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An ultra-compact 1 × 2 demultiplexer based on multimode interference (MMI) waveguide is proposed to separate the 1310 nm and 1550 nm wavelengths, in which Si3N4/SiNx/Si3N4 sandwiched structure is used to realize polarization insensitivity. Firstly, how to use Si3N4/SiNx/Si3N4 sandwich structure to achieve polarization-independent is discussed. Keeping the width of MMI waveguide WMMI unchanged, the beat lengths of two orthogonal polarization states at same wavelength versus refractive indexes of SiNx are calculated. Similar simulation curves with different WMMI values and wavelengths are also provided. The result shows that there are crossing points in the beat length curves. It means that the beat lengths for the two orthogonal polarization states at the same wavelength can be identical by choosing the proper refractive index of the SiNx. More importantly, under exactly the same premise, for the two wavelengths, their crossing points are almost identical. Then, how to realize the function of wavelength separation is studied. A variable called the beat length ratio is given, which is defined as the beat length ratio of two working wavelengths under the same polarization state. When the beat length ratio equals an even number divided by an odd number, one wavelength is even multiple of beat length and the other wavelength is odd multiple of beat length, and vice versa, that is to say, a single image and a mirror image for the two working wavelengths are formed respectively. Therefore, the two working wavelengths will output from different output ports, therefore the two wavelengths are successfully separated from each other. The demultiplexer based on Si3N4/SiO2 platform has a compact structure, easy integration and good tolerance. Three-dimensional finite-difference time-domain method is used for simulation, and the results show that the size of the MMI waveguide is 4.6 μm × 227.7 μm; the insertion loss and crosstalk are as low as 0.18 dB and –25.7 dB respectively; a broad 3-dB bandwidth of 60 nm is achieved. Moreover, the fabrication deviation of the key structural parameters about the device is discussed in detail, and the insertion loss and crosstalk are considered. 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 wavelengths of 1310 nm and 1550 nm simultaneously. It has potential application value in future integrated optical circuits.
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Keywords:
- multimode interference /
- Si3N4/SiO2 platform /
- polarization-insensitive /
- sandwiched structure
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图 1 (a) 三明治结构示意图; (b) quasi-TE, (c) quasi-TM基模在三明治波导中的场分布(
${n_0} > {n_1}$ )Figure 1. (a) Schematic configuration of the sandwiched structure; field distributions for the (b) quasi-TE and (c) quasi-TM fundamental mode in a sandwiched waveguide (
${n_0} > {n_1}$ ).
图 2 解复用器结构示意图 (a) 俯视图; (b) MMI波导截面示意图
Figure 2. Schematic configuration of the demultiplexer structure: (a) Top view; (b) cross section of the MMI waveguide.
图 3
${L_{\text{π}}}$ 随n (SiNx)的变化 (a) WMMI = 3 µm; (b) WMMI = 4 µm; (c) WMMI = 5 µmFigure 3. Beat length
${L_{\text{π}}}$ as a function of n (SiNx) when the MMI width WMMI is: (a) 3 µm; (b) 4 µm; (c) 5 µm.
图 4 器件满足偏振无关条件时, n(SiNx)随WMMI的变化关系
Figure 4. n(SiNx) as functions of WMMI when the demultiplexer is polarization-insensitive.
图 5 器件满足偏振无关条件时 (a)
${L_{\text{π}}}$ 和(b) M随WMMI的变化Figure 5. (a)
${L_{\text{π}}}$ and (b) M as functions of WMMI when the demultiplexer is polarization-insensitive.
图 6 R随WMMI的变化
Figure 6. R as functions of WMMI.
图 7 MMI型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 7. Field distributions of the MMI 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 8 Port2和Port3两端口归一化输出光功率随波长的变化 (a) 1310 nm波段; (b) 1550 nm波段
Figure 8. Output powers (normalized to the input power) from Port2 and Port3 as the wavelength varies: (a) 1310 nm band; (b) 1550 nm band.
