Nanoimprint Lithography is a promising high-throughput technology for the fabrication of optical nanostructures over large areas in the centimeter range. However, there are limitations (cost, proprietary and tool specific) of the commercial transfer resist. In this work, the photo-resist AZ1518 is investigated as a viable nanoimprint resist mask with a tefloncoated silicon mold. The results are comparable with a commercial nanoimprint resist. To our knowledge, the application of a conventional photoresist as the nanoimprint mask with teflon-coated mold is novel, providing a critical solution for cost-effective, flexible and high-throughput fabrication of optical nanostructures over large areas. Periodic gratings with lateral width of 100 nm and 200 nm pitch have been fabricated using this approach. The nanoimprint process parameters (pressure and temperature) are optimized to improve the release of the mold from the resist. In addition, the Teflon-coated mold improves the release process to avoid tearing of the mask.
The design and applications of one- or two-dimensional photonic crystal microcavity filters have been widely investigated and reported over the last several years. The functionality of these devices can be tailored to suit any specific application such as optical filters, sensors and optical memory. However, the coupling of light into these miniature devices has always been a challenge, in particular, when light transits the waveguide region to the photonic crystal structures. This modal transition results in scattering losses leading to low optical transmission. In this work, twodimensional photonic crystal microcavity filter structures with mode-matching features embedded in ridge waveguides have been designed using Finite Domain Time Difference modeling tool and fabricated on GaAs/AlGaAs substrate using Electron Beam Lithography and Reactive Ion Etching. An increase in optical transmission of about 80 % is obtained by the addition of the mode-matching features.
The applications of Bragg-grating concepts in a multitude of photonic device functionalities are well established, in particular, in the design of planar and chip-based miniature device components for dense photonic integrated circuits. In many situations, the Bragg-grating structures are designed to function as a broad or narrow band-pass filter, as a multichannel coupled defects filter, an optical waveguide and an optical sensor. In this work, Bragg-grating concepts are applied in several different scenarios with applications ranging from Bragg-grating optical microcavity filter, Bragg-grating optical waveguide and a Bragg-slot waveguide. The Bragg-grating structures integrated with slot waveguide are shown to be very promising candidates for label-free optical sensing applications with sensitivity as high as 500nm/RIU. This work demonstrates the versatility of Bragg-grating structures for multiple device functionalities through design for a wide range of devices applications in several scientific and technological areas.
The development of miniature and label-free optical sensors is very critical for applications in a wide range of areas such
as medicine, environment, forensic and food quality control. In this report, a Bragg-grating air-slot waveguide is
designed (using Finite Domain Time Difference modeling (FDTD)) and fabricated (using Electron beam lithography and
Reactive ion etching) on a silicon-on-insulator substrate to develop a label-free optical sensor. The Bragg gratings
constitute of recesses in the 140 nm wide air-slot waveguide. The grating structures generate a band-gap for certain
frequencies and the spectral shift of the lower band-edge is used as the mechanism to sense fluids or bio-molecules in the
air-slot. Based on the 3-D FDTD and experimental results, the sensitivity of the device is 620 nm/RIU, which is higher
than other recently reported sensors. Due to the high electric field intensity in the air slot, this area becomes very
sensitive to index variations caused by bio-molecules or fluids in the air-slot.
Photonic crystals (PhCs) exhibiting negative refraction have attracted much attention in recent years, with a vast majority of this research focusing on subwavelength imaging. Although the possibility of an open cavity using such a PhC is mentioned in Notomi's pioneering work, fewer researchers have addressed this issue except one study of an open cavity using three 60-degree PhC wedges of the hexagonal lattice. This paper reports our study of several different open cavity configurations in hexagonal and square lattices. To form an open cavity using PhC with negative refraction, there are many parameters to optimize, such as the lattice type, lattice period, the diameter of the hole or rod, materials, and the geometrical configurations. We first propose several configurations for open cavities in general, including two square slabs, two or more prism slabs, and one slab with two reflectors; Then we demonstrate some results obtained from photonic crystals with square and hexagonal lattices, simulated by the use of the finite-difference time-domain (FDTD) method. It is shown that resonance can occur at the first band and higher bands. The Q-factor obtained is about 280 to 400, which can be improved by optimizing the surface terminations of the photonic crystal prisms.
