DWDM source with precise channel spacing and good reliability

Sun, Yiming (2025) DWDM source with precise channel spacing and good reliability. PhD thesis, University of Glasgow.

Abstract

This thesis discusses advancements in photonic integrated circuits, focusing on monolithic semiconductor laser arrays and narrow linewidth laser designs around 1550 nm. The research proposes efficient solutions to the challenges of laser fabrication and integration, contributing to high-capacity optical communication systems.

Four major innovations are presented. First, a four-channel laser array based on four-phase shifted distributed feedback (DFB) lasers was demonstrated. The array achieves a uniform 100 GHz channel spacing, with each laser exhibiting a single-mode suppression ratio (SMSR) exceeding 50 dB. The integration of a semiconductor optical amplifier enables an output power of 33 mW, making the array suitable for dense wavelength-division multiplexing (DWDM) applications. Second, a DFB laser with a distributed phase shift region at the cavity centre was developed to achieve narrow linewidth operation. Compared to conventional π phase-shifted DFB lasers, the optimised DPS design enables stable single-longitudinal-mode operation over a broader current range, with lower threshold current, higher slope efficiency, and improved SMSR. The minimum linewidth was reduced from 1.3 MHz to 220 kHz, demonstrating potential for high-precision applications such as LiDAR and coherent optical communications. Third, a novel grating modulation technique was proposed to enhance wavelength control in DFB laser arrays. By introducing an arithmetic phase progression, this method enables channel spacings of 0.493 nm, 0.949 nm, and 1.956 nm while maintaining a strong coupling coefficient and improving fabrication tolerance. Finally, asymmetric twin waveguide integration was implemented, demonstrating an integrated four-phase-shifted DFB laser array with 0.873 nm channel spacing, an SMSR exceeding 45 dB, and an electro absorption modulator extinction ratio over 10 dB. These advancements enable scalable, precise, and efficient photonic integration.

Collectively, this work advances semiconductor laser technology, offering new solutions for linewidth narrowing, wavelength control, and integration, with applications in telecommunications, metrology, and quantum technologies.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: T Technology > T Technology (General)
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Hou, Dr. Lianping
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85294
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 04 Jul 2025 08:31
• Last Modified: 04 Jul 2025 08:33
• Thesis DOI: 10.5525/gla.thesis.85294
• URI: https://theses.gla.ac.uk/id/eprint/85294

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