Real-time optical sensor based on one dimensional photonic crystals with defects

A previous theoretical study of a finite one-dimensional photonic crystal composed of 12 unit cells with two defects had shown the existence of Photonic Pass Band (PPB) inside the Stop Band, which was suggested as a useful refractive index sensor due to the sensitive variation of PPB with respect to the change of refractive index of defect layer material. We report in this presentation our successful fabrication of a prototype of this system by means of electron beam evaporation equipment in a sample chamber at pressure of 10^-3 Pa with BK-7 glass substrate at temperature 573 K. Each of the photonic cells is composed of a high index layer of OS-5 with refractive index of n =3D2.10, and an equal thickness low index layer of MgF₂ with n =3D 1.38. In the first defect cell, the high index layer has twice the thickness of the other layers with the low index layer left unchanged, while in the second, defect cell is separated by 6 unit cells, and the first layer is void to be filled with the sample solution. The device was used for measuring the refractive index of sugar solution with concentration range of 20-500 g/L in the real time mode. The result was found to achieve determination coefficient more than 90%. Further measurement performed has demonstrated a result in good agreement with theoretical prediction reported previously.