^--N) significantly affected the NO emission (p<0.05).

Directional torsion and temperature discrimination based on a multicore fiber with a helical structure

We propose and experimentally demonstrate a directional torsion sensor based on a Mach-Zehnder interferometer formed in a multicore fiber (MCF) with a ~570-μm-long helical structure (HS). The HS was fabricated into the MCF by simply pre-twisting and then heating with a CO₂ laser splicing system. This device shows the capability of directional torsion measurement from -17.094 rad/m to 15.669 rad/m with the sensitivity of ~0.118 nm/(rad/m). Moreover, since the multiple interferences respond differently to torsion and temperature simultaneously, the temperature cross-sensitivity of the proposed sensor can be eliminated effectively. Besides, the sensor owns other merits such as easy fabrication and good mechanical robustness.

Phototriggered N2-Generating Submicron Particles for Selective Killing of Cancer Cells

Killing of cancer cells by applying mechanical disruption has been an appealing emerging strategy for cancer treatment in recent years. In this study, photoresponsive submicron particles based on diazo-resin that are able to release N₂ under UV irradiation were prepared through a polyamine-salt aggregation method. After surface modification with hyaluronic acid, the particles could be internalized selectively by cancer cells and were mainly located in lysosomes after 6 h incubation. The viability of cancer cells decreased obviously after they were co-cultured with photoresponsive particles and UV irradiation due to the integrity damage of lysosomes by phototriggered N₂ generation and the subsequent increased number of reactive oxygen species.

Preparation of photo-responsive poly(ethylene glycol) microparticles and their influence on cell viability

Intelligent colloidal particles have been widely used as carriers for delivery of bioactive molecules due to the ability of controlled release. However, attention is mainly paid to the effects of their payloads, whereas the impacts of carriers are largely ignored. In this study, photo-responsive polyethylene glycol (PEG) microparticles were fabricated by using 8-arm-PEG with terminal amine groups (8-arm-PEG-NH₂) and a photo-cleavable cross-linker. Due to the cleavable CO bond in the cross-linker, under UV irradiation the PEG particles could be decomposed gradually, leading to particle swelling and eventual disappearance. The PEG particles could be internalized by smooth muscle cells and HepG2 cells, and located in lysosomes. Their intracellular photo-response induced significant decrease of cell viability and increase of reactive oxygen species level.

Design of elliptical-core mode-selective photonic lanterns with six modes for MIMO-free mode division multiplexing systems

Elliptical-core few mode fiber (EC-FMF) is used in a mode division multiplexing (MDM) transmission system to release multiple-input-multiple-output (MIMO) digital-signal-processing, which reduces the cost and the complexity of the receiver. However, EC-FMF does not match with conventional multiplexers/de-multiplexers (MUXs/DeMUXs) such as a photonic lantern, leading to extra mode coupling loss and crosstalk. We design elliptical-core mode-selective photonic lanterns (EC-MSPLs) with six modes, which can match well with EC-FMF in MIMO-free MDM systems. Simulation of the EC-MSPL using the beam propagation method was demonstrated employing a combination of either step-index or graded-index fibers with six different sizes of cores, and the taper transition length of 8 cm or 4 cm. Through numerical simulations and optimizations, both types of photonic lanterns can realize low loss transmission and low crosstalk of below -20.0  dB for all modes.

Towards large dynamic range and ultrahigh measurement resolution in distributed fiber sensing based on multicore fiber

Featuring a dependence of Brillouin frequency shift (BFS) on temperature and strain changes over a wide range, Brillouin distributed optical fiber sensors are however essentially subjected to the relatively poor temperature/strain measurement resolution. On the other hand, phase-sensitive optical time-domain reflectometry (Φ-OTDR) offers ultrahigh temperature/strain measurement resolution, but the available frequency scanning range is normally narrow thereby severely restricts its measurement dynamic range. In order to achieve large dynamic range and high measurement resolution simultaneously, we propose to employ both the Brillouin optical time domain analysis (BOTDA) and Φ-OTDR through space-division multiplexed (SDM) configuration based on the multicore fiber (MCF), in which the two sensors are spatially separately implemented in the central core and a side core, respectively. As a proof of concept, the temperature sensing has been performed for validation with 2.5 m spatial resolution over 1.565 km MCF. Large temperature range (10 °C) has been measured by BOTDA and the 0.1 °C small temperature variation is successfully identified by Φ-OTDR with ~0.001 °C resolution. Moreover, the temperature changing process has been recorded by continuously performing the measurement of Φ-OTDR with 80 s frequency scanning period, showing about 0.02 °C temperature spacing at the monitored profile. The proposed system enables the capability to see finer and/or farther upon requirement in distributed optical fiber sensing.

