Silicon photonic MEMS switches based on split waveguide crossings

The continuous push for high-performance photonic switches is one of the most crucial premises for the sustainable scaling of programmable and reconfigurable photonic circuits for a wide spectrum of applications. Large-scale photonic switches constructed with a large number of 2$\times$2 elementary switches impose stringent requirements on the elementary switches. In contrast to conventional elementary switches based on mode interference or mode coupling, here we propose and realize a brand-new silicon MEMS 2$\times$2 elementary switch based on a split waveguide crossing (SWX) consisting of two halves. With this structure, the propagation direction of the incident light can be manipulated to implement the OFF and ON states by splitting or combining the two halves of the SWX, respectively. More specifically, we introduce refractive-index engineering by incorporating subwavelength-tooth (SWT) structures on both reflecting facets to further reduce the excess loss in the ON state. Such a unique switching mechanism features a compact footprint on a standard SOI wafer and enables excellent photonic performance with low excess loss of 0.1-0.52/0.1-0.47dB and low crosstalk of $\lt$-37/-22.5dB over an ultrawide bandwidth of 1400-1700nm for the OFF/ON states in simulation, while in experiment, excess loss of 0.15-0.52/0.42-0.66dB and crosstalk of $\lt$-45.5/-25dB over the bandwidth of 1525-1605 nm for the OFF/ON states have been measured.Furthermore, excellent MEMS characteristics such as near-zero steady-state power consumption, low switching energy of sub-pJ, switching speed of {\mu}s-scale, durability beyond 10^9 switching cycles, and overall device robustness have been achieved. Finally, a 16$\times$16 switch using Benes topology has also been fabricated and characterized as a proof of concept, further validating the suitability of the SWX switches for large-scale integration

Efficiency-boosted semiconductor optical amplifiers via mode-division multiplexing

Semiconductor optical amplifiers (SOAs) are a fundamental building block for many photonic systems. However, their power inefficiency has been setting back operational cost reduction, circuit miniaturization, and the realization of more complex photonic functions such as large-scale switches and optical phased arrays. In this work, we demonstrate significant gain and efficiency enhancement using an extra degree of freedom of light—the mode space. This is done without changing the SOA’s material design, and therefore high versatility and compatibility can be obtained. Light is multiplexed in different guided modes and reinjected into the same gain section twice without introducing resonance, doubling the interaction length in a broadband manner. Up to 87% higher gain and 300% higher wall-plug efficiency are obtained in a double-pass SOA compared to a conventional single-pass SOA, at the same operating current, in the wavelength range of 1560–1580 nm

Notch1 is required for hypoxia-induced proliferation, invasion and chemoresistance of T-cell acute lymphoblastic leukemia cells

Background Notch1 is a potent regulator known to play an oncogenic role in many malignancies including T-cell acute lymphoblastic leukemia (T-ALL). Tumor hypoxia and increased hypoxia-inducible factor-1α (HIF-1α) activity can act as major stimuli for tumor aggressiveness and progression. Although hypoxia-mediated activation of the Notch1 pathway plays an important role in tumor cell survival and invasiveness, the interaction between HIF-1α and Notch1 has not yet been identified in T-ALL. This study was designed to investigate whether hypoxia activates Notch1 signalling through HIF-1α stabilization and to determine the contribution of hypoxia and HIF-1α to proliferation, invasion and chemoresistance in T-ALL. Methods T-ALL cell lines (Jurkat, Sup-T1) transfected with HIF-1α or Notch1 small interference RNA (siRNA) were incubated in normoxic or hypoxic conditions. Their potential for proliferation and invasion was measured by WST-8 and transwell assays. Flow cytometry was used to detect apoptosis and assess cell cycle regulation. Expression and regulation of components of the HIF-1α and Notch1 pathways and of genes related to proliferation, invasion and apoptosis were assessed by quantitative real-time PCR or Western blot. Results Hypoxia potentiated Notch1 signalling via stabilization and activation of the transcription factor HIF-1α. Hypoxia/HIF-1α-activated Notch1 signalling altered expression of cell cycle regulatory proteins and accelerated cell proliferation. Hypoxia-induced Notch1 activation increased the expression of matrix metalloproteinase-2 (MMP2) and MMP9, which increased invasiveness. Of greater clinical significance, knockdown of Notch1 prevented the protective effect of hypoxia/HIF-1α against dexamethasone-induced apoptosis. This sensitization correlated with losing the effect of hypoxia/HIF-1α on Bcl-2 and Bcl-xL expression. Conclusions Notch1 signalling is required for hypoxia/HIF-1α-induced proliferation, invasion and chemoresistance in T-ALL. Pharmacological inhibitors of HIF-1α or Notch1 signalling may be attractive interventions for T-ALL treatment

