Extending hybrid integrated diode lasers to multi-frequency oscillation

J. Mak

Research output: ThesisPhD Thesis - Research UT, graduation UT

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Diode lasers with low-loss dielectric feedback circuits based on hybrid integration are attractive because they are compact, can be efficiently driven via an electric current, and can be seamlessly integrated with advanced waveguide circuits. A central motivation to investigate these lasers is that they offer a significantly increased cavity photon lifetime, which has enabled single-frequency lasers with an extremely narrow intrinsic (Schawlow-Townes) linewidth of the laser frequency.

In this thesis, we extend this linewidth narrowing concept beyond the generation of only a single frequency, using long, tunable feedback circuits based on low-loss silicon nitride (Si3N4) waveguides. The generation of multiple frequencies with well-controlled frequency spacings opens up the path to additional applications that make use of other wavelength ranges, such as the technologically mature radiofrequency (RF) range, where information can be easily retrieved, processed, and stored using standard, low-noise electronics.

We realize a tunable hybrid dual-frequency laser for generating narrow beat frequencies in the microwave and THz domain. Generating a microwave beat frequency in the order of 10 GHz as an example, we observe a narrow intrinsic linewidth of the beat frequency of around 2 kHz. This value is, to our knowledge, about a factor of 13 lower than the narrowest intrinsic microwave linewidth reported so far for microwave generation using fully chip-integrated dual-frequency lasers.

We then extend this approach to more frequency lines, by generating a set of equally spaced optical frequencies, i.e., an optical frequency comb, using a mode-locked diode laser. We demonstrate that also in diode laser frequency combs, the approach of cavity extension with dielectric waveguides leads to significant linewidth reduction of the individual laser lines. We observe a narrow linewidth of 34 kHz of the individual comb lines. At the time of publication this was the narrowest value for all fully chip-integrated frequency comb diode lasers, by more than a factor of seven.

Finally, aiming on applications that require low repetition rates, e.g., for higher resolution and easier detection, we explore frequency comb generation in hybrid integrated diode lasers toward denser comb line spacings.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • University of Twente
  • Boller, K.-J., Supervisor
Award date17 Feb 2023
Place of PublicationEnschede
Print ISBNs978-90-365-5524-1
Electronic ISBNs978-90-365-5525-8
Publication statusPublished - 17 Feb 2023


  • Integrated photonics
  • Semiconductor lasers
  • Dual-frequency lasers
  • Frequency combs
  • Linewidth


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