Ultracompact programmable inverse-designed nanophotonic devices based on digital subwavelength structures.

Inverse design is a powerful approach to achieve ultracompact nanophotonic devices. Here, we propose an ultracompact programmable near-infrared nanophotonic device platform to dynamically implement inverse-designed near-infrared devices with different functions by programming the state of the phase-change material filled in each pixel. By tuning PCM block by block, the subwavelength condition for inverse-designed ultracompact devices is satisfied with large tuning pixel size. Based on the inverse-design device platform with a footprint of 6.4µm×8µm, we design and theoretically demonstrate four power splitters with different split ratios and one mode multiplexer working in the near-infrared band. The average excess losses for the power splitters with ratios of 0:1,1:1, 2:1, and 3:1 are less than 0.82, 0.65, 0.82, and 1.03 dB over a wavelength span of 100 nm, respectively. Meanwhile, the insertion losses of the mode multiplexer are 1.4 and 2.5 dB for T E 0 and T E 1 mode, respectively, and the average crosstalk is less than -20 and -19d B, respectively. The five different devices could be configured online in a nonvolatile way by heating phase change materials with an off-chip laser, which may significantly enhance the flexibility of on-chip optical interconnections.

Direct modulation bandwidth enhancement of uncooled DFB laser operating over a wide temperature range based on groove-in-trench waveguide structure.

Uncooled direct modulation DFB laser offers high speed transmission rate over a wide temperature range with high reliability and low cost, making it a cost-effective light source choice for 5G fronthaul and data center applications. However, a significant 3dB bandwidth decrease can be observed in high temperature for conventional DFB lasers. We present an uncooled DFB laser operating up to 85°C with extended direct modulation bandwidth and high reliability based on a novel groove-in-trench ridge waveguide structure, where two narrow grooves penetrating the active layer are etched symmetrically in the two conventional trenches by deep wet etching, respectively. By optimizing the distance between the groove and the mesa stripe, we obtain a 3dB bandwidth of 15.3 GHz at 85°C, which is a 3.7 GHz improvement compared with the conventional ridge waveguide DFB laser. Transmissions of 25 Gb/s NRZ signal at 25°C and 85°C with clear eye openings have been demonstrated. It also achieves 25 Gb/s transmission over 10 km optical fiber with a low power penalty of 0.5 dB for a bit error rate of 10-12 at 85°C. In addition, the result of 2000-hour aging test shows that the proposed groove-in-trench structure DFB lasers have the same excellent reliability as the conventional ones.

Experiment demonstration of high speed 1.3 µm grating assisted surface-emitting DFB lasers.

Surface emitting lasers are attractive light sources for silicon integrated photonic circuits. High speed direct operation is of great importance for these lasers in high capacity and low cost on-chip communication system. Here, we demonstrate a 1.3 µm surface emitting ridge-waveguide distributed feedback (DFB) laser with second order grating and λ/4 phase shift grating, which can achieve a 24 Gb/s operation over a wide temperature. The fabricated lasers can achieve low threshold current as 6.8 mA, and 12.5 mA at 20, and 70°C, respectively. Stable single mode operation has been observed with high side mode suppression ratio (SMSR) > 40 dB at all temperatures (20-70 °C). Meanwhile, the surface emitting optical power can reach 1.7 mW at high temperature as 70 °C. 3 dB bandwidth of small signal response is 21 GHz and 12 GHz at 20 °C and 70 °C respectively. The far-field divergence angle of surface emitting beam is 13.4°×20.2° of 10 µm length second order grating coupler. The proposed laser may have great advantages of single mode, high speed modulation and good temperature tolerance. In addition, compared with conventional DFB lasers, the surface emitting DFB laser has no additional manufacturing process, which is simple to fabricate and easy to integrate with silicon platform.

[The quantitative analysis of Ub and UbE1 in focus of traumatic epilepsy].

OBJECTIVE: To study the expression of ubiquitin proteasome system (UPS) in the traumatic epilepsy pathogenesis and its value in traumatic epilepsy by quantitative analysis. METHODS: Fifteen specimens from human epileptic temporal cortex from PTE were collected as the PTE group. Fifteen specimens from non-PTE were collected as the non-PTE group. Fifteen normal cerebral cortex specimens died from acute traffic accident were collected as the control group. The expression of mRNA and protein of Ub and UbE1 were detected by RT-PCR and Western blot. Statistical analysis was used to compare the data between three groups. RESULTS: The expression of mRNA and protein of Ub and UbE1 were the following order: PTE group(high), non-PTE group(middle) and control group(low). CONCLUSION: The study confirms that UPS is up-regulated in the epilepsy's focus, especially in traumatic epilepsy. The activation of UPS may be an important pathological change in neurons in pathogenesis of traumatic epilepsy.

[Morphology changes of ubiquitin-proteasome system in traumatic epilepsy].

OBJECTIVE: To investigate the value of ubiquitin(Ub) and ubiquitin-activating enzymel(UbE1) for the appraisement of post traumatic epilepsy (PTE). METHODS: Fifteen specimens from human epileptic temporal cortex originating from PTE were collected as the PTE group. Fifteen specimens from non-PTE were collected as the non-PTE group. Meanwhile, 15 normal cerebral cortex specimens from people dead from acute traffic accident were collected as the control groups. Observe morphology changes of each group with HE, then with immunohistochemistry of Ub and UbE1. RESULTS: Compared to the control group, morphology changes of neuron quantity reduction, neuron denaturation and so on were observed both in the PTE group and the non-PTE group under HE, especially in the PTE group. Ub and UbE1 mainly expressed in the nucleus and cytoplasm of the neurons in epilepsy spot without extracellular expression. The expression of Ub and UbE1 is PTE group > non-PTE group > control group (P < 0.05). CONCLUSIONS: The neuron denaturation are one of the main pathology changes of epilepsy, and it is more obvious in the PTE group. Immunohistochemistry of Ub and UbE1 may be more helpful to distinguish PTE and non-PTE than HE staining.