Comparative study of 1D defective photonic structures composed of single and double defect layers

Abstract

In this study, we investigated the sensing capabilities of 1D defective photonic crystal designs composed of single and double defect layers. These structures can detect and distinguish minor refractive index changes of various organic samples infiltrated one by one into defect layer regions of the respective designs. We have used the standard transfer matrix method to analyze the transmission properties of both structures at normal incidence. The normal incidence has been chosen to overcome the experimental difficulties associated with oblique incidence. The performance of the proposed designs has been examined by measuring the shift in the position of the defect modes inside PBGs of respective structures depending upon the change in the refractive index of various organic solvents, called samples. We can also find adulteration in the organic samples by comparing the observed data with the experimentally available standard data of pure organic samples. Moreover, double defect photonic structure possesses pair of two defect modes inside PBG. These pair of defect modes are located on either side of bandgap edges that cannot be found in 1D defective PCs composed of a single defect. This intriguing property of double defect PC structure is due to the quasi Fabry–Perot cavity nature of the structure. Finally, we have compared sensing and detection features of both the designs made up of single and double defect photonic structures. It has been noticed that the double defect photonic structure also improves the transmittance of defect peak to unity compared to the single defect photonic structure. Moreover, the FWHM of two pairs of defect modes in double defect PC are opposite in nature. This remarkable feature of double defect photonic design may be very useful for improving the performance of photonic bio-sensors. It may be very helpful for designing some advanced bio-sensing designs whose defect mode properties are mirror image in nature.