Trench etched polarisation pinned multimode vertical cavity surface emitting lasers

Lei, Danqi (2022) Trench etched polarisation pinned multimode vertical cavity surface emitting lasers. PhD thesis, University of Glasgow.

Abstract

In this thesis, stable polarisation VCSELs for SPIC systems are fabricated, characterised and analysed. The application requires VCSELs to satisfy the polarisation preference of a buttcoupling coupler in the structure and be embedded into the planar SPICs system to provide light for an EDWA. The design of the VCSELs considered device polarisation characteristics and device structure. Discussions about it is presented in the thesis.

VCSELs with 30μm wide and 9μm deep trenches etched next to it are fabricated by a repeatable fabrication process. Deep trenches with sharp edges were accomplished by dry etching techniques presented in this fabrication flow. Devices with diameter of 40μm, 30μm, 20μm and 10μm are achieved by this fabrication process that has a potential of large-scale production.

Device characteristics including output power, contact resistance, slope efficiency, wall-plug efficiency, emission spectra, polarisation direction, polarisation ratio and nearfield images are examined. The properties of different diameter devices are discussed. 40μm diameter device achieves the highest output power of 4.6mW with a power loss of 76% in the substrate. It was found that 40μm and 30μm diameter devices produced stable polarisation selection, however, 20μm and 10μm diameter devices show unstable polarisation characteristics.

An investigation of polarisation properties of the fabricated trench-etched VCSELs is carried out using polarised near-field and spectral measurements. The nearfield images took at subthreshold have been compared between orthogonal polarisation states for different diameter devices. A spontaneous emission intensity difference is found for 40μm and 30μm diameter devices. It is possible that gain distribution is different on orthogonal polarisation states. A further birefringence study is presented for 40μm trench-etched VCSELs at around threshold and above threshold. Around threshold, spatially overlapping lasing modes allow the birefringence and hence strain to be mapped, indicating higher strain in the centre of the device. For high currents, it is observed that the lasing of different polarisations occurs in different regions of the device, as opposed to being a temporal phenomenon.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Hogg, Professor Richard
• Date of Award: 2022
• Depositing User: Theses Team
• Unique ID: glathesis:2022-82782
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 04 Apr 2022 09:17
• Last Modified: 08 Apr 2022 16:38
• Thesis DOI: 10.5525/gla.thesis.82782
• URI: https://theses.gla.ac.uk/id/eprint/82782