An approach to achieve all-angle, polarization-insensitive and broad-band self-collimation in 2D square-lattice photonic crystals

Abstract

Abstract. We have investigated the possibility for achieving (in the same structure), an all-angle, polarization-insensitive and broad-band self-collimation (SC), one of the most urgent requirements in the field of optical integration. To obtain these attractive SC features in 2D square-array photonic crystals, we have used several strategies and performed testing calculations, using plane-wave expansion and finite-difference time-domain methods. We have not complicated the basic structure for the SC and ensured its simple geometry. The all-angle SC can arise when the optical material of a hole-type structure is high-index. Our results have testified that the SC in the hole-type structure is less dependent on the light polarization, if compared with a similar rod-type one. Our optimized SC structure has a bandwidth of Δf/f c = 2.61% and supports the all-angle SC for both TE and TM polarizations at the expense of small (~ 3) deviation of light from the unique collimation direction. Notice that the latter can be tolerated in many integrated optical devices.

Self‐Collimation in Photonic Crystals: Applications and Opportunities

“…Considering appropriate minimum index contrast in any filling ratio rather than using ultra‐high index materials helps to achieve PISC merged with an all‐angle SC characteristic . The study revealed that all‐angle PISC exists within a bandwidth of 2.61% for the optimized parameter choice at the expense of considering 3° deviation from the ideal SC . The outcome of this study, showing the possibility of achieving PISC in a square array, is indicated in Figure .…”

“…The propagation direction of light in PCs is determined by the group velocity (, ω is the optical frequency at wave vector k ), which is normal to EFCs . Therefore, the SC effect originates from the flat parts of EFCs and a number of studies have been devoted to tailor the dispersion properties (shape of the EFCs) of PCs considering various lattice symmetries, material parameters, and geometrical shapes of the scatterers to control the electromagnetic waves artificially for the desired applications …”

“…A recent study demonstrated that the rod‐type square lattice PC cannot present all‐angle PISC for any radius and index contrast; however, the hole‐type structure favors these characteristics for proper parameter choice. Considering appropriate minimum index contrast in any filling ratio rather than using ultra‐high index materials helps to achieve PISC merged with an all‐angle SC characteristic . The study revealed that all‐angle PISC exists within a bandwidth of 2.61% for the optimized parameter choice at the expense of considering 3° deviation from the ideal SC .…”

“…As a highly qualified platform for the development of devices for optical integration, self‐collimating PCs must provide broadband and wide‐angle operation for both TE and TM polarizations . In recent years, a great number of studies have been devoted to broaden the frequency range for SC phenomena, expand the incident angle range, achieve PISC, and reduce the reflections from the interfaces …”

“…EFCs for TE and TM polarizations for the normalized frequency of a / λ = 0.097, for the optimized structure. Reproduced with permission . 2015, UJPO.…”