Design of 4*2 Optical Encoder using Hexagonal Shaped Photonic Crystal Ring Resonator

Transcription

1 Design of 4*2 Optical Encoder using Hexagonal Shaped Photonic Crystal Ring Resonator Subhalakshmi G,Robinson S * Department of Electronics and Communication Engineering, Mount Zion College of Engineering and Technology, Pudukkottai, Tamilnadu, India mail2robinson@gmail.com (Received 10 th May, 2018; Revised 16 th June, 2018; Accepted 20 th June, 2018; Published: 08 th July, 2018) Abstract- In this paper, 4*2 optical encoder is designed on the triangular lattice using 2-Dimensional Photonic Crystal (2DPC). The line defects and hexagonal shaped ring resonator are introduced in this proposed structure. The performance of the encoder is simulated by using 2D Finite Difference Time Domain Method (2D-FDTD) and Plane Wave Expansion method (PWE). The functional parameter such as switching frequency and time delay are determined. The switching rate and time delay of the proposed encoder is 10THz and 0.1ps respectively. The entire size of the proposed encoder is 14.8μm x 11.6μm.The proposed encoder is suitable for optical integrated devices. Key Words: Photonic crystal, encoder, Resonator, FDTD, triangular lattice. 1. INTRODUCTION A rapid growth of technology leads to wide range of various high speed applications such as Optical telecommunication and Fiber optic communication, etc. hence increase in demand of optical components and devices. Most of the optical components and devices are designed during past and recent years due to high speed of operation in the range of terahertz. Among these photonic crystal based components are mostly used for designing the optical devices since, it has the properties of photonic band gap that allows the propagation of light through desired PC design with certain range of wavelength[1]. The band gaps of variety of 2D-PC lattices such as hexagonal and square lattice were studied in the literature by Solli and Hickmann [2]. PC has the unique qualities such as compactness, high speed, and low power consumption [3]. 2D PC is mostly used for designing the optical devices due to easy fabrication and better confinement [4]. The logic gates [5-6], encoder [7], decoder [8-10] multiplexer [11] and demultiplexer [12] are some of the optical components for transferring and receiving the large amount of data in high speed communication systems. Optical encoder is a logic device that generates the N-bit binary codes from 2 N inputs using the binary logic 0 and logic 1.It consists of 2 N inputs and 2 outputs in which only one input is turn ON at a time and remaining outputs are turn OFF. It converts the analog signal in to digital signal by using the suitable digital binary code in analog to digital convertor. It compressed the digital data for transmission and storage in optical data processing [13]. Several designs have been proposed for recognizing PC based optical encoders in previous decades. Siamak Gholamnejad and Mahdi Zavvari were proposed an optical 4x2 encoder using non-linear PhCCR.Fast response and the low intensity input are the advantages of these proposed design [14]. Farhad Mehdizadeh et al. proposed an optical encoder by implement the buffer and OR gate in the structure. The delay time and the switching time of an encoder is 200fs and 5 THz [15].The elliptical rings and waveguide are introduced in the structure of encoder is proposed by Mahdi Hassangholizadeh et al. It is a reversible encoder that reduce the loss of data in optical signal processing [16].Tina Daghooglil et al. had proposed a decoder with six non-linear PHCRR and it act as a optical switches. The decoder has a crosstalk of the range between and -38dB and insertion loss is between and -20dB [17].Hamed Alipour-banaei et al. presented an optical encoder by the combination of beam splitter and mirror along with self-collimated effect. The response speed of the proposed device is 1400 fsec [18].The structure of encoder is designed by Farhad Mehdizadeh et al. which is composed of optical power splitter and four-port optical switch. The maximum switching speed is 2GHz and operating at about 20W/μm 2 [19].Optical coherent en/decoder is realized by using PC based phase shifter and time delayer by Chongfu Zang. The performance characteristics such as reflection, transmission, time delay were theoretically and numerically analyzed [20]. In this work, an optical 4x2 encoder is designed based on 2DPC using a hexagonal based ring resonator hence it has high transmission efficiency. The guided mode of propagation and PBG are determined using the PWE method. The proposed PC structure has four input waveguides and two output waveguides which are coupled to hexagonal shaped resonator. The transmission behaviour of the proposed encoder is analyzed using 2D FDTD method. It works in the second optical window and it is fit for all optical integrated circuits. The rest of the paper is structured as follows: Section 2 describes the design of 4x2 optical encoder. Section 3 describes the simulation results and discussion of proposed encoder. Sections 4 conclude the proposed work. 2. DESIGN OF 4*2OPTICAL ENCODER A proposed encoder is designed on the triangular lattice of an array of 21 x 23 rods along the X direction and Z direction. It consists of multiple inputs and multiple outputs. Fig. 1 shows the block diagram of 4x2 encoder. Table 1 represents Page 4