This paper reports a new super-resolution, "saturated" imaging method using a flat slab of photonic
crystal with negative refraction. The photonic crystal has hexagonal lattice with holes in dielectric material
with an index of 3.6. When the operating normalized frequency is around 0.30, the effective refractive
index is -1. Such a flat slab lens can tolerate disk deformation of approximately one-wavelength or more
while maintaining the same super-resolution as the near-field imaging of the photonic crystal slab. The
object distance can be as large as twice the slab thickness, and the resolution is about 0.43λ.
Photonic devices that exploit photonic crystal (PhC) principles in a planar environment continue to provide a fertile field of research. 2D PhC based channel waveguides can provide both strong confinement and controlled dispersion behaviour. In conjunction with, for instance, various electro-optic, thermo-optic and other effects, a range of device functionality is accessible in very compact PhC channel-guide devices that offer the potential for high-density integration. Low enough propagation losses are now being obtained with photonic crystal channel-guide structures that their use in real applications has become plausible. Photonic wires (PhWs) can also provide strong confinement and low propagation losses. Bragg-gratings imposed on photonic wires can provide dispersion and frequency selection in device structures that are intrinsically simpler than 2D PhC channel guides--and can compete with them under realistic conditions.
Compact photonic crystal (PhC) microcavity filters in a ridge waveguide format could play a useful role for wavelength division multiplexing (WDM) and de-multiplexing functionality in dense integrated photonic circuits. The microcavity filters are embedded in ridge waveguides with high lateral refractive-index contrast because good lateral confinement and efficient coupling of light into the device can be achieved using this established waveguide technology. However, this configuration leads to significant modal mismatch at the interfaces between the PhC and waveguide sections, contributing to reflection losses and reduced transmission over much of the useful spectrum. By the same token, mode-matching features consisting of two rows of PhC holes with a different filling factor and displaced to mirror-image positions with respect to the outer two rows of the main PhC mirrors have been implemented to enhance the optical transmission by more than a factor of two. Furthermore, an increase in Q-factor (more than 100 %) is achieved by the addition of two further rows of PhC holes on either side of the microcavity. Moreover, Bragg-grating concepts have been applied in several other filter designs using the same hexagonal PhC lattice configuration, in an attempt to control the filter response. This work involves the design, fabrication (using electron-beam lithography and reactive ion etching) and characterization of such hexagonal-lattice PhC microcavity filters embedded in ridge waveguides.
This paper highlights photonic crystal Mach-Zehnder structures that use W1 channel waveguide in 2D hexagonal photonic crystal structures and have channel orientation along GammaK directions. The FDTD software, Fullwave, from RSoft has been used to simulate photonic crystal channel waveguides, Y-junction and bend in order to design a complete Mach-Zehnder interferometer structure in epitaxial II-V semiconductor material for operation at 1550nm. It is our near-future aim to use these Mach-Zehnder structures as the basis for thermo-optic switching devices. Electro-Beam lithography (EBL) and reactive ion etching (dry-etching) processes have been used to fabricate these devices
The words of this title may at first seem incompatible. We review a range of experiments where dynamic structures have been created. We show that it is possible to construct gas and plasma shapes using colliding shocks cigars and cylinders, curved waveguides, and even waveguides with rectangular cross sections. The colliding plasma lens/isolator lead to the colliding shock lens. We now suggest that colliding shock waveguides could find application in laser acceleration and soft X ray schemes. Colliding shock waveguides can be as long as necessary unlike gas jets.