Low-loss chip-scale programmable silicon photonic processor

Chip-scale programmable optical signal processors are often used to flexibly manipulate the optical signals for satisfying the demands in various applications, such as lidar, radar, and artificial intelligence. Silicon photonics has unique advantages of ultra-high integration density as well as CMOS compatibility, and thus makes it possible to develop large-scale programmable optical signal processors. The challenge is the high silicon waveguides propagation losses and the high calibration complexity for all tuning elements due to the random phase errors. In this paper, we propose and demonstrate a programmable silicon photonic processor for the first time by introducing low-loss multimode photonic waveguide spirals and low-random-phase-error Mach-Zehnder switches. The present chip-scale programmable silicon photonic processor comprises a 1×4 variable power splitter based on cascaded Mach-Zehnder couplers (MZCs), four Ge/Si photodetectors, four channels of thermally-tunable optical delaylines. Each channel consists of a continuously-tuning phase shifter based on a waveguide spiral with a micro-heater and a digitally-tuning delayline realized with cascaded waveguide-spiral delaylines and MZSs for 5.68 ps time-delay step. Particularly, these waveguide spirals used here are designed to be as wide as 2 µm, enabling an ultralow propagation loss of 0.28 dB/cm. Meanwhile, these MZCs and MZSs are designed with 2-µm-wide arm waveguides, and thus the random phase errors in the MZC/MZS arms are negligible, in which case the calibration for these MZSs/MZCs becomes easy and furthermore the power consumption for compensating the phase errors can be reduced greatly. Finally, this programmable silicon photonic processor is demonstrated successfully to verify a number of distinctively different functionalities, including tunable time-delay, microwave photonic beamforming, arbitrary optical signal filtering, and arbitrary waveform generation

Distinguishing s±s^{\pm} and s++s^{++} electron pairing symmetries by neutron spin resonance in superconducting NaFe0.935_{0.935}Co0.045_{0.045}As

A determination of the superconducting (SC) electron pairing symmetry forms the basis for establishing a microscopic mechansim for superconductivity. For iron pnictide superconductors, the $s^\pm$-pairing symmetry theory predicts the presence of a sharp neutron spin resonance at an energy below the sum of hole and electron SC gap energies ($E\leq 2\Delta$) below $T_c$. On the other hand, the $s^{++}$-pairing symmetry expects a broad spin excitation enhancement at an energy above $2\Delta$ below $T_c$. Although the resonance has been observed in iron pnictide superconductors at an energy below $2\Delta$ consistent with the $s^\pm$-pairing symmetry, the mode has also be interpreted as arising from the $s^{++}$-pairing symmetry with $E\ge 2\Delta$ due to its broad energy width and the large uncertainty in determining the SC gaps. Here we use inelastic neutron scattering to reveal a sharp resonance at E=7 meV in SC NaFe$_{0.935}$Co$_{0.045}$As ($T_c = 18$ K). On warming towards $T_c$, the mode energy hardly softens while its energy width increases rapidly. By comparing with calculated spin-excitations spectra within the $s^{\pm}$ and $s^{++}$-pairing symmetries, we conclude that the ground-state resonance in NaFe$_{0.935}$Co$_{0.045}$As is only consistent with the $s^{\pm}$-pairing, and is inconsistent with the $s^{++}$-pairing symmetry.Comment: 9 pages, 8 figures. submitted to PR

Ultra-compact lithium niobate photonic chip for high-capacity and energy-efficient wavelength-division-multiplexing transmitters

Recently, high-performance thin-film lithium niobate optical modulators have emerged that, together with advanced multiplexing technologies, are highly expected to satisfy the ever-growing demand for high-capacity optical interconnects utilizing multiple channels. Accordingly, in this study, a compact lithium-niobate-on-insulator (LNOI) photonic chip was adopted to establish four-channel wavelength-division-multiplexing (WDM) transmitters, comprising four optical modulators based on ultracompact 2 × 2 Fabry-Perot cavities and a four-channel WDM filter based on multimode waveguide gratings. The fabricated chip with four wavelength channels has a total footprint as compact as 0.3 × 2.8 mm2, and exhibits an excess loss of ~0.8 dB as well as low inter-channel crosstalk of < –22 dB. Using this LNOI photonic chip, high-capacity data transmissions of 320 Gbps (4 × 80 Gbps) on-off-keying signals and 400 Gbps (4 × 100 Gbps) four-level pulse amplitude signals were successfully realized with the ultra-low power consumption of 11.9 fJ/bit