Communications in Physics, Vol. 21, No. 1 (2011), pp. 89-96 INVESTIGATION OF 1D PHOTONIC CRYSTAL BASED ON NANO-POROUS SILICON MULTILAYER FOR OPTICAL FILTERING DO THUY CHI Thai Nguyen College of Education, Thai Nguyen University BUI HUY AND NGUYEN THUY VAN Institute of Materials Science, VAST PHAM VAN HOI Institute of Materials Science, VAST and University of Engineering and Technology, Hanoi National University Abstract. We present the fabrication, simulation, and measurements of 1D photonic crystal based on nano-porous silicon multilayer designed as an optical interference filter. Using electro- chemical etching with timely repeat steps of applied current densities, we fabricated a multilayer structure composed of alternating high- and low-index layer which achieved 90% power reflectivity at wavelength range of 1400-3000 nm. The simulation is relying on the Transfer Matrix Method (TMM) to design and predict the optical properties of nano-porous silicon multilayer as well as the relation between anodization parameters with reflection spectra. The measured reflection and transmission spectra of the nano-porous silicon multilayer show good agreement with simulation. This technique could provide a convenient and economical method to produce filters, cavities, and graded-index dielectric waveguides in the future. I. INTRODUCTION Several techniques have been used to fabricate optical-band multilayer filters, includ- ing stacking and assembly of semiconductor, ceramics, and plastic films [1-3] and other dielectrics. Thick film sputter-deposition method has also been used to fabricate multi- layer of silicon, oxides and other semiconductors [4]. Polymer nanoparticle composites have been used to provide additional flexibility in controlling the effective refractive index of layers [5]. Nano-porous silicon (nano-PS) is an easily fabricated nanoscale composite of air and silicon that has been shown to be suitable for optical filters [6]. The considerable and controllable variations in refractive index of nano-PS fabricated by an electro-chemical etching make it become a promising material as photonic crystal. In the porous structure, PS consists of many pores and silicon residuals and, usually, can be described as a homo- geneous mixture of silicon, air and, eventually, silicon dioxide. Based on porosity, PS can be classified into three types: nano-, meso- and macro-pores. In the case of PS nano- and meso-pores, the size of both the silicon residuals and the air voids (pores) can be in the range of few nanometers to tens ones. Since infrared light has wavelengths of micrometers,