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An ultra-compact 1×2 demultiplexer based on directional coupler (DC) waveguide is proposed to separate the 1310 nm wavelength from 1550 nm wavelength, in which a new Si3N4/SiNx/Si3N4 sandwiched structure is used to realize polarization insensitivity. Firstly, the new sandwiched structure is designed to be polarization-independent. The coupling lengths of two orthogonal polarization modes at the same wavelength versus the gap between two parallel SiNx waveguides g1 are calculated with several groups of structure parameters of the demultiplexer. The result shows that the coupling lengths for the two orthogonal polarization modes at the same wavelength can be identical by choosing the proper g1. Then, how to realize the function of wavelength separation is studied. When one wavelength propagates at even multiple of coupling length and the other wavelength propagates at odd multiple of coupling length, and vice versa, the two working wavelengths will output from different output ports, thereby the two wavelengths are successfully separated. Under the premise of satisfying such conditions, a comparison of size and performance among the devices with different groups of structure parameters is given to find the best one. The demultiplexer based on Si3N4/SiO2 platform has a compact structure, easy integration and good tolerance. Three-dimensional(3D) finite-difference time-domain method is used for simulation, and the results show that the length of the DC waveguide is only 23 μm; the insertion loss and crosstalk are as low as 0.1 dB and–26.23 dB respectively; a broad 3-dB bandwidth of 200 nm is achieved. To demonstrate the transmission characteristics of the demultiplexer, the evolution of the excited fundamental mode in the demultiplexer is also given. The novel demultiplexer is polarization-independent and can work at 1310 nm and 1550 nm wavelengths simultaneously. It has a potential application value in future integrated optical circuits.
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Keywords:
- directional coupler /
- Si3N4/SiO2 platform /
- polarization-insensitive /
- sandwiched structure
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图 1 (a) 夹层结构示意图; (b) TE偏振模在夹层波导中的场分布(n0 > n1); (c) TM偏振模在夹层波导中的场分布(n0 > n1)
Figure 1. (a) schematic configuration of the sandwiched structure; (b) field distributions for the TE fundamental mode in a sandwiched waveguide (n0 > n1); (c) field distributions for the TM fundamental mode in a sandwiched waveguide(n0 > n1).
图 2 解复用器结构示意图 (a) 俯视图; (b) DC波导截面示意图
Figure 2. Schematic configuration of the demultiplexer structure: (a) Top view; (b) cross section of the DC waveguide.
图 3 当W0 = 0.6 μm, W1 = 0.7 μm, g1 = 0.1 μm时, (a) Lc, (b) ΔLc(λ)随n(SiNx)的变化关系
Figure 3. (a) Lc, (b) ΔLc(λ) as a function of n(SiNx) when W0 = 0.6 μm, W1 = 0.7 μm, g1 = 0.1 μm.
图 4 当 (a) W0 = 0.4 µm, W1 = 0.6 µm, (b) W0 = 0.4 µm, W1 = 0.7 µm, (c) W0 = 0.5 µm, W1 = 0.7 µm, (d) W0 = 0.5 µm, W1 = 0.8 µm时, Lc随g1的变化关系
Figure 4. Lc as a function of g1 when (a) W0 = 0.4 µm, W1 = 0.6 µm, (b) W0 = 0.4 µm, W1 = 0.7 µm, (c) W0 = 0.5 µm, W1 = 0.7 µm, (d) W0 = 0.5 µm, W1 = 0.8 µm.
图 5 当 (a) W0 = 0.4 µm, W1 = 0.6 µm, (b) W0 = 0.4 µm, W1 = 0.7 µm, (c) W0 = 0.5 µm, W1 = 0.7 µm, (d) W0 = 0.5 µm, W1 = 0.8 µm时, ΔLc(λ)随g1的变化关系
Figure 5. ΔLc(λ) as a function of g1 when (a) W0 = 0.4 µm, W1 = 0.6 µm, (b) W0 = 0.4 µm, W1 = 0.7 µm, (c) W0 = 0.5 µm, W1 = 0.7 µm, (d) W0 = 0.5 µm, W1 = 0.8 µm.
图 6 偏振无关1×2 DC解复用器件的光场分布图 (a) 1310 nm, TE波; (b) 1310 nm, TM波; (c) 1550 nm, TE波; (d) 1550 nm,TM波
Figure 6. Field distributions of the DC demultiplexer: (a) Quasi-TE mode, at 1310 nm; (b) quasi-TM mode, at 1310 nm; (c) quasi-TE mode, at 1550 nm; (d) quasi-TM mode, at 1550 nm.
图 7 Port2和Port3两端口归一化输出光功率随波段的变化 (a) 1310 nm波段; (b) 1550 nm波段
Figure 7. Output powers (normalized to the input power) from Ports 2 and 3 as the wavelength varies: (a) 1310 nm band; (b) 1550 nm band.
表 1 DC型偏振无关解复用器的结构参数
Table 1. Structural parameters of the polarization-insensitive DC demultiplexer.
