Stress tuning of the fundamental absorption edge of pure germanium waveguides

One-dimensional stress dependence on the fundamental absorption edge of pure germanium (Ge) waveguide has theoretically and experimentally been studied, considering built-in two-dimensional stress-tensile Ge grown on Si. Based on the results, we have designed Ge Franz-Keldysh (FK) electroabsorption (EA) modulators to work at 1550 nm. Application of one-dimensional [110] compressive stress above -350 MPa on a pure Ge [-110] waveguide should allow 1550 nm light transmission, unless otherwise a pure Ge modulator can only operate at 1600 nm or longer due to the built-in two-dimensional tensile stress in Ge. The prediction has experimentally been verified using a SiNx stressor film. This concludes that the presented stress-tuning approach of the pure Ge waveguides should expand the operation wavelength of Ge FK-EA modulators to C band. Since stress tuning can be locally done in the back-end-of-line of complementary metal oxide semiconductor (CMOS) process, the presented stress-tuning method should enable "field-programable" control of the operation wavelengths of the monolithically integrated Ge modulators in Si photonics platform.

Local bandgap control of germanium by silicon nitride stressor

We have proposed a new approach to tune the operation wavelength of Franz-Keldysh Ge electro-absorption modulation in Si photonics by controlling the local strain environment to cover the whole range of C + L bands (1.53 - 1.62 μm). The present paper shows a proof of strain-tuning modulator concept by the shift of the Ge absorption edge using SiN(x) stressor films and Franz-Keldysh effect in strain-controlled Ge.

Candesartan prevents the progression of glomerulosclerosis in genetic hypertensive rats

The renin-angiotensin system (RAS) has been implicated in the development of hypertensive glomerulosclerosis. However, there are no experimental findings clearly demonstrating activation of glomerular RAS in hypertensive nephropathy. Using the stroke-prone spontaneously hypertensive rat (SHRSP) as an animal model of hypertensive glomerulosclerosis, we examined the relationship between the sequential changes in urinary albumin excretion (UAE), renal morphology, and glomerular mRNA expression for transforming growth factor-beta (TGF-beta) and fibronectin (FN) and glomerular mRNA levels for RAS components, and determined the effects of the angiotensin II (Ang II) type 1 (AT-1) receptor antagonist (candesartan) and equihypotensive hydralazine on these parameters. In SHRSP, UAE was normal at nine weeks of age and increased by 12 weeks. Plasma renin activity, plasma Ang II concentration, and angiotensin converting enzyme (ACE) activity were not higher in 9- and 12-week-old SHRSP than in WKY. RNase protection assay revealed higher glomerular mRNA levels for angiotensinogen, ACE, and AT-1a and AT-1b receptors in 9-, 12-, and 14-week-old SHRSP than in WKY. The glomerular mRNA levels for TGF-beta and FN in SHRSP were increased from nine weeks of age. SHRSP had a greater glomerulosclerosis index (GSI) at 24 weeks of age than did WKY. Administration of candesartan for two weeks, but not of hydralazine, markedly reduced UAE and normalized mRNA levels for TGF-beta, FN, and RAS components. Candesartan administration for 12 weeks virtually prevented the progression of glomerulosclerosis in rats. We conclude that in SHRSP, RAS activation and increased sensitivity to Ang II in glomeruli play important roles in the progression of glomerulosclerosis.

Involvement of angiotensin II in glomerulosclerosis of stroke-prone spontaneously hypertensive rats

Renal plasma flow (RPF), glomerular filtration rate (GFR), glomerular pathology and glomerular TGF-beta gene expression were examined in 12- and 24-week-old stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar Kyoto rats (WKY). These parameters were also examined in SHRSP treated with equihypotensive doses of angiotensin II receptor antagonist (CV-11974:CV) and hydralazine (Hyd) for 12 weeks. Twelve-week-old SHRSP showed a decrease in RPF and GFR, and an increase in filtration fraction (FF) and urinary protein excretion (UP) compared to WKY. CV normalized these parameters, whereas although Hyd showed improved levels they were not to the levels achieved by the WKY. Glomerular TGF-beta expression was increased 2.0-fold in 12- and 24-week-old SHRSP, and CV, but not Hyd, decreased it to the control levels of WKY. At 24 weeks old, SHRSP showed a higher glomerulosclerosis index (GI) than WKY. CV, but not Hyd, lowered the GI to the level of the WKY controls. These data indicate that renal hemodynamic changes are closely associated with an increased TGF-beta expression in SHRSP and that this condition is caused by angiotensin II.