No abstract

We report the observation of four-wave mixing phenomenon in a simple silicon wire waveguide at the optical powers normally employed in communications systems. The maximum conversion efficiency is about -35 dB in the case of a 1.58-cm-long silicon wire waveguide. The nonlinear refractive index coefficient is found to be 9x10-18 m2/W. This value is not negligible for dense wavelength division multiplexing components, because it predicts the possibility of large crosstalk. On the other hand, with longer waveguide lengths with smaller propagation loss, it would be possible to utilize just a simple silicon wire for practical wavelength conversion. We demonstrate the wavelength conversion for data rate of 10-Gbps using a 5.8-cm-long silicon wire. These characteristics are attributed to the extremely small core of silicon wire waveguides.

Phenylketonuria (PKU) is an autosomal recessive genetic disease caused by the defects in the phenylalanine hydroxylase (PAH) gene. Individuals homozygous for defective PAH alleles show elevated levels of systemic phenylalanine and should be under strict dietary control to reduce the risk of neuronal damage associated with high levels of plasma phenylalanine. Researchers predict that plant phenylalanine ammonia-lyase (PAL), which converts phenylalanine to nontoxic t-cinnamic acid, will be an effective therapeutic enzyme for the treatment of PKU. The problems of this potential enzyme therapy have been the low stability in the circulation and the antigenicity of the plant enzyme. Recombinant PAL originated from parsley (Petroselinum crispum) chemically conjugated with activated PEG2 [2,4-bis(O-methoxypolyethyleneglycol)-6-chloro-s-triazine] showed greatly enhanced stability in the circulation and was effective in reducing the plasma concentration of phenylalanine in the circulation of mice. PEG-PAL conjugate will be an effective therapeutic enzyme for the treatment of PKU.

Optical properties of P+ ion-implanted Si(100) wafers have been studied using spectroscopic ellipsometry (SE). The P+ ions are implanted at 150 keV with fluences ranging from 1×1014 to 2×1015 cm−2 at room temperature. An effective-medium-approximation analysis suggests that the ion-implanted layer can be explained by a physical mixture of microcrystalline and amorphous silicon. The ε(E) spectrum of the microcrystalline component is found to differ appreciably from that of single-crystalline silicon, especially in the vicinity of the sharp critical-point features. This difference in ε(E) can be successfully interpreted by increasing the broadening parameter at each critical point. Considering these and previous data, we obtain an expression, A=(5.13×1011/EacM)1.872, which enables us to estimate the amorphization-threshold fluence A for silicon implanted with optional ion species of mass number M at energy Eac in keV. No clear change in the original structure of silicon surface after P+ ion implantation has been observed by atomic force microscopy. SE has been proven to be an easy, fast, and nondestructive technique which can be used to assess important ion-implantation parameters.

No abstract