Single step fabrication of nano scale optical devices using binary contact mask deep UV interference lithography.

Interference Lithography (IL) is a powerful and inexpensive tool for large area precision nanoscale patterning of periodic structures. In this work we extend IL's capability to create features in arbitrary shapes and locations through the use of binary contact masks with wavefront division deep-UV interference lithography. Grating couplers for use in a streak measurement system and a focal plane division polarimeter are created to demonstrate the viability and versatility of the technique. Simultaneous fabrication of 90nm and 20µm features proves the potential of this process to simplify and streamline common fabrication processes in research and in industrial applications.

High efficiency geometric-phase polarization fan-out grating on silicon.

We report the design, fabrication and characterization of a 1-by-5 geometric-phase polarization fan-out grating for coherent beam combining at 1550 nm. The phase profile of the grating is accurately controlled by the local orientation of the binary subwavelength structure instead of the etching depth and profile empowering the grating to be more tolerant to fabrication errors. Deep-UV interference lithography on silicon offers an inexpensive, highly efficient and high damage threshold solution to fabricating large-area fan-out gratings than electron beam lithography (EBL) and photoalignment liquid crystals. The theoretical and experimental diffraction efficiency of the grating is 87% and 85.7% respectively. Such a fan-out grating may find application to high-power beam combining in the infrared regime.

Low control-power wavelength conversion on a silicon chip.

We demonstrate controlled wavelength conversion on a silicon chip based on four-wave mixing Bragg scattering (FWM-BS). A total conversion efficiency of 5% is achieved with strongly unbalanced pumps and a controlling peak power of 55 mW, while the efficiency is over 15% when using less asymmetric pumps. The numerical simulation agrees with the experimental results. Both time domain and spectral domain noise measurements show as low as 2 dB signal-to-noise ratio (SNR) penalty because of the strong pump noise, two-photon absorption, and free-carrier absorption in silicon. We discuss how the scheme can be used to implement an all-optically controlled high-speed switch.