Chemiresistive response of silicon nanowires to trace vapor of nitro explosives.

Silicon nanowires are observed to behave as chemically modulated resistors and exhibit sensitive and fast electrical responses to vapors of common nitro explosives and their degradation by-products. The nanowires were prepared with a top-down nano-fabrication process on a silicon-on-insulator wafer. The surface of the silicon nanowires was modified by plasma treatments. Both hydrogen and oxygen plasma treatments can significantly improve the responses, and oxygen plasma changes the majority carrier from p- to n-type on the surface of silicon nanowire thin films. The sensitivity is found to increase when the cross-section of the nanowires decreases.

Reduction of scattering loss of silicon slot waveguides by RCA smoothing.

Because of stronger optical confinement density, silicon slot waveguides tend to have higher scattering loss than normal ridge waveguides with same sidewall roughness. A wet chemical process is found to be highly effective in reducing the surface roughness and scattering loss. A reduction in scattering loss by 10.2 dB/cm for TE and 8.5 dB/cm for TM polarizations has been achieved.

A reflective microring notch filter and sensor.

We present a new design of wavelength selective reflector composed of a Y junction and a singly coupled microring resonator, and demonstrate its biochemical sensing applications with a prototype device. In contrast with other reflectors like distributed Bragg reflectors, this device acts as notch filter at its reflection port. One promising application of the device is for remote sensing of harsh or inaccessible site, where only one optical fiber is required to transmit the input and reflected light signal over a long distance. The design can also be used to make microring cavity lasers.

Efficient fiber coupler for vertical silicon slot waveguides.

A mode size converter for efficient fiber coupling to silicon slot waveguides was proposed and demonstrated. It consists of two inverted lateral tapers that extend from the two strips of the silicon slot waveguide, and an overlaid low index waveguide with expanded mode size. Parameters including taper length and taper tip width were optimized with computer simulations. Samples were fabricated with a combined electron beam and photolithography process on a silicon-on-insulator wafer. The measured coupling loss to a standard single mode optical fiber was reduced by 8 dB for TE mode and 5.2 dB for TM mode with the converter.

Direct electron beam writing of electro-optic polymer microring resonators.

Electro-optic polymer waveguides in electron beam sensitive polymethyl methacrylate (PMMA) polymer matrix doped with organic nonlinear chromophores could be directly patterned by electron beam exposure with high resolution and smoothness. The polymer in the exposed regions was removed with standard electron beam resist developer and without damaging the chromophore containing polymer waveguides. Feature sizes on the order of 100 nm could be clearly resolved. High quality microring resonators made of YL124/PMMA electro-optic polymer were successfully fabricated with this technique. The measured resonance extinction ratios were more than 16 dB and quality factors were in the range of 10(3) approximately 10(4).

Polarization selective electro-optic polymer waveguide devices by direct electron beam writing.

A novel technique for the fabrication of polarization selective electro-optic polymer waveguide devices with direct electron beam writing was described. Birefringence induced by the electric field poling in the electro-optic polymer film was erased in the electron beam exposed regions. The formed waveguides had stronger confinement for the light polarized along the poling direction. High fabrication resolution on the 100 nm scale or smaller could be achieved. Fabrication of polymer polarizer and polarization selective microring resonators with this technique was reported. The highest polarization extinction ratio was measured to be 21.4 dB.