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@PHDTHESIS{Ghannam:1020819,
      author       = {Ghannam, Ibrahim Abdel-Aziz Moh'd},
      othercontributors = {Witzens, Jeremy and Boller, Klaus-Jochen},
      title        = {{D}esign and characterization of a silicon nitride external
                      cavity laser with alignment tolerant multi-mode
                      {RSOA}-to-{PIC} interface},
      school       = {Rheinisch-Westfälische Technische Hochschule Aachen},
      type         = {Dissertation},
      address      = {Aachen},
      publisher    = {RWTH Aachen University},
      reportid     = {RWTH-2025-09255},
      pages        = {1 Online-Ressource : Illustrationen},
      year         = {2025},
      note         = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
                      University; Dissertation, Rheinisch-Westfälische Technische
                      Hochschule Aachen, 2025},
      abstract     = {Motivation, Goal and Task of the Dissertation External
                      cavity lasers (ECLs) have become indispensable in
                      applications that demand a narrow linewidth and a wide
                      tunability, including coherent optical communications,
                      quantum technologies, optical sensing, biophotonics, and
                      metrology. ECLs can benefit from the high gain and mature
                      fabrication of III-V semiconductor amplifiers while taking
                      advantage of low-loss photonic integrated circuits (PICs)
                      for extending the laser cavity, achieving narrow linewidths,
                      and combining with compact on-chip functionalities. However,
                      a major obstacle for the practical implementation of ECLs is
                      the stringent sub-micrometer alignment typically required
                      between the gain chip and the PIC. This complicates
                      assembly, increases manufacturing cost and time, and
                      prevents cost-effective mass production. This dissertation
                      addresses these challenges with the development and
                      experimental demonstration of a hybridly integrated ECL with
                      relaxed alignment tolerances. Specifically, it focuses on an
                      ECL formed by coupling a silicon nitride (SiN) PIC to a
                      reflective semiconductor optical amplifier (RSOA) by means
                      of a novel alignment tolerant edge coupler. The methodology
                      encompasses the design of the alignment-tolerant edge
                      coupler, the optimization and incorporation of two
                      high-quality-factor ring resonators arranged in Vernier
                      configuration for wideband single-mode tunability, and the
                      development of simple techniques to reduce parasitic
                      back-reflections in edge couplers used for outcoupling.
                      Experimentally, it was verified that a narrow linewidth, a
                      high laser output power, and a wideband tunability could be
                      obtained together with reduced assembly requirements,
                      thereby paving the way for scalable, mass-producible laser
                      sources assembled by pick-and-place technology. Major
                      Scientific Contributions. This work demonstrates an ECL
                      incorporating an alignment-tolerant edge coupler, which
                      simplifies coupling between the RSOA and the SiN PIC. The
                      alignment tolerance in the lateral direction, parallel to
                      the chip edge, is improved by a factor of three compared to
                      conventional edge couplers. The ECL sustains lasing for
                      lateral displacements of up to ±6 μm, which is well
                      within reach of state-of-the-art pick-and-place technology.
                      These gains in tolerance simplify the assembly process and
                      promise higher yields in high-volume manufacturing.
                      Leveraging high-confinement SiN waveguides, the ECL retains
                      a compact footprint while achieving very good performance
                      metrics. Systematic measurements showed that the laser could
                      be tuned across more than 100 nm, from approximately 1488 nm
                      to 1593 nm, effectively spanning the C-band and parts of the
                      S- and L-bands. A Lorentzian linewidth of 39 kHz was
                      measured, indicating excellent coherence—which is
                      important for applications such as high-speed data
                      transmission and is well within specification for
                      state-of-the-art coherent long-haul communication systems.
                      Altogether, these results confirmed that high-performance
                      operation could be maintained alongside significantly
                      relaxed alignment requirements, marking a step towards
                      manufacturable, cost-effective ECLs integrated at the chip
                      scale for communications, sensing, quantum technologies, and
                      other applications.},
      cin          = {616710},
      ddc          = {621.3},
      cid          = {$I:(DE-82)616710_20150519$},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.18154/RWTH-2025-09255},
      url          = {https://publications.rwth-aachen.de/record/1020819},
}