CMOS-Compatible Key Engineering Devices for High-Speed Silicon-Based Optical Interconnections by Jing Wang

Author:Jing Wang
Language: eng
Format: epub, pdf
ISBN: 9789811333781
Publisher: Springer Singapore

2.Design and optimization of the second Y-junction.

In order to avoid using a mode converter between first Y-junction and second Y-junction, we made the root waveguide width of the second Y-junction W Wm. The function of the second Y-junction is to convert the TM input from the root waveguide to the TM mode of the narrow arm waveguide, while maintaining the TE mode into the wide arm waveguide. Figure 3.22a–b show the relationship between the conversion efficiency from the TE/TM mode in the root to the TE/TM mode in the wide/narrow arm respectively when the width W of the narrow arm waveguide is from 250 nm to 310 nm. Here, the gap between the two arm at the output end is set to Gm to reduce the coupling between the output waveguides and to improve the polarization extinction ratio (PER) of the device. It can be seen from the figure that when the Y-junction length is relatively small, the efficiency of mode conversion does not always increase with the increase of Y-junction length L. This may be because some input power is coupled to multiple modes in the arm waveguide, resulting in some mode interference or reflection. Here, we select Wm and Lm for the second Y-junction to guarantee high mode conversion efficiency. At this time, the width of the corresponding wide arm is Wm, which is large enough to support 3 guided modes, which will contribute to the design of the third Y-junction. At the same time, there is no need to add an assisted tapered mode converter between the second Y-junction and third Y-junction. Figure 3.22c–d show the mode propagation of the TE/TM input mode from the root waveguide in the optimized second Y-junction, respectively.

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