Spatially resolved multimode excitation for smooth supercontinuum generation in a SiN waveguide.

We propose a method of supercontinuum light generation enhanced by multimode excitation in a precisely dispersion-engineered deuterated SiN (SiN:D) waveguide. Although a regularly designed SiN-based nonlinear optical waveguide exhibits anomalous dispersion with the fundamental and first-order multimode operation, the center-symmetric light pumping at the input edge has so far inhibited the full potential of the nonlinearity of SiN-based materials. On the basis of numerical analysis and simulation for the SiN:D waveguide, we intentionally applied spatial position offsets to excite the fundamental and higher-order modes to realize bandwidth broadening with flatness. Using this method, we achieved an SNR improvement of up to 18 dB at a wavelength of 0.6 µm with an offset of about 1 µm in the Y-axis direction and found that the contribution was related to the presence of dispersive waves due to the excitation of TE10, and TE01 modes.

Cross-gain modulation-based photonic reservoir computing using low-power-consumption membrane SOA on Si.

We demonstrate photonic reservoir computing (RC) utilizing cross-gain modulation (XGM) in a membrane semiconductor optical amplifier (SOA) on a Si platform. The membrane SOA's features of small active volume and strong optical confinement enable low-power nonlinear operation of the reservoir, with 101-mW-scale power consumption and 102-µW-scale optical input power. The power consumption is about an order of magnitude lower than that of conventional SOAs that exhibit saturable nonlinearity. The XGM-based reservoir is configured by injecting a delayed feedback signal into the SOA from a direction opposite to the input signal. This configuration provides robust operation of the feedback circuit because of the phase insensitivity and the elimination of loop oscillation risk. The RC performance is evaluated via the information processing capacity (IPC) and a nonlinear benchmark task. It is revealed that the XGM-based reservoir performs strong nonlinear transformation of input time-series signals. The series of results consistently show that the membrane SOA performs RC-applicable nonlinear operations through XGM at a low power scale.

Heterogeneously integrated widely tunable laser using lattice filter and ring resonator on Si photonics platform.

We fabricated a tunable laser consisting of a Si lattice filter, a Si ring resonator, and a III-V gain region. The lattice filter, a cascade of interferometers with the same delay length, has periodic transmission peaks with a wide free spectral range (FSR). By connecting the lattice filter to a ring resonator with a narrow FSR, the lasing mode is selected from one of the resonance modes of the ring resonator. The lasing wavelength can be tuned by changing the transmission peak wavelength of the lattice filter, in which an integrated micro heater controls the refractive index of the longer or shorter arm. Since the length of the refractive index control region on both arms of the lattice filter can be extended while maintaining a wide FSR, a wide tuning range can be obtained. This laser facilitates the control of the lasing wavelength because of the simple configuration. The Si lattice filter and the Si ring resonator were fabricated on a Si photonics platform by a Si photonics foundry, and III-V gain region was heterogeneously integrated. The lasing wavelength is shifted to a longer (shorter) one by heating the longer (shorter) arm of the lattice filter, in which the tuning wavelength is 1529 to 1561 nm and side-mode suppression ratio is more than 40 dB. A Lorentzian linewidth for lasing wavelengths narrower than 40 kHz is also demonstrated.

Direct f-3f self-referencing using an integrated silicon-nitride waveguide.

We have achieved the simultaneous generation of a 2.6-octave-wide supercontinuum (SC) spectrum over 400-2500 nm and third-harmonic light solely by a dispersion-controlled silicon-nitride waveguide (SiNW). To increase the visible intensity of the SC light component, we fabricated low-loss 5-mm-long deuterated SiNWs with spot-size converters by low-temperature deposition. We succeeded in measuring the carrier-envelope-offset (CEO) signal with a 34-dB signal-to-noise ratio because this short deuterated SiNW provides a large temporal overlap between the f and 3f components. In addition, we have demonstrated this method of CEO locking at telecommunications wavelengths with f-3f self-referencing generated solely by the SiNW without the use of highly nonlinear fiber and an additional nonlinear crystal. Compared with the method of CEO locking with a highly nonlinear fiber and a standard f-2f self-referencing interferometer, this method is not only simple and compact but also stable.

Cold shock protein RBM3 is upregulated in the autophagy-deficient brain.

Neural autophagy plays an important role in regulating protein quality control, brain homeostasis, and body temperature. However, the mechanism that links a defect in autophagy to body temperature has not been elucidated. Here, we report that RNA binding motif protein 3 (RBM3) is a potential candidate that regulates body temperature. We found that the body temperatures of Nestin-Cre ; Atg7 f/f conditional KO (cKO) mice were lower than that of wild-type (WT) mice. Moreover, RBM3 was upregulated in the Nestin-Cre ; Atg7 f/f brain. These data suggest that RBM3 is an implicit target that maintains body temperature influenced by neural autophagy.

Integration of a high-efficiency Mach-Zehnder modulator with a DFB laser using membrane InP-based devices on a Si photonics platform.

