Design of Three-mode Multi/Demultiplexer Based on 2-D Photonic Crystals for Mode-Division Multiplexing Transmission

Transcription

1 Journal of Physics: Conference Series PAPER OPEN ACCESS Design of Three-mode Multi/Demultiplexer Based on 2-D Photonic Crystals for Mode-Division Multiplexing Transmission To cite this article: PeiDong Fu and Heming Chen 2017 J. Phys.: Conf. Ser View the article online for updates and enhancements. Related content - Design and numerical optimization of a mode multiplexer based on few-mode fiber couplers Yiwei Xie, Songnian Fu, Hai Liu et al. - Surface waves on the boundary of photonic crystals and tunnelling coupling between two photonic crystals via these waves B A Usievich, V V Svetikov, D Kh Nurligareev et al. - Generation of difference terahertzfrequency signals in a system of compound one-dimensional photonic crystals E V Petrov, V A Bushuev and B I Mantsyzov This content was downloaded from IP address on 23/01/2019 at 18:59

2 Design of Three-mode Multi/Demultiplexer Based on 2-D Photonic Crystals for Mode-Division Multiplexing PeiDong Fu, Heming Chen * Transmission Department of Opto-Electronics, Nanjing University of Posts and Telecommunications, Nanjing , China Bell Honors School, Nanjing University of Posts and Telecommunications, Nanjing , China *chhm@njupt.edu.cn Abstract :A three mode division multiplexer and demultiplexer (MMUX/DEMMUX) base on 2-D photonic crystal at 1550 nm was designed. Two asymmetrical directional couplers are included in this MMUX/DEMMUX, which can achieve modes conversion function of TE 0,TE 1 and TE 2 modes. In order to avoid phase mismatching in bus waveguide, taper directional is applied at waveguide junction which can reduce the insertion loss effectively. Plane waves method (PWM) and finite difference time domain (FDTD) methods were used to simulating the performance of MMUX/DEMMUX. Numerical simulations show that the designed device has the potential for high-capacity MDM optical communication systems with a low insertion loss (<0.27dB) and a low mode crosstalk (< 25.4 db). 1. Introduction In order to increases the capacity of optical networks effectively, WDM technology [1,2] has become an important form of optical network technologies. However, it is well known that the capacity of WDM is approaching the Shannon limit of sing-mode optical fiber system. One of the promising approach for increasing the capacity is mode-division multiplexing (MDM) transmission in which each optical mode is exploited as an independent channel for transferring optical data. In the mode multiplexed optical transmission system, MMUX/DEMMUX has become a hot research area as key components, which can be realized by using PLC-based asymmetrical parallel waveguides (APW) [3-7], asymmetrical Y-junction [8 10], as well as few-mode fibers [11 13]. MMUX/DEMMUX based on chip Y-splitter were designed by Jeffrey B. Driscoll in Columbia University [8], which can realize (de)multiplex two modes of the same polarization with a low insert loss ranging from 0.1to 0.7dB. However, these devices are very sensitive to process errors about the angle between Y-junction arms. Yue-De in University of Hong Kong have successfully multi/demultiplexed three modes by quasi phase-matching (QPM) the modes of asymmetrical parallel waveguides [3], but its worst channel crosstalk is only -10dB. In this paper, a three mode multiplexer and demultiplexer using asymmetrical parallel waveguides (APW) base on the 2-D Si square lattice photonic crystal is proposed. In this MMUX/DEMMUX, the single-mode waveguide formed by removing a row of Si dielectric cylinders. Adjusting the size of two rows of Si dielectric cylinders forms TE 0 and TE 1 modes waveguide which can satisfy the phase matching condition. The multi-mode waveguide of TE 0, TE 1 and TE 2 modes formed by adjusting the size of three rows of Si dielectric cylinders. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by Ltd 1

