A tunable broadband-binary photonic crystal detector for the detection of organic chemical compounds

In this work, we theoretically investigate the reflectance property of 1D defective photonic crystal with inserted defect of infiltrated cavity layer. The structure of the proposed 1D defect layer photonic crystal sensor consists of a cavity layer sandwiched between alternate layers of GaAs and SiO₂ periodically organized and designed as [(A₁A₂)³/C/(A₁A₂)³]. With, A₁, A₂ and C refer to the GaAs layer, SiO₂ layer and infiltrated cavity layers, respectively. The insert cavity layer consists of different organic chemical compounds (OCCs) such that Pentane, n-Hexane, n-Heptane and n-Octane. The reflectance spectra with the optimized structural parameters show two adjacent photonic band gaps (PBGs) separated by a defect mode with reflectance zero. By increasing the defect refractive index of the organic materials infiltrated into the cavity region up to 1.39 (refractive index of n-Octane), the defect mode wavelength shifted towards a higher value. It has been shown that the localized defect mode within the structure can detect minute refractive index changes based on the type of chemical compound. By increasing the incident angle the structure exhibited a sensitivity that varies between a 725.5 nm/RIU at θ = 0^o and a 1039 nm/RIU for θ = 80^o and reached the value of 2672.5nm/RIU at a thickness of 600 nm of incorporated Pentane cavity layer. Also, the quality factor and figure of merit were calculated to show the sensing capabilities further. Compared to recently published works, the current OCC biosensor based on 1D binary photonic crystal detector reached the highest sensitivity. It showed an excellent performance that can be useful for sensing applications in the industrial and biochemical fields.