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<p>Crosstalk suppression is a critical issue in waveguide optical switches for high-capacity optical fiber communication networks. Conventional Mach–Zehnder interferometer (MZI)-based waveguide optical switches suffer from crosstalk at the through port when the optical power coupling ratio of directional couplers deviates from the optimal value of 0.5. In this study, the operating characteristics of optical switches composed of two MZIs cascaded mirror-symmetrically or point-symmetrically are numerically analyzed and compared with that of a single-stage MZI. The results show that, in the mirror-symmetrically cascaded configuration, crosstalk appears at the through port when the coupling ratio deviates from the optimal value, similar to the single-stage MZI. In contrast, in the point-symmetrically cascaded configuration, crosstalk at both the through and cross ports can be theoretically eliminated by appropriately adjusting the phase difference in the ON state. These results indicate that the point-symmetrically cascaded configuration provides high robustness against fabrication errors and is an effective structure for realizing high-performance optical switches without requiring complex control schemes.</p>

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Crosstalk elimination in point-symmetrically cascaded Mach–Zehnder interferometer optical switch

  • 期刊论文

  • 发表日期：

    2026年7月30日

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  • Hirokazu Nakamura,
  • Toshio Watanabe,
  • Tsutomu Nagayama,
  • Seiji Fukushima

摘要

Crosstalk suppression is a critical issue in waveguide optical switches for high-capacity optical fiber communication networks. Conventional Mach–Zehnder interferometer (MZI)-based waveguide optical switches suffer from crosstalk at the through port when the optical power coupling ratio of directional couplers deviates from the optimal value of 0.5. In this study, the operating characteristics of optical switches composed of two MZIs cascaded mirror-symmetrically or point-symmetrically are numerically analyzed and compared with that of a single-stage MZI. The results show that, in the mirror-symmetrically cascaded configuration, crosstalk appears at the through port when the coupling ratio deviates from the optimal value, similar to the single-stage MZI. In contrast, in the point-symmetrically cascaded configuration, crosstalk at both the through and cross ports can be theoretically eliminated by appropriately adjusting the phase difference in the ON state. These results indicate that the point-symmetrically cascaded configuration provides high robustness against fabrication errors and is an effective structure for realizing high-performance optical switches without requiring complex control schemes.