Few-mode optical fiber based simultaneously distributed curvature and temperature sensing

The few-mode fiber (FMF) based Brillouin sensing operated in quasi-single mode (QSM) has been reported to achieve the distributed curvature measurement by monitoring the bend-induced strain variation. However, its practicality is limited by the inherent temperature-strain cross-sensitivity of Brillouin sensors. Here we proposed and experimentally demonstrated an approach for simultaneously distributed curvature and temperature sensing, which exploits a hybrid QSM operated Raman-Brillouin system in FMFs. Thanks to the larger spot size of the fundamental mode in the FMF, the Brillouin frequency shift change of the FMF is used for curvature estimation while the temperature variation is alleviated through Raman signals with the enhanced signal-to-noise ratio (SNR). Within 2 minutes measuring time, a 1.5 m spatial resolution is achieved along a 2 km FMF. The worst resolution of the square of fiber curvature is 0.333 cm^-2 while the temperature resolution is 1.301 °C at the end of fiber.

Highly sensitive strain sensor based on helical structure combined with Mach-Zehnder interferometer in multicore fiber

Optical fiber sensors for strain measurement have been playing important roles in structural health monitoring for buildings, tunnels, pipelines, aircrafts, and so on. A highly sensitive strain sensor based on helical structures (HSs) assisted Mach-Zehnder interference in an all-solid heterogeneous multicore fiber (MCF) is proposed and experimentally demonstrated. Due to the HSs, a maximum strain sensitivity as high as −61.8 pm/με was experimentally achieved. This is the highest sensitivity among interferometer-based strain sensors reported so far, to the best of our knowledge. Moreover, the proposed sensor has the ability to discriminate axial strain and temperature, and offers several advantages such as repeatability of fabrication, robust structure and compact size, which further benefits its practical sensing applications.

Ultra-high capacity WDM-SDM optical access network with self-homodyne detection downstream and 32QAM-FBMC upstream

Towards 100G beyond large-capacity optical access networks, wavelength division multiplexing (WDM) techniques incorporating with space division multiplexing (SDM) and affordable spectrally efficient advanced modulation formats are indispensable. In this paper, we proposed and experimentally demonstrated a cost-efficient multicore fiber (MCF) based hybrid WDM-SDM optical access network with self-homodyne coherent detection (SHCD) based downstream (DS) and direct detection optical filter bank multi carrier (DDO-FBMC) based upstream (US). In the DS experiments, the inner core of the 7-core fiber is used as a dedicated channel to deliver the local oscillator (LO) lights while the other 6 outer cores are used to transmit 4 channels of wavelength multiplexed 200-Gb/s PDM-16QAM-OFDM signals. For US transmission, 4 wavelengths with channel spacing of 100 GHz are intensity modulated with 30 Gb/s 32-QAM-FBMC and directly detected by a ~7 GHz bandwidth receiver after transmission along one of the outer core. The results show that a 4 × 6 × 200-Gb/s DS transmission can be realized over 37 km 7-core fiber without carrier frequency offset (CFO) and phase noise (PN) compensation even using 10 MHz linewidth DFB lasers. The SHCD based on MCF provides a compromise and cost efficient scheme between conventional intradyne coherent detection and intensity modulation and direct detection (IM/DD) schemes. Both US and DS have acceptable BER performance and high spectral efficiency.

