Nanoimprint is an emerging lithographic technology that promises high-throughput patterning of nanostructures. Based on the mechanical embossing principle, nanoimprint technique can achieve pattern resolutions beyond the limitations set by the light diffractions or beam scatterings in other conventional techniques. This article reviews the basic principles of nanoimprint technology and some of the recent progress in this field. It also explores a few alternative approaches that are related to nanoimprint as well as additive approaches for patterning polymer structures. Nanoimprint technology can not only create resist patterns as in lithography but can also imprint functional device structures in polymers. This property is exploited in several non-traditional microelectronic applications in the areas of photonics and biotechnology.

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/48920/d4_11_r01.pdf?sequence=2

Recent progress in nanoimprint technology and its applications

Electromechanical devices are rapidly being miniaturized, following the trend in commercial transistor electronics. Miniature electromechanical devices--now with dimensions in the deep sub-micrometer range--are envisioned for a variety of applications as well as for accessing interesting regimes in fundamental physics. Among the most important technological challenges in the operation of these nanoelectromechanical systems (NEMS) are the actuation and detection of their sub-nanometer displacements at high frequencies. In this Review, we shall focus on this most central concern in NEMS technology: realization of electromechanical transducers at the nanoscale. The currently available techniques to actuate and detect NEMS motion are introduced, and the accuracy, bandwidth, and robustness of these techniques are discussed.

Electromechanical transducers at the nanoscale: actuation and sensing of motion in nanoelectromechanical systems (NEMS).

Integrated quantum photonic applications, providing physically guaranteed communications security, subshot-noise measurement, and tremendous computational power, are nearly within technological reach. Silicon as a technology platform has proven formidable in establishing the micro-electronics revolution, and it might do so again in the quantum technology revolution. Silicon has taken photonics by storm, with its promise of scalable manufacture, integration, and compatibility with CMOS microelectronics. These same properties, and a few others, motivate its use for large-scale quantum optics as well. In this paper, we provide context to the development of quantum optics in silicon. We review the development of the various components that constitute integrated quantum photonic systems, and we identify the challenges that must be faced and their potential solutions for silicon quantum photonics to make quantum technology a reality.

/pdf/silicon-quantum-photonics-5d3kuhgp9n.pdf

Silicon Quantum Photonics

Recent fabrication advances have enabled compact semiconductor microring resonators to be fabricated with high-finesse values and picosecond cavity lifetimes. These devices have potential applications in optical signal processing as all-optical switches, multiplexers and logic gates. Theoretical analysis shows a maximum reduction in the switching power proportional to the fourth power of the field enhancement in the microring. An enhancement in the wavelength conversion efficiency by four-wave mixing which is proportional to the eighth power of the field enhancement is also predicted and experimentally confirmed. Experimental results demonstrating bistability, picosecond switching using pump and probe excitation, optical time-division demultiplexing, spatial pulse routing and four-wave mixing in GaAs-AlGaAs microring resonators are reported. Apart from the bistable response, which was thermally induced, the nonlinear effects observed in the microrings were caused by the two-photon absorption process. Applications of microrings to realize all-optical logic gates are also proposed.

Optical signal processing using nonlinear semiconductor microring resonators

We present an analytical model to quantify losses in resonators and bends without uncertain contributions from fiber coupling in/out or waveguide cleavage facets. With resonators in add-drop configuration, intrinsic losses are calculated from the free spectral range, through-port extinction and drop-port bandwidth. We fabricated and characterized silicon-on-insulator resonator for loss analysis. At 1.55 µm, racetrack resonators with a bending radius of 4.5 µm show intrinsic losses as small as 0.14±0.014 dB/round-trip. Meanwhile, intrinsic losses increase up to 1.23 dB/round-trip in the racetrack resonator that has a bending radius of 2.25 µm. Losses in a 180o bend are estimated as a half of the intrinsic losses in these racetrack resonators, i.e., 0.07±0.007 dB/turn for a bending radius of 4.5 µm and 0.62 dB/turn for a bending radius of 2.25 µm. Loss in a 90° bend with a radius of 4.5 µm is determined to be 0.06±0.006 dB/turn at 1.55 µm. The losses in 180° or 90° bends are found to be mainly due to the transition loss between waveguide bends and straight waveguides.

Modeling and measurement of losses in silicon-on-insulator resonators and bends.

We report propagation loss measurements in single-mode GaAs-AlGaAs racetrack microresonators with bending radii from 2.7 /spl mu/m to 9.7 /spl mu/m. The experimental data were found to be in good agreement with a physical-loss model which accounts for the bending loss, the scattering loss due to surface roughness on the waveguide sidewalls, and the transition loss at the straight-to-bend waveguide junctions. The model also enables us to identify the dominant loss mechanisms in semiconductor microcavities. We found that for racetracks with large bending radii (greater than 4 /spl mu/m, in our case) the loss due to surface-roughness scattering in the curved waveguides dominates, whereas for small-radius rings, the modal mismatch at the straight-to-bend waveguide junctions causes the biggest loss. This result suggests that circular-shaped rings are preferable in the realization of ultrasmall low-loss microcavities. We also show that the round-trip propagation loss in small-radius racetrack microresonators can be minimized by introducing a lateral offset at the straight-to-bend waveguide junctions.

P.P. Absil

Papers

Propagation loss in single-mode GaAs-AlGaAs microring resonators: measurement and model