Nonlinear-optical phase modification in dispersion-engineered Si photonic wires.

The strong dispersion and large third-order nonlinearity in Si photonic wires are intimately linked in the optical physics needed for the optical control of phase. By carefully choosing the waveguide dimensions, both linear and nonlinear optical properties of Si wires can be engineered. In this paper we provide a review of the control of phase using nonlinear-optical effects such as self-phase and cross-phase modulation in dispersion-engineered Si wires. The low threshold powers for phase-changing effects in Si-wires make them potential candidates for functional nonlinear optical devices of just a few millimeters in length.

Evanescent interferometric lithography.

Simulation results are presented to illustrate the main features of what we believe is a new photolithographic technique, evanescent interferometric lithography (EIL). The technique exploits interference between resonantly enhanced, evanescently decaying diffracted orders to create a frequency-doubled intensity pattern in the near field of a metallic diffraction grating. It is shown that the intensity in a grating's near field can be enhanced significantly compared with conventional interferometric lithography. Contrast in the interference pattern is also increased, owing to a reduction in the zeroth-order transmission near resonance. The pattern's depth of field reduces as the wavelength is increased beyond cutoff of the first-order diffracted components, and results are presented showing the trade-offs that can be made between depth of field and intensity enhancement. Examples are given for a 270-nm-period grating embedded in material with refractive index n = 1.6 and illuminated with wavelengths near 450 nm. Under these conditions it is predicted that high-intensity, high-contrast patterns with 135-nm period can be formed in photoresists more than 50 nm thick.

Contrast in the evanescent near field of lambda/20 period gratings for photolithography.

Light propagation through gratings with periods as small as lambda/20 is investigated computationally by use of the multiple multipole method in two dimensions. High image contrast is evident close to the grating. Strong evanescent decay of the high spatial frequency components is observed with the region of high contrast shrinking linearly as the period of the grating is decreased. Simulations were performed for TE and TM polarizations with the TM polarization providing the dominant contrast compared with TE, which is strongly attenuated owing to the polarizing effect of the gratings. These results show good promise for optical contact lithography in the evanescent near field of a shadow mask to attain feature sizes smaller than lambda/20.