We investigate slow light propagation in monomode photonic crystal waveguides with different spectral features such as constant group index, high bandwidth and low group velocity dispersion. The form of the waveguide mode alters dramatically and spans three different spectral intervals by tuning the size of the boundary holes. Namely, slope of the band gap guided mode changes sign from negative to positive toward the Brillouin zone edge. In between there is a transition region where modes have nearly zero slopes. Maximum group index occurs at these turning points at the expense of high dispersion and narrow bandwidth. The apparent trade-off relationship between group index and bandwidth is revealed systematically. We show that as the radius of the innermost hole is increased above a certain value, the former one decreases and the latter one increases both exponentially but with a different ratio. The product of average group index and bandwidth is defined as a figure of merit which reaches up to a value of approximately 0.30 after a detailed parametric search. The findings of the frequency domain analysis obtained by plane wave expansion method are confirmed via finite-difference time-domain study.

We explore slow light behavior of a specially designed optical waveguide by carrying out structural dispersion using numerical techniques. The structure proposed is composed of square-lattice photonic crystal waveguide integrated with side-coupled cavities. We report three orders of magnitude reduction in group velocity at around υ(g) ≅ 0.0008c with strongly suppressed group velocity dispersion. The analysis is performed by using both plane-wave expansion and finite-difference time-domain methods. For the first time, we succeeded to show such a low group velocity in photonic structures. Slow light pulse propagation accompanied by light tunneling between each cavity is observed. These achievements show the feasibility of photonic devices to generate extremely large group index which in turn will eventually pave the way to new frontiers in nonlinear optics, optical buffers and low threshold lasers.

In this article, we propose a large bandwidth mode-order converter design by dielectric waveguides with equal lengths but different cross-sectional areas. The efficient conversion between even and odd modes is verified by inducing required phase difference between the equal length waveguides of different widths. Y-junctions are composed of both tapered mode splitter and combiner to connect mono-mode waveguide to multi-mode waveguide. The converted mode profiles at the output port show that the device operates successfully at designed wavelengths with wide bandwidth. This study provides a novel technique to implement compact mode order converters and direction selective/sensitive photonic structures.

In this paper, we present silicon nitride metamaterial absorber designs that accomplish large bandwidth and high absorption in the long wave infrared (LWIR) region. These designs are based on the metal-insulator-metal topology, insulator (silicon nitride), and the top metal (aluminum) layers are optimized to obtain high absorptance values in large bandwidths, for three different silicon nitride based absorber structures. The absorption spectrum of the final design reaches absorptance values above 90% in the wavelength interval between 8.07 μm and 11.97 μm, and above 80% in the wavelength interval between 7.9 μm and 14 μm, in the case of normal incidence. The difficulty in the design process of such absorbers stems from the highly dispersive behavior of silicon nitride in the LWIR region. On the other hand, silicon nitride is a widely used material in microbolometers, and accomplishing wide band absorption in silicon nitride is crucial in this regard. Therefore, this study will pave the way for more efficient infrared imaging devices, which are crucial for defense and security systems. Additionally, such designs may also find applications in thermal emitters.