2 the truth table of 4x2 encoder.the band diagram is depicted in the Fig. 2.The mode propagation inside the PC is determined using PWE method. The wavelength range is selected as TE mode of 0.3a/λ to a/λ is 1319nm to 2133nm. present on the right and left side of hexagonal shaped resonator. The design is optimized to reduce the radius of the left and right side of the input A4 and input A2 is 45nm.The length of the input waveguide A1 is slightly vary than the length of the input waveguide A3.The refractive index is varied half of the length in order to avoid back reflection. The 3D view of the proposed encoder is described the overall size of the device as shown in the Fig. 4. Fig. 1: Block diagram of optical 4*2encoder Table 1: Truth Table for 4*2 optical encoder S. No. Input Output A1 A2 A3 A4 O1 O Fig. 3: Schematic structure of optical 4*2encoder Fig. 4: 3D view of the proposed 4*2 optical encoder Fig. 2: Band diagram of proposed 4x2 encoder The structure of 4*2 optical encoder consists of a triangular lattice of an array of 21x23 rods. The line defects and hexagonal shaped waveguide are used to design the 4x2 encoder. The refractive index of silica material is 3.46 and radius of rods present in the whole structure is 110 nm. The space between the two neighbor rod is known as lattice constant and it is denoted as a which is equal to 640 nm. An encoder is constructed by creating six waveguides and hexagonal shaped resonator is placed on the center of the waveguides. The four waveguides are used as the input waveguide and it is represented as A1, A2, A3 and A4 respectively. The remaining two waveguides are used as the output waveguide and it is denoted as O1 and O2.The radius of the rod r1 and r2 is optimized to 45nm and 55nm which are 3. SIMULATION OF 4*2 OPTICAL ENCODER The performance of the proposed encoder is simulated for four different states of inputs. Fig. 5 shows the optical field distribution of 4*2 encoder. The resonant wavelength of the device is 1550nm which is applied as the input for four input waveguides. When A1 is ON, the optical signal does not pass through the resonant ring hence O1 and O2 will be OFF. where the normalized output at O1and O2 is 8.4% and 9.4%. When A2 is ON, the optical signal propagate through the resonant ring but only reaches the O2 and it goes to ON and O1 is OFF. Where the output power at O1and O2 is 21% and 100%.When A3 is ON, the optical signal coupled to the resonant ring and dropped only at O1 and it is ON and O2 become OFF. where 82% at O1 and 20% at O2. When A4 is ON, the optical signal coupled with the resonant ring and the signal is dropped at both output ports and hence both the O1 Page 5

3 and O2 become ON due to resonant effect of the ring. Their normalized output power reaches the O1 ando2 are 92%. Fig. 6 Shows the output performance of the 4x2 encoder and describes its functional performance. Table 2 represents the normalized output transmission of the proposed encoder. This is briefly discussed above in the section. Fig. 5 Optical field distribution of proposed encoder at (c) A3=1, A1=A2=A4=0, O1=1, O2=0 and (c) A3=1, A1=A2=A4=0, O1=1, O2=0 Page 6