Few-mode fiber based Raman distributed temperature sensing

We proposed and experimentally demonstrated a few mode fiber (FMF) based Raman distributed temperature sensor (RDTS) to extend the sensing distance with enhanced signal-to-noise ratio (SNR) of backscattered anti-Stokes spontaneous Raman scattering. Operating in the quasi-single mode (QSM) with efficient fundamental mode excitement, the FMF allows much larger input pump power before the onset of stimulated Raman scattering compared with the standard single mode fiber (SSMF) and mitigates the detrimental differential mode group delay (DMGD) existing in the conventional multimode fiber (MMF) based RDTS system. Comprehensive theoretical analysis has been conducted to reveal the benefits of RDTS brought by QSM operated FMFs with the consideration of geometric/optical parameters of different FMFs. The measurement uncertainty of FMF based scheme has also been evaluated. Among fibers being investigated and compared (SSMF, 2-mode and 4-mode FMFs, respectively), although an ideal 4-mode FMF based RDTS has the largest SNR enhancement in principle, real fabrication imperfections and larger splicing loss degrade its performance. While the 2-mode FMF based system outperforms in longer distance measurement, which agrees well with the theoretical calculations considering real experimental parameters. Using the conventional RDTS hardware, a 30-ns single pulse at 1550nm has been injected as the pump; the obtained temperature resolutions at 20km distance are estimated to be about 10°C, 7°C and 6°C for the SSMF, 4-mode and 2-mode FMFs, respectively. About 4°C improvement over SSMF on temperature resolution at the fiber end with 3m spatial resolution within 80s measuring time over 20km 2-mode FMFs have been achieved.

Non-covalent assembly of poly(allylamine hydrochloride)/triethylamine microcapsules with ionic strength-responsiveness and auto-fluorescence

Ionic strength-responsive microcapsules with auto-fluorescence were fabricated by incubation of poly(allylamine hydrochloride) (PAH)-doped CaCO₃ particles in triethylamine (Et₃N), followed by core removal using HCl. Based on the combination of hydrophobic interaction and hydrogen bonding, PAH and Et₃N formed a complex with a molar ratio of 3:1 (repeating unit of PAH: Et₃N). The as-prepared capsules showed extraordinary stability against 1M HCl, 1M NaOH and 6M urea solutions, and could swell or shrink reversibly in response to the ionic strength. Furthermore, the capsules possessed auto-fluorescence, allowing easily tracking of capsules during applications. Such interaction may be expanded to formation of stimuli-responsive multilayer films and other colloidal particles.

Downregulation of PCK2 remodels tricarboxylic acid cycle in tumor-repopulating cells of melanoma

For cancer cells to proliferate, a balance must be built between biomass-forming, glucose-metabolized intermediates and ATP production. How intrinsic glucose carbon flow regulates this balance remains unclear. Here we show that mitochondrial phosphoenolpyruvate carboxykinase (PCK2), the hub molecule linking tricarboxylic acid (TCA) cycle, glycolysis and gluconeogenesis by conversion of mitochondrial oxaloacetate (OAA) to phosphoenolpyruvate, regulates glucose carbon flow direction in stem-like cells that repopulate tumors (tumor-repopulating cells (TRCs)). PCK2 downregulation accelerated biosynthesis and transportation of citrate from mitochondria to the cytosol, leading to cytosolic glucose carbon flow via OAA-malate-pyruvate and acetyl-CoA-fatty acid pathways in TRCs. On the other hand, downregulating PCK2 hindered fumarate carbon flows in TCA cycle, leading to attenuated oxidative phosphorylation. In pathological terms, PCK2 overexpression slowed TRC growth in vitro and impeded tumorigenesis in vivo. Overall, our work unveiled unexpected glucose carbon flows of TRCs in melanoma that have implications for targeting metabolic aspects of melanoma.

Spatial-division multiplexed Brillouin distributed sensing based on a heterogeneous multicore fiber

We have experimentally investigated spatial-division multiplexed (SDM) Brillouin optical time-domain analysis in a heterogeneous multicore fiber whose central core and six outer cores are made from different preforms, showing a ∼70  MHz Brillouin frequency shift (BFS) difference between them. It reveals that the heterogeneous central core and the outer cores have different temperature sensitivities, but their strain sensitivities are almost the same. By making use of the distinct temperature coefficients of these two kinds of cores, simultaneous and discriminative temperature and strain measurements are achieved. The bending-induced Brillouin gain spectrum (BGS) broadening issue in off-center cores has been clarified, and a solution has been proposed to eliminate the uncertainty caused by a bending-induced BFS shift, by averaging the BFS variations of two symmetrical outer cores. We show a new perspective for discriminative measurement in Brillouin distributed sensors based on SDM solutions.

