Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan.
Graduate Institute of Translational Medicine, College of Medical Science and Technology, Taipei Medical University, Taipei 11031, Taiwan.
Sensors (Basel). 2020 Feb 15;20(4):1054. doi: 10.3390/s20041054.
We design and compare the splitting ratio wavelength flatness of directional coupler (DC), Mach-Zehnder directional coupler (MZDC), and tandem MZDC. All coupler responses are analyzed, and tandem MZDC performance is the best in the wavelength insensitivity compared with the other two. An MZDC with any coupling ratio could be utilized to match the maximum flatness in a 40-nm wavelength range. To extend a broad flatness range, the tandem MZDC is proposed and still follows the Mach Zehnder structure taking two MZDCs as couplers connected through a decoupled region. Unlike DC, MZDC with the flat wavelength response has a non-linear output phase. Hence, using two wavelength-insensitive MZDCs as the coupling function in a tandem MZDC could demonstrate a more extensive decoupled phase term to maximize the flat wavelength response. The tandem MZDC theoretically demonstrates the splitting ratio with 100-nm flatness in the wavelength range from 1250 nm to 1350 nm. Finally, a point spread function through the tandem MZDC shows a 24-dB signal-to-noise ratio improvement in optical coherence tomography applications.
我们设计并比较了定向耦合器 (DC)、马赫-曾德尔定向耦合器 (MZDC) 和串联 MZDC 的分光比波长平坦度。分析了所有耦合器的响应，与其他两种相比，串联 MZDC 在波长不敏感性方面的性能最佳。任何耦合比的 MZDC 都可以用于匹配 40nm 波长范围内的最大平坦度。为了扩展更宽的平坦度范围，提出了串联 MZDC，它仍然采用马赫-曾德尔结构，由两个通过去耦区连接的 MZDC 作为耦合器。与 DC 不同，具有平坦波长响应的 MZDC 具有非线性输出相位。因此，在串联 MZDC 中使用两个波长不敏感的 MZDC 作为耦合函数，可以展示更广泛的去耦相位项，以最大限度地提高平坦波长响应。串联 MZDC 在 1250nm 到 1350nm 的波长范围内理论上展示了 100nm 平坦度的分光比。最后，通过串联 MZDC 的点扩散函数在光学相干断层扫描应用中提高了 24dB 的信噪比。
