Shangsen Sun, Zhiqiang Yang, Juanli Wang, Runsen Zhang, Fengchun Zhang, Ning Zhu, Lei Wan, Zhaohui Li, "Ultra-sharp silicon multimode waveguide bends based on double free-form curves," Photonics Res. 10, 1484 (2022)

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- Photonics Research
- Vol. 10, Issue 6, 1484 (2022)

Fig. 1. Proposed MWB based on the DFFC design. DFFC consists of curve A and curve B, and W S is the width of the MWB. The inset shows a schematic diagram of the change of curvature radius, and R A is the equivalent radius of the free-form curve A.

Fig. 2. Proper combinations of (a) curve A and (b) curve B are given. Here the ordinate represents a multiple of the equivalent radius.

Fig. 3. Simulation results of the DFFC–MWB with an input width W S = 1.1 μm . (a)–(c) Simulated optical field distributions in the designed MWB based on the DFFC with TE 0 , TE 1 , and TE 2 modes, respectively. (d)–(f) Calculated transmission spectra for three modes in the wavelength range of 1.5–1.6 μm. Herein the dotted line corresponds to the axis on the left, and the real line corresponds to the axis on the right.

Fig. 4. Simulation results of the DFFC–MWB with an input width W S = 1.48 μm and an equivalent radius of 10 μm. (a)–(d) Simulated optical field distributions in the device with four mode channels at 1.55 μm. (e)–(h) Calculated transmission spectra of the four-mode bent waveguide in the wavelength range of 1.5–1.6 μm. Herein the dotted line corresponds to the axis on the left, and the real line corresponds to the axis on the right.

Fig. 5. Transmittance spectra of the MWB based on the DFFC with Δ W varying from − 80 to 80 nm. (a)–(d) Transmission efficiencies of the four modes at 1550 nm. Simulation results show that this device has large fabrication tolerance.

Fig. 6. Microscopic view of the fabricated silicon multimode bends with four mode channels. The multiplexer and demultiplexer are connected with (a) straight multimode waveguide or (b) eight cascaded 90° MWBs based on the DFFC. (c) SEM image of the cascaded MWBs.

Fig. 7. Measured spectra of the normalized transmittances of a single four-mode waveguide bend. (a)–(h) Measurement results of a single 90° four-mode bend based on (a)–(d) DFFC or (e)–(h) SFFC.
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Table 1. Calculated Results Related to Different Device Parameters for Comparisona
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Table 2. Comparison of the Reported Results of Silicon Multimode Waveguide Bendsa

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