3 In order to inhibit mismatch problem between the different multi-mode waveguide, taper waveguide is adopted between each bus waveguide. Therefore, TE 0, TE 1 and TE 2 modes MMUX/DEMMUX can be achieved which has a great value of the mode multiplexed optical communication system with advantages of small size, low insert loss, low mode crosstalk and easily integrated. 2. Structural model and MDM mechanism 2.1 Structural model The structure of 2-D MMUX/DEMMUX based on photonic crystal, which has Si dielectric cylinder compositions is shown in Figure 1. There are two asymmetrical parallel waveguides (APW) as mode conversion function in the structure. One of APW(P 01) is formed by putting a rectangular single-mode waveguide (G1) close to the multi-mode waveguide (G2), another APW(P 02) is formed by putting a rectangular single-mode waveguide (G3) close to the multi-mode waveguide (G4). G1&G3 is formed by removing a row of Si dielectric cylinders. G2 is formed by adjusting the size of two rows of Si dielectric cylinders which supports two guided modes (TE 0 and TE 1). G3 is formed by adjusting the size of three rows of Si dielectric cylinders which supports two guided modes (TE 0, TE 1 and TE 2). In order to ensure that all the various modes of bus waveguide couples effectively, we proposed a taper waveguide structure, which includes waveguide width of the gradient and Si dielectric cylinder radius of gradient. Fig.1. The structure of three-mode photonic crystal MMUX/DEMMUX Structural parameters of the device are set as below: lattice constant is a = 0.55μm, Si dielectric cylinders radius is r 1 = 0.1μm, Si refractive index is n 1 = 3.4, single-mode waveguide width is w 1 = 2a = 1.1μm. The multi-mode waveguide width and silicon dielectric cylinder radius are set as w 2 = 3a = 1.65μm, r 2 = μm The AWP interaction length is set to be L 1 = 26a = 14.3μm, gap of the AWP is d = a = 0.55μm. Taper waveguide length is L 2 = 1.65μm, the width of which increases linearly with a slope equal to a / 3. Structural parameters TE 0 and TE 2 mode conversion area are set as below: multi-mode waveguide Si dielectric cylinder radius is r 3 = μm, width is w 3 = 4a = 2.2μm. The AWP interaction length and gap are set to be L 3 = 36a = 19.8μm, d = a = 0.55μm. the width of which increases linearly with a slope equal to a / MMUX/DEMMUX mechanism Mode conversion is realized by quasi-phase matching principle [14-17] in this paper. In the mode conversion region P 01, the propagation constant of TE 0 in rectangular single-mode waveguide should be equal to that of TE 1 in the multi-mode waveguide. And in mode 2

4 conversion area P 02, propagation constant of TE 0 in rectangular single-mode waveguide equals to that of TE 2 in the multi-mode waveguide. Normalized propagation constant of TE 0 at 1.55μm wavelength is in this structure. The curve of propagation constant and radius of Si dielectric cylinder in multi-mode waveguide (G2) by simulation is shown in Fig.2, The curve of propagation constant and radius of Si dielectric cylinders in multi-mode waveguide (G4) by simulation is shown in Fig.2. As shown in the Fig.2-, in order to satisfy the phase matching condition, we set the radius of Si dielectric cylinders to be μm and μm in G2 and G4, respectively. The light wave transmitted in the mode conversion region P 01 and P 02 can be seen in Fig.2(c)-(d). The coupling length in P 01 and P 02 are 26a and 36a, respectively. (c) (d) Fig.2. propagation constant curve of G2 propagation constant curve of G4 (c) the steady field intensity distribution for mode conversion TE 0 andte 1 (d) the steady field intensity distribution for mode conversion TE 0 andte 2 When TE 0 mode at 1550nm is launched from port1, port2 and port3, respectively, TE 0 will convert to TE 1 and enter into bus waveguide in the mode conversion region P 01, and TE 0 will convert to TE 2 in P 02. Finally, they output from port4 together. The structure can be also used as a DEMMUX because the parallel waveguide has a symmetric property. During demultiplexing process, the TE 0, TE 1 and TE 2 modes are excited from port4, and all converted to TE 0 modes and output from port1, port2 and prot3, respectively. Based on the above analysis, stable mode fields of MMUX/DEMMUX are as shown in Fig.3-(c). 3

5 (c) Fig.3. the steady field intensity distribution for three-mode MMUX/DEMMUD TE 0 TE 0 and TE 1(c)TE 0 and TE 2 3. Properties and analysis 3.1 The simulation of MMUX In this paper, the capability of the device is analyzed using 2-D FDTD method. For MMUX function, we input CW light of TE 0 at 1550nm into port1, and light intensity are observed at port2, port3 and port4 respectively, the intensity of port4(t 1-4), port2(s 1-2) and port3(s 1-3) are shown in Fig.4-(c). Similarly, the intensity of port4(t 2-4), port1(s 2-1) and port3(s 2-3) are shown in Fig.4-(f), when CW light of TE 0 at 1550nm is put into port2. The intensity of port4(t 3-4), port1(s 3-2) and port2(s 3-1) are shown in Fig.4(g)-(i), when CW light of TE 0 at 1550nm is put into port3. It could be seen that transmittance of the device is higher than 96% and the worst crosstalk is less than -25.4dB. (c) (e) (f) (d) (h) (i) (g) Fig.4. the transmission rate of three-mode MMUX T 1-4S 1-2(c)S 1-3(d)T 2-4(e)S 2-1(f)S 2-3(g)T 3-4(h)S 3-2(i)S The simulation of DEMMUX For DEMMUX function, we put CW light of TE 0 mode at 1550nm into port4, and light intensity are observed at port1, port2 and port3, respectively. the intensity of port1(t 4-1), 4

