Aref Bakhtazad

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).

1-D slab photonic crystal k-vector superprism demultiplexer: analysis, and design

The design of a complete demultiplexer based on the k-vector superprism in a 1-D slab photonic crystal is proposed. This design scales to resolve 32 channels spaced by 0.8 nm (100 GHz) in the C band for a dense wavelength division multiplexing system. It is shown that a prism area of 0.017 mm;2 is sufficient for the required wavelength resolution using typical silicon-on-insulator technology and that the total chip size would be 4x3 mm;2. In order to achieve this, the modest angular dispersion of a 1-D slab photonic crystal is enhanced by considerably expanding the input beam through the superprism region and employing etched mirrors to collimate and focus the light into and out of the superprism. The plane wave expansion method is used to obtain the wave vector diagram and from this we develop design equations based on conventional ray tracing. We then present an optimization approach which minimizes the prism area whilst maintaining the necessary dispersion. Finally the non-uniformity of phase velocity dispersion across the desired spectral window is addressed.

First-Band S -Vector Photonic-Crystal Superprism Demultiplexer Design and Optimization

In this paper, we present a complete approach to the design of a wavelength demultiplexer based on the S-vector superprism photonic-crystal phenomenon. We make use of a full 3-D modeling approach based on plane-wave-expansion method, which allows the full dynamics of beam propagation to be considered. This reveals significant nonuniformities in beam divergence and dispersion as a function of wavelength, which has been neglected in previous 2-D models and which reduces the scalability of these devices. We examine 1-D and 2-D photonic-crystal lattices and show that the 1-D lattice results in the smallest superprism area as a function of channel count. This is due to its lower band curvature relative to 2-D square and hexagonal lattices, even though it has much lower angular dispersion. We also modify the previous S-vector superprism design so that, for each channel, the prism region extends only as far as necessary for channel resolution at a specified crosstalk level. Based on silicon-on-insulator (SOI) technology, with a top silicon layer of 260 nm and minimum feature size of 75 nm, we present the design of a four-channel coarse-wavelength-division-multiplexing demultiplexer with theoretical crosstalk of 20 dB, which has a superprism area of 1367 mum2

Mechanical sensitivity enhancement of silicon based photonic crystal micro-pressure sensor

We describe here a sensor consisting of a line defect photonic crystal waveguide suspended over a silicon substrate. Under applied pressure, the photonic crystal waveguide is deflected toward the substrate, causing a decrease in optical transmission due to the coupling of the waveguide field to the silicon substrate. Bridge engineering can increase the mechanical sensitivity of the bridge: maintaining constant bridge footage, we are able to increase sensitivity by about 5.5 times.

Periodic arrays of gold nano-disks coupled with evanescent spectroscopy

We study and analyze various spectral features of gold nano-disk arrays coupled with the evanescent field of an optical waveguide using finite difference time domain simulations for comparison to our previous work on this topic [Jiang et al., J. Lightwave Technol. 27(13), 2264–2270 (2009)]. We find that the quadrupolar and dipolar peaks are both heavily dependent on the coherent interactions of the periodic array and show comparable performance for refractive index sensing applications. We also find sharp extinction peaks and dips in the simulated spectra, but they are not sensitive to the index change of the surface-bound layer. A detailed analysis on these sharp features reveals that the sharp extinction peaks are grating-induced quadrupolar modes and the dips represent the suppressed plasmon resonances caused by the photonic band gap.

Dispersion optimization of a 1-D superprism based on phase velocities

We apply Floquet-Bloch theory to determine the parameters of a 1-D superprism which give the maximum angular dispersion. For a silicon-air structure with an incident wavelength of 1550 nm this is 0.195 /spl deg//nm.

Superprism effect with planar 1D photonic crystal

Here we report a new type of dispersive structure for wavelength multiplexing/demultiplexing, based on a planar 1-D photonic crystal prism. We introduce a computationally efficient technique for simulating this structure. Simulations are carried out to determine the angular dispersion as a function of period, slant angle in the prism area and prism apex angle. The design has been optimized for good performance in a moderate refractive index contrast system (silica and silicon nitride) and promises reduced scattering losses when compared with existing 2-D superprism designs.

Cryogenic shallow reactive ion etch process for profile control on silicon on insulator platform

A cryogenic reactive ion etch (RIE) process is presented to fabricate shallow two-dimensional photonic crystal type dense pattern microstructures (usually with thickness less than 500 nm and with low aspect ratios ∼1–4) on a silicon on insulator (SOI) platform. Deep RIE etching of silicon has been previously investigated particularly with respect to etch rate, etch profile, and selectivity. While using an oxide layer as an etch stop has also been investigated, the profile control near the oxide interface is usually not very important due to the large aspect ratios. However, for shallow structures with low aspect ratios, profile control near the oxide interface is important while the etch rate and the selectivity are not as much of a concern. The authors show how the presence of an insulating layer close to the silicon etch surface makes the cryogenic etch process different from that of bulk silicon in many respects. Under these circumstances, the effects of various etch process parameters, including O2 fl...

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.

Wavefront engineering with photonic crystal structures in slab waveguides

Light can interact with periodic microstructures, also known as photonic crystals, in many ways. In this talk we will consider the use of photonic crystals to modify the wavefront and wavevector direction of waves propagating in photonic crystal slab waveguides and will compare these effects with those at arise from modification of the Poynting vector. We will discuss the underlying principles and will consider applications of these devices, in particular for wavelength demultiplexing. We will illustrate our investigation by considering the design of 1-D and 2-D photonic crystal superprism demultiplexers, and show that compact (<4 mm chip size) and high resolution (100 GHz) multichannel devices can be obtained.