We measure electronic and thermal nonlinear refractive indices of periodically nano-patterned and un-patterned siliconon- insulator (SOI) in comparison with that of bulk silicon, using a fast reflection Z-scan setup with a high-repetition-rate fs laser (at 800 nm wavelength), and a new procedure for discrimination between electronic and thermal nonlinearities. The electronic nonlinear response of nano-structured SOI is strongly enhanced in comparison with those of un-patterned SOI and of bulk Si. These results could be important in silicon photonics for optical devices with nonlinearity controlled by periodic nano-structuring.
In view of the development of superconducting fault current limiters, the properties of switching and recovering of YBa2Cu3O7−δ/Au (YBCO/Au) thin films are studied at 77 K and 50 Hz for overcurrents. The bilayers present an abrupt transition to a high dissipative state leading to a current limitation at a maximum value of about 2.5 times the critical current Ic, and allow the development of electric fields of 3 kV m−1 without any damage. After the overcurrent regime, the recovery of the superconducting state under the rated current In is studied as a function of overcurrent parameters. These results show clearly the strong potential of YBCO/Au thin films which can recover their superconducting state under nominal mode. This last point is crucial for transformer connection, as experimentally shown in this paper.
A novel class of large-bandwidth wavelength demultiplexers, based on digital planar holography for on-chip spectroscopy applications, was fabricated in high refractive index contrast SiO2/Si3N4 planar waveguides. The devices consist of computer-generated digital planar holograms (DPHs) encoding the transfer function of the demultiplexers, engraved on the core layer of the optical waveguide. An optimized fabrication process has been developed to produce DPHs with an etching depth as low as 10 nm in Si3N4. The first spectrometer devices exhibit overall bandwidths as large as 98 nm and spectral channel spacings down to 0.3 nm/channel.
The advances in nanosciences, micro- and nanotechnology are driving the research and development efforts to fabricate micro- and nano-structures with a high precision in a wide variety of materials using novel lithography methods. These emerging techniques, which include self-assembly, scanning probes, micro-contact printing, and nanoimprint lithography (NIL), are intensively studied to, on the one hand, assess to what degree they meet the demands of ultrahigh precision and high density of nanostructures posed by the semiconductor industry and, on the other hand, to examine them with respect to cost-efficiency to produce components for photonic, data storage, sensing and fluidic or biological applications. This chapter focuses on recent advances in nanoimprint lithography as it is perhaps among the most mature emerging nanofabrication methods. Nanoimprint lithography technology faces some challenges to reach the requirements of the semiconducting integrated circuits manufacturers in terms of overlay accuracy, defectivity and throughput but it meets already some needs of data storage, light extraction, fluidic and biological applications. Significant efforts are currently being made to develop parallel printing on large area and step and repeat techniques. In this chapter, we review the principles of nanoimprint lithography and its capability to scale-up the replication of nanostructures by parallel printing, step and stamp and by step and flash, the latter a technique that use UV curable resist. We identify current capabilities of the different variations of nanoimprint lithography and provide examples of the fabrication of three-dimensional structures and nanostructures in inorganic sol-gel materials. Finally, an overview of the wide range of applications realized so far by nanoimprint lithography is given.
A concept of digital optical spectrometer-on-chip is proposed and results of their fabrication and characterization are reported. The devices are based on computer-designed digital planar holograms which involves millions of lines specifically located and oriented in order to direct output light into designed focal points according to the wavelength. Spectrometers were fabricated on silicon dioxide and hafnium dioxide planar waveguides using electron beam lithography and dry etching. Optical performances of devices with up to 1000 channels for a central wavelength of 660 nm are reported.