4 are the merits of proposed structure and it is appropriate for all high speed Optical integrated circuits. S. No. (c) A3=1, A1=A2=A4=0, O1=1, O2=0 Fig. 6: Output response of the proposed encoder at (c) A3=1, A1=A2=A4=0, O1=1, O2=0 and Table 2: Output performance of 4*2 optical encoder Input Output % A1 A2 A3 A4 O1 O CONCLUSION The 2D PC based encoder is designed using triangular lattice. The proposed encoder is composed of the effect of line defects and hexagonal shaped ring resonator. The proposed encoder is simulated and analyzed the optical behaviour using the FDTD method. The simulation result shows the switching rate and time delay of the proposed device is 10THz and 0.1ps.The normalized power for ON state is above 80% and OFF state is below 25%. The smart structure and fast response REFERENCES [1] A. Salmanpour, S. Mohammadnejad, and A. Bahrami, Photonic crystal logic gates: an overview, Opt. and Quant. Elect., vol. 47, no. 7, pp , [2] D. R. Solli, and J. M. Hickmann, Study of the properties of 2D photonic crystal structures as a function of the air-filling fraction and refractive index contrast, Opt. Mat., vol. 33, no. 3, pp , [3] W.-P. Lin, Y.-F. Hsu, and H.-L. Kuo, Design of Optical NOR Logic gates using Two dimensional Photonic Crystals, Am. J. of Mod. Phy., vol. 2, no. 3, pp , [4] S. Robinson, and R. Nakkeeran, Investigation of parameters affecting the performance of two dimensional photonic crystal based pass band filter, Opt. and Quant. Elect., vol. 43, no. 6-10, pp , [5] E. H. Shaik, and R. Nakkeeran, Photonic crystal structure for realization of NAND and NOR logic functions by cascading basic gates, J. of Comp. Elect., vol. 17, no. 1, pp , [6] E. H. Shaik, and R. Nakkeeran, Multi- mode interference based photonic crystal logic gates with simple structure and improved contrast ratio, Phot. Net. Comm., vol. 34, no.1, pp , [7] Y.-P. Yang et al., All-optical photonic-crystal encoder capable of operating at multiple wavelengths, Optik, vol. 142, pp , [8] S. Serajmohammadi, H. Alipour-Banei, and F. Mehdizadeh, All optical decoder switch based on photonic crystal ring resonators, Opt. and Quant. Elect., vol. 47, no.5, pp , [9] H. Alipour-Banei, F. Mehdizadeh, S. Serajmohammadi, and Hassangholizadeh Kashtiban, A 2*4 all optical decoder switch based on photonic crystal ring resonators, J. of Mod Opt., vol.162, no. 6, pp , [10] S. Khosravi, and M. Zavvari, Design and analysis of integrated all-optical 2x4 decoder based on 2D photonic crystals, Phot. Net. Comm., vol. 35, no. 1, pp , [11] G. Manzacca, D. Paciotti, A. Marchese, M. S. Moreolo, and Gabrillacincotti, 2D photonic crystal cavity-based WDM multiplexer, Phot. and Nanost.-Fund. and App., vol. 5, no. 4, pp , [12] R. Talebzadeh, M. Soroosh, Y. S. Kavin, and F. Mehdizadeh, All- optical 6- and 8-channel demultiplexers based on photonic crystal multilayer ring resonators in Si/C rods, Phot. Net. Comm., vol. 34, no. 2, pp , [13] I. Ouahab, and R. Naoum, A Novel All Optical 4x2 Encoder Switch Based on Photonic Crystal Ring Resonators, Optik, vol. 127, no. 19, pp , [14] S. Gholamnejad, and M. Zavvari, Design and analysis of all-optical 4-2 binary encoder based on photonic Page 7

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