Photodetection in silicon beyond the band edge with surface states

Silicon is an extremely attractive material platform for integrated optics at telecommunications wavelengths, particularly for integration with CMOS circuits. Developing detectors and electrically pumped lasers at telecom wavelengths are the two main technological hurdles before silicon can become a comprehensive platform for integrated optics. We report on the generation of free carriers in unimplanted SOI ridge waveguides, which we attribute to surface state absorption. By electrically contacting the waveguides, a photodetector with a responsivity of 36 mA/W and quantum efficiency of 2.8% is demonstrated. The photoconductive effect is shown to have minimal falloff at speeds of up to 60 Mhz

Axial, induced pseudoscalar, and pion-nucleon form factors in manifestly Lorentz-invariant chiral perturbation theory

We calculate the nucleon form factors G_A and G_P of the isovector axial-vector current and the pion-nucleon form factor G_piN in manifestly Lorentz-invariant baryon chiral perturbation theory up to and including order O(p^4). In addition to the standard treatment including the nucleon and pions, we also consider the axial-vector meson a_1 as an explicit degree of freedom. This is achieved by using the reformulated infrared renormalization scheme. We find that the inclusion of the axial-vector meson effectively results in one additional low-energy coupling constant that we determine by a fit to the data for G_A. The inclusion of the axial-vector meson results in an improved description of the experimental data for G_A, while the contribution to G_P is small.Comment: 21 pages, 9 figures, REVTeX

Low-energy electron beam focusing in self-organized porous alumina vacuum windows

Micromachined, micron-thick porous alumina membranes with closed pore endings show high electron transparency above an energy of 5 keV. This is due to the channeling of electrons along the negatively charged insulating pores after surmounting the thin entrance layer. We also find a sharp hightransparency energy window at energies as low as 2 keV which may be the result of a local maximum of channeling, as predicted by simulations, and positive charge up of the entrance layer causing electron electrostatic focusing. Applications for these membranes range from atmospheric electron spectroscopy to self-assembled, nanoscale, large-area electron collimators

Design of a tunable, room temperature, continuous-wave terahertz source and detector using silicon waveguides

We describe the design of a silicon-based source for radiation in the 0.5-14 THz regime. This new class of devices will permit continuously tunable, milliwatt scale, cw, room temperature operation, a substantial advance over currently available technologies. Our silicon terahertz generator consists of a silicon waveguide for near-infrared radiation, contained within a metal waveguide for terahertz radiation. A nonlinear polymer cladding permits two near-infrared lasers to mix, and through difference-frequency generation produces terahertz output. The small dimensions of the design greatly increase the optical fields, enhancing the nonlinear effect. The design can also be used to detect terahertz radiation

Photonic Crystal Nanocavities and Waveguides

Fabrication of optical structures has evolved to a precision which allows us to control light within etched nanostructures. Nano-optic cavities can be used for efficient and flexible concentration of light in small volumes, and control over both emission wavelength and frequency. Conversely, if a periodic pattern is defined in the top semitransparent metal layer by lithography, it is possible to efficiently couple out the light out of a semiconductor and to simultaneously enhance the spontaneous emission rate. Here we demonstrate the use of photonic crystals for efficient light localization and light extraction

Photonic Crystals and their Applications to Efficient Light Emitters

When combined with high index contrast slabs in which light can be efficiently guided, microfabricated two-dimensional photonic bandgap mirrors provide us with the geometries needed to confine and concentrate light into extremely small volumes and to obtain very high field intensities. Fabrication of optical structures has now evolved to a precision which allows us to control light within such etched nanostructures. Sub-wavelength nano-optic cavities can be used for efficient and flexible control over both emission wavelength and frequency, and nanofabricated optical waveguides can be used for efficient coupling of light between devices. The reduction of the size of optical components leads to their integration in large numbers and the possibility to combine different functionalities on a single chip. We show uses of such crystals in functional nonlinear optical devices, such as lasers, modulators, add/drop filters, polarizers and detectors