Aju Jugessur

Compact and integrated 2-D photonic crystal super-prism filter-device for wavelength demultiplexing applications

A two-dimensional photonic crystal (PhC) super-prism integrated with one-dimensional photonic crystal microcavity filters has been designed using the plane wave expansion (PWE) and 2-D Finite Difference Time Domain (FDTD) methods based on Silicon-on-Insulator (SOI) technology. The super-prism operates as a coarse spatial filter with an average response bandwidth of 60 nm, while the 1-D PhC microcavity filters operate as narrow band-pass transmission filters with an average filter response line-width of 10 nm. This work demonstrates the simultaneous operation of two photonic devices for de-multiplexing applications on a single platform that could be useful in future Photonic Crystal Integrated Circuits (PCICs).

Imaging properties of dielectric photonic crystal slabs for large object distances

We extend the understanding of the imaging properties of dielectric photonic crystal slabs to object distances that are larger than the slab thickness. We specifically consider hexagonal crystal lattices in the second band. For object distances smaller than the slab thickness, the image distance is a negative linear function of the object distance as expected for negative refractive index materials. The effective refractive index extracted from this linear object-image relation is close to the negative unity value calculated for infinite photonic crystal using the plane wave expansion method. In contrast to previous predictions, we find that a real image can still be formed for object distances up to twice the slab thickness. In this regime the image distance changes little as the object distance increases, and can thus be described as the saturated image regime. Sub-wavelength resolution performance can be approximately maintained even for these larger object distances. The full-width half-maximum spot size at the image is approximately (0.43-0.55)lambda up to object distances 1.5 times the slab thickness. By evaluating the image angular frequency spectrum we show that this sub-wavelength resolution imaging at larger object distances is due to evanescent waves that arise within the slab, rather than being directly transferred from the object. The eventual loss of image resolution is due to interference side lobes which enter the image plane.

Observation of continuous-wave second-harmonic generation in semiconductor waveguide directional couplers.

We report the observation of continuous-wave second-harmonic generation in waveguide directional couplers. We employ a GaAs/AlGaAs system and observe four resonance peaks in a ~15nm spectral range, with a maximal conversion efficiency of 1.6%W(-1)cm(-2). This observation is theoretically explained by the coupled-mode theory. This new configuration has the potential to open a new range of applications for nonlinear frequency conversion.

A shallow-etched multilayer grating-based wavelength demultiplexer in SOI

A very shallow multilayer etched-grating is proposed as a wavelength demultiplexer. Two different configurations are compared for diffraction efficiency and resolution. Single-step-etch fabrication designs are presented and modeled for their grating efficiency and overall performance

Open cavities using photonic crystals with negative refraction

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 Notomis 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.

1-D Photonic Crystal as an Anti-Reflection Layer for First Band Photonic Crystals

A 1-D photonic crystal (PC) when placed in front of a bulk PC can play the role of anti-reflection layer (ARL). A five-fold reduction in reflection is obtained for a first band PC

Integration of a 2-D photonic crystal superprism with 1-D photonic crystal microcavity filters for high channel selectivity

A 2-D photonic crystal superprism-filter device for demultiplexing applications has been designed using plane wave expansion and 2-D finite difference time domain methods. High channel selectivity with peak transmission linewidths of 15 nm is achievable.

Photonic crystal and photonic wire device structures

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.

A Shallow-Etched Distributed-Grating Wavelength Demultiplexer in SOI

A shallow-etched, distributed grating is proposed as a wavelength demultiplexer. Modeling results predict up to 94% efficiency over a 120nm wavelength range. Early fabrication results, using electron-beam lithography and electron-cyclotron-resonance single-step etching, are presented.

2-D photonic crystals microcavity filters based on hexagonal lattice structures embedded in ridge waveguides

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.