Photonic Crystals with a Defect Fabricated by Two-Photon Polymerization for the Infrared Spectral Range

One-dimensional photonic crystals composed of alternating layers with high- and low-density were fabricated using two-photon polymerization from a single photosensitive polymer for the infrared spectral range. By introducing single high-density layers to break the periodicity of the photonic crystals, a narrow-band defect mode is induced. The defect mode is located in the center of the photonic bandgap of the one-dimensional photonic crystal. The fabricated photonic crystals were investigated using infrared reflection measurements. Stratified-layer optical models were employed in the design and characterization of the spectral response of the photonic crystals. A very good agreement was found between the model-calculated and measured reflection spectra. The geometric parameters of the photonic crystals obtained as a result of the optical model analysis were found to be in good agreement with the nominal dimensions of the photonic crystal constituents. This is supported by complimentary scanning electron microscope imaging, which verified the model-calculated, nominal layer thicknesses. Conventionally, the accurate fabrication of such structures would require layer-independent print parameters, which are difficult to obtain with high precision. In this study an alternative approach is employed, using density-dependent scaling factors, introduced here for the first time. Using these scaling factors a fast and true-to-design method for the fabrication of layers with significantly different surface-to-volume ratios. The reported observations furthermore demonstrate that the location and amplitude of defect modes is extremely sensitive to any layer thickness non-uniformities in the photonic crystal structure. Considering these capabilities, one-dimensional photonic crystals engineered with defect modes can be employed as narrow band filters, for instance, while also providing a method to quantify important fabrication parameters.

Multimode Robust Lasing in a Dye-Doped Polymer Layer Embedded in a Wedge-Shaped Cholesteric

Cholesteric liquid crystals (CLCs) with induced defects are one of the most prominent materials to realize compact, low-threshold and tunable coherent light sources. In this context, the investigation of optical properties of induced defect modes in such CLCs is of great interest. In particular, many studies have been devoted to the spectral control of the defect modes depending on their thickness, optical properties, distribution along the CLC, etc. In this paper, we investigate the lasing possibilities of a dye-doped polymer layer embedded in a wedge-shaped CLC. We show that multimode laser generation is possible due to the observed multiple defect modes in the PBG that enlarges the application range of the system. Furthermore, our simulations based on a Berreman 4 × 4 matrix approach for a wide range of CLC thickness show both periodic and continuous generation of defect modes along particular spectral lines inside the PBG. Such a robust spectral behaviour of induced defect modes is unique, and, to our knowledge, is not observed in similar CLC-based structures.

Wave Propagation in an Optimized Tunable Multi-channel Flter based on One-dimensional Nano Superconductor Photonic Crystal

Although there has been a focus on THz lters so far, there is a signifcant defciency in advancing low-temperature THz lters. According to the needs, we proposed a tunable THz lter that selectively permits the desired incident frequencies to be propagated in relevance with our purpose. The presence of a low-temperature nano superconductor and an undoped semiconductor layers in the proposed structure resulted in a multi-channel THz lter, which could be highly tuned with several parameters such as lattice constants, applied temperature, etc. The achieved transmittance spectra revealed that the emerged transmittance couples and stacks follow exact regulations. Furthermore, the structure exhibited omnidirectional band-gaps for both TE and TM polarized waves. Moreover, the use of a central defect layer gave some transmittance defect modes in the forbidden areas. This structure could be used in some THz devices such as switches, optimized sensors as well as in space industry and telecommunications.