Tunable Narrow-Linewidth Si3N4 Cascaded Triple-Ring External-Cavity Semiconductor Laser for Coherent Optical Communications

Wang, Tong; Hu, Yuchen; Zhou, Wen; Wang, Ye

doi:10.3390/photonics13010072

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Tunable Narrow-Linewidth Si₃N₄ Cascaded Triple-Ring External-Cavity Semiconductor Laser for Coherent Optical Communications

¹

State Key Laboratory of Integrated Chips and Systems, Fudan University, Shanghai 200433, China

²

School of Future Information Science and Technology, Fudan University, Shanghai 200433, China

³

China Mobile Jiangsu Company Limited, Nanjing 210029, China

^*

Author to whom correspondence should be addressed.

Photonics 2026, 13(1), 72; https://doi.org/10.3390/photonics13010072

Submission received: 12 December 2025 / Revised: 6 January 2026 / Accepted: 12 January 2026 / Published: 13 January 2026

(This article belongs to the Special Issue Signal Processing and System Integration for Next-Generation Optical Communication)

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Abstract

We propose an external-cavity laser that combines wide tunability with narrow linewidth. The design utilizes a low-loss Si₃N₄ waveguide and a thermally tuned cascaded triple-ring resonator to enable continuous wavelength tuning. The numerical simulations indicate that the proposed laser exhibits a tuning range of 64 nm with a sub-kHz linewidth, an SMSR of more than 80 dB, an output power of 24 mW and a linewidth of 193 Hz at 1550 nm. Furthermore, we perform comparative system-level simulations using QPSK and 16QAM coherent optical fiber links at 50 Gbaud over 100 km. Under identical conditions, when the laser linewidth is reduced from 1 MHz level to 193 Hz, the BER of 16QAM decreases from 1.5 × 10⁻³ to 5.3 × 10⁻⁵. These results indicate that a narrow linewidth effectively mitigates phase noise degradation in high-order modulation formats. With its narrow linewidth, wide tuning range, high SMSR, and high output power, this laser serves as a promising on-chip light source for high-resolution sensing and coherent optical communications.

Keywords: ring; narrow-linewidth; external-cavity laser; coherent optical communications

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MDPI and ACS Style

Wang, T.; Hu, Y.; Zhou, W.; Wang, Y. Tunable Narrow-Linewidth Si₃N₄ Cascaded Triple-Ring External-Cavity Semiconductor Laser for Coherent Optical Communications. Photonics 2026, 13, 72. https://doi.org/10.3390/photonics13010072

AMA Style

Wang T, Hu Y, Zhou W, Wang Y. Tunable Narrow-Linewidth Si₃N₄ Cascaded Triple-Ring External-Cavity Semiconductor Laser for Coherent Optical Communications. Photonics. 2026; 13(1):72. https://doi.org/10.3390/photonics13010072

Chicago/Turabian Style

Wang, Tong, Yuchen Hu, Wen Zhou, and Ye Wang. 2026. "Tunable Narrow-Linewidth Si₃N₄ Cascaded Triple-Ring External-Cavity Semiconductor Laser for Coherent Optical Communications" Photonics 13, no. 1: 72. https://doi.org/10.3390/photonics13010072

APA Style

Wang, T., Hu, Y., Zhou, W., & Wang, Y. (2026). Tunable Narrow-Linewidth Si₃N₄ Cascaded Triple-Ring External-Cavity Semiconductor Laser for Coherent Optical Communications. Photonics, 13(1), 72. https://doi.org/10.3390/photonics13010072

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

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Tunable Narrow-Linewidth Si₃N₄ Cascaded Triple-Ring External-Cavity Semiconductor Laser for Coherent Optical Communications

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