Monolithic 1.55-µm passively semiconductor mode-locked laser diodes for optical clock and multi-wavelength / frequency-comb microwave photonics

Al-Rubaiee, Mohanad (2026) Monolithic 1.55-µm passively semiconductor mode-locked laser diodes for optical clock and multi-wavelength / frequency-comb microwave photonics. PhD thesis, University of Glasgow.

Abstract

Semiconductor mode-locked lasers are attractive sources for compact and low-cost microwave photonics because they can generate stable optical pulse trains, low-noise RF signals, and multi-line optical spectra from a monolithic chip. This thesis investigates the design, modelling, and experimental demonstration of several passively mode-locked laser platforms operating near 1.55 µm, targeting optical clock generation, multi-/dual-wavelength operation for mmWave and low microwave photonic signal generation, and broadband optical frequency comb sources.

The work begins with the development of an ultrastable 10 GHz passively mode-locked laser fabricated on a semi-insulating InP substrate. Fundamental and subharmonic RF injection locking, as well as optical injection locking, are investigated to stabilise the repetition rate and strongly suppress timing jitter. Sub-Hertz RF linewidths and sub-100-fs timing jitter are demonstrated, highlighting the potential of this device as a compact optical clock source.

Next, two monolithic multi-wavelength mode-locked DFB laser platforms are presented, both based on cavity and grating engineering to control the number of wavelengths and their spacing within a single chip. The first platform employs chirped conventional and four-phase shifted sampled Bragg gratings to realise stable four- and six-wavelength mode-locked operation with uniform channel spacing and high spectral purity. The second platform uses waveguide Bragg grating microcavities to demonstrate controllable tri-, four-, six-wavelength, and dual-wavelength operation, enabling compact single-cavity sources suitable for multiple optical carriers and mmWave photonic beating, while maintaining a fabrication-friendly process flow.

Finally, a broadband, high-repetition-rate frequency-comb source is demonstrated using an asymmetric multiple-quantum-well (AMQW) passively mode-locked laser diode. The device produces a 100 GHz comb with 14 optical lines within a 10.14 nm (−3 dB) bandwidth centred near 1525 nm, and sub-picosecond pulses with a deconvolved pulse duration down to 0.52 ps.

Overall, the results of this thesis establish practical monolithic semiconductor mode-locked laser platforms that combine stabilisation techniques, multi-/dual-wavelength spectral control, and broadband comb generation, supporting future integrated microwave-photonic systems for clocking, communication, and signal-processing applications.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Hou, Professor Lianping and Sweeney, Professor Stephen
• Date of Award: 2026
• Depositing User: Theses Team
• Unique ID: glathesis:2026-86190
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 21 Aug 2026 10:17
• Last Modified: 21 Aug 2026 10:25
• Thesis DOI: 10.5525/gla.thesis.86190
• URI: https://theses.gla.ac.uk/id/eprint/86190

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