结构参数 P g1/µm LDC/µm W0 = 0.4 µm, W1 = 0.6 µm 0 0.08 26.5 W0 = 0.4 µm, W1 = 0.7 µm 2 0.08 27 W0 = 0.4 µm, W1 = 0.8 µm 0 0.08 23 W0 = 0.5 µm, W1 = 0.7 µm 2 0.07 26 W0 = 0.5 µm, W1 = 0.8 µm 2 0.06 37 W0 = 0.5 µm, W1 = 0.9 µm 0 0.07 35 
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表 2 DC型偏振无关解复用器的透过率
Table 2. Transmittance of the polarization-insensitive DC demultiplexer.
结构参数 T(1310
nm, TE)T(1310
nm, TM)T(1550
nm, TE)T(1550
nm, TM)W0 = 0.4 µm, W1 = 0.6 µm 0.942 0.931 0.81 0.8 W0 = 0.4 µm, W1 = 0.7 µm 0.941 0.936 0.82 0.814 W0 = 0.4 µm, W1 = 0.8 µm 0.977 0.964 0.93 0.84 W0 = 0.5 µm, W1 = 0.7 µm 0.925 0.95 0.84 0.87 W0 = 0.5 µm, W1 = 0.8 µm 0.96 0.964 0.907 0.848 W0 = 0.5 µm, W1 = 0.9 µm 0.98 0.967 0.853 0.916
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表 3 偏振无关1 × 2 DC解复用器的性能参数
Table 3. Performances of the polarization-insensitive DC demultiplexer.
性能参数 IL/dB CT/dB 1310 nm, TE 0.1 –20.92 1310 nm, TM 0.16 –21.62 1550 nm, TE 0.32 –26.23 1550 nm, TM 0.76 –24.2
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表 4 DC型偏振无关解复用器的性能参数比较
Table 4. Comparison of performances of the polarization-insensitive DC demultiplexer.
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[1] Walker R G, Urquhart J, Bennion I, Carter A C 1990 IEE P-Optoelectron 137 33
Google Scholar
[2] Zhang S, Ji W, Yin R, Li X, Gong Z, Lv L 2018 IEEE Photonics Technol. Lett. 30 107
Google Scholar
[3] Shih T T, Wu Y D, Lee J J 2009 IEEE Photonics Technol. Lett. 21 18
Google Scholar
[4] Hibino Y 2002 IEEE J. Sel. Top. Quantum Electron. 8 1090
Google Scholar
[5] Song J H, Lim J H, Kim R K, ET AL 2005 IEEE Photonics Technol. Lett. 17 2607
Google Scholar
[6] Song J H, Kim K Y, Cho J, ET AL 2005 IEEE Photonics Technol. Lett. 17 1668
Google Scholar
[7] 刘耀东, 李志华, 余金中 2019 物理 48 82
Google Scholar
Liu Y D, Li Z H, Yu J Z 2019 Physics 48 82
Google Scholar
[8] Roeloffzen C G H, Hoekman M, Klein E J, ET AL 2018 IEEE J. Sel. Top. Quantum Electron. 24 121
[9] Sacher W D, Huang Y, Liang D, ET AL 2014 Optical Fiber Communications Conference & Exhibition. IEEE, San Francisco, CA, USA, March 9–13, 2014 pTh1A.3
[10] Gupta R K, Chandran S, Krishna B 2018 3 rd International Conference on Microwave and Photonics, Dhanbad, India, February 9–11, 2018 p1
[11] Chen J Y, Shi Y C 2017 J. Lightwave Technol. 35 5260
Google Scholar
[12] Xu H N, Shi Y C 2017 IEEE Photonics Technol. Lett. 29 1265
Google Scholar
[13] Shi Y C, Anand S, He S L 2008 Asia Optical Fiber Communication & Optoelectronic Exposition & Conference, Shanghai, China, October 30–November 2, 2018 p1
[14] Chen J Y, Liu L, Shi Y C 2017 IEEE Photonics Technol. Lett. 29 1975
Google Scholar
[15] Shi Y C, Anand S, He S L 2009 J. Lightwave Technol. 27 1443
Google Scholar
[16] Hardy A, Streifer W 1985 J.Lightwave Technol. LT-3 1135
[17] Chen Y, Joines W T 2003 Opt. Commun. 228 319
Google Scholar
[18] Fujisawa T, Koshiba M 2006 IEEE Photonics Technol. Lett. 18 1246
Google Scholar
[19] Chiang K S, Liu Q 2011 IEEE Photonics Technol. Lett. 23 1277
Google Scholar
[20] 汪静丽, 陈子玉, 陈鹤鸣 2020 69 054206
Google Scholar
Wang J L, Chen Z Y, Chen H M 2020 Acta Phys. Sin. 69 054206
Google Scholar
[21] Lee C C, Chen H L, Hsu J C, Tien C L 1999 Appl. Opt. 38 2078
Google Scholar
[22] 邹祥云, 苑进社, 蒋一祥 2012 61 148106
Google Scholar
Zou X Y, Yuan J S, Jiang Y X 2012 Acta Phys. Sin. 61 148106
Google Scholar
[23] Wang Q, He S L 2003 J. Opt. A: Pure Appl. Opt. 5 449
Google Scholar
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