Person:

Adibi, Ali

Permanent Link

https://hdl.handle.net/1853/71044

Associated Organization(s)

Organizational Unit

School of Electrical and Computer Engineering

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Publication Search Results

Now showing 1 - 9 of 9

Preconditioned superprism-based photonic crystal demultiplexers: analysis and design

(Georgia Institute of Technology, 2006-11) Momeni, Babak ; Adibi, Ali

We present the analysis and design of a new type of photonic crystal (PC) demultiplexers (i.e., preconditioned demultiplexer), in which the simultaneous existence of the superprism effect and the negative effective index for diffraction results in a compact structure by canceling the second-order spectral phase to avoid beam broadening inside the PC. This approach considerably relaxes the requirements for the large area of the structure and the small divergence of the input beam. As a result, the size of the preconditioned demultiplexers varies as N².⁵ (N being the number of wavelength channels) compared to the N⁴ variation in the conventional superprism-based PC demultiplexers. We use a generalized effective index model to analyze, design, and optimize these demultiplexing structures. This approximate model can be used to extract all the basic properties of the PC device simply from the band structure and eliminates the need to go through tedious simulations especially for three-dimensional structures. Our results show that the preconditioned superprism-based PC demultiplexers have 2 orders of magnitude smaller size compared to the conventional ones.
Compact wavelength demultiplexing using focusing negative index photonic crystal superprisms

(Georgia Institute of Technology, 2006-03) Momeni, Babak ; Huang, Jiandong ; Soltani, Mohammad ; Askari, Murtaza ; Mohammadi, Saeed ; Rakhshandehroo, Mohammad ; Adibi, Ali

Here, we demonstrate a compact photonic crystal wavelength demultiplexing device based on a diffraction compensation scheme with two orders of magnitude performance improvement over the conventional superprism structures reported to date. We show that the main problems of the conventional superprism-based wavelength demultiplexing devices can be overcome by combining the superprism effect with two other main properties of photonic crystals, i.e., negative diffraction and negative refraction. Here, a 4-channel optical demultiplexer with a channel spacing of 8 nm and cross-talk level of better than -6.5 dB is experimentally demonstrated using a 4500 μm² photonic crystal region.
Observation of large parity-change-induced dispersion in triangular-lattice photonic crystal waveguides using phase sensitive techniques

(Georgia Institute of Technology, 2006-02) Huang, Jiandong ; Reinke, Charles M. ; Jafarpour, Aliakbar ; Momeni, Babak ; Soltani, Mohammad ; Adibi, Ali

We experimentally studied W1 triangular-lattice photonic crystal waveguides (PCWs) fabricated on semiconductor-on-insulator substrates using phase-sensitive lock-in techniques. In addition to the improved signal-to-noise ratio for power transmission measurements, we observed two large group delay peaks at frequencies corresponding to the photonic mode gap and parity changes of Bloch modes inside the PCWs.
Nonlinear finite-difference time-domain method for the simulation of anisotropic, chi((2)), and chi((3)) optical effects

(Georgia Institute of Technology, 2006-01) Reinke, Charles M. ; Jafarpour, Aliakbar ; Momeni, Babak ; Soltani, Mohammad ; Khorasani, Sina ; Adibi, Ali ; Xu, Yong ; Lee, Reginald K.

A two-dimensional (2-D) finite-difference timedomain (FDTD) code for the study of nonlinear optical phenomena, in which both the slowly varying and the rapidly varying components of the electromagnetic fields are considered, has been developed. The algorithm solves vectorial Maxwell’s equations for all field components and uses the nonlinear constitutive relation in matrix form as the equations required to describe the nonlinear system. The stability of the code is discussed and its effectiveness is demonstrated through the simulations of self-phase modulation (SPM) and second-harmonic generation (SHG). The authors also show that the combination of nonlinear effects with PCs can result in a significant improvement in device size and integrability, using the example of a Mach–Zehnder interferometer (MZI).
Adiabatic matching stage for coupling of light to extended Bloch modes of photonic crystals

(Georgia Institute of Technology, 2005-10) Momeni, Babak ; Adibi, Ali

In this letter, we present a matching stage for reflection reduction based on the principle of gradual change to efficiently couple light to propagating modes of photonic crystals (PCs). Basic physical considerations in designing these matching stages are investigated and a systematic yet simple design procedure is suggested. We show that matching stages obtained using this method are wideband in frequency, have a wide acceptance angle, and are robust against fabrication imperfections. Therefore, they are the preferred choice in general-purpose matching stages to be used along with dispersion-based PC devices
Systematic design of superprism-based photonic crystal demultiplexers

(Georgia Institute of Technology, 2005-07) Momeni, Babak ; Adibi, Ali

In this paper, design of photonic crystal demultiplexers based on superprism effect is discussed. Figures of merit for performance of these demultiplexers are defined and a systematic design procedure is presented. We consider different design schemes, based on equal angular separation between channels and equal frequency separation between channels, and find the optimum structures among conventional photonic crystal lattices for each case. Our results provide design solutions for a range of current applications.
An approximate effective index model for efficient analysis and control of beam propagation effects in photonic crystals

(Georgia Institute of Technology, 2005-03) Momeni, Babak ; Adibi, Ali

Propagation of optical beams through a photonic crystal (PC) is analyzed and modeled. It is shown that the propagation effects for beams with slow spatial variations can be effectively modeled by diffraction behavior obtained directly from band structure. In particular, we present here an approximate model based on defining an effective index for the PC that can be used to analyze the propagation of optical beams inside the PC using the well-known analytic formulas for wave propagation in bulk media. The model presented here allows for considerable reduction in computation time and complexity. It also allows us to obtain more intuitive and design-oriented information about beam propagation effects inside PCs. We apply this model to several practical cases and show that its results agree very well with direct (time-consuming) numerical simulations.
Investigation of physical mechanisms in coupling photonic crystal waveguiding structures

(Georgia Institute of Technology, 2004-10) Badieirostami, Majid ; Momeni, Babak ; Soltani, Mohammad ; Adibi, Ali ; Xu, Yong ; Lee, Reginald K.

We explain the fundamental physical mechanisms involved in coupling triangular lattice photonic crystal waveguides to conventional dielectric slab waveguides. We show that the two waveguides can be efficiently coupled outside the mode gap frequencies. We especially focus on the coupling of the two structures within the mode gap frequencies and show for the first time that the diffraction from the main photonic crystal structure plays an important role on the reflection of power back into the slab waveguide. The practical importance of this effect and possible strategies to modify it are also discussed.
General methods for designing single-mode planar photonic crystal waveguides in hexagonal lattice structures

(Georgia Institute of Technology, 2003-06) Wu, N. ; Javanmard, M. ; Momeni, Babak ; Soltani, Mohammad ; Adibi, Ali ; Xu, Yong ; Lee, Reginald K.

We systematically investigate and compare general methods of designing single mode photonic crystal waveguides in a two-dimensional hexagonal lattice of air holes in a dielectric material. We apply the rather general methods to dielectric-core hexagonal lattice photonic crystals since they have not been widely explored before. We show that it is possible to obtain single mode guiding in a limited portion of the photonic bandgap of hexagonal lattice structures. We also compare the potentials of different photonic crystal lattices for designing single-mode waveguides and conclude that triangular lattice structures are the best choice.