We demonstrate a wafer-level integration of a distributed feedback laser diode (DFB LD) and high-efficiency Mach-Zehnder modulator (MZM) using InGaAsP phase shifters on Si waveguide circuits. The key to integrating materials with different bandgaps is to combine direct wafer bonding of a multiple quantum well layer for the DFB LD and regrowth of a bulk layer for the phase shifter. Buried regrowth of an InP layer is also employed to define the waveguide cores for the LD and phase shifters on a Si substrate. Both the LD and phase shifters have 230-nm-thick lateral diodes, whose thickness is less than the critical thickness of the III-V compound semiconductor layers on the Si substrate. The fabricated device has a 500-µm-long DFB LD and 500-µm-long carrier-depletion InGaAsP-bulk phase shifters, which provide a total footprint of only 1.9 × 0.31 mm2. Thanks to the low losses of the silica-based fiber couplers, InP/Si narrow tapers, and the phase shifters, the fiber-coupled output power of 3.2 mW is achieved with the LD current of 80 mA. The MZM has a VπL of around 0.4 Vcm, which overcomes the VπL limit of typical carrier-depletion Si MZMs. Thanks to the high modulation efficiency, the device shows an extinction ratio of 5 dB for 50-Gbit/s NRZ signal with a low peak-to-peak voltage of 2.5 V, despite the short phase shifters and single-arm driving.

Membrane buried-heterostructure DFB laser with an optically coupled III-V/Si waveguide.

We have developed a membrane buried-heterostructure (BH) distributed feedback (DFB) laser consisting of an optically coupled III-V/Si waveguide and SiN surface grating. A 230-nm-thick membrane III-V layer enables us to construct an optical supermode in a 220-nm-thick Si waveguide and control the optical confinement factor in both the III-V and Si layers by changing Si waveguide width. This makes it possible to use a conventional Si photonics platform because the Si waveguides widely used on it are around 220-nm thick. To fabricate the BH-the key component for constructing a membrane laser with a lateral current-injection structure-we used direct wafer bonding and regrowth by metalorganic vapor phase epitaxy. Light output from the DFB laser is transferred to the Si waveguide through a short inverse-taper InP waveguide. A fiber-chip interface constructed by using inverse-taper Si waveguides and SiOx waveguides provides 2-dB fiber coupling loss. Fiber coupling power of 7.9 mW is obtained with a λ/4-shifted DFB laser with a 500-µm-long cavity. Single-mode lasing with a side-mode suppression ratio of 50 dB and lasing up to 120°C are also demonstrated.

Membrane InGaAsP Mach-Zehnder modulator with SiN:D waveguides on Si platform.

A high-efficiency InGaAsP Mach-Zehnder modulator is integrated with hydrogen-free deuterated silicon nitride (SiN:D) waveguide circuits on a Si substrate. A thin InP-based layer provides a high optical confinement factor of around 50% and enables easy optical coupling to the SiN:D waveguides, which are fabricated by a low-temperature backend process. The fabricated Mach-Zehnder modulator with a 300-µm-long phase shifter shows a VπL of 0.4 Vcm, insertion loss of ~4.5 dB, and an error-free operation for 40-Gbit/s non-return-to-zero signal.

IL-1alpha induces angiogenesis in brain endothelial cells in vitro: implications for brain angiogenesis after acute injury.

Inflammation is a major contributor to neuronal injury and is associated with poor outcome after acute brain injury such as stroke. The pro-inflammatory cytokine interleukin (IL)-1 is a critical regulator of cerebrovascular inflammation after ischemic injury, mainly through action of both of its isoforms, IL-1α and IL-1ß, at the brain endothelium. In contrast, the differential action of these ligands on endothelial activation and post-stroke angiogenesis is largely unknown. Here, we demonstrate that IL-1α is chronically elevated in the brain after experimental stroke suggesting that it is present during post-stroke angiogenic periods. Furthermore, we demonstrate that IL-1α is a potent mediator of endothelial activation and inducer of angiogenic markers in endothelial cells in vitro. Using brain endothelial cell lines, we found that IL-1α was significantly more potent than IL-1ß at inducing endothelial cell activation, as measured by expression of the pro-angiogenic chemokine CXCL-1. IL-1α also induced strong expression of the angiogenic mediator IL-6 in a concentration-dependent manner. Furthermore, IL-1α induced significant proliferation and migration of endothelial cells, and promoted formation of tube-like structures that are established key hallmarks of angiogenesis in vitro. Finally, all of those responses were blocked by the IL-1 receptor antagonist (IL-1RA). In conclusion, our data highlights a potential new role for IL-1 in brain repair mechanisms and identifies IL-1α as a potential new therapy to promote post-stroke angiogenesis. Inflammation is a major contributor to neuronal injury and is associated with poor outcome after neurotrauma. We demonstrate that cytokine IL-1α is chronically elevated in the brain after experimental stroke suggesting that it is present chronically post-stroke. We demonstrate that IL-1α is a potent mediator of endothelial activation and inducer of angiogenic markers in endothelial cells. Our data highlights a new role for IL-1 in brain repair mechanisms and identifies IL-1α as a potential therapy to promote post-stroke angiogenesis.