Spatial-division multiplexed hybrid Raman and Brillouin optical time-domain reflectometry based on multi-core fiber

Spatial-division multiplexed (SDM) hybrid Raman- and Brillouin- optical time-domain reflectometry (RODTR and BODTR) utilizing the multi-core fiber has been proposed and experimentally demonstrated. The solution is proposed in order to overcome the incompatible input pump power required for hybrid ROTDR and BOTDR in single mode fiber (SMF), while ensuring the capability of discriminative measurement between temperature and strain. What's more, the central core has been intentionally chosen to implement BOTDR so as to avoid bending-induced cross-sensitivity on Brillouin frequency shift (BFS) measurement. The proposed system utilizes a single laser source, shared pump generation devices, but separate interrogation fiber channels, thus enabling efficient input power management for the two reflectometry, allowing for simultaneous measurement of spontaneous Raman scattering and Brillouin scattering. The worst temperature and strain resolutions are estimated to be about 2.2 °C and 40 με respectively in 6 km sensing range with 3 m spatial resolution.

Heterogeneous all-solid multicore fiber based multipath Michelson interferometer for high temperature sensing

A compact high temperature sensor utilizing a multipath Michelson interferometer (MI) structure based on weak coupling multicore fiber (MCF) is proposed and experimentally demonstrated. The device is fabricated by program-controlled tapering the spliced region between single mode fiber (SMF) and a segment of MCF. After that, a spherical reflective structure is formed by arc-fusion splicing the end face of MCF. Theoretical analysis has been implemented for this specific multipath MI structure; beam propagation method based simulation and corresponding experiments were performed to investigate the effect of taper and spherical end face on system's performance. Benefiting from the multipath interferences and heterogeneous structure between the center core and surrounding cores of the all-solid MCF, an enhanced temperature sensitivity of 165 pm/°C up to 900°C and a high-quality interference spectrum with 25 dB fringe visibility were achieved.

Nile Red Loaded PLGA Nanoparticles Surface Modified with Gd-DTPA for Potential Dual-Modal Imaging

Here, a novel poly(lactic-co-glycolic acid) (PLGA)-based nanoparticles (NPs) for magnetic resonance (MR) and fluorescence imaging was developed for cell imaging. PLGA NPs loaded with fluorescent dye Nile red (NR) and surface-coated with poly(ethyleneimine) (PEI) were produced in a single step nanoprecipitation process. Diethylenetriamine pentaacetic dianhydride (DTPA) was conjugated to PLGA/NR@PEI NPs through amidation reaction between -COOH of DTPA and -NH2 of PEI, which can chelate gadolinium (Gd3+) as an MR imaging contrast agent. The PLGA/NR@PEI-DTPA-Gd NPs exhibited a uniform particle size of -200 nm and were stable in culture medium. These NPs had a high T relaxivity (R1) of 28.36 mM(-1)S(-1). They did not introduce serious cytotoxicity against A549 lung cancer cells. Furthermore, fluorescence and MR imaging studies on A549 lung cancer cells in vitro revealed that PLGA/NR@PEI-DTPA-Gd NPs can serve as an efficient fluorescence/MR dual-modality imaging nanoprobe.

Enhanced Cellular Uptake of Bowl-like Microcapsules

Among several properties of colloidal particles, shape is emerging as an important parameter for tailoring the interactions between particles and cells. In this study, bowl-like multilayer microcapsules were prepared by osmotic-induced invagination of their spherical counterparts in a concentrated polyelectrolyte solution. The internalization behaviors of bowl-like and spherical microcapsules were compared by coincubation with smooth muscle cells (SMCs) and macrophages. The bowl-like capsules tended to attach onto the cell membranes from the bend side and could be enwrapped by the membranes of SMCs, leading to a faster uptake rate and larger accumulation inside cells than those of their spherical counterparts. These results are important for understanding the shape-dependent internalization behavior, providing useful guidance for further materials design especially in biomedical applications.