Aliakbar Jafarpour

Nonlinear finite-difference time-domain method for the simulation of anisotropic, /spl chi//sup (2)/, and /spl chi//sup (3)/ optical effects

A two-dimensional (2-D) finite-difference time-domain (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 Maxwells 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).

A new method for the calculation of the dispersion of nonperiodic photonic crystal waveguides

We present a new method for the calculation of the dispersion diagrams of general nonuniform waveguides. The method is based on the spatial Fourier transform (SFT) of the electromagnetic field distribution along the guiding direction. We demonstrate the validity and robustness of the SFT technique using several test cases. As an application, we apply the method to analyze the dispersion of biperiodic photonic crystal waveguides and show that the guiding bandwidths of these waveguides can be significantly enhanced by a proper choice of the two distinctive spatial periods of the biperiodic waveguides.

Observation of large parity-change-induced dispersion in triangular-lattice photonic crystal waveguides using phase sensitive techniques

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.

Photonic band structure of Abrikosov lattices in superconductors

We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field, leading to nonlinear behavior of the band structure, which also has nonlinear dependence on the temperature. The similar analysis for every arbitrary lattice structure is also possible to be developed by this approach as presented in this work. We also present some examples and discuss the results.

Integrated optical functionalities featuring bi-periodic photonic crystals

The results of a study on bi-periodic photonic crystal structures are presented. We show that not only straight waveguides, but also other optical functionalities can show significantly better performances, when bi-periodicity is introduced.

Integrable planar photonic crystal devices in silicon using nonlinear effects

This paper is focused on nonlinear photonic crystal (PC) structures from theoretical, fabrication, and practical points of views. The material platform for these structures is Si photonic crystals (fabricated using electron beam lithography and dry etching) infiltrated with nonlinear optical polymers. A two-dimensional finite-difference time-domain (FDTD) simulation tool based on a modification of the original Yees FDTD algorithm is developed.

Efficient characterization of dispersion in photonic crystal waveguides using spectral interferometery

We show that femtosecond optical pulses at optical communication wavelengths can be used for real time dispersion measurement of photonic crystal waveguides. Spectral resolutions on the order of one nanometer and bandwidths as large as tens of nanometers are demonstrated in real time measurements. Preliminary results are shown and discussed.

Measurement of large group delay in photonic crystal waveguides using phase sensitive lock-in techniques

We present measurements of the transmission and group delay properties of W1 triangular-lattice photonic crystal waveguides (PCWs) using a phase sensitive lock-in technique. Using a lock-in amplifier improved the SNR of the power transmission measurements by at least one order of magnitude, and also correlated features in the group delay spectra (obtained from phase measurements) to the complex transmission properties of the PCWs. We observed large group delay dips at two specific frequencies, which can be attributed to the edge of the photonic mode gap (PMG) and modal parity changes between the even and the odd modes.

Mode engineering in ultra-low loss bi-periodic photonic crystal waveguides

We present a new platform for designing ultra-low loss wideband photonic crystal (PC) structures using bi-periodic PC waveguides. We show that optimal PC waveguides allow for single-mode guiding over a wide frequency range with linear dispersion below the light line. We present several high-level structures (especially bends and couplers) using this new platform and compare theoretical and experimental results.

Optimization of bi-periodic photonic crystal waveguides for optical integrated circuits

A second periodic it yof the dielectric constant adjacent to the core of photonic crystal waveguides shifts the peak of distributed Bragg reflections toward the edge of the photonic bandgap. We report here, the complete investigation of mode spectrum in these waveguides to explain different features of the experimental results.