6 port2(s 4-2) and port3(s 4-3) as shown in Fig.5-(c). Similarly, the intensity of port2(t 4-2), port1(s 4-1) and port3(s 4-3) when CW light of TE 1 at 1550nm is put into port4, as shown in Fig.5-(f). It is observed that transmittance is higher than 94%. The intensity of port3(t 4-3), port1(s 4-2) and port2(s 4-1) when CW light of TE 2 at 1550nm is put into port4, as shown in Fig.5(g)-(i). we can obtain that the DEMMUX performs with a lower crosstalk of 10-4 order of magnitude and the worst transmittance of 94%. (c) (e) (f) (d) (h) (i) (g) Fig.5. the transmission rate of three-mode DEMMUXT 4-1S 4-2(c)S 4-3(d)T 4-2(e)S 4-1(f)S 4-3(g)T 4-3(h)S 4-2(i)S Performance index Analysis of MMUX/DEMMUX Insertion loss and crosstalk between channels are important factors of MMUX/DEMMUX. Channel crosstalk is defined as: S C=10lg T (1) where S represents the radiation intensity from transmission channel into the adjacent channel, T represents transmission intensity of the transmission channel. Insertion loss is defined as: P o CT=-10lg (2) P i The Po indicates the power of the inputting light, Pi represents the transmission power, in formula (2). The performance of crosstalk in MMUX function and DEMMUX function is shown as table1-. 5

7 Table 1. the crosstalk of the device MMUX DEMMUX Crosstalk TE 0 TE 1 TE 2 Crosstalk TE 0 TE 1 TE 2 TE 0-35dB -42.8dB TE dB -43.2dB TE 1-43dB -37.3dB TE dB -37.2dB TE dB -39.9dB TE dB -39.1dB In MMUX function, the insertion loss of three TE 0 modes are 0.17dB, 0.13dB and 0.09dB, respectively. In DEMMUX function, the insertion loss of TE 0, TE 1 and TE 2 modes are 0.17dB, 0.27dB and 0.13dB, respectively. The simulation results show that insertion loss of this device is less than 0.27dB and channel crosstalk is less than -25.4dB. 4. Conclusion In this paper, a new three mode MMUX/DEMMUX base on 2-D photonic crystals at 1550 nm is designed. The MMUX/DEMMUX can multi/demultiplex TE 0, TE 1 and TE 2 modes at 1550nm with introducing two pairs of parallel asymmetrical waveguide. The parameters of this device are analyzed using FDTD method. Numerical simulations show that the insertion loss is less than 0.27dB, channel crosstalk is less than 25.4dB. At the same time, dimensions of the device are only 53μm 12μm. It has a great value to mode division multiplexing system for its ultra-compact size and excellent performance. Reference 1. T. Niemi, L.H. Frandsen, K.K Hede, Wavelength-division demultiplexing using photonic crystal waveguides, IEEE Photonics Technology Letters 18, (2006). 2. K. Nozaki, E. Kuramochi, A. Shinya, and M. Notomi, 25-channel all-optical gate switches realized by integrating silicon photonic crystal nanocavities, Opt. Express 22, (2014). 3. Y.D Yang, Y Li, Y.Z Huang, Silicon nitride three-mode division multiplexing and wavelength-division multiplexing using asymmetrical directional couplers and microring resonators, Opt. Express 22, (2014). 4. Y. Kawaguchi, K. Tsutsumi, Mode multiplexing and demultiplexing devices using multimode interference couplers, Electronics Letters 38, (2003). 5. T. Uematsu, Y. Ishizaka, Y. Kawaguchi, Design of a Compact Two-Mode Multi/Demultiplexer Consisting of Multimode Interference Waveguides and a Wavelength-Insensitive Phase Shifter for Mode-Division Multiplexing Transmission, Journal of Lightwave Technology 30, (2012). 6. N. Hanzawa, K. Saitoh, T. Sakamoto, T. Matsui, K. Tsujikawa, T. Uematsu, and F. Yamamoto, PLC-based four-mode multi/demultiplexer with LP11 mode rotator on one chip, J. Lightwave Technol. 33, (2015). 7. Y. Ding, J. Xu, F. Ros, On-chip two-mode division multiplexing using tapered directional coupler-based mode multiplexer and demultiplexer, Opt. Express 21, 6

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