1st International Conference on Advances in Science, Engineering and Robotics Technology 2019 (ICASERT 2019) 978-1-7281-3445-1/19/$31.00 ©2019 IEEE Performance evaluation of an optical drop filter based on simple homogeneous photonics crystal resonator Md. Aminur Rahman, A.K.M Ehtesanul Islam Dept. of Electrical and Electronic Engineering Ahsanullah Univeristy of Science and Technology Dhaka, Bangladesh aminur.rahman.eee@gmail.com, ehtesan@aust.com Abstract— In this paper we proposed a novel drop filter structure based on Photonic Band Gap (PBG) for the 1550nm communication wavelength. The filter is designed and then simulated using Finite Element Method (FEM) and Plane Wave Expansion Method (PWEM) method. The filter shows 91% efficiency at the mentioned wavelength. We also analyzed how the target wavelength can be varied by changing various aspects of the structure. The design utilizes all homogeneous method which is easier to fabricate and introduce in photonic integrated circuit. Keywords—Photonic Integrated Circuit, drop filter, photonic band gap (PBG), photonic crystal I. INTRODUCTION Photonic crystal (PC) structure gained tremendous popularity in the last decade. Though the one dimensional photonic crystal (1DPC) was proposed in 1887, after the introduction of 2D (2DPC) and 3D Photonic(3DPC) crystal in 1987 the potential of PC structure were fully realized [1 ,2]. Due to the lack of computational power in the early stage not many structure was analyzed. As the computational power increased, analysis of different structure is easier than ever before. Electromagnetic wave can be controlled by manipulating periodic dielectric structure. Most commonly used design to guide EM wave is metallic pipe waveguide and dielectric guide [3]. They are used mostly in the infrared, visible or microwave range. Waveguide which are based on total internal reflection are restricted by heavy losses in the bends. But by creating defect or engineered structure in a Photonic band gap (PBG) material, EM wave can be confined as such it does not show high radiation losses in the bend. A linear defect in a PBG material can be used as a waveguide. This type of waveguide work as the defect results in a guided band in-between TM band gap. So, the conventional optical fiber use index guiding whereas the PBG structure use band gap confinement to confine light. Band gap confinement works better as this minimizes losses, nonlinearities, and any other unwanted properties of the material [4]. In all optical computing, photonic integrated circuit or an optical communication system PCs can be used extensively due to their longer life period, better confinement, high speed and small size [5-10]. In a dense wavelength division multiplexing system (DWDM) due to the high spectral selectivity, low loss and high quality factor of PC structure, the conventional strip based micro-ring resonator can be replaced by PCs [11-14]. PBG structure can be classified broadly as homogeneous and heterogeneous structure. In a heterogeneous structure, different sections use different reflective index or the reflective index of the material can be actively changed (in case of electro-optic/ magneto-optic/ acousto-optic materials) [15,16]. Hetero structure is useful on its own ground but it is difficult to fabricate. On the other hand, homogeneous structure has material with single reflective index which is easy to fabricate. Many different structure based on PBG have been proposed, analyzed and fabricated. L-shaped bends, T shaped power splitter, [18,19] X shaped, quasi square, tri quarter square etc. [20]. Filters made out of various structures designed as band pass, add/drop or device demultiplexer in WDM system are studied extensively. In most of the filters, they showed various way to manipulate the filter characteristics. Tuning the wavelength changing the add/ drop frequency, increasing the transmission coefficient can be done by changing dielectric constant, radius of the rod, changing lattice constant etc. In this paper we have investigated a drop filter design created by introducing linear gap in the structure to create the waveguide and then creating a simple structure in the gap to create resonant cavity, which performs as a drop filter in the 1550nm range. The next section introduces the structure used in the simulation. In section 3 we describe the simulation results. Section 4 describe the working principle of the structure. Section 5 summarize the finding in the paper. II. GEOMETRY OF THE FILTER STRUCTURE The drop filter is designed to be operated in the 1550nm wavelength range. A square dialectic rod lattice with a lattice constant of ‘a’ and dielectric rod with radius “r=.2*a” is chosen for the structure. To design the filter, first the photonic band gap of the square lattice was determined to find out the range of frequency the filter can be used for. Using the lattice parameter and r=.2*a, relative permeability εr = 16, relative permittivity, µr= 1 using Plane Wave Expansion Method (PWEM) dispersion diagram was determined (Fig. 1). While calculating different bands the material in-between the dialectic rod is considered as air. For transverse electric (TE) polarization the dispersion diagram shows there is a complete photonic gap for the range 0.2451 ≤   ⁄ ≤ .3871. The complete photonic gap (PBG) can be seen in Fig. 1 as yellow region. Inside this region the square lattice will not pass any TM polarized EM wave. (there is no allowed mode in this range of frequency). This is the primary concept in band gap confinement. By creating line defect in perfect lattice structure guided mode can be crated in between the photonic band gap. Two waveguides made out of line defect was created to pass TM polarized Authorized licensed use limited to: Ahsanullah University of Science & Technology. Downloaded on January 04,2022 at 06:56:46 UTC from IEEE Xplore. Restrictions apply.