图 9 性能参数随LMMI的变化 (a) IL; (b) CT
Figure 9. Performance parameters as functions of LMMI: (a) IL; (b) CT.
图 10 性能参数随h(SiNx)的变化 (a) IL; (b) CT
Figure 10. Performance of parameters as functions of h(SiNx): (a) IL; (b) CT.
表 1 MMI型解复用器的性能参数
Table 1. Performances of the MMI demultiplexer.
性能参数 IL/dB CT/dB 1310 nm, TE 0.25 –21.32 1310 nm, TM 0.18 –24.40 1550 nm, TE 0.65 –20.97 1550 nm, TM 0.38 –25.70 
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表 2 输入、输出波导均为直波导时的MMI型解复用器的性能参数
Table 2. Performances of the MMI demultiplexer when input and output waveguides are straight.
性能参数 IL/dB CT/dB 1310 nm, TE 0.500 –17.73 1310 nm, TM 0.173 –23.80 1550 nm, TE 1.380 –14.21 1550 nm, TM 0.460 –22.54
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[1] Walker R G, Urquhart J, Bennion I, Carter A C 1990 IEE Proc.: Optoelectron. 137 33
Google Scholar
[2] Choi C H, Kim N K, Jo S B, Lee M W, O B H, Lee S G, Park S G 2005 Proc. SPIE 5723 368
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] Triki S, Najjar M, Rezig H 2007Icton Mediterranean Winter Conference, Sousse, Tunisia, December 6–8, 2007 p104
[6] Zhang S, Ji W, Yin R, Li X, Gong Z, Lv L 2018 IEEE Photonics Technol. Lett. 30 107
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, Barwicz T, Jared C, Mikkelsen J C, Taylor B J F, Lo G Q, Poon J K S 2014 Optical Fiber Communications Conference & Exhibition IEEE, San Francisco, CA, USA, March 9–13, 2014 pTh1A.3
[10] Mu J, Sergio A. Vázquez-Córdova, Sefunc M A, Yong Y S, García-Blanco S M 2016 J. Lightwave Technol. 34 3603
Google Scholar
[11] Lin Y J, Lee S L 2002 Opt. Quantum Electron. 34 1201
Google Scholar
[12] Chack D, Kumar V, Singh D P 2016 International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS), Rome, Italy, February 27–29, 2016 p227
[13] Pan C, Rahman B M A 2016 IEEE Photonics J. 8 114
[14] Dai D, He S 2008 IEEE Photonics Technol. Lett. 20 599
Google Scholar
[15] Fujisawa T, Koshiba M 2006 IEEE Photonics Technol. Lett. 18 1246
Google Scholar
[16] Chiang K S, Liu Q 2011 IEEE Photonics Technol. Lett. 23 1277
Google Scholar
[17] Shi Y, Anand S, He S 2007 IEEE Photonics Technol. Lett. 19 1789
Google Scholar
[18] Soldano L B, Pennings E C M 1995 J. Lightwave Technol. 13 615
Google Scholar
[19] Bachmann M, Besse P A, Melchior H 1994 Appl. Opt. 33 3905
Google Scholar
[20] Fu Y, Ye T, Tang W, Chu T 2014 Photonics Res. 2 41
Google Scholar
[21] Lee C C, Chen H L, Hsu J C, Tien C L 1999 Appl. Opt. 38 2078
Google Scholar
[22] Lelièvre J F, Kafle B, Saint-Cast P, Brunet P, Magnan R, Hernandez E, Pouliquen S, Massines F 2019 Prog. Photovoltaics Res. Appl. 27 1007
Google Scholar
[23] Guler I 2019 Mater. Sci. Eng., B 246 21
Google Scholar
[24] 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
[25] Li B, Chua S J, Leitz C W, Fitzgerald E A 2002 Opt. Eng. 41 723
Google Scholar
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