In this paper, we introduce and analytically demonstrate a novel chemical sensor based on defective 1-D photonic crystals in total internal reflection geometry, where a gradient refractive index (GRIN) defect layer is located at the end of the structure. This configuration creates an open sensing interface for real-time detection with ultrahigh sensitivity. Using the GRIN lens in the structure not only helps to tune the resonance wavelength to a desired value but also as a consequence of its special refractive index distribution function, a ring-shaped reflectance distribution appears on the output plane of the structure that plays a key role in finding the optimized refractive index of the defect layer and achieving the best resonance of the cavity modes. The resonance angle of the cavity modes is highly sensitive to the effective refractive index of the fluid flowing above the sensor. The refractive index variation of $\Delta n_{F}=10^{-8}RIU$ that causes $\Delta \theta =3.2\times 10^{-6}$ degrees shift at the resonance angle can be detected by this sensor.

A Defective 1-D Photonic Crystal-Based Chemical Sensor in Total Internal Reflection Geometry

Using finite difference time domain (FDTD) method, we numerically investigate one-dimensional photonic crystals (1D PCs) with (AB)mC(BA)m structure, where A and B stand for different dielectric materials, and C the graded-index (GRIN) material. The transmission properties of the multilayer structure have been studied, and the results show that a tunable narrow band-pass filter (BPF) can be obtained by changing gradient coefficients of the GRIN defect layer. For an increasing incident angle, although the transmittance becomes smaller, positions of the resonant peak remain the same, which can act as the angle-insensitive filter.

Narrow band and angle-insensitive filter based on one-dimensional photonic crystal containing graded-index defect

Transmission properties of defect modes in one-dimensional photonic crystals containing gradient refractive index defects

In this chapter, a detailed study of the one-dimension electromagnetic band gap (1D-EBG) structures and their application in a directional antenna design are presented. To improve the ability and analyze and understand the behavior of 1D-EBG, three techniques of analysis are developed. The results show that the periodicity of the dielectric permittivity makes it possible to stop the waves propagation in certain frequency bands. A comparison between the different methods shows an excellent agreement. An evolution of the transmission coefficient of a structure consisting of six layers with a cavity of thickness equal a wavelength in the middle of the structure, shows that there is a peak of transmission which is formed at the center frequency of the band gap and reflects a resonance phenomenon. This phenomenon of frequency filtering is exploited for the design of a directive EBG antenna by introducing an excitation to the cavity center.

1D Electromagnetic Band Gap Analysis and Applications

The optical properties of a one-dimensional (1D) photonic heterostructure with graded-index nonlinear materials are demonstrated theoretically. The influence of the gradation profile of the graded-index nonlinear layers on the linear and nonlinear responses of the structure are analysed. It is shown that the Q-factor of the defect mode and the threshold input intensity to achieve the optical bistability in the used photonic heterostructure depend on the gradation profile of the graded-index nonlinear layers.

B Tavakkoly Moghaddam

Papers

Nonlinear properties of a graded-index photonic heterostructure