Longitudinal designs of DFB lasers on performance and stability

Abstract

In this study, the distributed feedback laser with various longitudinal grating structures is investigated for device performance parameters such as threshold current, slope efficiency, feedback tolerance. The structures are simulated, and the subsequent fabricated devices are characterised for the various performance parameters. The random facet phase effect arising from the fabrication process, which causes a variation in device performance is taken into account when comparing device performance of the various grating structures. Various designs were characterized for their threshold current, slope efficiency and Fc critical feedback level. While the upper and lower range of Fc measured for similar across different designs, the Fc is found to be correlated with the threshold current and slope efficiency of which the parametric distribution is altered by the grating design. Hence an estimate was made using this relation for achieving high yield in high Fc devices, where the λ/8 phaseshift design was suggested to have the highest yield compared to other single phaseshift and the standard non phaseshift design. The designs were also evaluated for yield based on their performance in other parameters such as output power, wavelength range and side mode suppression ratio (SMSR). The optimal design for yield was found to be very dependent on the yield criterion, with certain design features like the λ/4 phaseshift showing better yield for criterion that favours SMSR and wavelength range while the double phaseshift variant were shown to have more advantages in higher output power. Simulation was also done to explore different partial grating designs showing the flexibility of the design variant. Overall, the results of the fabricated devices were found to have good agreement with the simulations. It was found that the grating structures have great effect on how the facet phase effect is manifested, with the varying designs giving rise to different distributions for the various performance parameters. This leads to varying optimum designs for yield depending on the specification for the performance parameters.

Thesis is embargoed until 31 July 2029.

Date of Award	Jul 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	CDT PIADS & Sivers Photonics
Supervisor	Anthony Kelly (Supervisor) & Marty Gregg (Supervisor)